bluuebunny/crossref_metadata_2025 huggingface dataset:
Adult deficiencies and duplications of head and thoracic structures resulting from microcautery of blastoderm stage Drosophila embryos
Authors: Bownes Mary
Published: April 2021

Drosophila embryos were damaged by microcautery at the cellular blastoderm stage at the sites of presumptive imaginal cells, identified from fate maps. The resulting adults were analyzed for abnormal structures. Cautery of any of the presumptive imaginal regions can lead to defects in the adult cuticle, though the majority of adults which hatch are morphologically normal. The abnormal adults had one or more discs either deleted, incompletely formed, or misarranged. Several of the structures which were incomplete had duplicated regions. The results suggest that, from the time of their initial formation in the cellular blastoderm, a group of cells determined to be an ‘adult’ structure possesses a gradient of developmental capacity which is expressed by certain regions duplicating and other cells regenerating. The types of duplications found were similar to those resulting from other experimental treatments of imaginal discs at later stages in development, indicating that the presumptive imaginal disc cells, when they are first established in the cellular blastoderm, have a similar organization to mature imaginal discs.
Induction of triploidy in the mouse by cytochalasin B
Authors: Niemierko Anna
Published: April 2021

Mouse eggs fertilized in vivo were treated with cytochalasin B in vitro (5 µg/ml of culture medium) at the moment of extrusion of the second polar body (2·5, 3·0, 3·5 h after copulation). Cytochalasin B inhibits cytokinesis of the second maturation division, so that triploid digynic eggs are formed in over 50% of treated eggs.

Triploid eggs were transplanted to the oviducts of recipients. On the 4th and 5th day of development 41·7% of transplanted eggs were recovered. All embryos recovered on the 4th day were morulae, while on the 5th day blastocysts predominated. Recovered embryos were studied for cell number and ploidy. Twenty-three of 27 embryos with analysable metaphase plates were triploid and four were diploid (the latter were found in females into which both triploid and control diploid eggs were transplanted).

Sex chromosome constitution was determined in seven cases: four triploids were XX Y and three were XXX.

Preliminary observations showed that triploid embryos obtained by the use of cytochalasin B can implant and survive at least to the 9th day.
Neuroectodermal origin of avian hypothalamo-hypophyseal complex: the role of the ventral neural ridge
Authors: Takor T. Takor , Pearse A. G. E.
Published: April 2021

Embryonic discs from White Leghorn chick embryos (presomite to 12-somite stages) were examined in serial transverse and longitudinal sections. Later stages, up to 21 days, were also examined. The following observations were made: Lateral folding rather than head folding is the mechanism by which the avian embryo is delimited. The process takes place at two terminal points, one cephalic the other caudal.Thickening of the ventral ectoderm around the tip of the presumptive anterior neuropore, beginning at the 4-somite stage, subsequently extends the dorsal neural ridge to form a ventral neural ridge.The cephalic portion of the ventral neural ridge, extending from anterior neuropore to optic chiasma, is mainly incorporated into the alar plates of the diencephalon.The caudal portion, extending from optic chiasma to the stomodeum, gives rise to Rathke’s pouch and thus to the adenohypophysis.

We conclude that the latter is to be regarded as of neuroectodermal rather than ectodermal (stomodeal) origin, and that some or all of the neuroendocrine nuclei of the hypothalamus are similarly derived from the neuroectoderm of the neural ridge.

The hypothalamo-hypophyseal complex is thus to be regarded as a single rather than a composite entity.
Iron incorporation and haemoglobin synthesis in erythropoietic cells during the ontogenesis of the mouse
Authors: Schalekamp M. , Harrison P. R. , Paul J.
Published: April 2021

Iron incorporation (59Fe) into erythropoietic cells from adult and foetal (11-to 15-day) peripheral blood and from foetal (12-to 15-day) livers has been investigated. Ion-exchange chromatography of haemolysates from such cells revealed two groups of 59Fe-containing proteins. The first group (X-fraction) was eluted from CMC-columns in the void volume and was highest in lysates of immature erythropoietic cells. This fraction contained a radiolabelled haemprotein of high molecular weight as well as other S9Fe-containing proteins. The haemprotein does not appear to be related to haemoglobin.

The second group consisted of haemoglobins. One major (A1) and two minor (A2 and A3) haemoglobins were found in adult peripheral blood. In foetal liver lysates two major (F1 and A1) and two minor (F2 and A3) haemoglobins were present. The relative proportion of the major haemoglobins changed during development. Haemoglobin F1 was highest in the more mature livers. F1 proved to be different from A1 by chromatographic behaviour, in polypeptide chain composition and in fingerprints. A unique foetal polypeptide chain, intermediate in electrophoretic behaviour between the adult α-and β-chain, was identified. In young foetal peripheral blood (11-day), in which 95 % of the cells are of yolk-sac origin, one major (E1), two intermediate (E2 and E3) and one minor (F1) haemoglobin were demonstrable. Haemolysates of the peripheral blood of older embryos contain haemoglobins from erythroid cells of both yolk-sac and foetal liver origin. The haemoglobin pattern of such lysates is explicable in terms of the decreasing amount of embryonic haemoglobins (E1, E2 and E3) and the increasing amount of foetal haemoglobins (F1 and A1). Since A1 and E1 are the most prominent haemoglobins of livers from young embryos and yolk-sac erythrocytes respectively, and since they are very similar in chromatographic behaviour, foetal peripheral blood at all stages contains one dominant haemoglobin peak in the A1-E1 region. Most authors have neglected the relatively slight elevation of the foetal haemoglobin peak (F1) in front of A1-E1, the more because the F1-A1 region has been suspected sometimes to contain artificial haemoglobin components (Riggs, 1965). This probably explains why no foetal haemoglobin (F1) has been reported previously in the peripheral blood of foetal mice.
The ultrastructure of the polar lobe of Crepidula fornicata (Gastropoda, Prosobranchia)
Authors: Dohmen M. R. , Lok D.
Published: April 2021

Some novel structural features of the polar lobe of the egg of Crepidula are described. The significance of two kinds of aggregate is discussed in relation to the morphogenetic factors present in polar lobes generally. Surface configurations of the polar lobe are also described.
Embryogenesis of an insect nervous system:I. A map of the thoracic and abdominal neuroblasts inLocusta migratoria
Authors: Bate C. M.
Published: April 2021

Maps of the thoracic and abdominal neuroblasts have been prepared by reconstruction from serial sections of timed Locusta migratoria embryos. The maps are bilaterally symmetrical, periodic and consistent for embryos of the same age, with a fundamental arrangement of 7 rows of 4-10 cells plus 1 median neuroblast per segment. A map of 60+1 cells is repeated in each of the three thoracic segments, with an additional median cell developing late at the anterior end of the prothorax. The arrangement in the abdomen is similar, with 56+ 1 cells per segment. Neuroblasts differentiate and subsequently degenerate in an antero-posterior sequence, but construction of the thoracic ganglia involves a delayed degeneration of part of the original set in these segments. The maps show that the neuroblasts are as reliable in their number and arrangement as the adult cells they produce. The number of neuroblasts used in constructing the relatively complex thoracic ganglia is similar to that which produces the simpler abdominal ganglia. Some motorneurons have the same parent neuroblast. The maps are intended as a first step in an analysis of the relation between the progeny of different neuroblasts and the family of neurons which each neuroblast produces.
The formation of the gonadal ridge in Xenopus laevis: I. A light and transmission electron microscope study
Authors: Wylie C. C. , Heasman J.
Published: April 2021

In Xenopus laevis tadpoles, between stages 44 and 49 (Nieuwkoop & Faber, 1956), the primordial germ cells (PGCs) migrate from the dorsal mesentery of the gut to the site of the presumptive gonadal ridge. This paper describes the process at the light- and electronmicroscope levels. The PGCs in the mesentery, which at first are very large and yolk-laden, seem to lie entirely within the cellular matrix of the mesentery, although this is not obvious in light micrographs. Where the PGCs bulge out into the coelomic cavity, they stretch the somatic cell covering to a thin, cytoplasmic layer. The somatic cells of the mesentery are held together around them at this stage by well-differentiated desmosomes. At this, and subsequent stages, the PGCs have cytoplasmic processes, roughly the size of microvilli, which are irregularly distributed over their surfaces, and which are inserted between surrounding somatic cells. Whether these processes play any role in locomotion or exploration of the substrate is uncertain.

As the PGCs move laterally from the root of the mesentery to the presumptive gonadal ridge, the coelomic lining cells which cover them, initially with a very thin squamous layer, differentiate to form the cuboidal cells of the germinal epithelium. Several interesting ultrastructural features of these cells, and the PGCs, are described, particularly in the light of their surface interaction.

In the light of the morphological data presented here, particularly of the cell surfaces involved, we conclude that both active locomotion by the PGCs and passive movement by the morphogenetic movements of the cells around them contribute to the establishment of the early gonadal ridge.
Embryological evidence for a possible polyphyletic origin of the recent amphibians1
Authors: Nieuwkoop P. D. , Sutasurya Lien A.
Published: April 2021

The markedly different mode of mesoderm formation in anuran and urodelan amphibians (which is related to the early double-layered nature of the anuran blastula wall in contrast to its single-layered nature in the urodeles), but particularly the fundamentally different place and mode of origin of the primordial germ cells in the two groups of amphibians, strongly pleads in favour of a very ancient bifurcation in the phylogenetic history of the two groups, even suggesting a polyphyletic origin from different ancestral fishes.
The teratogenic effects of hydrocortisone on palatal development in the hamster
Authors: Shah Ravindra M. , Travill Anthony A.
Published: April 2021

The effect of different doses of hydrocortisone, administered at various times during gestation, on the fetal hamster and its palatal development was studied. Both the frequency of cleft palate and that of resorption depended upon the dose of hydrocortisone and the time of its administration. Two peaks in the incidence of cleft palate were observed, which appeared to be due to inhibition of different events.

Incidence of morphologically different types of cleft palate was related to the doses and gestational time of hydrocortisone treatment. A close association was observed between the frequency of cleft palate and fetal growth retardation and between the latter and the dose and time of drug administration. It was suggested that maternal physiology and the placental barrier may play a crucial role in cleft palate induction.
Regeneration of amputated limb-buds in early rat embryos
Authors: Deuchar Elizabeth M.
Published: April 2021

Rat embryos, dissected from the uterus at -days’ gestation, have been used to study the regenerative powers of the embryonic limb. One forelimb-bud of each embryo was amputated, via an incision in the membranes. Embryos were subsequently grown in roller-bottle cultures for 44 h, then examined histologically. Twenty-nine out of 32 healthy embryos had formed limb-bud regenerates, 14 of which were of normal size and shape. Eight of them had a normal apical ectodermal ridge. It is concluded that at this stage of development there is sufficient versatility in the embryonic cells for a limb rudiment to be replaced by adjacent mesenchyme and epidermal cells. The implications of this finding are discussed in connexion with previous studies on the regeneration of appendages in vertebrate embryos.
Effect of dorsal and ventral limb ectoderm on the development of the limb of the embryonic chick
Authors: Searls Robert L.
Published: April 2021

Limb ectoderm plus a small amount of subjacent mesoderm obtained from the dorsal or the ventral surface of each of the four limbs of the chick embryo were grafted to the dorsal surface of the right wing in either reversed or normal orientation. The host wings developed an abnormal humerus in all cases except when the graft was obtained from the dorsal surface of the right wing and was in normal orientation. However, the nature of the abnormalities varied with the source of the graft and with the orientation of the graft. It is unlikely that the abnormalities were related solely to the small amount of mesoderm grafted since previous experiments have demonstrated that the mesoderm would regulate. Flank ectoderm plus a small amount of flank mesoderm did not cause limb abnormalities when grafted in the same manner.
Postnatal cytochemical development of muscle fibers in segmental tail muscles of the rat
Authors: Ovalle W. K.
Published: April 2021

Postnatal development of extrafusal and intrafusal muscle fibers was examined histo-chemically in segmental tail muscles of the rat. At birth all fibers show a strong reaction for myosin ATPase, uniformity in diameter, and homogeneity in staining intensity. During the first postnatal week, the muscle fibers undergo gradual hypertrophy and hyperplasia but they all maintain the same intense homogeneous staining pattern for the enzyme. By day 9, further differentiation of the muscle fibers results in the formation of a second intrafusal fiber type while the extrafusal fibers are still relatively homogeneous. Finally, two kinds of extrafusal fiber and a third type of intrafusal fiber can be distinguished by day 21. This histochemical fiber pattern is essentially maintained in the adult.

These findings show that fiber type development in rat tail muscles lags behind the usual time course of myogenesis known to occur in more rostral regions of the animal. It also indicates that histochemical differentiation of intrafusal fibers in these muscles does not parallel that which occurs in extrafusal fibers. It is likely that arrival and initial contact of sensory nerve terminals on developing intrafusal fibers at day 7 directly influences their relatively early histochemical heterogeneity.
A histological study of embryonic death caused by heterozygosity for the T26H reciprocal mouse translocation
Authors: Boer P. De , Maar P. H. M. D. De
Published: April 2021

Male mice, heterozygous for the T26H reciprocal translocation, were mated to normal females. A systematic histological study at day 6 and day 8 of pregnancy, covering altogether 303 implantation chambers, yielded the following results: the average number of decidual reactions per female was 8 ·91, the average number of morphologically normal embryos at day 6 was 4 ·61 and at day 8, 4 ·25. No significant embryonic loss occurred between day 8 and the end of pregnancy. Most (89 ·0 %) of the embryonic loss due to genetically unbalanced (deficiencies combined with duplications) progeny occurs between the moment of the induction of a decidual reaction and day 6, i.e. in ±1 ·5 days. When the genetically unbalanced embryos were grouped in three classes according to the size of their deficiencies, the numbers and types of the aberrant histological pictures found could be reconciled with the expectations of the three classes, based on cytological analysis. According to this, embryos with the smallest deficiencies take just over 2 days before all have died. Embryos with mediumsized deficiencies take ±1 ·5 days, and the group with the largest deficiencies take just over 1 day. At day 6, 8 ·8 % of the implantation chambers had an intact epithelium whereas at day 8, this had dropped to 1 ·3 %. This is consistent with the view that erosion of the uterine epithelium at the site of implantation is an autonomous process, but helped by the phagocytic action of the trophoblast cells.
The use of ‘normal’ and ‘transformed’ gynandromorphs in mapping the primordial germ cells and the gonadal mesoderm inDrosophila
Authors: Gehring W. J. , Wieschaus E. , Holliger M.
Published: April 2021

The primordial germ cells and the gonadal mesoderm were mapped in the Drosophila embryo by analyzing the patterns of mosaicism in ‘normal’ and ‘transformed’ gynandromorphs. Relative to the adult cuticular markers the germ cells map as the posterior most structure, which coincides with their known location in the blastoderm embryo. These data support the hypothesis that the gynandromorph map reflects the real position of the pri-mordia in the embryo. Since after the blastoderm stage the primordial germ cells migrate anteriorly these data also indicate that the map in fact corresponds to the blastoderm stage and not to a later stage of development. The genital disc maps as a single median primordium anterior and ventral to the germ cells, the gonadal mesoderm is located anterior to the genital disc and also forms a single median primordium on the ventral side of the embryo. The primordia for the genital disc and the gonadal mesoderm are unusually large in size, which presumably reflects some indeterminacy of the cell lineage leading to an ‘expansion’ of the map.
La morphogenèse du pied de l’embryon de poulet étudiée à l’aide de malformations provoquées par le vert Janus
Authors: Pautou Marie-Paule
Published: April 2021

Morphogenesis of the chick embryo foot as studied by Janus green B-induced malformations

Janus green was injected into the amniotic sac of 6 ·5-day-old chick embryos at a single dose of 8 ·5 or 15 μg; the dye causes respectively 55 and 82 % malformations of the feet. Toes are affected by partial or total soft tissue syndactyly, hypophalangy and infrequently by hyperphalangy. Lateral toes are more severely and more frequently affected by syndactyly and hypophalangy than medium ones. Hyperphalangy is found exclusively in toes I and II and causes the formation of one excess phalanx at most. Syndactylous toes are joined by an overdeveloped digital membrane. Hypophalangic toes have a truncated (non-pointed) distal tip. Two phalanges are lacking at most.

These malformations are due to two distinct phases of the Janus green action. The first one, which is early and fast, inhibits interdigital programmed cell death, causing in term the non-regression of the interdigital membranes and thus syndactyly. The second one, which is late and slow, blocks the apical growth; this leads to hypophalangy.
Distortion of patches of retinal degeneration in chimaeric mice
Authors: West J. D.
Published: April 2021

Estimation of the proportion of degenerate retina in rd/rd and + / + (or + /rd) chimaeras, using a linear analysis of histological sections, suggests a considerable preponderance of the normal phenotype, while analyses based on the area of the surviving tissue suggest that the proportion of each component is similar to that in other tissues. This argues against the validity of the linear analyses used by other authors. It is suggested that cell movement occurs in the outer nuclear layer, following the degeneration of the rd/rd population, and results in a distortion of the original patches of normal cells.
Effect of ascorbic acid deficiency on mouse second molar tooth germs cultivatedin vitro
Authors: Levenson Gordon E.
Published: April 2021

Mandibular second molar tooth germs from two-day old mice were cultured in vitro, on millipore membranes, for periods of up to 20 days in liquid medium with or without added ascorbic acid. Tooth germs grown in ascorbate medium were characterized by relatively normal growth, differentiation, morphology and histology. Cuspation patterns were maintained. The epithelial root sheath continued to grow along the millipore membrane.

Tooth germs cultured in ascorbate-deficient medium manifested a consistent and striking failure in maintenance of differentiated odontoblastic and ameloblastic tissue with arrest of predentin synthesis, severe structural collapse and reduction in size. Cuspation patterns were lost in scorbutic molars, with sinking of surface layers into pulpal tissue and flattening of the entire organ. This resulted in a lack of recognizable morphology and in severe disorganization of tissues. Only growing areas of the root sheath with associated proliferation of pre-ameloblasts and pre-odontoblasts and adjacent pulpal tissue remained normal and refractory to ascorbate deficiency. Odontoblastic as well as ameloblastic layers were disrupted and cells were dedifferentiated. Newly differentiated odontoblasts became highly vacuolated when they became polarized and started to secrete extracellular matrix.
Biosynthesis of DNA, RNA and proteins by mouse embryos cultured in the presence of a teratogenic dose of chlorambucil
Authors: Sadler T. W. , Kochhar D. M.
Published: April 2021

The effect of chlorambucil on the rates of DNA, RNA, and protein synthesis in mouse embryos was investigated using a system of whole embryo culture. Embryos were isolated on the 11th day of gestation (33 ± 3 somites) and grown in culture media for periods of 4–8 h. Reichert’s membrane and most of the placental tissue was removed leaving only the amnion and visceral yolk-sac surrounding the embryo. In the presence of teratogenic doses of chlora-bucil (15 μg/ml) the rate of DNA synthesis was significantly decreased at 4 and 8 h. RNA and protein synthesis were not inhibited at either of these times. A trend toward decreasing rates of protein synthesis at some time beyond 8 h was noted, but not tested.
The developmental analysis of an embryonic lethal (c6H) in the mouse
Authors: Lewis Susan E. , Turchin Howard A. , Gluecksohn-Waelsch Salome
Published: April 2021

A development study of the effects of the c611 allele at the albino locus has identified the c6H homozygote as an early postimplantation lethal. Homozygous c6H embryos can first be recognized at days of gestation by abnormalities of the ectopiacental cone and parietal endoderm. At days, mutant embryos appear severely retarded with obvious abnormalities in all germ layers. All c6H homozygotes are dead and resorbed by 8 days of development. It is proposed that the mutation interferes with the normal differentiation of the parietal endoderm, ectoplacental cone and extra-embryonic ectoderm of the egg cylinder.
Scanning electron microscopy of lithium-induced exogastrulae of Xenopus laevis
Authors: Smith J. L. , Osborn J. C. , Stanisstreet M.
Published: April 2021

Lithium-induced exogastrulae are abnormal embryos which fail to complete gastrulation and do not form normal neural structures. Scanning electron microscopy has been used to compare the surface structure of the ectoderm cells of exogastrulae with that of the ectoderm cells of normal embryos and has shown that the appearance of ciliated cells is delayed in exogastrulae. In addition, the surface structure of endoderm cells, which remain exposed in these embryos, has been studied.
Morphological changes associated with the growth cycle of vibrissal follicles in the rat
Authors: Young R. D. , Oliver R. F.
Published: April 2021

Morphological changes which occur in the growth cycle of the rat vibrissal follicle during the transitional period between consecutive anagen phases are described. In contrast with pelage hair follicles, there is no shortening of the follicle, no formation of a papilla ‘rest’ and no close synchrony between club differentiation and follicle regression. Telogen is therefore considered to occur after loss of the matrix of the hair bulb and maximal diminution of the dermal papilla to a small aggregation of cells. These differences are discussed in relation to current nomenclature of the hair cycle and the function of the vibrissal follicle.
Direct exposure of postimplantation mouse embryos to 5-bromodeoxyuridinein vitroand its effect on subsequent chondrogenesis in the limbs
Authors: Agnish Narsingh D. , Kochhar Devendra M.
Published: April 2021

As maternally administered 5-bromodeoxyuridine (BudR) is very quickly degraded by the liver, a combination of whole embryo culture and organ culture techniques was adopted to expose postimplantation mouse embryos to the analog and to study the effects of long-term treatment on the subsequent differentiation of limb-buds. Early and mid-11th-day mouse embryos were exposed to increasing concentrations of BudR for 12 or 24 h. Forelimbs of the treated embryos were then organ-cultured in drug-free medium and the extent of cartilage development in the expiants examined. Exposure of embryos to 50–150 μg/ml of BudR for 24 h resulted in significant inhibition of chondrogenesis in the subsequent limb cultures and the effect was related to dose. After treatment with 150 μg/ml of the drug, the forelimbs of the early 11-day embryos (somite stage 26–29) showed an almost complete lack of cartilage, while the limbs of mid-11 th-day embryos (somite stage 32–34) were not nearly as sensitive and exhibited about 50 % reduction in the amount of cartilage development. We conclude that if embryos in which the limb development is at a very early stage of development are exposed to BudR, the future course of limb differentiation is permanently and irreversibly damaged, resulting in a partial or even complete suppression of chondrogenesis in the organ. As both the dose and perhaps also the duration of treatment were critical, we suggest that the rather low frequency of reported limb malformations after in vivo injection of teratological doses of BudR may be due to only a small amount of the chemical reaching the embryos.
Ultrastructural analysis of some functional aspects of Xenopuslaevispancreas during development and metamorphosis
Authors: Leone Fiorella , Lambert-Gardini Stefano , Sartori Claudia , Scapin Sergio
Published: April 2021

Morphological studies using both light and electron microscope were carried out with the aim of characterizing cells present in the larval and adult pancreas of Xenopus laevis. The following cell types have been seen: (1) exocrine cells, with a very well developed r.e.r. (rough endoplasmic reticulum), well defined Golgi complexes and numerous large secretory granules (A cells) ; (2) cells without either r.e.r. or secretory granules but with a large number of well developed mitochondria (B cells); (3) endocrine cells often clustered in the typical islets and with small membrane-coated granules showing a very dense central core surrounded by a light halo (C cells).

During development, the aspect is seen to change from an unorganized tissue in which the acinar structures are still not clearly visible (stage 42), to a more organized form in which the exocrine cells (A cells) are seen to be arranged around the lumen of the acinus together with some B cells.

At the stages 54–56, an increasing number of acini surrounded both by A and B cells was observed. At about stage 61, large quantities of necrotic cells were seen and it became more difficult to individualize the acinar organization found in the preceding stages. Finally, there are no necrotic cells in the adult but only A, B cells which are organized in well developed acinar structures and C cells.

The investigation also included a study of some pancreatic enzymes (lipase and amylase) synthesized during larval life. Lipase activity shows a peak at stage 54–56 in which the most well organized tissue of the entire larval life was observed. The activity then decreases, reaching a minimum at stage 66, after which it rapidly rises. Maximum amylase activity occurs at stage 51 after which there is a decrease, to a minimum at stage 66. The activity then remains at constant level.
Active ion transport and β-ecdysone induced differentiation ofDrosophila melanogasterimaginal discs culturedin vitro
Authors: Milner Martin J. , Sang James H.
Published: April 2021

The theory that β-ecdysone initiates developmental changes during insect metamorphosis by causing an increase in intranuclear levels of potassium, together with a concomitant decrease in sodium levels, has been investigated by two methods. First, imaginal discs from late third instar larvae have been cultured with 0·2 μg/ml of β-ecdysone together with inhibitors of active ion transport. Non-specific inhibitors, which may have general effects on sulphydryl groups, such as iodoacetic acid, N-ethylmaleimide, ethacrinic acid and furosemide, inhibit both eversion and differentiation at concentrations of from IO-3 M to 2 × 10−3 M. Ouabain, the only specific inhibitor of the active transport of Na+ and K+ across membranes, had no effect on development even at a concentration of 10−2 M. Second, a medium containing raised levels of K+, and reduced concentrations of Na+, neither initiated disc development in the absence of β-ecdysone, nor stimulated development induced by suboptimal levels (0·02 μg/ml) of β-ecdysone, either in the presence or absence of ouabain. These results suggest that β-ecdysone induced morphogenesis is not dependent upon Na+ and K+ concentrations, or on the activity of an ouabain-sensitive ion pump.
Characterization of an organ-specific differentiator substance in the planarianDugesia etrusca
Authors: Steele Vernon E. , Lange Christopher S.
Published: April 2021

A substance which inhibits brain formation in decapitated regenerating planarians {Dugesia etrusca) was characterized and partially purified. The substance’s inhibitory activity was followed during each purification procedure by adding freshly decapitated animals of a standard size to each fraction, and later measuring the resultant regenerated brain volume. The inhibitory activity remained in the supernatant after a 10000 g centrifugation of a cell-free homogenate. Most of the activity sedimented when the 10000 g supernatant was centrifuged at 32000 g. The degree of inhibitory activity increased with increased numbers of animals in the initial homogenate. The substance has an apparent molecular weight between 2x 105 and 4x 105 daltons. Digestion by pronase destroyed the activity, but treatment with RNase, DNase I, or lipase had no significant effect. The inhibiting substance has an isoelectric point (pl) of between 4·75 and 5·38 and migrates to the anode when electrophorezed in pH 6·8 buffer.
Temporary contacts formed between developing optic fibers in the chick
Authors: Arees Edward A. , Delong G. Robert
Published: April 2021

Temporary junctions were observed between developing optic fibers of the chick embryo and were distributed along the entire length of the axons from the cell body to the tip of the growth cone. These junctions were present in all material studied between days E-3 and E-18, the latter being the start of myelin formation of the optic tract. Junctions between adjacent axons were focal in nature and showed a decrease in the size of the intercellular space caused by a close apposition of the plasma membrane. With the experimental techniques used final identification of these junctions could not be made but are thought to be of two types - the gap and occludens junctions. Temporary fasciae adherentes junctions were observed at the end of the axon, between the growth cone and adjacent neural tissue. Speculation was made on the functional role of these temporary junctions.
Development of a placental blood circulation in rat embryosin vitro
Authors: New D. A. T. , Coppola P. T.
Published: April 2021

Rat embryos explanted with their membranes at head-fold stage ( days gestation) formed an allantoic placenta which enlarged in culture and developed a foetal blood circulation. Embryos explanted at early somite stages ( days) also formed a growing allantoic placenta but only after removal of most of the ectoplacental trophoblast. Assays of total protein in the embryo and placenta suggested that, in the absence of a maternal blood circulation to the placenta, embryo and placenta compete for the respiratory and nutritional resources obtained through the yolk-sac.
Induction of melanogenesis in the epidermal melanoblasts of newborn mouse skin by MSH
Authors: Hirobe Tomohisa , Takeuchi Takuji
Published: April 2021

The number of melanocytes positive to the dopa reaction in the epidermis was shown to increase after newborn mice were injected with α-MSH or DBc-AMP. The agents seemed to induce the initiation of melanogenesis in the pre-existing melanoblasts. Electron-microscopic observation also demonstrated that a-MSH induced not only maturation of melanosomes but also the formation of melanosomes.
Etude par immunofluorescence de l’apparition d’antigènes neuro-spécifiques d’adulte chez l’embryon de Poulet
Authors: Touzet N. , Jeanmaire-Zylberberg R. , Chaminade M.
Published: April 2021

Immunofluorescent study of the distribution of adult neuro-specific antigens in the chick embryo

The adult neuro-specific antigens have been localized by immunofluorescence techniques in diencephalon and mesencephalon of chick embryo. This study has been made using fresh or fixed tissues from embryos 72,48 or 36 h old. At 72 h of incubation the wall of diencephalon shows marked fluorescence; at 48 h of incubation the fluorescent cells are localized in an outer layer and an inner one. In the48h-old embryo the reaction is more distinct and intensive in fresh tissues than in fixed tissues. At 36 h of incubation no fluorescence has been detected either in fresh tissues or in fixed tissues.
Experimental studies on a mutant gene (p) causing premature death ofAmbystoma mexicanumembryos
Authors: Trottier Thomas M. , Armstrong John B.
Published: April 2021

The premature death (p) mutation is a recessive lethal, which, in the homozygous condition, gives rise to a complex of abnormalities. The mutant embryos develop only to stage 37, at which time disintegration of superficial tissue begins. Many of the abnormalities observed in sections of the stage-37 mutant embryo are related to its failure to establish a functioning circulatory system, or to the resulting edema and/or ascites that distend the abdomen and flanks. There are, however, abnormalities of heart, liver, gill and muscle development which cannot be attributed to lack of circulation and edema. All of these abnormalities can be indirectly related to the endoderm, particularly the anterior and dorsal endoderm. The findings, therefore, suggest that the mutation leads to a fairly general defect of the endoderm.
Properties of extra-embryonic ectoderm isolated from postimplantation mouse embryos
Authors: Rossant J. , Ofer L.
Published: April 2021

Extra-embryonic ectoderm isolated from the mouse embryo as late as days post coitum can form cells with the morphological characteristics of trophoblast giant cells both in ectopic sites and in vitro. This similarity to the properties of ectopiacental cone tissue provides further support for the postulated common origin of both tissues from the trophectoderm of the blastocyst.
Cell lineage and cell determination in the developing compound eye of the cockroach,Periplaneta americana
Authors: Shelton P. M. J. , Anderson H. J. , Eley S.
Published: April 2021

By grafting between eye colour mutants of the cockroach Periplaneta americana we have investigated (i) the hypothesis that cells within an ommatidium of the fused rhabdom type are clonally derived from a single mother cell and (ii) we have tested the suggestion that cells from non-prospective eye epidermis can form ommatidia when grafted next to eye tissue. Mosaic eyes containing cells of the two genotypes contain ommatidia with unpredictable combinations of the two sorts of cells at the host/graft border. This finding is inconsistent with the first hypothesis. Using grafts of prothoracic epidermis and head epidermis from non-prospective eye regions we have shown that only cells from the prospective eye region can form ommatidia. Possible ways that eye cells could be determined are discussed in the light of these findings.
Inhibition of cranial neural crest cell development by vitamin A in the cultured chick embryo
Authors: Hassell John R. , Greenberg Judith H. , Johnston Malcolm C.
Published: April 2021

Chick embryos at stage 8, prior to neural crest cell migration, were explanted on whole egg medium with or without vitamin A and cultured for 3 days. Sections through the head regions showed that the cranial neural crest cells had migrated into the first visceral arch in the controls but were absent from this structure in the treated embryos. These observations suggest that vitamin A inhibits neural crest cell development or migration, an effect which may in part account for the facial malformations produced by excess vitamin A.
Trophoblastic vesicles of preimplantation blastocysts can enter into quiescence in the absence of inner cell mass
Authors: Surani M. A. H. , Barton S. C.
Published: April 2021

Preimplantation mouse blastocysts were dissected into inner cell mass (ICM) and tropho-blast cells. These fragments were transferred to pseudo-pregnant mice which were left intact or ovariectomized. The latter group received progesterone to permit blastocysts and the dissected fragments to enter into quiescence, prior to injection of oestradiol to induce implantation. Trophoblastic vesicles, without ICM, entered into quiescence and implanted whereas the ICM did not. The entry of trophoblast into quiescence does not appear therefore to be governed by the ICM.
Ultrastructural observations on stumpy (stm) a new chondrodystrophic mutant in the mouse
Authors: Johnson D. R.
Published: April 2021

Stumpy (stm) is a new chondrodystrophic mutant in the mouse. Light microscopy of carti-lage reveals a slightly increased mitotic rate, more chondrocytes than is usual per lacuna and a wide zone of hypertrophy. Electron microscopy shows that many chondrocytes are in close approximation with some tight junctions: in cartilage from 14-day-old mice there is much interdigitation and folding of the cell membranes of adjacent chondrocytes.
Morphologic alterations in the parietal yolk-sac of the rat from the 12th to the 19th day of gestation
Authors: Jensh R.P. , Koszalka T. R. , Jensen M. , Biddle L. , Brent R. L.
Published: April 2021

The rat parietal yolk-sac and its adherent epithelial cells were examined at various stages of gestation using an en face technique. Specimens were observed at both the light and electron microscopic level. Diastase pretreatment and PAS-staining were used to determine the presence of glycogen. As early as the 12th day of gestation the cytoplasm of the parietal yolk-sac cells contained numerous ribosomes and mitochondria and a large amount of endoplasmic reticulum. The glycogen content of the epithelial cells increased from the 12th day of gestation and accumulated in large quantities by the 16th day. By the 17th day many cells exhibited variable degrees of degeneration. Cellular elements of degenerating cells appeared to be trapped within Reichert’s membrane. Contrary to the reports of other investigators, the present study indicates that the capsular portion of the parietal yolk-sac consisting of Reichert’s membrane and its adherent epithelial cells remained intact until at least the 18th day of gestation. Some of the unique characteristics of the parietal yolk-sac provide experimental models to study the effects of environmental factors on (1) the synthesis of basement membranes, (2) the ageing of cells and (3) the correlation of these histologic changes with the functions of the parietal yolk-sac.
A Gene for Uncomplicated Deafness in the Mouse
Authors: Deol M. S.
Published: April 2021

Deafness associated with locomotor disturbances of labyrinthine origin (head shaking, circular movements) has been known in the mouse for many years, and there are at least ten different gene mutations which produce this syndrome (with or without additional anomalies). Grüneberg (1947) remarked that at first sight it seems remarkable that all the known types of inherited deafness in rodents should be associated with locomotor disturbances. However, shaking and circling are too obvious to be missed, and once detected such mutants will of course be tested for their sense of hearing. Deafness not so ‘labelled’ is unlikely to be discovered in a mouse or rat unless specifically looked for and no such systematic search has so far been made. It is thus quite likely that the absence of ‘uncomplicated’ deafness in rodents is spurious and simply due to the bias against their detection. The fact that there are locomotor disturbances without deafness would seem to support such a suggestion.
The Formation of Sub-blastodermic Fluid in Hens’ Eggs
Authors: New D. A. T.
Published: April 2021

Chick blastoderms have been grown in vitro on pieces of vitelline membrane supported over albumen. The blastoderms were found to remove fluid from the albumen and to secrete it from their endodermal surfaces. It is concluded that this could be the mechanism by which the sub-blastodermic fluid is formed in ovo. The importance of the sub-blastodermic fluid to the developing embryo is discussed.
The Ectodermal Thickening and Ridge in the Limbs of Staged Human Embryos1
Authors: O’rahilly Ronan , Gardner Ernest , Gray D. J.
Published: April 2021

Serial sections of the limbs of seventy human embryos, ranging from developmental horizons 11 to 19 inclusive, were examined. In the upper limb an ectodermal thickening was present on the ventral aspect and lateral border at horizon 12. The lateral part of this thickening formed the ectodermal ridge at horizon 14. The ridge disappeared during horizon 17. These events occurred one horizon later for the similar thickenings and ridges on the lower limb. Changes in appearance and position of the limbs as seen in plaster reconstructions between horizons 12 and 17 are described. The limits of the thickenings and ridges were mapped out on these reconstructions and are illustrated. The significance of similar ridges in avian limbs is discussed.
On the possibility of sperm aster involvement in dorso-ventral polarization and pronuclear migration in the amphibian egg
Authors: Manes Mario E. , Barbieri Francisco D.
Published: April 2021

Sperm aster involvement in the determination of the plane of bilateral symmetry of the future embryo as well as pronuclear movement and orientation has been investigated in the amphibian egg. The procedure involved injecting very small amounts of disrupted sperm cells into the subcortical region of the egg of the toad Bufo arenarum. Using this procedure we have previously shown that structural integrity of the sperm cell is not required for the determination of the symmetry plane.

The present report deals with the cytological effects induced by the injection of sperm homogenate into the egg. As expected, an aster was always present in these eggs. This aster closely resembled that produced in the fertilized egg as the sperm nucleus migrates through the egg mass.

Sections of injected eggs have also shown the presence of two pigment trails similar in appearance to those produced by pronuclear movement after normal fertilization. The streak analogous to the sperm entrance track emerged from the point where the pipette was introduced.

None of these effects were observed in Ringer’s injected eggs. At the time of the rotation of symmetrization, the female pronucleus was seen within a clear area of cytoplasm located at a short distance below the egg cortex. An aster field organized around this clear area was probably formed as a result of the egg centriole activation. In no case was the egg nucleus seen to migrate towards the copulation site as was seen to occur in sperm homogenate-treated eggs.

The active agent was found to be a particulate component which sediments with the head but not the tail fraction of Bufo arenarum sperm.

Injection of blood cells caused a similar response to that elicited by the sperm homogenate.
Pattern formation inDictyostelium discoideum:I. Development of prespore cells and its relationship to the pattern of the fruiting body
Authors: Forman D. , Garrod D. R.
Published: April 2021

Immunofluorescent staining of the prespore cells of the cellular slime mould Dictyostelium discoideum was carried out using a heterologous spore antibody. The highly specific staining of the prespore vesicles (PSVs) within the prespore cells enabled quantitative determinations to be made of the rate and extent of development of these cells throughout the life cycle.

The results showed that PSVs first appeared in a large proportion of the cells shortly after the cells had chemotactically aggregated into multicellular masses. During the later phases of the life cycle, the proportion of cells containing PSV increased, as did the fluorescent intensity of their PSVs, until the early culmination stage of development when 85-90% of the total cell population contained PSVs. Lowering the temperature of development delayed the onset of vesicle formation and decreased the proportion of prespore cells in the total cell population. Changing the growth conditions of the cells prior to multicellular development also had a significant effect on the proportions of prespore cells, as did the use of a mutant known to give rise to fruiting bodies with a reduced number of spores.

The comparability between these estimates of prespore cell proportions at culmination and previously reported spore:stalk ratios within fruiting bodies confirms the view that PSVs are reliable indicators of prespore cells. The finding that temperature and growth conditions and the use of mutants all of which are known to affect spore:stalk ratios, also all affected prespore proportions in the expected direction, adds further weight to this argument.

The fact that prespore cells are beginning to differentiate early in the multicellular phase of the life cycle and the related finding that such differentiation always precedes formation of the grex tip are results of considerable importance to the development of a model for pattern formation in D. discoideum.
Mutations ofDrosophila melanogasterthat affect muscles
Authors: Deak I. I.
Published: April 2021

Eight X-chromosome mutations (falling into five complementation groups) that affect the development and morphology of the indirect flight muscles of Drosophila melanogaster were investigated using histological, behavioural and genetic techniques. All of these mutations result in flightlessness, in a marked reduction in the ability of the flies to jump, and in the wings being held in abnormal positions. Mutations in each of the complementation groups have different effects on the morphology of the muscles. Two (flapwing, vertical wing) result in absence of most of the indirect flight muscle fibres, a third (upheld) is required for the gross organization of muscle structure, another (heldup) is involved in the maintenance of muscle structure once formed, and the fifth seems to be necessary for the detailed architecture of the muscle fibre (indented thorax). The analysis of flies genetically mosaic with respect to each mutation by the technique of fate-mapping suggests that three (heldup, upheld and indented thorax) of the genes concerned have their primary site of action in the musculature itself, while the other two (flapwing and vertical wing) may function primarily in the fat-body and tracheae respectively.