bluuebunny/crossref_metadata_2025 huggingface dataset:
A Gene causing Ocular Retardation in the Mouse
Authors: Truslove Gillian M.
Published: April 2021

The development of the eyes in mice homozygous for the gene ocular retardation (or) is described here. Up to the age of 11 days the eyes of or/or embryos appear to be normal in their size and general proportions, but after this time they are reduced in size. This is due to the failure of the central artery and vein to establish a pathway along the choroid fissure, which closes completely. In the adult the lens is never crystalline and is always distorted in shape, while the retina contains no sensory cells, no optic nerves develop, and there is no optic chiasma. An orbit of normal size is filled with hypertrophied Harderian and lachrymal glands.
Cytoarchitecture of theXenopusthymus followingγ-irradiation
Authors: Russ Jane H. , Horton John D.
Published: April 2021

This paper describes in vitro and in vivo attempts to deplete the 4- to 8-month-old Xenopus laevis (J strain) thymus of its lymphocyte compartment. Gamma irradiation (2–3000 rad) of the excised thymus, followed by two weeks in organ culture, is effective in removing lymphocytes, but causes drastic reduction in size and loss of normal architecture. In contrast, in vivo whole-body irradiation (3000 rad) and subsequent in situ residence for 8–14 days proves successful in providing a lymphocyte-depleted froglet thymus without loss of cortical and medullary zones. In wvo-irradiated thymuses are about half normal size, lack cortical lymphocytes, but still retain some medullary thymocytes; they show no signs of lymphocyte regeneration when subsequently organ cultured for 2 weeks. Light microscopy of 1 μm, plastic-embedded sections and electron microscopy reveal that a range of thymic stromal cell types are retained and that increased numbers of cysts, mucous and myoid cells are found in the thymus following wholebody irradiation. In vivo-irradiated thymuses are therefore suitable for implantation studies exploring the role of thymic stromal cells in tolerance induction of differentiating T lymphocytes.
The role of 20-hydroxyecdysone in stimulating epidermal mitoses during the larval–pupal transformation of the tobacco hornworm, Manduca sexta
Authors: Kato Yoshiomi , Riddiford Lynn M.
Published: April 2021

Temporal and regional changes in mitotic frequency were examined in the dorsal epidermis of the fourth and fifth abdominal segments of Manduca sexta during metamorphosis. Mitoses occurred only in the middle intrasegmental region, but not in the segmental margins. The mitoses began early on day 5 and rose to maximum of 2·6–4·6% about 10 h later. When the integument from day 4 (wandering) larvae was cultured in Grace’s medium containing 0–3 to 1μgml−1 20-hydroxyecdysone (20HE), the mitotic index increased with a peak at 18– 24 h exposure approximately equal to that found in situ. The level of 20HE required to initiate mitoses was similar to that found in vivo during the beginning of the prepupal rise in ecdysteroid and therefore is likely to be the signal for these cells to decrease their ploidy level of 4– 32C to 2– 8C at this time. The polyploid cells had larger mitotic figures and required a longer exposure to 20-hydroxyecdysone to initiate mitosis. Some multipolar mitotic figures were observed.
Fate map of the eye-antennal imaginal disc of the tumorous-head mutant of Drosophila melanogaster
Authors: Andrew Deborah J.
Published: April 2021

In specific genetic backgrounds, a mutation in the tuh-3 gene results in the homeotic transformation of head structures to either leg disc derivatives or structures normally found in the extreme posterior end of wild-type animals. The origins of the homeotic structures were mapped to defined positions in the eye-antennal imaginal disc by transplanting abnormal regions of discs isolated from tuh-3 mutants into host mwh;e4 larvae. These metamorphosed implants were removed and differentiated structures were identified. Of 211 successfully recovered implants, 157 gave rise to homeotic tissue: abdominal tergite, male or female external genitalia and/or leg tissue. Transformations to abdominal tergite occurred primarily in cells taken from the eye region of the compound disc. Male and female genitalia arose most often in implants taken from the antennal portion of the disc, although some tissue taken from the lateral region of the eye disc also gave rise to external genitalia. Leg structures came exclusively from implants from the antennal region of the imaginal disc. These results suggest that cells from within specific regions of the eye-antennal compound disc are constrained in their developmental potential. An obvious constraint observed with this mutation is a dorsal/ventral one: Cells from the eye disc, a dorsal structure, primarily gave rise to other dorsal structures, abdominal tergite tissue. Cells from the antennal disc, a ventrally derived structure, primarily gave rise to other ventral structures including genital tissue and distal leg.
Polarization and density of Na-pumps in the inner ear of the chick embryo during early stages of development
Authors: Giraldez F. , Represa J. J. , Borondo Luisa , Barbosa E.
Published: April 2021

The otic vesicle consists of a pseudostratified epithelium with some features of transporting epithelia. The present work questions whether Na-pumps are polarized in this epithelium and what is the relation between the location or density of pumps and development. This was done by measuring the binding of [3H]ouabain to isolated otic vesicles in developmental stages 16 to 22. The results show the presence of specific ouabain-binding sites located in the inwardfacing membrane of the otic vesicle epithelium. Binding was saturable at increasing concentrations of ouabain and was highly sensitive to the external K+ concentration with half-maximal inhibition below 0 ·5 mM, indicating that the binding sites and Na-pump sites are identical. A transient stage-dependent increase in the density of Na-pumps during the period that precedes growth was observed. Evidence is given against this being directly related to an increased net fluid transport rate despite the fact that pump sites were always polarized throughout these stages. The conclusions are that (1) the otic vesicle epithelium is a polarized structure with the possibility of vectorial transport of solutes and water and (2) the increased number of pumps may operate as a regulatory mechanism during normal proliferative growth.
Regional specification within the mesoderm of early embryos ofXenopus laevis
Authors: Dale L. , Slack J. M. W.
Published: April 2021

We have further analysed the roles of mesoderm induction and dorsalization in the formation of a regionally specified mesoderm in early embryos of Xenopus laevis. First, we have examined the regional specificity of mesoderm induction by isolating single blastomeres from the vegetalmost tier of the 32-cell embryo and combining each with a lineage-labelled (FDA) animal blastomere tier. Whereas dorsovegetal (DI) blastomeres induce ‘dorsal-type’ mesoderm (notochord and muscle), laterovegetal and ventro-vegetal blastomeres (D2–4) induce either ‘intermediate-type’ (muscle, mesothelium, mesenchyme and blood) or ‘ventral-type’ (mesothelium, mesenchyme and blood) mesoderm. No significant difference in inductive specificity between blastomeres D2, 3 and 4 could be detected. We also show that laterovegetal and ventrovegetal blastomeres from early cleavage stages can have a dorsal inductive potency partially activated by operative procedures, resulting in the induction of intermediate-type mesoderm.

Second, we have determined the state of specification of ventral blastomeres by isolating. and culturing them in vitro between the 4-cell stage and the early gastrula stage. The majority of isolates from the ventral half of the embryo gave extreme ventral types of differentiation at all stages tested. Although a minority of cases formed intermediate-type and dorsal-type mesoderms we believe these to result from either errors in our assessment of the prospective DV axis or from an enhancement, provoked by microsurgery, of some dorsal inductive specificity. The results of induction and isolation experiments suggest that only two states of specification exist in the mesoderm of the pregastrula embryo, a dorsal type and a ventral type.

Finally we have made a comprehensive series of combinations between different regions of the marginal zone using FDA to distinguish the components. We show that, in combination with dorsal-type mesoderm, ventral-type mesoderm becomes dorsalized to the level of intermediate-type mesoderm. Dorsal-type mesoderm is not ventralized in these combinations. Dorsalizing activity is confined to a restricted sector of the dorsal marginal zone, it is wider than the prospective notochord and seems to be graded from a high point at the dorsal midline.

The results of these experiments strengthen the case for the three-signal model proposed previously, i.e. dorsal and ventral mesoderm inductions followed by dorsalization, as the simplest explanation capable of accounting for regional specification within the mesoderm of early Xenopus embryos.
Positional signalling and the development of the humerus in the chick limb bud
Authors: Wolpert L. , Hornbruch Amata
Published: April 2021

The positional signal model for specification of the cartilaginous elements in limb development has been tested by examining the effect on the humerus of grafting a polarizing region to different positions along the anteroposterior axis of the limb bud at stage 16. The humerus between the host and grafted polarizing region was largely normal though there were variations in width, particularly the distal epiphysis. The humerus often showed mirror-image symmetry along the anteroposterior axis. When the grafted polarizing region was in a very anterior position, there were a few cases where a second humerus developed. Anterior to the graft an additional humerus often developed. This was associated with the splitting of the bud into two domains. It is suggested that these results are not consistent with a positional signal model and that an additional mechanism involving an isomorphic prepattern may be involved in the specification of the cartilaginous elements.
Preparation and properties of monoclonal and polyclonal antibodies to mouse epidermal growth factor (EGF) receptors: evidence for cryptic EGF receptors in embryonal carcinoma cells
Authors: Weller Ann , Meek Jennifer , Adamson Eileen D.
Published: April 2021

Monoclonal antibodies to mouse epidermal growth factor (EGF) receptor were prepared by the immunization of rats with receptor glycoprotein purified from mouse liver by affinity chromatography on immobilized EGF. Purified mouse EGF receptor retained EGF-inducible autophosphorylating activity and was antigenic in rats and rabbits. The monoclonal antibodies cross react very poorly with human EGF receptor, while polyclonal rabbit antibodies immune precipitate human, rat and mouse EGF receptor equally well. The rabbit antibody blocks EGF binding to mouse fibroblast cells and, at 20-fold higher concentrations, stimulates uptake of tritiated thymidine into DNA. This indicates that antibodies bind at or close to the EGF-binding site and can mimic the effects of the growth factor. None of the monoclonals bind at the EGF site of the receptor.

Immunoprecipitation, immunoblotting, 125I-EGF cross linking, 125I-surface labelling, immunohisto-chemistry and autophosphorylation techniques were used to delineate the basis for the induction of EGF receptors when OC15 embryonal carcinoma (EC) cells differentiate into endodermal derivatives (END). EGF-stimulated autophosphorylation of a 170 × 103 Afr protein in solubilized OC15 EC cells is readily detectable, although intact EC cells do not bind or respond to EGF by all other tests. The results suggest that cryptic EGF receptors are present in EC stem cells, a finding with implications in development.
Biology of mammary fat pad in fetal mouse: capacity to support development of various fetal epithelia in vivo
Authors: Sakakura Teruyo , Kusano Itsuo , Kusakabe Moriaki , Inaguma Yutaka , Nishizuka Yasuaki
Published: April 2021

Epithelia from the lobular part of submandibular salivary gland, glandular stomach, intestine and colon of 14-day C3H/HeN fetuses, and from pituitary gland and pancreas of 12-day fetuses were recombined with 14-day mammary fat pad precursor tissue and syngrafted under the kidney capsule. The normal organogenetic development typical of the epithelium occurred. The same epithelia taken from earlier stage fetuses did not develop normally. Thus, 14-day fetal mouse mammary fat pad precursor tissue has the capacity to support normal organogenesis of various fetal epithelia of developmentally advanced stages. This supportive capacity is decreased in the fat pad precursor tissue of 17- to 18-day fetal mice and is entirely lost postnatally.
Autonomy of differentiation in avian brachial somites and the influence of adjacent tissues
Authors: Kenny-Mobbs Terry , Thorogood Peter
Published: April 2021

This study investigates the differentiative abilities of avian brachial somites at stages of development before, during and after the migration of somitic cells into the wing primordium. These somites are the source of cells that migrate into the forelimbs and there give rise exclusively, and totally, to the skeletal muscle lineage of the wing and yet show no morphological evidence of commitment to that fate when they leave the somites. The aim of the study was to see if the brachial somitic cells are committed to particular developmental pathways at these stages.

The brachial somites were isolated from HH stage-12, -15 and -18 chick embryos, either by microdissection or enzymatic dissociation, and grown in organ culture, in explant culture on different substrata or on the chorioallantoic membrane (CAM) of host chicks, either alone or in combination with adjacent tissues. Myogenesis and chondrogenesis occurred in all stage-18 enzymatically separated somites, regardless of the growth environment. Myogenesis was reduced in stage-15 somites and unobservable in stage-12 somites; however, recombination of stage-12 somites with epithelium or neural tube increased the incidence of myogenesis at this stage. The incidence of chondrogenesis was also less in the younger expiants. Unlike its effect on myogenic expression, recombination with epithelium resulted in a dramatic decrease in chondrogenesis in both stage-12 and -15 somites.

The recombination experiments suggest that conditions that maintain the normal spatial relationships within isolated somites permit expression of a pre-existing specification to a particular fate. They also show that the overlying epithelium can inhibit chondrogenesis in these somites. Overall, the results suggest that by the time migration of somitic cells into wing regions is finishing, brachial somitic cells have become stabilized in their ability to undergo both myogenesis and chondrogenesis for they will do so under a variety of growth conditions and in-dependently of adjacent tissues. However, immediately before (stage 12) and shortly after (stage 15) the onset of migration, both myogenic and chondrogenic expression by brachial somitic cells are still under the influence of interactions with adjacent tissues.
Determination and morphogenesis in the sea urchin embryo
Authors: Wilt Fred H.
Published: April 2021

The study of the sea urchin embryo has contributed importantly to our ideas about embryogenesis. This essay re-examines some issues where the concerns of classical experimental embryology and cell and molecular biology converge. The sea urchin egg has an inherent animal-vegetal polarity. An egg fragment that contains both animal and vegetal material will produce a fairly normal larva. However, it is not clear to what extent the oral-abpral axis is specified in embryos developing from meridional fragments. Newly available markers of the oral-aboral axis allow this issue to be settled. When equatorial halves, in which animal and vegetal hemispheres are separated, are allowed to develop, the animal half forms a ciliated hollow ball. The vegetal half, however, often forms a complete embryo. This result is not in accord with the double gradient model of animal and vegetal characteristics that has been used to interpret almost all defect, isolation and transplantation experiments using sea urchin embryos. The effects of agents used to animalize and vegetalize embryos are also due for re-examination. The classical animalizing agent, Zn2+, causes developmenal arrest, not expression of animal characters. On the other hand, Li+, a vegetalizing agent, probably changes the determination of animal cells. The stability of these early determinative steps may be examined in dissociation-reaggregation experiments, but this technique has not been exploited extensively.

The morphogenetic movements of primary mesenchyme are complex and involve a number of interactions. It is curious that primary mesenchyme is dispensable in skeleton formation since in embryos devoid of primary mesenchyme, the secondary mesenchyme cells will form skeletal elements. It is likely that during its differentiation the primary mesenchyme provides some of its own extracellular microenvironment in the form of collagen and proteoglycans. The detailed form of spicules made by primary mesenchyme is determined by cooperation between the epithelial body wall, the extracellular material and the inherent properties of primary mesenchyme cells.

Gastrulation in sea urchins is a two-step process. The first invagination is a buckling, the mechanism of which is not understood. The secondary phase in which the archenteron elongates across the blastocoel is probably driven primarily by active cell repacking. The extracellular matrix is important for this repacking to occur, but the basis of the cellular-environmental interaction is not understood.

There are new tools, especially well-defined specific antibodies and recombinant DNA clones, that may be applied to these problems and should help illuminate some of the underpinnings of embryogenesis in an organism that relies so heavily on cellular interactions as a develomental strategy.
Heat-shock-induced grey crescent formation in axolotl eggs and oocytes: the role of gravity
Authors: Beetschen Jean-Claude , Gautier Jean
Published: April 2021

Axolotl eggs were heat shocked (36·8°C, 10min) inside their jelly layers. Heat shock (HS) was shown to induce the precocious appearance of a grey crescent (GC) in a number of eggs immediately after fertilization (Benford & Namenwirth, 1974). It was also demonstrated that this phenomenon occurs in fertilized or artificially activated eggs only when they are shocked within after spawning. The GC forms still later in heated unfertilized, nonactivated eggs. The role of the jelly layers is considered to be mechanical: a proportion of eggs is maintained in a tilted position until the egg is able to orient animal pole upwards under the influence of gravity as a late consequence of activation. The jelly layers are not essential if the eggs are artificially tilted or rotated during HS. GC formation can also be induced in in vitro maturing oocytes, provided they are tilted during HS. Gravity thus plays an essential role in the cytoplasmic rearrangements leading to HS-induced GC formation. Our results indicate a synergistic action between heat and gravity in this process. The cytological appearance of the GC formed in those experiments is that of a ‘Born’s crescent’ with a conspicuous ‘vitelline wall’ (Pasteels, 1964).

When oocytes are enucleated before maturation, HS has no effect on GC formation. A nuclear factor is therefore essential, as has been demonstrated in early GC formation induced by inhibitors of protein synthesis.

Finally, incorporation of amino acids into oocyte proteins appears to be rapidly inhibited by HS (from 5 min). However, we cannot conclude that GC formation is in fact triggered by inhibition of protein synthesis. It is also likely that HS disrupts cytoskeletal structure, hence facilitating cytoplasmic rearrangements. Nevertheless, these results are in agreement with the scheme we recently proposed for GC formation in the rotated axolotl oocyte (Gautier & Beet-schen, 1985).
The spatial and temporal deployment ofDfdandScrtranscripts throughout development ofDrosophila
Authors: Martinez-Arias A. , Ingham P. W. , Scott M. P. , Akam M. E.
Published: April 2021

In Drosophila, the Deformed (Dfd) and Sex combs reduced (Scr) genes determine the developmental pathways followed by the most anterior metameric units. Using in situ hybridization, we have monitored the spatial distributions of transcripts from these two genes. Dfd RNA accumulates in parasegments 0 and 1; Scr RNA accumulation shows a dynamic pattern spanning parasegments 2 and 3. The expression of Dfd and Scr seems to change from parasegmental to segmental during formation of the gnathal appendages. Both genes are transcribed during imaginal development: Dfd in a portion of the eye-antennal disc; Scr in the labial and prothoracic discs. In addition, we find Scr RNA in the adepithelial cells of all mesothoracic discs.
Ontogeny of oestrogen-sensitive mesenchymal cells in the bursa of Fabricius of the chick embryo. An immunohistochemical study on progesterone receptor
Authors: Ylikomi Timo , Gasc Jean-Marie , Tuohimaa Pentti , Baulieu Etienne-Emile
Published: April 2021

The expression of progesterone receptor (PR) and its induction by oestradiol during the embryogenesis of the chick bursa of Fabricius (BF) were studied by immunohistochemistry using three different polyclonal antibodies to the chicken oviduct PR. Mesenchymal cells of the cloacal area surrounding the bursa primordium in controls (without exogenous oestrogen) express the PR between 9 and 11 days of incubation. In the same cells, PR was induced experimentally by oestradiol at 9 days. Mesenchymal cells in the bursa did not express PR after oestradiol treatment before the age of 11 days. The PR was not inducible in the bursal epithelium or in haemopoietic cells. None of the bursal cells expressed the PR to a detectable level during embryonic life without exogenous treatment. Some haemopoietic cells showed strong artefactual staining in their nuclei.

It is concluded that (1) the embryonic bursa of Fabricius is a sex-steroid-sensitive organ, (2) exogenous oestradiol is able to induce progesterone receptor in the mesenchymal cells, but (3) the PR is not expressed without exogenous oestrogen. This indicates that the PR becomes oestrogen inducible well before it is naturally expressed during sexual maturation and that the level of endogenous oestrogen during embryonic life is not high enough to affect the bursa significantly.
Localization and expression of msp130, a primary mesenchyme lineagespecific cell surface protein of the sea urchin embryo
Authors: Anstrom John A. , Chin Jia E. , Leaf David S. , Parks Annette L. , Raff Rudolf A.
Published: April 2021

In this report, we use a monoclonal antibody (B2C2) and antibodies against a fusion protein (Leaf et al. 1987) to characterize msp130, a cell surface protein specific to the primary mesenchyme cells of the sea urchin embryo. This protein first appears on the surface of these cells upon ingression into the blastocoel. Immunoelectronmicroscopy shows that msp130 is present in the trans side of the Golgi apparatus and on the extracellular surface of primary mesenchyme cells. Four precursor proteins to msp130 are identified and we show that B2C2 recognizes only the mature form of msp130. We demonstrate that msp130 contains A-linked carbohydrate groups and that the B2C2 epitope is sensitive to endoglycosidase F digestion. Evidence that msp130 is apparently a sulphated glycoprotein is presented. The recognition of the B2C2 epitope of msp130 is disrupted when embryos are cultured in sulphate-free sea water. In addition, two-dimensional immunoblots show that msp130 is an acidic protein that becomes substantially less acidic in the absence of sulphate. We also show that two other independently derived monoclonal antibodies, 1G8 (McClay et al. 1983; McClay, Matranga & Wessel, 1985) and 1223 (Carson et al. 1985), recognize msp130, and suggest this protein to be a major cell surface antigen of primary mesenchyme cells.
Reduced gap junctional communication is associated with the lethal condition characteristic of DDK mouse eggs fertilized by foreign sperm
Authors: Buehr Mia , Lee S. , Mclaren Anne , Warner Anne
Published: April 2021

Communication through gap junctions was examined in 8-cell zygotes generated by fertilization of eggs of the DDK inbred strain of mice with spermatozoa of the C3H strain. These zygotes spontaneously begin to extrude cells at the late 16-cell stage and 95 % die by the blastocyst stage. The transfer of Lucifer Yellow between cells of DDK/C3H zygotes that had not yet begun to express the defect was significantly slower than in DDK/DDK controls or in controls from other strains. Treatment with the weak base methylamine, to raise intracellular pH, speeded the transfer of Lucifer in all strains; transfer between cells of DDK/C3H zygotes became as fast as that between cells of control zygotes. DDK/C3H zygotes cultured in methylamine either from the 4- to 8-cell stage to the early 16-cell stage (19 h) or from the early to the late 16-cell stage (6h) showed significant rescue to the blastocyst stage. Once spontaneous decompaction of cells from DDK/C3H zygotes had begun (the late 16-cell stage onwards) methylamine treatment was no longer able to bring about rescue. We conclude that zygotes developed from eggs of the DDK strain fertilized by foreign spermatozoa are characterized physiologically by defective gap junctional communication. Improving gap junctional communication is sufficient to allow many zygotes to maintain the compacted state, suggesting a link between compaction and communication through gap junctions.
Multinucleation during myogenesis of the myotome of Xenopus laevis: a qualitative study
Authors: Boudjelida Hamid , Muntz Louise
Published: April 2021

Ultrastructural studies of myogenesis in the myotome of Xenopus laevis reveal that the myotubes developed by stage 33/34 have peripheral myofibrils but are still uninucleate with a single large nucleus. By stage 45, the cytoplasm of the muscle cells is filled with myofibrils and there are many small peripheral nuclei, resulting in multinucleate muscle fibres. With the electron microscope, we have examined myotomes from stages 33/34 to 59 of development and some stages were also investigated by autoradiography. There was no evidence from autoradiographic studies for DNA synthesis in muscle cells, and the increase in the number of myonuclei was accompanied by a decrease in their size. Satellite cells were not seen at the myotube stage but were first seen after the cells had become multinucleate, with many small nuclei close together forming rows. Constrictions were frequently observed in the large single nuclei.

It is concluded that division of the myonuclei by amitosis is mainly responsible for the multinucleation that occurs during development of the myotome muscle in Xenopus laevis.
Immunologically unique and common domains within a family of proteins related to the retina Ca2+-dependent cell adhesion molecule, NcalCAM
Authors: Crittenden Sarah L. , Pratt Rodney S. , Cook James H. , Balsamo Janne , Lilien Jack
Published: April 2021

Rabbit polyclonal antibodies raised to gp90, a fragment of the embryonic chick neural retina Ca2+dependent adhesive molecule, gp130, recognize gp130 and inhibit Ca2+-dependent cell-cell adhesion. When tested against a panel of 10-day embryonic tissues, one of these antisera recognizes a component with a molecular weight identical to that of gp130 in embryonic chick cerebrum, optic lobe, hind brain, spinal cord and neural retina only; the second antiserum recognizes a similar component in all of the embryonic chick tissues tested. These data imply the existence of an extended family of closely related cell surface components with immunologically distinct subgroups each of which may mediate Ca2+-dependent cell-cell adhesion. As the term CAM, or cell adhesion molecule, has become common usage we propose to refer to these molecules as calCAMs, reflecting their calcium dependence. Analysis of fragments and endoglycosidase digests of NcalCAM have allowed a comparison of its structure with similar molecules from different tissues and species that have been implicated in Ca2+-dependent cell-cell adhesion.
Teleost epiboly: a reassessment of deep cell movement in the germ ring
Authors: Wood Andrew , Timmermans Lucy P. M.
Published: April 2021

Using the prominent cell nucleus as an intrinsic marker, individual deep cell blastomeres have been monitored in vivo using Nomarski differential interference contrast microscopy during spreading of the teleost blastoderm. Involution of these cells has been recorded during early to mid stages of epiboly about an apparent point of shear located centrally within the germ ring. This involuting movement involves superficial deep cells, adjacent to the enveloping layer, as well as those located more centrally within the germ ring and is associated with a continuous vegetal displacement of the outer strata of deep cell blastomeres towards the edge of the blastodisc. During the early stages of epiboly this process is qualitatively similar at any location around the entire circumferential margin of the blastodisc. Postinvoluting deep cells are found close to the yolk syncytial layer, are surrounded by considerable intercellular space and illustrate less directional displacement. In contrast to the deep cell layer, the enveloping layer was never observed to invaginate. These results contradict the current view that no involution or global rearrangement of deep cells occurs during teleost gastrulation and present the first direct evidence of involution within the deep cell population during early epiboly.
Cortical positioning and the fate of oral structures during the sexual process in amicronucleate homopolar tandems ofParamecium
Authors: Ng Stephen F.
Published: April 2021

Paramecium tetraurelia normally resorbs the preexisting oral apparatus (and develops a new one) during sexual reproduction. Violation of this rule was found in amicronucleate cell lines. These cell lines generated chains of two cells (homopolar tandems) at a low frequency, as a result of incomplete binary fission during a transient growth depression period following emicronucleation. In autogamous chains, the proter resorbed the pre-existing oral structures, while some of the opisthes retained them. The oral structures in the opisthes of the chains were unusually close to the opisthes’ anterior end. The ectopic location of these oral structures might account for their retention, formally understood in terms of the theory of positional information. It is suggested that nongenic factors, likely involving components of the rigid cortical matrix, are involved in the fixation of positional values.
Morphological, cytochemical and neuropharmacological evidence for the presence of catecholamines in hydrozoan planulae
Authors: Kolberg Kathleen Joanne Sipes , Martin Vicki Joan
Published: April 2021

Planula larvae of Halocordyle disticha were examined for the presence of catecholamines using a multipronged approach. Transmission electron micrographs of planular sensory cells and ganglionic cells demonstrated dense-cored vesicles and electron-dense droplets in both cell types. These vesicles and droplets were similar in morphology to catecholamine-containing granules of vertebrates. Planulae processed with the SPG histofluorescence technique, specific only for catecholamines, exhibited blue-green fluorophores which were most prominent in the anterior ectoderm. Such fluorescence was associated with sensory cells, ganglionic cells and the neural plexus. Pretreatment of planulae with neuropharmacological agents which prevent reuptake (reserpine) or cause release (nicotine, ephedrine) of catecholamines caused a diminution of the fluorophores. Pretreatment of animals with 6-hydroxydopamine, which causes destruction of cat-echolamine-containing cells, prevented any fluorescent response. Ultrastructural examination of reser-pine-treated planulae revealed a dramatic reduction in the populations of dense-cored vesicles and electron-dense droplets. Furthermore, many of the vesicles and droplets remaining in reserpinized animals appeared washed out, i.e. stained faintly. Exposure of planulae to exogenous norepinephrine caused premature, rapid metamorphosis and produced polyps with slightly stunted tentacles and pitted, irregular hypostomes. Exposure of planulae to nicotine caused similar effects. Rearing planulae in sea water containing alpha blockers, phentolamine and tolazoline, had no discernible effect on behaviour (motility, phototactic response) or gross morphology. However, planulae raised in sea water containing propranolol, a beta blocker, ceased all movement, became tack-shaped and died within 72 h. These results meet multiple criteria for the identification of catecholamines in hydrozoan planulae and suggest that such catecholamines may function as neurotransmitters, neurohormones or neuromodulators during larval development.
The allocation of cells in the presomitic mesoderm during somite segmentation in the mouse embryo
Authors: Tam Patrick P. L.
Published: April 2021

Orthotopic grafts of wheat germ agglutinin-colloidal gold conjugate (WGA-gold) labelled cells were used to demonstrate differences in the segmental fate of cells in the presomitic mesoderm of the early-somite-stage mouse embryos developing in vitro. Labelled cells in the anterior region of the presomitic mesoderm colonized the first three somites formed after grafting, while those grafted to the middle region of this tissue were found mostly in the 4th-7th newly formed somites. Labelled cells grafted to the posterior region were incorporated into somites whose somitomeres were not yet present in the presomitic mesoderm at the time of grafting. There was therefore an apparent posterior displacement of the grafted cells in the presomitic mesoderm. Colonization of somites by WGA-gold labelled cells was usually limited to two to three consecutive somites in the chimaera. The distribution of cells derived from a single graft to two somites was most likely due to the segregation of the labelled population when cells were allocated to adjacent meristic units during somite formation. Further spreading of the labelled cells to several somites in some cases was probably the result of a more extensive mixing of mesodermal cells among the somitomeres prior to somite segmentation.
The accumulation of basement membrane components during the onset of chondrogenesis and myogenesis in the chick wing bud
Authors: Solursh Michael , Jensen Karen L.
Published: April 2021

The study describes the distribution of several basement membrane molecules in the embryonic chick wing bud from stages 23 to 26, during the onset of myogenesis and chondrogenesis, and then later at stage 28. Laminin is localized as early as stage 23, prior to the onset of myogenesis, in regions corresponding to the position of the future dorsal and ventral myogenic areas. Other matrix components, including fibronectin, do not differentially accumulate in these same regions. Fibronectin, basement membrane heparan sulphate proteoglycan and type IV collagen are more widespread in their distribution than laminin, and are even present between mesenchymal cells. These results suggest a role for laminin in the initial differentiation of the muscle masses and emphasize that components of basement membrane can also be associated with mesenchymal cells.
Suppression of chromosome condensation during meiotic maturation induces parthenogenetic development of mouse oocytes
Authors: Clarke H. J. , Rossant J. , Masui Y.
Published: April 2021

Mouse oocytes at metaphase I were treated with puromycin, which caused the chromosomes to become decondensed within an interphase nucleus. When the oocytes were allowed to resume protein synthesis, they returned to metaphase within 8 –10 h and neither synthesized DNA nor cleaved, indicating that they had not been parthenogenetically activated by the puromycin treatment. However, when dibutyryl cyclic AMP was added to the medium after protein synthesis resumed, the oocytes remained in interphase. These oocytes maintained in interphase began DNA synthesis beginning 20 h after puromycin withdrawal, even though no activation stimulus had been given to them. After transfer to the oviducts of foster mothers, the oocytes could develop to the blastocyst stage. These results indicate that oocytes whose chromosomes were decondensed by puromycin treatment at metaphase I could begin parthenogenetic development in the absence of an activating stimulus, provided that they were prevented from returning to metaphase. In contrast, when the puromycin-treated oocytes were allowed to return to metaphase, they became developmentally arrested at the end of maturation. This suggests that the mechanism responsible for the developmental arrest of mature oocytes at metaphase II depends on cytoplasmic conditions that cause chromosome condensation to the metaphase state.
Müllerian inhibiting substance production and testicular migration and descent in the pouch young of a marsupial
Authors: Hutson John. M. , Shaw Geoffrey , O Wai Sum , Short Roger V. , Renfree Marilyn B.
Published: April 2021

The ontogeny of Müllerian inhibiting substance (MIS) production by the developing testis of an Australian marsupial, the tammar wallaby (Macropus eugenii), was determined during pouch life using an organculture bioassay of mouse fetal urogenital ridge. This information was related to the morphological events during testicular migration and descent. MIS biological activity was found in testes (but not ovaries or liver) of pouch young from 2 to 85 days of age. MIS production had commenced by day 2, which is within a day of the first gross morphological signs of testicular differentiation. Müllerian duct regression occurred between 10 and 30 days, which partly coincided with testicular migration to the inguinal region and enlargement of the gubernacular bulb (15 to 30 days). These observations are consistent with the hypothesis that MIS may be involved in testicular transabdominal migration. The epididymis commenced development and growth only after the testis had descended through the inguinal ring. This provides no support for the suggestion that the epididymis is involved in testicular descent into the scrotum. The basic sequence of events in post-testicular sexual differentiation in the wallaby is sufficiently similar to that seen in eutherian mammals to make it an excellent experimental model for future studies of testicular differentiation, migration and descent.
Vitronectin production by human yolk sac carcinoma cells resembling parietal endoderm
Authors: Cooper Susan , Pera Martin F.
Published: April 2021

Normal mesenchymal cells, normal epithelial cells and many transformed epithelial cells require serum attachment factors and extracellular matrix proteins for growth and differentiation in vitro, and recent evidence strongly supports a role for extracellular matrix molecules in the regulation of cell movement in vivo during early embryogenesis. We previously described the isolation and characterization of cell lines representative of three types of stem cells most commonly found in human adult testicular teratomas, namely embryonal carcinoma cells, yolk sac carcinoma cells resembling visceral endoderm and yolk sac carcinoma cells resembling parietal endoderm (endodermal sinus tumour cells). Of these three cell types, only endodermal sinus tumour cells, which show particularly malignant behaviour in vivo, have no serum requirement for attachment and growth in vitro. Supernatants from endodermal sinus tumour cells support the attachment of embryonal carcinoma cells in serum-free medium. We demonstrate here that endodermal sinus tumour cells, but not other cell types isolated from testicular teratomas, secrete the serum attachment protein, vitronectin (also known as serum-spreading factor, S-protein or epibolin), as well as fibronectin, laminin and type IV collagen, into serum-free medium. Purified vitronectin from medium conditioned by endodermal sinus tumour cells supported both attachment and spreading of embryonal carcinoma cells in vitro, whereas cells attached but did not spread properly on surfaces coated with fibronectin or laminin. Peptides containing the RGD cell recognition sequence common to many attachment proteins blocked attachment of endodermal sinus tumour cells to untreated tissue-culture plastic in serum-free medium. The results suggest a possible role for vitronectin in regulating cell motility and growth in early development, and in the invasion and spread of teratomas in vivo.
Changes in the expression of the carbohydrate epitope HNK-1 associated with mesoderm induction in the chick embryo
Authors: Canning David R. , Stern Claudio D.
Published: April 2021

We report that a monoclonal antibody, HNK-1, identifies specific regions and cell types during primitive streak formation in the chick blastoderm. Immunohistochemical studies show that the cells of the forming hypoblast are HNK-1 positive from the earliest time at which they can be identified. Some cells of the margin of the blastoderm are also positive. The mesoderm cells of the primitive streak stain strongly with the antibody from the time of their initial appearance. In the epiblast, some cells are positive and some negative at pre-primitive-streak stages, but as the primitive streak develops a gradient of staining intensity is seen within the upper layer, increasing towards the primitive streak. At later stages of development, the notochord and the mesenchyme of the headfold are positive, while the rest of the mesoderm (lateral plate) no longer expresses HNK-1 immunoreactivity. This antibody therefore reveals changes associated with mesodermal induction: before induction, it recognizes the ‘inducing’ tissue (the hypoblast) and reveals a mosaic pattern in the responding tissue (the epiblast); after primitive streak formation, the mesoderm of the primitive streak that results from the inductive interactions expresses the epitope strongly.

Affinity purification of HNK-l-related proteins in various tissues was carried out, followed by SDS-PAGE to identify them. The hypoblast, mesoderm and epiblast of gastrulating chick embryos have some HNK-l-related proteins in common, while others are unique to specific tissues. Attempts have been made to identify these proteins using Western blots and antibodies known to recognize HNK-l-related molecules, but none of the antibodies used identify the bands unique to any of the tissues studied. We conclude that these proteins may be novel members of the HNK-1/L2 family, and that they may have a role in cell interactions during early development.
Fertilization and ooplasmic movements in the ascidian egg
Authors: Sardet Christian , Speksnijder Johanna , Inoue Shinya , Jaffe Lionel
Published: April 2021

Using light microscopy techniques, we have studied the movements that follow fertilization in the denuded egg of the ascidian Phallusia mammillata. In particular, our observations show that, as a result of a series of movements described below, the mitochondria-rich subcortical myoplasm is split in two parts during the second phase of ooplasmic segregation. This offers a potential explanation for the origin of larval muscle cells from both posterior and anterior blastomeres.

The first visible event at fertilization is a bulging at the animal pole of the egg, which is immediately followed by a wave of contraction, travelling towards the vegetal pole with a surface velocity of 1·4 μms-1. This wave accompanies the first phase of ooplasmic segregation of the mitochondria-rich subcortical myoplasm. After this contraction wave has reached the vegetal pole after about 2 min, a transient cytoplasmic lobe remains there until 6 min after fertilization. Several new features of the morphogenetic movements were then observed: between the extrusion of the first and second polar body (at 5 and 24−29 min, respectively), a series of transient animal protrusions form at regular intervals. Each animal protrusion involves a flow of the centrally located cytoplasm in the animal direction. Shortly before the second polar body is extruded, a second transient vegetal lobe (‘the vegetal button’) forms, which, like the first, resembles a protostome polar lobe. Immediately after the second polar body is extruded, three events occur almost simultaneously: first, the sperm aster moves from the vegetal hemisphere to the equator. Second, the bulk of the vegetally located myoplasm moves with the sperm aster towards the future posterior pole, but interestingly about 20 % remains behind at the anterior side of the embryo. This second phase of myoplasmic movement shows two distinct subphases: a first, oscillatory subphase with an average velocity of about 6 μm min-1, and a second steady subphase with a velocity of about 26 μm min-1. The myoplasm reaches its final position as the male pronucleus with its surrounding aster moves towards the centre of the egg. Third, the female pronucleus moves towards the centre of the egg to meet with the male pronucleus. Like the myoplasm, the migrations of both the sperm aster and the female pronucleus shows two subphases with distinctly different velocities. Finally, the pronuclear membranes dissolve, a small mitotic spindle is formed with very large asters, and at about 60−65 min after fertilization, the egg cleaves.
Diacylglycerol-induced multihead formation in Hydra
Authors: Müller Werner A.
Published: April 2021

Diacylglycerol (DAG) mediates transmembrane transduction for a wide variety of extracellular signals. Though pattern formation in multicellular organisms is, as a rule, based on intercellular signalling, reports on the participation of DAG in pattern-forming processes are lacking. Here evidence is presented for the involvement of DAG in pattern control in Hydra. Upon daily exposure to 1,2-dioctanoyl-sn-glycerol, wild-type polyps form ectopic heads along the gastric column in a periodic pattern and transform into phenocopies of a multiheaded mutant. The appearance of ectopic head structures is preceded by a (wave-like) increase in the positional value. Long before ectopic tentacles appear in the intact animal and, beginning with the first pretreatment, excised segments progressively fail to regenerate feet, form heads also at their lower end and eventually over the entire segment. DAG is the first physically defined substance found to induce, in hydra, an increase in the positional value and to evoke ectopic head formation.
Lineage-specific gene expression and the regulative capacities of the sea urchin embryo: a proposed mechanism
Authors: Davidson Eric H.
Published: April 2021

Three aspects of early sea urchin development are reviewed, and conclusions derived that lead to a unified concept of how the initial specifications of differential gene activity may occur in this embryo, i. The embryo has an invariant cell lineage, and the lineage founder cells can be considered as regulatory spatial domains. That is, from each of these cells descend clones of progeny the members of which express the same set of lineage-specific genes, ii. From the extensive classical literature on blastomere plasticity, and some key modern experiments, are derived a system of inductive blastomere interactions, which accounts for the conditionality of lineage founder cell specification. That is, the fates of many of the lineage founder cells can apparently be altered if the normal spatial interrelationships within the embryo are perturbed, iii. Recent studies have been carried out by gene transfer, and are supported by in vitro analyses of DNA-protein interactions in the regulatory regions of two genes that are expressed in a lineage-specific manner. Expression of both of these markers of cell fate specification is controlled by diffusible DNA-binding factors (i.e. within each nucleus). A molecular mechanism is proposed, based on inductive effects on gene regulatory factors, which in principle provides a specific explanation of the regulative capacities for which this embryo is famous.