bluuebunny/crossref_metadata_2025 huggingface dataset:
On the determination of the dorso-ventral polarity in the amphibian embryo: suppression by lactate of the formation of Ruffini’s flask-cells
Authors: Landström Ulf , Løvtrup-Rein Huguette , Løvtrup Søren
Published: April 2021

Cells isolated from the vegetal hemisphere of the blastula of Ambystoma mexicanum differentiate spontaneously into ffbroblast-like cells. Similar cells may be formed from animal cells, provided they are induced either by vegetal cells or by Li+.

We have found that lactate and various inhibitors of RNA synthesis suppress the spontaneous cell differentiation. The effect of lactate differs from that of the other agents in so far as lactate must be present before the second day of culture to suppress the outgrowth of fibroblasts on the third day; the other inhibitors are active also when added on the second day. An explanation of this difference may possibly be found in the fact that lactate suppresses incorporation of RNA but only by 40 %. The effect on the differentiation of various substances supposed to interfere with the metabolism of lactate was established. The results obtained were suggestive, but not conclusive.

It is concluded that the effect of anaerobiosis may be explained as a lactate inhibition. The amounts of lactate under aerobic conditions are so slight that it is unlikely, but not impossible, that lactate is directly involved in the control of differentiation.
The development of Drosophila embryos after partial u.v. irradiation
Authors: Bownes M. , Sander K.
Published: April 2021

U.v. irradiation of the anterior pole of nuclear multiplication stage Drosophila eggs produces embryos with defective anterior structures. At a low frequency embryos resembling some phenotypes of the bicaudal syndrome of Drosophila were observed. These embryos had no head or thorax and the eight abdominal segments were spread to the anterior of the embryo. Sometimes spiracles, characteristic of the most posterior embryonic segment were observed at the anterior of the embryo. The development of these embryos was followed, and abnormalities occurred as early as blastoderm formation. The extent of the blastoderm defects correlated well with the final abnormality in the embryo.
Blastemal kinetics and pattern formation during amphibian limb regeneration
Authors: Maden M.
Published: April 2021

To investigate whether the uniqueness of proximal and distal limb regenerates could be attributed simply to differing blastema) growth characteristics, their increase in volume, cell number and cell-cycle times were determined. With respect to these parameters proximal and distal blastemas were identical and, furthermore, no evidence could be found for the existence of separate growth zones such as an apical proliferation centre or a progress zone within the blastema. It was therefore concluded that level-specific properties of the blastemal cells play the major role in determining the structure of the regenerate, not their growth characteristics. The only discernible difference was in the cell number within the two types of blastema at the onset of cartilage redifferentiation - proximal regenerates had 60 % more cells. Thus it seems that the larger the pattern to be regenerated (the more proximal the amputation plane), the larger the primordium within which that pattern first appears. These two conclusions are discussed in relation to current theories of pattern formation during limb regeneration and development and a new way of envisaging the regeneration of pattern is described.
Biosynthetic events of hydrid regeneration II. Patterns and profiles of RNA synthesis during distal morphogenesis
Authors: Brooks Dennis C. , Voland Joseph R. , Lesh-Laurie Georgia E.
Published: April 2021

The pattern of RNA synthesis during the first 48 h of distal regeneration in Hydra oligactis has been investigated. In addition the RNA synthetic profiles during selected time periods have been studied.

RNA synthesis was found to increase five-fold during the first 3 h of regeneration and remained high throughout the rest of the 48 h period. An additional increase was observed 27-30 h following subhypostomal excision, immediately preceding the appearance of the first tentacle pair. The RNA synthetic level then returned to that found at 3 h of regeneration. This pattern was similar to that reported previously for DNA synthesis.

Profiles of radioactively labeled RNA remained constant during most of the times studied, showing the presence of newly synthesized 28S, 18S, 5S, and4S RNA. During two time periods, 28-32 h and 36-40 h, a novel 8S RNA species was observed. The occurrence of this species coincided with times of increased overall RNA synthesis and immediately preceded tentacle elaboration.
Sex determination in germ line chimeras ofDrosophila melanogaster
Authors: Deusen E. B. Van
Published: April 2021

Of 55 flies developing from blastoderms which had received male or female pole cell transplants, 15 (7 females and 8 males) were shown by progeny testing to be germ line chimeras. Since donor and host pole cells were genetically marked with contrasting X- or Y-linked alleles, the progeny testing scheme enabled the genotypic sex of the donor component undergoing gametogenesis to be identified as either the same as (‘homosexual’ chimeras) or opposite (‘heterosexual’ chimeras) that of the host.

All seven of the fematechimeras were identified as ‘homosexual’ chimeras carrying only chromosomally female donor and XX host germ cells. Similarly, all eight males were shown to be ‘homosexual’ chimeras with chromosomally male XYdonor and JfThost germ cells. The chromosomal sex of the donor component undergoing gametogenesis was in every case the same as the phenotypic sex of the host.

Since there is an equal probability of constructing either a ‘homosexual’ or a ‘heterosexual’ chimera during pole cell transplantation, the ability of pole cells to differentiate functional gametes in hosts of the opposite sex was tested 50% of the time even if sex reversal of these donor pole cells could not be demonstrated. Thus the absence of ‘heterosexual’ chimerism strongly supports the interpretation that the phenotypic sex of a germ cell in Drosophila is determined entirely by its own chromosome constitution, not by that of the gonadal mesoderm.
Effects of extremely low osmolarity on fertilized mouse eggs
Authors: Opas Jolanta
Published: April 2021

When fertilized one-cell eggs are subjected to distilled water treatment for 2-6 min, cytoplasm bulges through the sperm-slit in the zona pellucida and forms a cytoplasmic fragment (CF). CFs were observed in 86·5% of eggs; in 20·9% of cases CFs contained a pronucleus (or pronuclei). In 53·4 % of eggs permanent incorporation of the second polar body (2 P.B.) into the egg cytoplasm occurred.

These phenomena occurring in different combinations produced 6·2 % of haploid eggs, 10·3 % of diploid eggs with a pronucleus replaced by 2 P.B. nucleus, and 43·1 % of triploid eggs. 4·4 % of eggs were enucleated. The remaining group comprised diploid eggs which were either not affected by the treatment (6·4 %) or lost a certain amount of cytoplasm by formation of an anucleate CF (29·6 %). The frequencies of the types of reaction were related to the post-fertilization stage of eggs.

All eggs except the enucleated ones were able to develop to the stage of morula or blasto-cyst. Triploids developed until the 12th day of pregnancy and diploids that had lost up to 15 % of the cytoplasm developed to term. There was a twofold reduction in the percentage of preimplantation development when treated eggs originated from induced rather than spontaneous ovulation.
Control of anteroposterior pattern in the axolotl forelimb by a smoothly graded signal
Authors: Slack J. M. W.
Published: April 2021

In the accompanying paper (Slack, 1977), it is suggested that the normal anteroposterior pattern of the amphibian limb arises as a consequence of an interaction between the prospective limb and the flank. It has been shown that that part of the limb rudiment which is adjacent to flank tissue in the embryo becomes a posterior edge. So far we have considered neither the mechanism of this ‘posterior determination’, nor the mechanism of limb individuation, that is the process whereby cells in different anteroposterior positions differentiate to form a characteristic pattern of muscles and cartilages.
Reactivity of rat placental cells with alloantisera
Authors: Ferguson Frederick G. , Palm Joy
Published: April 2021

The nature of the protection afforded the placental structure against the immunologic consequences that could result from maternal exposure to paternal alloantigens remains obscure. One problem has been difficulty in antigenically defining the individual cellular components of the intact placenta. These studies were designed to examine serologically, with specific antisera, five cell types isolated from the rat placenta. The results indicate that non-Ag-B antigens are present on the cytotrophoblast cells, while Ag-B antigens are absent on all the cells except an undefined population of fibroblasts. Of particular significance is the obvious absence of detectable surface antigens on the cells directly in contact with the maternal tissues, the trophoblast mononuclear giant cells.
Studies on Embryonic Induction using Radioactive Tracers
Authors: Sirlin J. L. , Brahma S. K. , Waddington C. H.
Published: April 2021

Organizer and other tissues of urodele gastrulae were labelled by cultivation in glycine-Cu, methionine-Sss, or adenine-8-Ci4. They were then either inserted into the blastocoel of unlabelled hosts or made into ‘sandwiches’ between two flaps of gastrula presumptive ectoderm. Two or three days later the location of the tracer was investigated by stripping film autoradiography. The sandwich experiments gave the clearer results. The tracer passed into the tissues surrounding the graft and was accumulated mainly in the nuclei, though some was also present in the cytoplasm. A higher concentration was reached in the induced neural tissue and outermost layer of the epidermis than in other tissues. A greater fraction of adenine was mobile than of the amino-acids. The evidence suggests that there is no massive transfer of cytoplasmic particles and that there is considerable diffusion of tracer in the form of small molecules. It does not rule out the possibility of a relatively slight transfer of cytoplasmic particles, and, indeed, suggests that there is some specific migration of tracer into induced tissues, though it remains uncertain in what form this occurs.
Reduction of the rate of outgrowth, cell density, and cell division following removal of the apical ectodermal ridge of the chick limb-bud
Authors: Summerbell Dennis
Published: April 2021

Removal of the apical ectodermal ridge causes a reduction in the rate of outgrowth of the wing-bud and the loss of distal parts. More specifically it causes a short-term increase in cell density and cell death and a decrease in the rate of cell proliferation. The evidence supports the hypothesis of density-dependent control of cell division and suggests that there may also be a mechanism regulating skeletal length at the time of differentiation. An informal model is presented to explain the observations.
Intercellular junctions, intramembranous particles and cytoskeletal elements of deep cells of theFundulusgastrula
Authors: Hogan James C. , Trinkaus J. P.
Published: April 2021

The fine structure of motile deep cells of the gastrula stage of Fundulus heteroclitus was studied with transmission electron microscopy, using both thin sectioning and freeze-cleave techniques. Gastrula deep cells form extensive non-junctional appositions with each other, in which the apposed plasma membranes are parallel and separated by a distance of 26 –28 nm. They also form gap junctions. Tight junctions, desmosomes, and extensive interdigitations of apposed plasma membranes were not observed. The plasma membranes of deep cells contain numerous unclustered intramembranous particles. Cytoplasmic microtubules were found, but they appear to be small in number, sparsely distributed, and mainly randomly oriented. Microfilaments are also present and are localized largely in the cortical cytoplasm and in thin cell extensions. The significance of these findings for the contact and locomotory behavior of deep cells is discussed.
Somatic nuclei in amphibian oocytes: evidence for selective gene expression
Authors: Robertis E. M. De , Partington G. A. , Longthorne R. F. , Gurdon J. B.
Published: April 2021

Previous work has shown that multiple HeLa nuclei injected into Xenopus oocytes remain transcriptionally active for many days and that the expression of HeLa genes in oocytes can be detected by 2-D gel electrophoresis.

We show here that of 25 proteins which have the electrophoretic properties of HeLa gene products, only 3 are expressed in injected oocytes. To test that these proteins are products of HeLa genes, and not products of activated oocyte genes, we have injected HeLa nuclei into enucleated oocytes. Three days later, several HeLa proteins were synthesized.

The turning off of most HeLa genes in injected oocytes is apparently not at the translational level. This is indicated by the fact that adenovirus mRNA is efficiently translated when injected into Xenopus oocytes. When adenovirus-infected HeLa cell nuclei are injected into oocytes the adenovirus genes are not expressed, although some HeLa genes are expressed by the same nuclei.

The same HeLa genes as are expressed or switched off in injected Xenopus oocytes are also preferentially expressed or switched off in injected oocytes of a Urodele amphibian, Pleurodeles. This suggests that conditions or molecules may exist in oocytes which selectively impose on injected nuclei a new programme of gene expression.
Pattern formation inDictyostelium discoideum:II. Differentiation and pattern formation in non-polar aggregates
Authors: Forman D. , Garrod D. R.
Published: April 2021

Cells of the cellular slime mould D. discoideum were allowed to form into spherical aggregates, by shaking vegetative cells as a suspension in phosphate buffer. In such conditions, grex polarity is never established and surface sheath is not formed (Loomis, 1975 a). Despite the absence of such characteristics of normal development, differentiation of prespore cells, as tested for by immunofluorescent staining, and the organization of such cells into a patterned structure still occurred within the aggregates.

Differentiation of prespore cells was found to occur within the cultures at times equivalent to those in the normal life cycle; such differentiation could be advanced by pulsation of the cultures with cyclic-AMP. When cell contact and aggregate formation was prevented, differentiation never occurred within the single cells. Our results suggest that the prespore cells develop randomly within the aggregate and that a pattern is subsequently formed as a result of sorting out of cell types within the cell mass. Aggregates shaken for extended periods of time showed development into cyst-like structures.

The process of pattern formation that occurred within these aggregates which possess neither polarity nor a grex tip, would be unlikely to involve any mechanism of positional information signalling. The relevance of polar organization in the generation of pattern in the normal life cycle may therefore be questionable. We present a model of pattern formation in the slime mould in which sorting out of predetermined cell types is viewed as the major mechanism in bringing about patterned organization of the grex precursor cells.
Abnormal oogenesis and embryogenesis resulting from centrifugingDrosophila melanogasterfemales
Authors: Bownes Mary
Published: April 2021

Females of Drosophila melanogaster were centrifuged at 2400 g and 4200 g for 3 h in a number of different orientations. The oocytes in various stages of vitellogenesis become separated into three layers; a centrifugal yolk layer, a central cytoplasmic layer, and a centripetal lipid layer. The direction of layering is related to the orientation of the female. The process of recovery of the ovaries was followed and the development of the eggs laid analysed. Many of the eggs laid over the subsequent 3 days die very early in development and fail to produce any differentiated structures. Some hatch into normal larvae and others produce defective embryos. The most common defect being a misarrangement of the segmentation. The differences in the kinds of experimentally inducible pattern aberrations in Drosophila and other diptera is discussed.
Growth of opossum embryosin vitroduring organogenesis
Authors: New D. A. T. , Mizell M. , Cockroft D. L.
Published: April 2021

Opossum embryos, explanted between primitive streak and late fetal stages, were grown in culture for periods of 20–30 h. Many of the explants had a good heartbeat and blood circulation in embryo and yolk sac after 12 h, and a few after 24 h. Growth of the embryos included formation of the neural tube and body flexures, increase in the number of somites, differentiation of the limbs and digits, and development of the amnion and allantois. Embryos explanted during the last day of gestation showed persistent and vigorous body movements in culture, particularly of the forelimbs, head and tongue.
The formation of discrete muscles from the chick wing dorsal and ventral muscle masses in the absence of nerves
Authors: Shellswell G. B.
Published: April 2021

It is well known that the different muscles in the vertebrate limb develop by a series of splittings and subdivisions of dorsal and ventral muscle masses. The mechanism for this process is not clear, and the suggestion from previous studies that tension exerted by the growing limb stimulates these splittings is now thought unlikely. It has also been proposed that nerves play an important part in the separations by physically pushing the muscle mass apart. There is also the possibility that nerves could stimulate differential contraction of parts of the muscle mass, leading to a shearing effect and resulting in separation.

In this study, peripheral nerves are removed by the administration of the nicotinamide analogue 3-acetylpyridine before the start of muscle mass division. The resulting pattern of muscle is normal although nerves are completely absent. This clearly rules out any major role of nerves in the formation of the muscle pattern, although many authors have shown that innervation is important for the maintenance and later development of the separated muscles.

While the mechanism of the process of division of the muscle masses remains unknown, it is suggested that there are changes in cellular behaviour at areas corresponding to the future spaces between the muscles. These changes may be specified by some aspect of positional information within the limb. They might involve muscle cells stopping or reversing their differentiation as muscle in the areas forming the future spaces, or perhaps change the adhesion properties of the muscle cells to cause them to ‘sort out’ and separate. Alternatively, a localized invasion of non-muscle mesenchymal cells at the future spaces could lead to separation of discrete muscles. These possibilities are at present under investigation.
Effects of the teratogenic folic acid antagonist, 9-methyl pteroylglutamic acid, on hydroxyproline levels in fetal rat limbs
Authors: Schmidt R. R. , Chepenik K. P. , Paynton B. V.
Published: April 2021

Pregnant rats were subjected to either a folic-acid-deficient regimen that produces multiple congenital skeletal malformations, or a control folic-acid-supplemented regimen. Fetal limbs were extirpated on days 16 and 18 of gestation, pooled from each litter, homogenized, and aliquots set aside for hydroxyproline, protein and DNA determinations. We found that (1) the amount of protein recovered per treated limb was approximately half that of controls on both days, (2) the amount of protein recovered per treated or control day-18 limb was twice that of a day-16 limb, (3) treated limbs constituted the same percentage of total body weight as in controls on day 16, but a smaller percentage than in controls on day 18, and (4) the concentration of hydroxyproline (μg/mg protein) was significantly less for treated limbs than for controls on day 18 of gestation. We noted also that: (1) lowest hydroxyproline concentrations were found in limbs from treated fetuses with gross limb malformations, (2) intermediate concentrations were found in limbs of treated fetuses not exhibiting gross limb malformations, and (3) highest concentrations were found in control limbs. We suggest that the treatment resulted in (1) a decreased rate of accumulation of protein in limbs prior to day 16, but not from day 16 to day 18, (2) a decreased rate of accumulation of some non-protein component(s) in treated limbs from day 16 to day 18, and (3) an altered collagen metabolism.
The culture of mouse blastocysts in the presence of uterine flushings collected during normal pregnancy, delayed implantation and pro-oestrus
Authors: Aitken R. J.
Published: April 2021

When day-3 mouse embryos were cultured in a simple medium supplemented with uterine fluids of mice autopsied on day 4 of pregnancy, 48 h after administration of oestradiol, or during pro-oestrus, the percentage of blastocysts hatching from the zona pellucida was significantly greater than in unsupplemented medium. In the presence of uterine fluids recovered during delayed implantation this stimulation of blastocyst hatching was not observed. When the culture medium was supplemented with dialysed uterine flushings containing 20 or 30 μg protein/ml, both ‘day 4’ and ‘delay’ uterine proteins were equally effective in enhancing hatching frequency (P < 0·05). The results suggested that ‘delay’ uterine fluids may contain a dialysable inhibitor of blastocyst activity. The putative inhibitor was not effective in the presence of serum, since uterine fluids recovered both on day 4 of pregnancy and during delayed implantation significantly increased the size attained by blastocyst outgrowths in the presence of foetal calf serum (P < 0·001). The percentage of blastocysts exhibiting giant cell transformation and outgrowth was also increased (P < 0·02) by these uterine fluids when the concentration of FCS in the medium was minimal (0·25 %).
Development of cytochalasin B-induced tetraploid and diploid/tetraploid mosaic mouse embryos
Authors: Tarkowski A. K. , Witkowska A. , Opas J.
Published: April 2021

By subjecting F1 (CBA × C57/BL) × A eggs at the time of 2nd cleavage to 10 μg/ml of cytochalasin B (CB), tetraploidy was produced in 52 % of 2-cell eggs and 35 % of 3-cell eggs. 2n/4n mosaic embryos were produced from 2-, 3- and 4-cell eggs and amounted to 20 % of all treated eggs. 80 % of tetraploid embryos developed in vitro into regular blastocysts with half the cell number of control diploids. The effectiveness of CB in producing tetraploid embryos is limited by the asynchrony of 2nd cleavage, both between eggs and between sister blastomeres. Two-cell presumed tetraploids were transplanted to recipients and examined between the 6th and 11th day of pregnancy. Up to days development is normal and most embryos form egg-cylinders. At days the embryonic part of the cylinders is underdeveloped and in later development fails to form an embryo. Development of foetal membranes is much less affected and in the most successfully developing egg-cylinders their formation can be fully accomplished. Failure of embryonic development appears to be due to subnormal activity of the primitive streak, resulting in shortage of mesoderm. Postimplantation development of 2n/4n mosaics was normal. While in embryos tetraploid cells were either absent or in very low proportion (below 4 %), their contribution to the foetal membranes amounted in some cases to up to 50 °/o . Elimination of tetraploid cells from mosaic embryos suggests that they have a lower proliferation rate than diploid cells.
Effets de l’hybridation sur la population germinale embryonnaire et juvénile de canes issues du croisement Pékin ♂ × Barbarie ♀ (Anas platyrhynchos ×Cairina moschata)
Authors: Deray Armand
Published: April 2021

Ovarian development has been studied in a hybrid duck (Anas platyrhynchos ♂ × Cairina moschata ♀) and in females of the parental Peking and Barbary species. In the hybrid, the gonadal ridge when it first forms is smaller than in either parental species, and after 16 days of incubation there is less cortical growth and less oogonial proliferation. At hatching, the left ovary of the hybrid contains fewer follicles, perhaps because the reduced size of the hybrid gonadal ridge limits germ cell colonization. However, the hybrid follicles develop very rapidly after hatching, and laying begins earlier in the hybrid than in Peking and Barbary ducks.
Localization of trophoblast-defined surface antigens during early mouse embryogenesis
Authors: Searle R. F. , Jenkinson E. J.
Published: April 2021

The binding pattern of a rabbit antiserum raised against mouse ectoplacental-cone trophoblast on component cell populations in the pre-implantation and early post-implantation mouse embryo has been examined at the electron-microscope level using an immunoperoxi-dase-labelling technique. Binding was not detectable on the 1-cell stage, appeared at low levels at the 8-cell stage and was heavy on the trophectoderm and its trophoblast giant cell and extra-embryonic ectoderm descendants in the post-implantation embryo. In contrast, immunosurgically isolated day inner cell masses (ICM) showed only slight labelling, whilst ICM derivatives in the -day embryo were unlabelled.

The results indicate that the antiserum may be identifying a trophoblast-specific surface determinant(s), which appears with the differentiation of the trophectoderm and is maintained on some of the cell populations derived from this tissue at least until the early postimplantation stages.
Parthenogenetic activation of mouse oocytes induced by inhibitors of protein synthesis
Authors: Siracusa G. , Whittingham D. G. , Molinaro M. , Vivarelli E.
Published: April 2021

Recently ovulated mouse oocytes at the Metaphase II stage undergo parthenogenetic activation (as indicated by the formation of pronuclei) when incubated for 6 h in the presence of cycloheximide or puromycin; the activation response increases progressively with the concentration of inhibitor. Activation is induced with concentrations of cycloheximide that depress protein synthesis by more than 70 %. Pronoculear formation occurs when protein synthesis is almost totally inhibited. Incubation of oocyte in Actinomycin D failed to initiate activation. The results show that the Metaphase II oocyte of the mouse synthesizes protein factor(s) which are necessary for the maintenance of the meiotic block. Other protein(s) having opposite effects and a different rate of turnover may also participate in activation since when the oocytes are treated with a high concentration of cycloheximide (10 μg ml-1) for varying periods of time, or with varying concentrations for a short period of time (1 h), a more complex activation response curve is obtained.

Oocytes activated with cycloheximide are capable of further development, following transfer to the oviducts of pseudopregnant recipients, in a proportion similar to that of oocytes activated in other ways.
Ultrastructural localization of non-specific alkaline phosphatase during cleavage and blastocyst formation in the mouse
Authors: Mulnard Jacques , Huygens Roger
Published: April 2021

The localization of non-specific alkaline phosphatase activity during cleavage and blastocyst formation has been investigated in the mouse by electron microscopy. The activity is detectable for the first time at the two-cell stage and is localized on the surface of the interblastomeric plasma membranes and on small cytoplasmic inclusions. It increases in the following stages, predominantly on the interblastomeric membranes, the outside membranes remaining devoid of reaction. From the four-cell stage on, small reactive grains are also observed in the crystalloid plates of the cytoplasm. At the morula stage, the plasma membranes of the inner mass cells are entirely marked by the reaction whereas the trophoblastic ceils are polarized, with their inner surfaces positive and outside surfaces negative. At the blastocyst stage the enzyme is gradually eliminated from the membranes bordering the blastocoel and from the interblastomeric furrows of the trophoblast and primary endoderm. The significance of the differential localization of the enzyme is discussed, especially in relation to the differentiation mechanisms of the trophoblast and inner cell mass.
The onset of osteogenesis in the developing chick limb
Authors: Holder Nigel
Published: April 2021

The pattern of the onset of osteogenesis in each of the skeletal elements of the developing limbs of the chick embryo is described using Alizarin-red-stained whole mounts. Grafting experiments where 6-day unossified cartilage rudiments are placed into 4-day host wings show the initiation of ossification to be a programmed event. Truncation experiments show this to be the case not only for the initial onset of osteogenesis, but also for each region of each element. These results are discussed in terms of morphogenetic events occurring in the early wing bud.
Crystalline inclusion bodies in rabbit embryos
Authors: Daniel Joseph C. , Kennedy John R.
Published: April 2021

Crystalline inclusion bodies (CIB) may be found as prominent ultrastructural components of the trophoblast cells of rabbit blastocysts and of progestational uterine endometrium. In the work reported here we have sought to describe developmental steps in crystal formation, to correlate these events with embryonic age and to determine if the uterus is essential (either as a source or an environment) for crystal formation in the embryo.

CIB, which are of a size and periodicity to make them appear to be clusters or packages of microtubules, are first detectable in embryos 4 days 6 h post coitum and by days are well established in significant numbers. Another structural component, granular vesicles, may be seen in embryos as early as days post coitum, and decrease in number during the same time the CIB are increasing. We believe that the CIB originate from the pre-existing granular vesicles and present electron micrograph evidence of crystal formation progressing from such vesicles.

CIB formation does not occur in -to 5-day-old embryos which have been locked in the oviduct by a suture around the utero-tubal junction. However, when such tube-locked embryos are transplanted into the uterus, they develop crystals within 36 h thereafter. We conclude that the uterus is essential for CIB formation to occur in the rabbit embryo.
Neuronal adjustments in developing nuclear centers of the chick embryo following transplantation of an additional optic primordium
Authors: Narayanan C. H. , Narayanan Y.
Published: April 2021

Following transplantation of an additional optic primordium into the orbital mesenchyme of chick embryos of approximately 2 days of incubation age, the changes in cell number in the ciliary ganglion, accessory oculomotor and trochlear nuclei were studied at various stages of development. Cell counts were made at 1-day intervals from days 9 through 15 for ciliary ganglion, and from days 13 through 15 for the accessory oculomotor and trochlear nuclei. Cell counts for the ciliary ganglion on days 9 and 11 were similar on the operated and control sides which suggests that grafting of an additional optic primordium, and thus enlarging the periphery, is not involved in the control of proliferation. Comparison of the number of cells for the ciliary ganglia and the accessory oculomotor nuclei at days 13 and 15 showed an increase on the affected side ranging from 8 to 27 %, and 9 to 33 % respectively. We interpret this increase on the experimental side as a reduction in the number of degenerating cells that occur in normal development, as a result of an enlargement of the peripheral field of innervation. Three cases showed an increase in the number of cells in the trochlear nucleus ranging from 9 to 29 %. This increase was attributed to an increase in the size of the superior oblique muscle of the operated side as determined by volumetric measurements. On the basis of the evidence we conclude that an enlarged periphery acts by regulating the level of naturally occurring cell death by reducing the amount of cell loss, leading to a corresponding increase in final cell number.
Control of somite number in normal and amputated mutant mouse embryos: an experimental and a theoretical analysis
Authors: Flint O. P. , Ede D. A. , Wilby O. K. , Proctor J.
Published: April 2021

A regulation is shown for size and number of serially repeated axial structures, the somites, in a mammalian embryo. The mammalian embryo is normally inaccessible to operation at post-implantation stages. This problem is resolved by the quantitative analysis of somite size, number and development in a recessive mutant of the mouse, amputated, whose axial length is greatly reduced. The effect of the gene simulates an experiment ablating part of the embryonic tissue available for somitic segmentation. Regulation occurs at the time when the somite is first formed, by control of the quantity of cells included in each new somite. A model is devised for the control of somitic segmentation which explains most of the features observed and which can be simulated on a computer.
Genetic analysis of vitellogenesis inDrosophila melanogaster: the identification of a temperature-sensitive mutation affecting one of the yolk proteins
Authors: Bownes M. , Hames B. D.
Published: April 2021

A number of female sterile mutations on the first and third chromosomes of Drosophila melanogaster have been screened for defects in the yolk proteins using polyacrylamide gel electrophoresis. Two new mutants were identified. 6m45 accumulates all three yolk proteins (YP1, YP2 and YP3) in the haemolymph but they are all absent from the ovaries suggesting it is a yolk-protein-uptake mutant. In contrast, 1163 is a temperature-sensitive mutation with a large reduction in the quantity of YP1 in the haemolymph and ovaries at 29 °C. Both mutants are autonomous in ovary transplant experiments.
On the origin of the ciliary ganglion in birds studied by the method of interspecific transplantation of embryonic brain regions between quail and chick
Authors: Narayanan C. H. , Narayanan Y.
Published: April 2021

The development of the ciliary ganglion with reference to the site and cells of origin have been investigated by the method of quail-to-chick transplantation of embryonic fore-, mid- and hindbrain regions, and by the method of transplantation of cranial neural crest from specific brain levels. In chimaerical embryos, quail cells originating from the graft end up in the ciliary ganglion, only when the graft is from the midbrain level of quail embryo donors. In fore- and midbrain grafts the ciliary ganglia of chimaerical embryos are composed of chick cells only. The results indicate that the mesencephalon is the principal site for the pre-cursor cells of the ciliary ganglia and clearly rules out any contribution to the ganglia from either the forebrain or hindbrain levels.

In interspecific transplantation of cranial neural crest, quail cells originating from the graft are observed consistently in the ciliary ganglion of the operated side when the grafted neural crest mateiial is derived from the mesencephalon of quail embryo donors. On the basis of the evidence provided, it is concluded that the mesencephalon is the principal site and the cranial neural crest of this level the source from which the precursor neurons of the ciliary ganglia are derived.
Influence of embryonic stage on the transdifferentiation of chick neural retina cells in culture
Authors: De Pomerai D. I. , Clayton R. M.
Published: April 2021

Neural retina cells from chick embryos up to 15 days of incubation can transdifferentiate in culture into both lentoids and pigment cells. Some transdifferentiation into pigment cells but none into lentoids was found in cultures of 17-day embryonic neural retina. No trans-differentiation occurred in cultures of neural retina from embryos immediately before hatching. In general, lentoids and pigment cells develop more rapidly and in greater numbers in cultures of neural retina from the earlier embryonic stages, and lens-specific crystallins also appear earlier and accumulate in greater amounts in these cultures. Delta crystallin accumulation is much greater in transdifferentiating cultures of early embryonic neural retina, whereas α and β crystallins become proportionately more prominent in cultures of late embryonic neural retina. Traces of α and β but not δ crystallin are detectable in 60-day cultures of 17-day embryonic neural retina. Analogies between these results and the ontogeny of crystallin polypeptides in lens cells in vivo are discussed.
Induced segmental reorganization in sabellid worms
Authors: Berrill N. J.
Published: April 2021

Processes of regeneration and reorganization are analyzed in two sabellid polychaetes. Abdominal pieces of Branchiomma nigromaculata, during head regeneration, ordinarily reorganize only a fraction of the number of segments typical of the thorax. In pieces transected in the vertical plane, but obliquely with regard to the main axis of the worm, the extent of reorganization is greatly enhanced. The same number of segments transform on the right and left sides, the surviving damaged segments transforming on one side and a corresponding number of more posterior, undamaged segments transforming on the other. Reorganization is shown, in abdominal pieces of Sabella melanostigma, to involve destruction and inversed dorso-ventral reconstitution of all parapodial structures in the segments affected, the conversion of intestine to thoracic stomach, and the invasion of previously abdominal segments by a pair of large nephridia which grow posteriorly after being formed in the basal portion of the head blastema. All three events exhibit a time-graded character, starting soonest at the anterior end and progressively later posteriorly, and apparently independently of one another. Abdominal type segments are formed only from the anterior region of the caudal, prepygidial zone of growth, successively, never by transformation. The dorso-ventrality of abdominal segments is the inverse of the thoracic, with the antero-posterior polarity unchanged, in all circumstances. Only during posterior regeneration from thoracic segments are thoracic segments produced from the posterior zone of growth, but only two or three are thus formed, the zone of growth then changing to the production of abdominal segments. It is concluded that the unique feature of sabellid-serpulid organization is the complete inversion of the dorso-ventrality of the posterior zone of growth as the result of emancipation from the generally dominating dorsal field emanating from the anterior end.
A trypsin-like oviducal proteinase involved in Bufo arenarum fertilization
Authors: Miceli Dora C. , Fernández Silvia N. , Raisman Jorge S. , Barbieri Francisco D.
Published: April 2021

When the jelly-less eggs removed from the most cephalic region of the oviduct (pars recta) of the toad Bufo arenarum were inseminated at a high sperm concentration, high frequencies of fertilization were obtained. On the other hand, control eggs removed from the pleuroperitoneal cavity (coelomic eggs) were neither fertilized upon insemination under identical conditions, nor with the water extract of the jelly. Under these inseminating conditions, however, a high frequency of fertilization was obtained when coelomic eggs were pre-incubated in the presence of the fluid secreted by the epithelium of the pars recta or of an extract prepared from pars recta homogenate.

Experimental evidence is presented showing that the component responsible for this effect acts on the vitelline envelope of the egg, increasing its susceptibility to sperm lysin. It is probable, therefore, that it induces successful fertilization of coelomic eggs by making the vitelline envelope more easily penetrable by sperm.

The active factor was partially purified by Sephadex chromatography. The product obtained was of high activity and, as judged by its inhibition with soybean trypsin inhibitor and lima-bean trypsin inhibitor, it is likely to be a trypsin-like enzyme. The molecular weight of the factor was estimated to be 47000 by Sephadex chromatography. Secretion of the pars recta factor is hypophysis-dependent and its activity is not influenced by pH within the range tested (6·0–8·4).
Composition of the Foetal Fluids of the Rabbit
Authors: Davies J. , Routh J. I.
Published: April 2021

The composition of the foetal fluids of the rabbit at different stages of gestation has been described with reference to nitrogenous materials, electrolytes, total reducing substance, and fructose.

The composition of the amniotic and exocoelomic fluids resembles that of the foetal biood-serum except for the low total protein of the former. These findings are consistent with the origin of these fluids as a dialysate of the foetal blood. The allantoic fluid is characteristically opalescent largely due to the presence of colloidal fat. Its composition also differs from that of the foregoing fluids. Thus the total protein is lower while the level of urea nitrogen and creatinine is higher. Sodium, chlorides, and inorganic phosphates are lower; calcium and potassium are higher. Total reducing substances are about the same in all three fluids when allowance is made for the higher non-fermentable reducing substance of the allantoic fluid: all are lower than the foetal blood-levels. The fructose content is low and about the same in all fluids.

The presence of allantoic fluid from about the 13 th to the 24th day of gestation coincides with the period of function of the foetal mesonephros as judged by embryological and histological criteria. The structure of the nephron of the mesonephros is briefly described and the presence of alkaline phosphatase, fat, and periodic acid Schiff-reacting substances in the proximal tubules is illustrated. The evidence is consistent with the origin of the allantoic fluid as wholly or in part a product of the foetal mesonephros.
The Composition and Origin of the Foetal Fluids of the Pig
Authors: McCance R. A. , Dickerson J. W. T.
Published: April 2021

Many of the unicellular organisms have a greater concentration of osmotically active material within their body fluids than there is in the medium surrounding them, and the higher animals have glands like the kidney and sweat glands which are able to elaborate fluids with much lower concentrations of sodium and chloride than the body-fluids from which they were derived. The concentrations of sodium and chloride in hypotonic urine and sweat are much lower than those in the serum, and consequently the total osmolar concentrations are also lower, but the urea is characteristically higher. There is no proof that the process is one involving the secretion of water; and, indeed, the kidney is now thought to produce a hypotonic urine by the active reabsorption of sodium from the distal tubule, the walls of which are impermeable to water unless there is posterior pituitary hormone in the circulation.
Tracer Studies on Chick Embryosin vitro
Authors: Pantelouris E. M. , Mulherkar L.
Published: April 2021

Chick blastoderms of the definite primitive streak stage were cultured in vitro for about 24 hours with radioactive DL-methionine-S35 added to the medium. It was shown by autoradiography that the neural tube and especially its roof and also adjacent areas of the ectoderm (neural crest) take up more activity than other structures. Mesodermal structures such as the notochord, somites, and myoepicardium also reach a high level of uptake, presumably correlated with their differentiation. Tissues of the host, the induced axis, and self-differentiating (non-labelled) grafts take up activity from the culture medium at the same rate. If a labelled organizer is grafted on to a host blastoderm, the induced neural tube takes up a substantial amount of labelled molecules but the host does not. Experiments involving dilution with unlabelled methionine or grafting of labelled peripheral organizer tissue, produced evidence for the view that the activity is carried to the induced tissues by diffusion or exchange of free aminoacid molecules; transfer of macromolecules does not occur on a scale detectable by the methods used but it cannot be excluded that it might occur on a smaller scale. In cases of induction caused by organizer graft the notochord, mesenchyme, and, occasionally, tissues lining the foregut associated with the induced axis are contributed by the graft.
The Development of Gastric Tumours in Drosophila Larvae
Authors: El Shatoury H. H. , Waddington C. H.
Published: April 2021

A sex-linked factor in Drosophila, lethal-no-imaginal-buds (1-nib) produces two main effects: reduction, or even complete absence of the imaginal buds; and excessive proliferation of the epithelium of the stomach, leading to occlusion of the gut and death from starvation. The intensity with which these two effects are expressed varies independently in different stocks. This paper is primarily concerned with the formation of the gastric tumour. The first pair of lymph glands, after their breakdown in the later part of the first instar, usually regenerate only incompletely. With increasing abnormality of the glands, there was an increasing tendency for excessive proliferation, or for cellular degeneration, in the testes, hind-gut primordia, and stomach, in that order. In severely affected larvae, the lymph glands degenerate at the end of the second instar. This is followed by, and is thought to be the cause of, a strong hypertrophy of the gastric epithelium, which leads to the filling up of the gut lumen with cells and anuclear cytoplasmic masses. It is probable that a preliminary stage in the development of this hypertrophy is the proliferation of the cells of the mid-gut imaginal primordia. Similar proliferation and/or hypertrophy occurs in the hind-gut and salivary gland primordia. The cells of all these proliferations eventually undergo degenerative processes involving the deposition of melanin, when they become converted into melanotic ‘tumours’. These are usually anchored to their places of origin, in contrast to the free tumours found in some other Drosophila stocks. Preliminary experiments indicate that the development of the proliferations can be suppressed by the injection of normal lymph glands into early third instar larvae. In individuals from which the cephalic buds are missing, there is no development of the optic glomeruli in the brain. In the stock lethal-malignant (Shatoury, 1955) the lymph glands undergo pathological changes of a different type; they become excessively hypertrophied in the late third instar, and develop into a metastasizing tumour which eventually undergoes various degenerative changes. In this stock also the gastric epithelium begins to exhibit excessive hypertrophy at the same time as the lymph glands become abnormal. A full gastric tumour may develop; in this case the basement cells are involved in addition to the main epithelium. It is suggested that the complex interrelations between the lymph glands, the migratory cells given off from them (oikocytes), and the apparently hormonally controlled proliferative tendencies of tissues such as the gastric epithelium, constitute a novel type of epigenetic system, which may be special to the larvae of holometabolous insects or even of Drosophila alone.
Total Replacement of the Yolk of Chick Embryos
Authors: Grau C. R. , Klein N. W. , Lau T. L.
Published: April 2021

Isolation of the avian embryo from its normal food material is an essential step in a fundamental study of embryonic nutrition. With present methods, however, it has not been possible to grow embryos in culture for much longer than one day. In 1932 Waddington described methods of growing explanted embryos on serum clots. Several years later Spratt (1947, 1952) devised simplified media for embryos cultured on agar with which he studied various aspects of morphogenesis and carbohydrate needs of the young embryo. New (1955) has recently reported another technique for growing explanted embryos which allows development to proceed to about 60 hours, 40 hours of which are in vitro.