bluuebunny/crossref_metadata_2025 huggingface dataset:
Palate morphogenesis:V. Effects of cholinergic agonists and antagonists on rotation in embryo culture
Authors: Wee Elizabeth L. , Phillips Nancy J. , Babiarz Bruce S. , Zimmerman Ernest F.
Published: April 2021

Morphological studies have shown that the pterygopalatine ganglion in the day-14·5 mouse palatal shelf lies adjacent to the putative contractile system of region-2 cells in the posterior palate. It is of interest to learn whether the ganglion could influence rotation of the palate. Results of embryo culture experiments showed that acetylcholine appeared to play a role in posterior shelf rotation since cholinergic agents (pyridostigmine, bethanechol and carbachol) stimulated elevation of that end of the palate. To characterize the putative receptors mediating the effects of the cholinergic agonists on palate shelf elevation, muscarinic or nicotinic antagonists were introduced into the embryo culture system. Atropine, a muscarinic blocking agent, did not produce any significant effect on palate shelf rotation when tested in overnight and 2 h embryo cultures at 3 × 10−5 M and 10−4 M, respectively. Neither did atropine inhibit significantly the stimulation produced by 10−8 M bethanechol. Thus, the cholinergic effect was probably not on muscarinic receptors of the contractile system. However, hexaméthonium, a nicotinic antagonist, at 10−6 M and 10−4 M profoundly inhibited posterior shelf rotation to about 35 % of the control value in a 2 h incubation. In addition, 10−4 M hexaméthonium inhibited posterior palate rotation to 11 % of the control value after overnight culture. Furthermore, hexaméthonium was able to reverse the stimulation of posterior rotation produced by carbachol. Partial inhibition of palate rotation by hexaméthonium was also demonstrated when pregnant dams were injected with drug at doses approximately corresponding to 10−6 and 10−4 M. Hexaméthonium treatment resulted in approximately 30% of the palates not completely rotated at day 15·5 compared to only 9·3 % in the control. Hexaméthonium also produced a significant increase in the palate gap and a comparable decrease in palate fusion. These effects were slightly greater at the posterior end of the palate. Thus, the cholinergic ganglion in the posterior palate may play a role in regulating shelf rotation at that end through a nicotinic pathway.
Aggregation between teratocarcinoma cells and preimplantation mouse embryos
Authors: Stewart Colin
Published: April 2021

The ability of two embryonal carcinoma (EC) cell lines, F9 and PCI3, to aggregate with preimplantation 8-cell mouse embryos is described. Both adhere to the embryonic cells and subsequently compact with the embryos. The aggregates form blastocysts in culture. The blastocysts sometimes contain the EC cells, located almost always in their inner cell mass. Differentiated derivatives of EC cells, namely PYS-1 and PYS-2, as well as STO fibroblasts do not aggregate with embryos.
A gradient of morphogenetic information involved in muscle patterning
Authors: Williams G. J. A. , Caveney S.
Published: April 2021

The results of grafts performed in the larva of the beetle Tenebrio molitor reveal that the position at which certain adult muscle attachments form is specified by a regulative, rather than a mosaic, mechanism. The results of grafts involving the rotation of squares of integument through 180° or 90°, or the antero-posterior transposition of two adjacent rectangles of integument, show that the site of muscle attachments in the antero-posterior axis of an abdominal sternite is specified by an epidermal segmental gradient of positional information. This gradient is presumed to be identical to the gradient which specifies cuticular patterns in this insect. There is a good correlation between the effect of grafts on adult muscle morphology and cuticular patterns.
Formation of feathers on chick foot scales: a stage-dependent morphogenetic response to retinoic acid
Authors: Dhouailly Danielle , Hardy Margaret H. , Sengel Philippe
Published: April 2021

In the chick embryo, large scales (scuta) form on days 9 –11 on the anterior face of the shank and the upper surface of the toes; smaller scales (scutella) appear on day 11 on the posterior face of the shank; most of the smallest scales (reticula) form on days 12 and 13 on the plantar surface of the foot.

A single injection of 125 μg of retinoic acid (RA) into the amniotic cavity caused the formation of feathers on the foot scales in locations and percentages differing according to the age of embryos at the time of treatment. Injection at 10 days caused feathers to form on the feet in 57 % of the embryos, almost all of which bore feathers on their scuta and scutella; a few reticula were occasionally affected. When treated at 11 days, 48 % of embryos had feathered feet, the tarsometatarsal scutella and digital reticula being most frequently affected. Treatment at 12 days resulted in feathers on the feet of 15 % of the embryos, all of which bore feathers on the reticula only, while the scuta and scutella were not affected.

It was concluded that the foot skin regions which were affected by RA treatment were those in which scale morphogenesis was starting or about to start at the time of injection. These regions contained pre-placodal or placodal stages of scuta and scutella, and the preelevation or elevation stages of reticula.
Scanning electron microscopy of wound healing inXenopusand chicken embryos
Authors: Stanisstreet Martin , Wakely Jennifer , England Marjorie A.
Published: April 2021

Wound closure in the ectoderm of Xenopus early neurulae and chick primitive-streak embryos has been studied by scanning electron microscopy (SEM). Initial gaping of the wound and a cobble-stone appearance of cells peripheral to the wound in both Xenopus and chick confirm that the ectoderm is under lateral tension at these stages. Healing is rapid: in Xenopus embryos wound closure has started within 5 min of wounding; in chick healing is almost complete within 30 min in some cases. The SEM observations suggest that in Xenopus embryos changes in cell shape are the major mechanism for wound closure. In chick embryos wound healing is also accompanied by changes in the shape of the marginal cells, but evidence is presented that in this system cell proliferation is important. The mechanisms of wound healing in Xenopus and chick embryonic ectoderm are compared with those of wound healing in other tissues.
The in vitro transmission frequency of the t12 mutation in the mouse
Authors: McGrath James , Hillman Nina
Published: April 2021

Male mice which are heterozygous for a recessive lethal mutation ( + /tL) transmit the tL mutation in non-Mendelian ratios. In the present studies, spermatozoa obtained from + t12 males were used to fertilize ova from + t12 females in vitro. The frequency of transmission of the t12 mutation determined from these in vitro studies was compared with the frequency of transmission of this mutation in normal and delayed matings. The data show that the transmission frequency of the t12 mutation, in vitro, is Mendelian and is the same as the transmission frequency of the t12 mutation in vivo when matings are delayed until the time of ovulation.
Immunohistochemical localization of cyclic AMP in the developing rodent secondary palate
Authors: Greene Robert M. , Shanfeld Joseph L. , Davidovitch Zeev , Pratt Robert M.
Published: April 2021

During development of the mammalian secondary palate, medial-edge epithelia (MEE) from apposing palatal shelves adhere and undergo autolysis allowing palatal mesenchymal regions to unite. In a prior study (Greene & Pratt, 1979), we reported a transient increase in levels of cyclic AMP (cAMP) in the mouse and rat palate during epithelial adhesion and cell death. The objective of this study was to examine the distribution of cyclic AMP in the developing rodent secondary palate using immunohistochemistry to localize cyclic AMP. Staining for cAMP was observed in the epithelium just prior to and during epithelial fusion (day 16 in the rat; day 14 in the mouse). Cyclic AMP was distributed throughout the epithelial cytoplasm whereas no staining was seen in nuclei. Epithelial staining for cAMP was faint or absent 24 and 48 h prior to epithelial contact. Mesenchymal staining for cAMP was minimal and associated with the plasma membrane at all stages studied. These results demonstrate that elevated levels of cAMP in the rat and mouse palate during epithelial adhesion and cell death are mainly due to increases of the nucleotide in palatal epithelium. This observation suggests that a transient increase in epithelial cAMP may play a role in palatal epithelial differentiation.
Ommatidium assembly and formation of the retina-lamina projection in interspecific chimeras of cockroach
Authors: Nowel Mark S.
Published: April 2021

By grafting operations, interspecific eye chimeras of the cockroaches Gromphadorhina portentosa and Leucophaea maderae were produced. Mechanisms involved in the development of both the compound eye and the retina-lamina projection have been studied. Most cell types composing the eyes of these cockroaches are cytologically distinguishable in the chimera; also, retinula axons forming the retina-lamina projection in the two species are of vastly different lengths. At the border between host and graft eye tissue, individual ommatidia are formed containing cells of both types. In particular, it is shown that the four cone cells can be found in any of the possible combinations of the two cell types. This shows that the cone cells within one ommatidium are not necessarily related by lineage. These results are in agreement with the hypothesis that cells within an ommatidium are determined by position rather than by a lineage mechanism. Furthermore, formation of mosaic ommatidia suggests that mechanisms governing eye formation are similar in these two species. The formation of the projection from donor retina to host lamina shows that axon elongation is not rigidly programmed, but that the axons grow until they reach a suitable target at which point connexions are made.
Chimaeric rabbits from immunosurgically-prepared inner-cell-mass transplantation
Authors: Babinet C. , Bordenave G. R.
Published: April 2021

Rabbit inner cell masses (ICM’s) have been prepared by immunosurgery from 96-h-old blastocysts. Their properties are described. It is shown that ICM’s prepared this way retain their developmental potentialities. In particular if they are injected into host blastocysts, they appear to be able to participate in the development of the composite blastocysts thus obtained: upon implantation into a foster-mother the latter give rise, in a high proportion of cases, to chimaeric rabbits. Immunoglobulin allotypic markers as well as progeny test were used to assess chimaerism.
Expression of Forssman antigen in the post-implantation mouse embryo
Authors: Stinnakre M. G. , Evans M. J. , Willison K. R. , Stern P. L.
Published: April 2021

The expression of Forssman antigen on the surface of cells of post-implantation mouse embryos between 5 and days old and of cells of the gonads from days has been followed using the monoclonal antiserum Ml/22.25. In the early post-implantation embryo a lineage-related distribution is found.

The inner cell mass of the blastocyst was previously shown to be Forssman antigen positive and its derivative tissues the epiblast of the 5-day embryo and the primary embryonic endoderm are also positive. The endoderm cells remain positive both over the embryonic and extraembryonic portions of the embryo but the epiblast becomes Forssman antigen negative as it differentiates into embryonic ectoderm. The extraembryonic ectoderm which is derived from the Forssman negative trophectoderm remains negative throughout. The primordial germ cells are Forssman antigen positive from their first appearance in the germinal ridge until day 14 when they become negative but after that time it is other cells not related by direct lineage which become Forssman antigen positive. These are tentatively identified as Sertoli cells precursors as it is the Sertoli cells which are the antigen-positive population in the adult testis.
Developmental analysis of the homoeotic mutationbithoraxoidofDrosophila melanogaster
Authors: Kerridge Stephen , Sang James H.
Published: April 2021

The homoeotic transformations caused by bxd are described in detail. The anterior histoblast nests of the first abdominal segment are missing, and are replaced by one or two leg discs ventrally. Mainly anterior compartment patterns are found in the ectopic, abdominal legs of adult flies. However, cell lineage analyses show that both anterior and posterior polyclones are established early in the development of these ectopic legs, but the posterior polyclone is smaller. Cells of the anterior polyclone may regulate later in development to adjust for this and form pattern elements normally derived from the posterior polyclone. In addition, experiments show that bxd+ is required by the second larval instar stage, and possibly as early as the blastoderm stage.
Pattern re-establishment – transplantation and regeneration of the leg in the cricket Teleogryllus commodus (Walker)
Authors: Biggin Robert J.
Published: April 2021

Regeneration and grafting experiments were carried out on the prothoracic leg of the cricket Teleogrylhts commodus (Walker) to examine the precision with which surface cuticular structures and internal epidermal derivatives are reformed. By comparing regenerated and grafted limbs with normal limbs it was found that the three-dimensional structure of epidermal derivatives is not restored. This is despite the fact that regenerated and grafted limbs appear similar in their external morphology to normal limbs. The implication of these results are discussed in the context of theories of pattern formation.
Ultrastructural and histochemical observations in the developing iris musculature in the chick
Authors: Narayanan Y. , Narayanan C. H.
Published: April 2021

Irises from chick embryos and from 2- and 3-week-old chicks were studied using ultrastructural and histochemical methods in order to clarify the relationship between cell loss in the ciliary ganglion and the establishment of permanent peripheral connections between the ciliary neurons and the iris muscle. The iris muscle undergoes morphological and biochemical differentiation between 11 and 13 days of incubation. This period coincides with the critical period in the development of the ciliary ganglion when massive cell degeneration occurs. During this period, the iris develops typical sarcomeric structure, with AChE activity in the nuclear envelope, Golgi, and the ‘T’ system. At 15 days of incubation AChE activity is found localized in discrete areas on the muscle fiber, forming specific neuromuscular junctions. Between 13 and 15 days of incubation, there is a shift in the localization of AChE activity in the iris muscle, from the sarcoplasmic structures to the junctional membranes.

Few synaptic terminals are observed in the iris musculature prior to 11 days of incubation. There is a marked increase in the number of synaptic terminals between 11 and 13 days of incubation which also coincides with the period of cell loss in the ciliary ganglion. The establishment of neuromuscular junctions at 15 days of incubation corresponds with the period when the number of neurons in the ciliary ganglion has attained the adult level. The time table of the events described above, leads us to conclude that during development only those neurons in the ciliary ganglion which make peripheral contacts survive, and only such contacts differentiate into mature neuromuscular junctions on the iris muscle. This will imply that neurons which are doomed to die, although they may send out fibers to the periphery, do not make peripheral contacts before death.
Mouse egg ribosomes: evidence for storage in lattices
Authors: Bachvarova R. , Leon V. De , Spiegelman I.
Published: April 2021

The ribosomes of mouse ova were labeled by exposure of growing ovarian oocytes to [3H]uridine. The ribosomes of ova lysed and dispersed in hypotonic medium were contained in particles with an unusually low buoyant density in CsCl density gradients. These particles sedimented at 9000g or less, and electron microscopy of the pellet revealed ribosome-like particles embedded in a fibrillar network. These results indicate that the ribosomes are present in a proteinaceous superstructure, probably the lattices seen in situ by transmission electron microscopy.
Formation of the retina-lamina projection of the cockroach: no evidence for neuronal specificity
Authors: Nowel Mark S.
Published: April 2021

There is a topographical mapping of neural elements onto the lamina neuropile of the optic lobe of the cockroach, such that adjacent ommatidia project to adjacent points (optic cartridges) in the lamina neuropile. Postembryonic growth of the compound eye occurs by addition of new ommatidia to its growing margin. Retinula axons grow from the newly formed ommatidia to the lamina. By transplantation experiments in which the position or the orientation of retinal material is altered, it is shown that retinula axons do not make connections in the lamina with respect to their old position and orientation, but rather, in keeping with their new situations, apparently maintaining a retinotopic mapping upon the optic lobe.
Postembryonic growth of the compound eye of the cockroach
Authors: Nowel Mark S.
Published: April 2021

The postembryonic growth of the compound eye of the cockroach Periplaneta americana involves increases in the size of the individual ommatidia as well as a 35-fold increase in the number of ommatidia. These ommatidia are added to the anterior, dorsal, and ventral margins of the eye by means of an almost continuous process of cell division in the proliferation zone in these margins. This proliferation phase is followed by a process of maturation of bundles of ‘pre-ommatidial’ cells into mature ommatidia, a process which involves further cell division. Processes involved in compound-eye development are investigated by eye margin grafting, histological techniques and cell proliferation studies.
An experimental study on neural crest migration in Barbus conchonius (Cyprinidae, Teleostei), with special reference to the origin of the enteroendocrine cells
Authors: Lamers C. H. J. , Rombout J. W. H. M. , Timmermans L. P. M.
Published: April 2021

A neural crest transplantation technique is described for fish. As in other classes of vertebrates, two pathways of neural crest migration can be distinguished: a lateroventral pathway between somites and ectoderm, and a medioventral pathway between somites and neural tube/notochord. In this paper evidence is presented for a neural crest origin of spinal ganglion cells and pigment cells, and indication for such an origin is obtained for sympathetic and enteric ganglion cells and for cells that are probably homologues to adrenomedullary and paraganglion cells in the future kidney area. The destiny of neural crest cells near the developing lateral-line sense organs is discussed. When grafted into the yolk, neural crest cells or neural tube cells appear to differentiate into ‘periblast cells’; this suggests a highly activating influence of the yolk. Many neural crest cells are found around the urinary ducts and, when grafted below the notochord, even within the urinary duct epithelium. These neural crest cells do not invade the gut epithelium, even when grafted adjacent to the developing gut. Consequently enteroendocrine cells in fish are not likely to have a trunk- or rhombencephalic neural crest origin. Another possible origin of these cells will be proposed.
Mitochondrial number, cytochrome oxidase and succinic dehydrogenase activity in Xenopus laevis oocytes
Authors: Marinos E. , Billett F. S.
Published: April 2021

An estimate has been made of the numbers of mitochondria in the mitochondrial cloud (Balbiani body) of Xenopus laevis oocytes ranging in size from 50 to 250 μm. The mito-chondrial number is expressed in terms of a ‘standard’ organelle measuring 2 μm in length and 0·2 μm in diameter and is derived by measurements on electron micrographs of sections through the cloud. It is found that the amount of mitochondrial material rises very rapidly as the oocyte grows in size. At the time the cloud disperses, in oocytes of about 300μm in diameter, it is estimated that there are the equivalent of over 500000 mitochondria in each cell. The rate of increase is very similar to the rate of accumulation of mitochondrial DNA during the same period of growth.

Using a polarographic technique the specific activity of cytochrome oxidase and succinic dehydrogenase was determined in mitochondrial fractions isolated from oocytes over a size range of 80–1200μm in diameter. Although the specific activity of succinic dehydrogenase remains constant that of cytochrome oxidase falls sharply during the period when the mitochondria are replicating rapidly, i.e. up to about 300μm diameter. In larger oocytes the specific activity of enzymes appears to remain constant but increasing contamination of the isolated mitochondrial fraction does not allow conclusions to be drawn from the enzyme loading of the mitochondria once they have dispersed from the cloud.

The results are discussed in relation to the possibility that mitochondrial replication preceeds, or at least outpaces, mitochondrial differentiation during the course of oogenesis.
Control of maintenance and anteroposterior skeletal differentiation of the anterior mesenchyme of the chick wing bud by its posterior margin (the ZPA)
Authors: Hinchllffe J. R. , Gumpel-Pinot M.
Published: April 2021

If the posterior half of the chick wing bud (stages 17–22) is excised, the anterior half which normally forms humerus (part), radius and digit 2, forms only a single skeletal element, either humerus or humerus fused with reduced radius. Beginning at 18 h after operation, and continuing to 48 h the anterior and distal mesenchyme in such anterior halves becomes necrotic and the AER regresses. By contrast, if the anterior half of the chick wing bud (stages 17-22) is excised, the posterior half develops as in the normal bud, and forms humerus (part), ulna and digits 3, 4 and 5. Such posterior halves develop no more mesenchymal necrosis than the normal contralateral wing buds and the AER remains healthy. Further, if the excision of the posterior part is made in such a way as to leave in place a part of the zone of polarising activity (ZPA), a normal wing with complete skeleton is formed. Thus in order to survive and differentiate, the anterior part of the wing bud needs a factor supplied by the posterior part containing the ZPA. These results support the view that the ZPA plays a role in controlling the anteroposterior differentiation of the normal wing bud.
Pattern formation along the anteroposterior axis of the chick wing: the increase in width following a polarizing region graft and the effect of X-irradiation
Authors: Smith J. C. , Wolpert L.
Published: April 2021

A study is made of the widening of the chick limb bud that occurs after a graft of an additional polarizing region. Such buds are about 50% wider than controls, after 36 h. By contrast, growth along the proximodistal axis is unaffected. This widening is reduced by treating the host embryo with 10 Gy X-irradiation and the altered pattern of digits is consistent with a diffusible morphogen model for the specification of positional information along the anteroposterior axis.
Experiments on Anuran limb buds and their significance for principles of vertebrate limb development
Authors: Maden M.
Published: April 2021

A standard set of six experiments performed on the limb buds of two species of Anurans - Rana temporaria and Xenopus laevis - are described. The experiments are limb-bud amputation, distal to proximal shifts, proximal to distal shifts, inversion of the dorsoventral axis inversion of the anteroposterior axis and inversion of both axes. The results are compared to those previously reported for Urodeles and chicks to determine whether any principles of vertebrate limb development can be formulated. It appears that the proximodistal axis becomes increasingly mosaic from the Urodeles through Anurans to chicks. In the transverse axes however, there is much more uniformity of behaviour in the production of supernumerary limbs. The relation between the type of limb development (regulative or mosaic) and the subsequent regenerative powers of the adult limb is discussed.
Significance of cell-to-cell contacts for the directional movement of neural crest cells within a hydrated collagen lattice
Authors: Davis Edward M. , Trinkaus J. P.
Published: April 2021

Neural tubes whose neural crest had just begun migration were isolated from stage-14 chick embryos, cleaned with 0·1% trypsin, and cultured in transparent hydrated collagen lattices (HCL) in an effort to stimulate in part the three-dimensional environment through which neural crest cells migrate in situ, in the embryo. The concentration of collagen in the lattices varied from 50 μ g/ml to 390 μ g/ml. The mode of movement and contact behaviour of neural crest cells migrating from the neural tube under these conditions were recorded directly with time-lapse cinemicrography. Both their shape and their rate of translocation were dependent on the concentration of collagen in the HCL. In low concentrations (50 μ g/ ml to 105 μ g/ml), neural crest cells have elongate spindle shapes and translocate at an average rate of 1 μ m/min, whereas in high concentrations (190μ g/ml to 390μ g/ml), their shape is rounded, and they translocate at an average rate of only 0·5 μ m/min. Neural crest cells migrate from neural tubes in these preparations principally in loose clusters, with a few single cells in the lead. The cells in these groups display leading-to-trailing edge adhesions and form tongues or streams of cells directed away from the neural tube. The paths of migration of both individual cells and groups of cells are aligned with the collagen fibrils of the HCL, which radiate from the neural tube. The classical visible characteristic of contact inhibition of movement, change in direction of cell movement after contact with other cells, was not observed; neither the rate of translocation nor the time spent migrating away from the tube is dependent on the number of contacts between cells. It is concluded that the directional movement of neural crest cells in HCL cultures does not depend on contact inhibition of movement.
Muscle nerve branches do not develop in chick wings devoid of muscle
Authors: Lewis Julian , Chevallier Alain , Kieny Madeleine , Wolpert Lewis
Published: April 2021

If the somitic mesoderm of a 2-day chick embryo is destroyed by X-irradiation, the adjacent limb develops with a normal pattern of connective tissues, but is devoid of muscle. The innervation of muscleless wings produced in this way was examined in silver-stained whole mounts, fixed 3 to 8 days later. The main nerve trunks and their cutaneous branches developed normally; but the nerve branches which in a normal limb would lead to individual muscles were generally absent. In almost all those exceptional cases where muscle nerve branches were present, muscle was found to be present also, despite the X-irradiation. Where there was no muscle, the muscle nerve branches apparently did not even begin to form. As a control for side effects of the X-irradiation, wing buds were grafted from normal to irradiated embryos and vice-versa, and again analysed for their innervation. The results confirmed that the absence of muscle nerve branches was due to the absence of muscle cells in the limb. Thus

(1) the routes taken through a limb by the main mixed nerve trunks and by their cutaneous branches are determined by the connective tissues, and not by any mechanisms requiring muscle cells; but (2) muscle cells are necessary to provoke the formation of the side branches leading to the sites of individual muscles.
Influence of the entoderm on mesodermal expansion in the area vasculosa of the chick
Authors: Augustine J. M.
Published: April 2021

To determine whether expansion of the splanchnic mesoderm of the area vasculosa is influenced by the entodermal substratum on which it occurs, entoderm was separated from a small area of splanchnic mesoderm. The splanchnic mesoderm then contracted and thickened, decreasing to 7 % of its original area in 16 h. By then entoderm had reattached to most of it, and it expanded, reaching 11 % of its original area by 24 h. It was concluded that attachment to entoderm may be required for expansion of the splanchnic mesoderm, but the small amount of expansion obtained made this conclusion tentative.

For technical reasons subsequent investigation was done on mesodermal transplants, which attached to the host’s entoderm in 6 h, by which time they had contracted to 15% of their original area. They then expanded, reaching 30% by 16 h and 49% by 24 h. The onset of their expansion was also accompanied by the formation of connexions between their blood vessels and those of the host, and by the resumption of blood flow in them. To see whether their expansion was due to resumption of blood flow or to attachment to entoderm, other transplants were made in which the middle one-third was separated from the host’s entoderm by a piece of Millipore filter. This portion failed to expand although it became connected to the host’s blood vessels and flow of blood resumed in it, while the two lateral thirds, which regained attachment to entoderm, expanded. Transplants were also rotated so that their splanchnic mesoderm attached to ectoderm instead of entoderm. These transplants also formed connexions with the host’s vessels and blood flow resumed in them, but they expanded only slightly compared to non-rotated controls, in which the splanchnic mesoderm attached to entoderm.

It was concluded that while flow of blood undoubtedly promotes splanchnic mesodermal expansion as others have shown, attachment of the splanchnic mesoderm to entoderm is also important, and without it the promotive effect of blood flow does not occur. Evidence was also obtained that attachment to entoderm maintains the thinness of the splanchnic mesoderm, and that a vascular growth stimulus may be produced by the unvascularized entoderm distal to the mesoderm.
Evidence for regulation of growth, size and pattern in the developing chick limb bud
Authors: Summerbell Dennis
Published: April 2021

This paper examines the hypothesis that the developing chick limb bud has mechanisms for regulating the control of growth, size and pattern. The tests included: surgical removal of selected parts of the limb field, X-irradiation, temperature shock and the manipulation of known limb organizer regions (removal of the apical ectodermal ridge, or the addition of an extra zone of polarizing activity). The results strongly support the idea that there are regulatory mechanisms controlling both the pattern and the size of the limb and suggest that they involve regulation of the growth rate via control of cell division throughout the embryonic period. Possible mechanisms are discussed.
The effect of removing posterior apical ectodermal ridge of the chick wing and leg on pattern formation
Authors: Rowe Donene A. , Fallon John F.
Published: April 2021

Recent experiments, in which barriers were inserted between anterior and posterior tissues of the chick wing bud, resulted in deletion of structures anterior to the barrier (Summerbell, 1979). From these data it was concluded that blockage of morphogen from the polarizing zone by the barrier resulted in the observed failure of specification of anterior structures. We suggest an alternative interpretation, viz. the interruption of the apical ridge by the barrier caused the deletions. This hypothesis was tested by removal of increasing lengths of ridge. This was done beginning at either the anterior or posterior junction of the wing bud with the body wall and proceeding posteriorly or anteriorly, respectively, to each half-somite level between 16/17 and 19/20. With removal of progressively greater lengths of anterior ridge, more anterior limb elements failed to develop. These data were used to construct a map of the ridge responsible for each digit. To test our hypothesis we removed posterior sections of apical ridge, as described above. Removal of posterior ridge to a level which was expected to allow outgrowth of digits anterior to the level of removal resulted in wings without digits in the majority of cases. An exception occurred when ridge posterior to the mid-19 somite level was removed. In almost half of these cases digits 2 and 3 did develop. In most cases the retention of only a half-somite piece of ridge with all other ridge removed, also resulted in deletion of all digits. Again the exception occurred when ridge posterior to somite level mid-19 and anterior to level 18/19 was removed, leaving only that ridge between somite level 18/19 and mid-19. In many of these cases digit 3 did develop. We conclude from these data that, in the wing bud, ridge anterior to the mid-19 somite level must be connected to more posterior ridge to function.

The leg ridge does not exhibit the asymmetrical, low anterior, high posterior configuration, which appears in the wing. Because the leg ridge is symmetrically high anteriorly and posteriorly, we questioned whether or not leg would also require a continuity between anterior and posterior ridge for anterior ridge to function. It did not. When posterior ridge was removed, structures developed under remaining anterior ridge and the elements which developed were complementary to those which developed after anterior ridge removal to the same somite level. Those leg elements, which failed to develop, were truncated at the appropriate proximodistal levels as indicated by the fate map we have constructed for the leg.

The data reported here do not rule out a role for the polarizing zone in specification of anterior structures. It is apparent that posterior ridge removal in the wing results in loss of structures anterior to the removal. However, this is not true for the leg.
Cellular contacts between hindbrain and prospective ear during inductive interaction in the axolotl embryo
Authors: Model Pat G. , Jarrett Lonny S. , Bonazzoli Robin
Published: April 2021

In the amphibian embryo, beginning in the late neurula and continuing through midtailbud stages, the developing medulla exerts an inductive influence on the prospective ear, effecting its determination. Fine structural analysis of the region of closest apposition between the two tissues in the axolotl (Ambystoma mexicanum) reveals that during this period, there is a significant increase in the surface area of the apposed cells through the projection of long finger-like processes that traverse the medulla–ear interspace and the appearance of many focal contacts between the two cell types. These contacts are small, varying in diameter from 10–30 nm and they exhibit the septilaminar appearance and 2–4 nm intercellular cleft characteristic of gap junctions. Once the ear has been determined, both the cell processes and the focal junctions between apposed cells virtually disappear.

We suggest that the projection of processes from the surfaces of the apposed cells enhances the opportunity for cell interaction through the formation of very small gap junctions and that the junctions could provide the structural substrate for direct communication between medulla and ear during their inductive interaction.
Postimplantation development of CB-induced triploid mouse embryos
Authors: Niemierko Anna
Published: April 2021

By subjecting A strain eggs at the time of fertilization and polar body extrusion to 5 μg/ml cytochalasin B, digynic triploidy was produced in 80 % fertilized eggs. Triplonucleate eggs were transplanted to recipients and examined between 9–11th day of pregnancy. Development of triploid mouse embryos up to day 7 is normal and most embryos form early egg cylinder. At day 8 the embryonic part of the cylinders is under-developed and later development fails to form an embryo. Development of foetal membranes is much less affected, CB-induced triploids survive to 10th-day of pregnancy.
Time-lapse film analysis of cytoplasmic streaming during late oogenesis ofDrosophila
Authors: Gutzeit Herwig O. , Koppa Roswitha
Published: April 2021

Cytoplasmic streaming in follicles of Drosophila has been analysed in vitro by means of time-lapse films. Late vitellogenic follicles develop normally in vitro as judged by morphological criteria. Furthermore, follicles (stage 10 and younger) which were cultured in vitro for the same length of time as follicles which were filmed, developed normally in vivo after injection into a host fly. The recorded cytoplasmic movements are, therefore, unlikely to be an in vitro artefact.

At early vitellogenic stages (up to stage 9; King, 1970) no cytoplasmic streaming can be detected, but at stage 10A cytoplasmic movements are initiated within the oocyte. At stage 10B, when the nurse cells start degenerating, nurse cell cytoplasm can be seen to flow into the growing oocyte. At stage 11 a central stream of nurse-cell cytoplasm reaches the oocyte within a minute. The ooplasmic streaming is most rapid at stage 10B and stage 11 and only an oocyte cortex up to 7 μm thick remains stationary. Once the bulk of the nurse-cell cytoplasm has poured into the oocyte (stage 12) the cytoplasmic movement ceases, first in the nurse cells and later in the ooplasm. In mature oocytes no cytoplasmic streaming can be detected.
Preferential paternal X inactivation in extraembryonic tissues of early mouse embryos
Authors: Harper Mary I. , Fosten Mandy , Monk Marilyn
Published: April 2021

The preferential expression of the maternal X chromosome seen in certain extraembryonic membranes of the mouse was studied by investigating the tissues from which these membranes are derived during early development. The electrophoretic variant of the X-coded enzyme PGK-1 (phosphoglycerate kinase) was used to distinguish the expression of the maternal from the paternal X chromosome in heterozygous females.

Both the extraembryonic ectoderm and primary endoderm of -day female egg cylinders gave almost exclusive expression of the maternal form of the enzyme whereas the epiblast gave near equal expression of the two parental alleles. No paternal PGK-1 band could be detected in samples of pooled -day blastocysts, but after 3 or 4 days of culture in vitro a faint paternal band was seen in the resultant outgrowths. The activity of the maternal band in these latter samples had increased greatly from that of the blastocysts, consistent with preferential expression of the maternal Pgk-1 allele in the trophoblastic cells of the outgrowths, while both alleles are expressed in inner-cell-mass cells. The results strongly support the idea that non-random X-chromosome expression is due to preferential paternal X inactivation in trophectoderm (from which extraembryonic ectoderm is derived) and in primary endoderm, and not to cell selection.
Localization of microfilament bundles in the upper layer of the primitive-streak-stage chick blastoderm
Authors: Vakaet L. , Vanroelen CH.
Published: April 2021

Transmission electron microscopy of medium-streak-stage chick blastoderms revealed the presence of 4-6 nm microfilament bundles just under the apical surface of upper layer cells, in close association with the junctional complex. The presence of these microfilament bundles was not restricted to the centre of the primitive streak, but they were also observed in the presumptive neural plate and lateral to the anterior half of the primitive streak. The microfilament bundles are thought to be involved in every morphogenetic movement in the upper layer and not to be restricted to groove formation.
Influence of a temporary embryonic testis graft on the regression of Müllerian ducts in female chick embryo
Authors: Maraud R. , Rashedi M. , Stoll R.
Published: April 2021

Whole testes of 13-day-old chick embryos grafted according to an original method into the extraembryonic coelom of 3-day-old recipients were next removed up to day 6.

The temporary presence of a testis allowed the Müllerian ducts to retrogress, from day 8, in a high percentage of female hosts. It can be concluded that the graft secreted into the blood of the embryo enough ‘anti Müllerian hormone’ to provoke regression of ducts at least 2 days after its removal and that the reaction of ducts depends on the appearance of their sensitivity to this hormone.
Investigation of cell lineage and differentiation in the extraembryonic endoderm of the mouse embryo
Authors: Gardner R. L.
Published: April 2021

The technique of injecting genetically labelled cells into blastocysts was used in an attempt to determine whether the parietal and visceral endoderm originate from the same or different cell populations in the early embryo. When the developmental potential of 5th day primitive ectoderm and primitive endoderm cells was compared thus, only the latter were found to colonize the extraembryonic endoderm. Furthermore, single primitive endoderm cells yielded unequivocal colonization of both the parietal and the visceral endoderm in a proportion of chimaeras. However, in the majority of primitive endodermal chimaeras, donor cells were detected in the parietal endoderm only, cases of exclusively visceral colonization being rare. Visceral endoderm cells from 6th and 7th day post-implantation embryos also exhibited a striking tendency to contribute exclusively to the parietal endoderm following blastocyst injection.

The above findings lend no support to a recent proposal that parietal and visceral endoderm are derived from different populations of inner cell mass cells. Rather, they suggest that the two extraembryonic endoderm layers originate from a common pool of primitive endoderm cells whose direction of differentiation depends on their interactions with non-endo-dermal cells.
A genetic analysis of the determination of cuticular polarity during development inDrosophila melanogaster
Authors: Gubb D. , García-Bellido A.
Published: April 2021

The polarity mutants pk, sple, mwh, fz and in alter the orientations of cuticular processes in several regions of the body. The mutant polarity patterns are constant and do not result from alterations in cell lineage. Polarity patterns are locus specific rather than allele specific (new alleles express the same polarity patterns as the original alleles). In the wing, polarity formation is largely cell autonomous and is independent of the anteroposterior compartment boundary. By genetic and physiological manipulation it is shown that the mutant polarity patterns are unaffected by the size of the wing blade or the number of cells that form it. Mutants which remove parts of the wing margin or alter the distribution pattern of wing veins do not alter the mutant polarity patterns. Thus, neither the wing margins nor the pattern of vein tissue act as spatial references for polarity formation. The determination of mutant polarity patterns is not dependent on the overall topology of the wing blade but is region-specific. The mutants affect several independent functions. The possible wild-type function of the loci in polarity formation is discussed.
Regulation of ciliary pattern in Dileptus (Ciliata).:I. Sensory cilia and their conversion into locomotor cilia
Authors: Golinska Krystyna
Published: April 2021

The surface of Dileptus contains three different regions: locomotor, oral and sensbry. Each region has cilia with a specific structure and arranged in a characteristic pattern. In the morphogenetic situation when a sensory region transforms into a locomotor one, sensory cilia undergo structural changes converting them into locomotor cilia. The evidence for this is that cilia are found in the transforming region with an inner microtubular pattern intermediate between that of sensory and locomotor cilia. There are also changes in distribution of sensory units leading to a pattern characteristic of locomotor cilia. The conversion of sensory cilia into locomotor ones is also confirmed by a complete lack of evidence for resorption of sensory units within the transforming region, although the resorption is usually very easily observed with the transmission electron microscope. Transformation lasts about 5 h after the operation ; afterwards locomotor cilia of normal appearance occupy the transformed region.

This way of regulation of ciliary pattern has not been previously described. Its most surprising feature is the regulation of inner structure in an already differentiated ciliary unit. Some aspects of mechanisms which could control this kind of pattern regulation, are discussed.
Preimplantation development of gynogenetic diploid mouse embryos
Authors: Borsuk Ewa
Published: April 2021

Diploid gynogenetic mouse embryos were produced in a three-step procedure : fertilization in vitro, suppression of the 2nd polar body formation by Cytochalasin B, and microsurgical removal of the male pronucleus. The operated eggs were transplanted to the oviduct of recipient females for 72 or 96 h. The overall recovery rate was 73%, but compacted morulae and blastocysts constituted only 28-6% of transplanted eggs. After 72 h blastocysts were rare (3·5%) but 24 h later their incidence increased to 21·2%. In eggs homozygous for T6 chromosome it was possible to prove karyologically that the male pronucleus was effectively removed and that the diploid genome was of purely maternal origin.
An autoradiographic analysis of tissue potency in different regions of the embryonic ectoderm during gastrulation in the mouse
Authors: Beddington R. S. P.
Published: April 2021

In vitro chimaeras have been produced by injecting [3H]thymidine-labelled 8th day embryonic ectoderm, derived from the anterior, distal or posterior regions of the egg cylinder, into unlabelled synchronous embryos. Injected embryos were cultured for 36 h and the distribution of donor cells was analysed autoradiographically. One series of orthotopic injections was carried out and the results indicate that the developmental fate of embryonic ectoderm in the posterior part of the embryo is to form mesoderm, both embryonic and extraembryonic. Heterotopic injections of distal and posterior embryonic ectoderm demonstrate that these tissues readily conform to the colonisation patterns characteristic of their new location. In contrast, anterior embryonic ectoderm showed some preference for definitive ectoderm differentiation following heterotopic transplantation. However, there was no evidence that the normal fate of tissue from the three regions studied could be explained by pre-existing mosaicism in the embryonic ectoderm.
Induction of bone by epithelial cell products
Authors: Hall Brian K. , van Exan R. J.
Published: April 2021

The bones of the head and face of vertebrate embryos only form after their progenitor cells have undergone an inductive interaction with embryonic epithelia. We have investigated whether epithelial cell products can substitute for epithelia in allowing mandibular ecto-mesenchyme to form bone. Mandibular epithelia from embryonic chicks were cultured on Millipore filters for 28 days to allow them to deposit an extracellular matrix, shown by electron microscopy to be a basal lamina-like material. Mandibular ectomesenchymal cells formed bone when placed on to these epithelial extracellular products and grafted to chorio-allantoic membranes of host embryos. Treatment of epithelial cultures with trypsin or L-azetidine-carboxylic acid removed both the extracellular products and their ability to induce bone formation. Hyaluronidase treatment did neither. We concluded that a protein-aceous component of epithelial basal lamina provides a sufficient inductive stimulus to initiate differentiation of bone within mandibular ectomesenchyme.