bluuebunny/crossref_metadata_2025 huggingface dataset:
Maternal messenger RNA distribution in silkmoth eggs: I. Clone Ec4B is associated with the cortical cytoskeleton
Authors: Kastern William H. , Watson Cornelius A. , Berry Spencer J.
Published: April 2021

We have constructed a cDNA library from mature egg RNA of the silkmoth, Hyalophora cecropia. Differential screening of the library using cDNA made against mRNAs from the yolky cytoplasm (soluble fraction) and the cortical cytoplasm (cytoskeletal-associated or cortical fraction) resulted in several clones that hybridized to a higher degree to the cDNA from the cytoskeletal-associated fraction. We selected and analyzed the clone giving the strongest signal (designated Ec4b) for its distribution in situ and found that it bound to mRNAs in the nurse cell cytoplasm, in the cortex and in the follicle cells of oocytes. Hybridization of the insert from Ec4b to both detergent-soluble and -insoluble (cortical) RNA on dot blots further supported the observation that the mRNA corresponding to Ec4b was enriched in this cytoskeletal fraction. The mRNA for Ec4b was approximately 500 bases long and the gene seems to be a member of a large multigene family in the H. cecropia genome. Analyses of the nucleotide and amino acid sequences reveal similarity to lepidopteran chorion genes and a lesser but convincing similarity to vertebrate cytokeratins. The filter and in situ hybridization data point to the association of specific messenger RNAs with the cortical cytoskeleton of silkmoth oocytes. Aspects of the structure of the protein encoded by this mRNA suggest that it is a structural component necessary for formation of the cellular blastoderm of the embryo. The association of this maternal mRNA with the cortical cytoskeleton presents the interesting possibility that mRNA bound to the cytoskeleton may be capable of participating in the synthesis of new cytoskeleton or related structures during blastoderm formation. Such an association between maternal mRNA and the cytoskeleton may indicate a general mechanism for the spatial distribution of determinative elements in eggs.
Sex-linked dosage-sensitive modifiers as imprinting genes
Authors: Sapienza Carmen
Published: April 2021

It is proposed that differential genome imprinting is the result of dosage-sensitive modifier genes located on the sex chromosomes. Parallels between variegating position-effects in Drosophila, the phenotype elicited by transgenes in the mouse and data from several pediatric tumors indicate that the net result of the activity of such modifier genes is often cellular mosaicism in the expression of affected alleles. The mechanism by which inactivation of affected alleles is achieved is proposed to be through the formation of heterochromatic domains.

Because the relevant sex-linked modifying loci are dosage sensitive in their activity, differential imprinting will occur even within homogeneous genetic backgrounds. The presence of allelic variants at these loci in non-inbred populations will give rise to variation in the observed expressivity and mode of inheritance of affected traits.
Gene expression and parental dominance in hybrid plants
Authors: Heslop-Harrison J. S.
Published: April 2021

Genomic imprinting, where the genes from one parent have different expression properties to those of the other parent, occurs in plants. It has potentially significant consequences because of the importance of hybrids in plant evolution and plant breeding, and provides a mechanism that can hide genetic variation for many generations. The study of nuclear organization shows that chromosome and genome position relates to imprinting in F1 hybrids, with peripheral genomes tending to be expressed preferentially. In some inbred, polyploid hybrids, such as Triticale (a wheat x rye hybrid), treatment with the demethylation agent azacytidine releases hidden variation, which was perhaps lost because of imprinting phenomena.
Acellularity of starfish embryonic mesenchyme cells as shown in vitro
Authors: Kaneko Hiroyuki , Takaichi Shigeko , Yamamoto Masamichi , Dan-Sohkawa Marina
Published: April 2021

Embryonic mesenchyme cells of the starfish are shown to be unexpectedly fusogenic in vitro. When archenteron complexes (archenterons and varying portions of the extracellular matrix {ECM} surrounding them) are isolated from starfish embryos and inoculated in sea water containing 4 % newborn bovine serum, the mesenchyme cells form large syncytia on the substratum underneath each archenteron. These syncytia break into smaller fragments interconnected by fine cell processes within 24 h. These networks have been studied morphologically, dynamically and ultrastructurally and found to lack cell borders between the constituent fragments. These fragments contain various numbers of nuclei ranging from 0 to 6 or more and move about constantly over the substratum, sometimes breaking into two and sometimes fusing with neighbouring fragments, so that the overall pattern of the network changes constantly. Our results also indicate that the network is threedimensional i.e. it has crossing sites, the frequency of which seems to depend on the amount of the ECM excreted on the substratum. A similar network pattern is found among mesenchyme cells in vivo, which suggests that the features found in vitro reflect those in vivo.
Neurogenic and antineurogenic effects from modifications at the Notch locus
Authors: Palka J. , Schubiger M. , Schwaninger H.
Published: April 2021

The best studied mutations at the Notch locus produce a neurogenic phenotype, with a massive overgrowth of the nervous system at the expense of epidermis. We report here that, in the development of the adult peripheral nervous system, the Abruptex alleles of Notch have the opposite phenotype, namely an underproduction of sensory organs or sensilla. This arises primarily not from an arrest of the lineages that produce sensilla, from the degeneration of sensillar cells, or from the transformation into neurons of cells that normally secrete the cuticular components of a sensillum (as can happen in Notch alleles). Rather, our evidence argues strongly that the sensillar mother cells never form. This implies that the Notch protein plays a role in the process that first generates a difference between sensillar mother cells and ordinary epidermal cells. The number of sensilla formed on the wing of flies carrying multiple doses of Notch* is virtually the same as that of wild type, i.e. the Abruptex phenotype is not reproduced to any significant extent. This suggests that the single amino acid substitutions that occur in Abruptex mutants confer on the protein some functionally distinctive feature, possibly more powerful intermolecular binding or altered stability.
Neurogenesis in the insect enteric nervous system: generation of pre-migratory neurons from an epithelial placode
Authors: Copenhaver* Philip F. , Taghert Paul H.
Published: April 2021

The enteric plexus (EP) is a major division of the enteric nervous system (ENS) in the moth Manduca sexta and contains a dispersed population of about 360 bipolar neurons, the EP cells. Previously we showed that embryonic EP cells achieve their mature distributions by extensive migration along the gut surface and then display position-specific phenotypes. We now demonstrate that the entire EP cell population is generated from an ectodermal placode that invaginates from the embryonic foregut. Individual EP cells become post-mitotic just as they leave the epithelium, but their terminal differentiation is subsequently delayed until after their migratory dispersal. Clonal analysis by injection of lineage-tracing dyes has shown that the EP cell population is derived from a large number of placodal cells, each of which contributes a limited number of neurons to the ENS. Placodally derived clones produce neurons exclusively, while clones arising from cells adjacent to the placode are incorporated into the gut epithelium. These results indicate that neurogenesis in the insect ENS involves a developmental strategy that is distinct from that seen in the insect CNS and which resembles the generation of certain cell classes in the vertebrate nervous system.
Identification of zona- and fucoidan-binding proteins in guinea-pig spermatozoa and mechanism of recognition
Authors: Jones Roy , Williams Rachel M.
Published: April 2021

Binding of guinea-pig spermatozoa to the zona pelluclda of homologous eggs has been reported to involve ‘receptors’ on the inner acrosomal membrane (Huang et al. 1981). These receptors can be blocked by sulphated polysaccharides such as fucoidan (Huang and Yanagimachi, 1984). The aims of the present investigation were to identify these putative zona receptors using 1251-fucoidan as a probe and examine their mechanism of recognition. Results show that 1251-fucoidan binds to several proteins extracted from guinea-pig spermatozoa with molecular m of 95, 60, 48, 34, 30 and 18-20xloJ (K) on SOS-PAGE. The 48K, 34K and 30K components represent Jroacrosln and two forms of acrosin, respectively. 1 1-zona pelluclda glycoproteins also bound strongly to the 48K, 34K and 30K sperm proteins. The other high and low mass binding proteins were not positively identified but cytochemlcal experiments with fluorescelnamine-fucoidan and FITC-soybean trypsin inhibitor indicate that they are intraacrosomal. The mechanism of binding of 1251-fucoidan to proacrosin/acrosln (and also the 95K, 60K and 18K-20K components) involves multiple sulphate groups on the polysaccharlde in a specific orientation to allow them to interact with basic residues on the protein. It is suggested that guinea-pig spermatozoa retain sufficient proacrosin/acrosin bound to the inner acrosomal membrane after the acrosome reaction to mediate binding to the zona pellucida and that functionally proacrosin is analogous to sea urchin bindin.
Mechanisms of neurulation: traditional viewpoint and recent advances
Authors: Schoenwolf G.C. , Smith J.L.
Published: April 2021

In this review article, the traditional viewpoint of how neurulation occurs is evaluated in light of recent advances. This has led to the formulation of the following fundamentals: (1) neurulation, specifically neural plate shaping and bending, is a multifactorial process resulting from forces both intrinsic and extrinsic to the neural plate; (2) neurulation is driven by both changes in neuroepithelial cell shape and other form-shaping events; and (3) forces for cell shape changes are generated by both the cytoskeleton and other factors. Several cell behaviors within the neural plate have been elucidated. Future challenges include identifying cell behaviors within non-neuroepithelial tissues, determining how intrinsic and extrinsic cell behaviors are orchestrated into coordinated morphogenetic movements and elucidating the molecular mechanisms underlying such behaviors.
The role of the nucleocytoplasmic ratio in development regulation of the early mouse embryo
Authors: Evsikov S. V. , Morozova L. M. , Solomko A. P.
Published: April 2021

The hypothesis suggesting that the blastocoele is able to form only at a definite nucleocytoplasmic ratio was tested. We compared the development of preimplantation mouse embryos under different conditions. The results demonstrated that the start of cavitation is not dependent on the number of cell divisions. Thus, a definite nucleocytoplasmic ratio is not required for blastocoele formation to start. Our studies on embryos with microsurgically altered cytoplasm content provided evidence for the following biological clock mechanism: a change in the cell program of morphogenesis needs definite concentration of the products of a previous genetic program.
Fibroblast growth factor during mesoderm induction in the early chick embryo
Authors: Mitrani E. , Gruenbaum Y. , Shohat H. , Ziv T.
Published: April 2021

A chick genomic clone that reveals a high degree of homology to the mammalian and Xenopus bFGF gene has been isolated. The pattern of expression of bFGF has been examined during early chick embryogenesis. RNA blot analysis revealed that chick bFGF is already transcribed at pregastrula stages. Immunolabeling analysis indicated that bFGF protein is present at these early developmental stages and is distributed evenly in the epiblast, hypoblast and marginal zone of the chick blastula. Substances that can inhibit FGF action were applied to early chick blastoderms grown in vitro under defined culture conditions (DCM). Both heparin and suramin were capable of blocking the formation of mesodermal structures in a dose-dependent manner. Our results indicate that FGF-like substances may need to be present for axial structures to develop although they may be acting earlier during the induction of non-axial mesoderm.
The micropyle: a sperm guidance system in teleost fertilization
Authors: Amanze Diala , Iyengar Arati
Published: April 2021

The micropylar region of the Rosy barb, Barbus conchonius, egg consists of 7-10 grooves and ridges, which drain directly into a funnel-shaped vestibule, the only point on the chorion through which sperm-egg contact is achieved during fertilization. Results of time-lapse video microscope study and computer-aided analysis of sperm motility pattern in the micropylar region showed that the fertilizing sperm, usually the first to enter the micropylar region, always travelled preferentially along the grooves into the micropylar pit. Subsequently, 86% of sperm arriving the micropylar region within 30 s travelled preferentially along the grooves into the immediate vicinity of the micropylar pit. The sperm guidance role of the micropylar region was calculated to enhance chances of egg penetration/fertilization by as much as 99.7% once sperm were within the micropylar region, possibly in response to some form of chemo-attractant(s) from the egg. Sperm agglutination postfertilization was also found to occur preferentially along the grooves. Results of our in vitro fertilization experiments showed association between point of sperm entry and blastodisc formation: the blastodisc formed directly beneath the micropyle in all undisturbed eggs.
The influence of cell interactions and tissue mass on differentiation of sea urchin mesomeres*
Authors: Khanert Oded , Wilt Fred
Published: April 2021

The developmental potential of different blastomeres of the sea urchin embryo was re-examined. We have employed a new method to isolate substantial numbers of different kinds of blastomeres from 16-cell-stage embryos, and we have used newly available molecular markers to analyze possible vegetal differentiation. We have found that, while isolated mesomere pairs behave according to the classical expectations and develop into ectodermal vesicles, there is a clear effect of reaggregat ing two or more mesomere pairs. They survive better in long-term culture and, after prolonged periods, they display an astonishing ability to express vegetal differen tiation. We also combined mesomeres with stained micromeres or macromeres from the vegetal hemi sphere. Although induction of guts and spicules was observed, there was little if any effect of varying the ratio of different blastomeres on the kinds of differentiation obtained.
Normal structure and expression of Zfy genes in XY female mice mutant in Tdy
Authors: Gubbay John , Koopman Peter , Collignon Jérôme , Burgoyne Paul , Lovell-Badge Robin
Published: April 2021

Zfy-1 and Zfy-2 are candidate genes for Tdy, the testis determining gene in mice. We have analysed these genes in a line of XY female mice that have been shown to be mutated in Tdy. We have used Southern blot analysis to show that the Zfy genes have not undergone any major structural alterations, and have also demonstrated that both genes are transcribed normally from the mutant Y chromosome (¥) in both adult XY¥ testis and X¥ female embryonic gonads. The fact that these genes show a normal structure and expression pattern in mice with a Y chromosome known to carry a mutation in Tdy and that mutant embryos develop into females despite Zfy-1 expression, strongly supports other recent evi dence that Zfy genes are not directly involved in primary testis determination.
Gonadal sex differentiation in the neonatal marsupial, Monodelphis domestica
Authors: Baker P. J. , Moore H. D. M. , Penfold L. M. , Burgess A. M. C. , Mittwoch U.
Published: April 2021

A quantitative and histological study of the gonads of newborn grey short-tailed opossums, Monodelphis domestica, is described. The pups were karyotyped, and comparisons were made within litters segregating for XX and XY sex chromosomes. A total of four litters including 25 pups were available. On the day of birth, developing testes were significantly larger than the ovaries of litter mates, and testes could be histologically distinguished by the formation of sex cords and a tunica albuginea. The data suggest that in this marsupial species gonadal differentiation may be initiated in utero.
Ammonia promotes accumulation of intracellular cAMP in differentiating amoebae of Dictyostelium discoideum
Authors: Riley Bruce B. , Barclay Stephen L.
Published: April 2021

We used sporogenous mutants of Dictyostelium discoid eum to investigate the mechanism(s) by which exogenous NH4CI and high ambient pH promote spore formation during in vitro differentiation. The level of NH4C1 required to optimize spore formation is correlated inver sely with pH, indicating that NH3 rather than NH4+ is the active species. The spore-promoting activity of high ambient pH (without exogenous NH4CI) was eliminated by the addition of an NH3-scavenging cocktail, sugges ting that high pH promotes spore differentiation by increasing the ratio of NH3:NH4+ secreted into the medium by developing cells. High ammonia levels and high pH stimulated precocious accumulation of intra cellular cAMP in both sporogenous and wild-type cells. In both treatments, peak cAMP levels equaled or exceeded control levels and were maintained for longer periods than in control cells. In contrast, ammonia strongly inhibited accumulation of extracellular Camp without increasing the rate of extracellular cAMP hy drolysis, indicating that ammonia promotes accumu lation of intracellular cAMP by inhibiting cAMP se cretion. These results are consistent with previous observations that factors that raise intracellular cAMP levels increase spore formation. Lowering intracellular cAMP levels with caffeine or progesterone inhibited spore formation, but simultaneous exposure to these drugs and optimal concentrations of NH4CI restored both cAMP accumulation and spore formation to nor mal levels. These data suggest that ammonia, which is a natural Dictyostelium morphogen, favors spore forma tion by promoting accumulation or maintenance of high intracellular cAMP levels.
The Action of Aminopterin on the Explanted Early Chick Embryo
Authors: O’Dell D. S. , McKenzie J.
Published: April 2021

One method of gaining insight into the mechanisms of growth and differentiation is based on the use of defined substances to alter normal development, but analysis of developmental changes so produced may be difficult or impossible if the substances used have an ill-defined biochemical action. The antimetabolites, however, do not have this disadvantage and, among them, folic acid antagonists are especially interesting.
The Embryology of Dacus tryoni 2. Development of Imaginal Discs in the Embryo
Authors: Anderson D. T.
Published: April 2021

The cephalic, wing, haltere, leg and median genital discs of D. tryoni develop in the embryo shortly after dorsal closure and involution of the head. The labial and lateral genital discs first appear in the mid-second larval instar. The wing and haltere discs arise as outgrowths of the ventral meso- and metathoracic discs. The remaining discs arise in the positions generally accorded to them by previous authors. Each pair of discs originates from cells in a definite location in the blastoderm. The relationship between the blastodermal locations of the presumptive discs and the segmental pattern of the larval ectoderm suggests that imaginai disc development in Cyclorrhapha resembles regeneration of a total field by a part.
DNA Synthesis and Nuclear Reproduction during Embryonic Development and Regeneration of Muscle Tissue
Authors: Zhinkin L. N. , Andreeva L. F.
Published: April 2021

Nuclear reproduction in myosymplasts and myotubes proceeds mitotically. Nuclei synthesizing DNA are found during the development of muscles. The percentage of 3H-thymidine labelled nuclei diminishes with the development of the embryo as mitotic activity decreases. A mitotic cycle in the nuclei of muscle fibres of a 17-day-old rat embryo takes about 20 hr. and the duration of mitosis itself is about 2·5 hr. A comparison of the number of nuclei participating in a mitotic cycle with the mitotic index allows us to suggest that as differentiation proceeds some nuclei provide the synthesis of specialized proteins while others undergo reproduction. During regeneration of muscle fibres, 2 days after operation, a considerable percentage of 3H-thymidine labelled nuclei is found at the ends of cut muscle fibres and, correspondingly, the mitotic index is high. The number of labelled nuclei, as well as that of mitoses, decreases with distance from the wound. Subsequently labelled nuclei move to muscle buds where they only very rarely undergo division. All the facts obtained show that the reproduction of muscle nuclei during embryonic development and during regeneration of muscle fibres in adult animals proceeds in the same manner as in any other cellular tissues where cell reproduction by mitosis is not in doubt.
The Population of Germ Cells in the Developing Female Chick
Authors: Hughes Gillian C.
Published: April 2021

Morphological and cytological changes occurring in the left (functional) ovary of the developing chick were studied by means of both histological and squash preparations. Counts were made of the numbers of oögonia and oöcytes at various stages of meiotic prophase in specimens aged 9 days’ incubation to 1 day after hatching. Neither the mitotic activity of oögonia nor the onset of the successive stages of meiotic prophase are synchronized throughout the ovary. The development of the germ cells is more advanced at the centre than at the extremities of the ovarian cortex. The process of oögenesis ceases at about the time of hatching. Appreciable numbers of oöcytes enter the pre-leptotene phase on the thirteenth day, zygotene and pachytene on the seventeenth, and diplotene on the nineteenth day of incubation. Degeneration of germ cells occurs throughout the developmental period studied. Oögonial mitoses are associated with an increase in the total population of germ cells from about 28,000 at 9 days’ incubation to some 680,000 on the seventeenth day. Subsequently, a high incidence of degenerating germ cells, together with a decline in the number of oögonial mitoses, account for a decrease in the total population between the seventeenth day of incubation and 1 day after hatching, when only about 480,000 oöcytes persist.
The Development of Somites in the Chick Embryo
Authors: Bellairs Ruth
Published: April 2021

In two groups of experiments the so-called ‘somite centres ‘were removed from chick blastoderms. Nevertheless, well-developed somites formed. It is concluded, therefore, that the ‘somite centres’ are not essential for somite formation. The same experiments, and others which are described, also provided evidence that somites can form in the absence of neural tissue. It is concluded, therefore, that neural tissue is not essential for somite formation. Experiments involving extirpation of the node confirmed the now generally accepted findings of various authors that neither the node nor the notochord are essential for the differentiation of somites. It is suggested that the regression movements may play a decisive rôle in influencing somite differentiation.
Behavior of fetal intestinal organ culture explanted onto a collagen substratum
Authors: Altmann G. G. , Quaroni A.
Published: April 2021

A model of organ culture of 18 day old fetal rat intestine (Quaroni, 1985) was modified and characterized in the present work with the purpose of developing an in vitro model for the study of intestinal epithelial cell behaviour. Fragments of this intestine were kept in suspension culture for 7 days and then explanted onto collagen (type I) matrix. Within a day, the fragments became anchored to the substratum and a circular monolayer grew out to about 1 cm diameter.

In the fragments, an outer layer of absorptive epithelial cells came to enclose a stroma, which was polarized into a loose (mesenchymal) and a dense portion. The dense portion contained a mixture of smooth muscle cells and primitive stem-type epithelial cells (‘p-cells’). After explantation, at the contact point with the matrix, the epithelium broke up and the mesenchyme grew into the matrix and anchored the fragment. The epithelial edges now became continuous with the developing monolayer. Radioautography with tritiated thymidine indicated a constant cell renewal in epithelium and monolayer apparently from foci of p-cells, a reserve population of which was seen to be sequestered among the smooth muscle cells. Activated stem cells could differentiate into three mature epithelial phenotypes, each differentiation pathway apparently being determined by the type of underlying stroma. Immunohistochemistry using gold- and fluorescein-labeled monoclonal antibodies indicated that adult differentiation-specific markers (e.g. brush border enzymes) were present in the fragment epithelium but not in the monolayer cells. On the other hand, the monolayer cells could be induced to express some of these markers by contact with mesenchymal cells or by co-culturing with fibroblastic cell lines. Matrigel sub-stratum mixed with collagen (type I) supported the appearance in monolayer of strands positive for amino-peptidase and lactase. The model thus appears to be suitable for the in vitro study of epithelial renewal and differentiation, and it has already provided some results in this respect.
Mammary glands in male marsupials: I. Primordla in neonatal opossumsDidelphis virginlanaandMonodelphls domestica
Authors: Renfree Marilyn B. , Robinson E. S. , Short R. V. , Vandeberg J. L.
Published: April 2021

Neonates of the American didelphid marsupials Didelphis virginiana and Monodelphis domestica were sexed by karyotype and histologically examined on the day of birth. Mammary anlagen were found in both sexes of both species, but the neonatal males had less than one-third of the full female complement of mammary glands. Male neonates of both species also had paired scrotal bulges anterior to the genital tubercle but these were never present in females, once again raising the question of whether the pouch and scrotum are homologous structures. Mammary anlagen are not found in male neonates of the Australian marsupial species so far studied, which suggests a dichotomy in the control of some aspects of sexual differentiation in the two marsupial lineages.
Characterization of protein kinase C in early Xenopus embryogenesis
Authors: Otte Arie P. , Kramer Ijsbrand M. , Mannesse Maurice , Lambrechts Caro , Durston Antony J.
Published: April 2021

Recently, we presented evidence that protein kinase C (PKC) is involved in mediating the endogenous signals that induce competent Xenopus ectoderm to differentiate to neural tissue. We report here that PKC is already strongly activated in neural-induced ectoderm from midgastrula embryos and that this activation runs parallel with an increase in the level of inositol phosphates. We further identify several proteins that are phosphorylated, both in natural neural-induced ectoderm and in TPA-treated ectoderm, suggesting that they are phosphorylated through the PKC route. We found no major changes in PKC activity among different pregastrula stages, including the unfertilized egg. However, PKC isolated from animal, ectodermal cells is highly sensitive to Ca2+ and can be activated by low concentrations, (6–25μM) of arachidonic acid, while PKC isolated from vegetal, endodermal cells is more insensitive to Ca2+ and cannot be activated by arachidonic acid. These results suggest that different PKC isozymes are present in animal and vegetal cells.
Morphological and radiochemical evidence for the metabolism of exogenous proteins by the preimplantation sheep blastocyst
Authors: Pullar Duncan , Kronnie Geertruy Te , Peiris I. Dammika , Taverne Nico , Jeacock Marjorie K. , Stroband Henri W. J. , Shepherd David A. L.
Published: April 2021

The ability of the trophoblast of the ovine preimplantation blastocyst to take up and metabolise proteins has been investigated using two experimental approaches, microscopical and radiochemical. The ultrastructure of the expanded blastocyst obtained from 14 and 17 day pregnant ewes was examined. The morphology of tissues maintained in culture for 24 h has been compared with that of fresh tissues. After culture, the cellular morphology of the explants was well preserved. Fresh and 24 h cultured tissues were incubated with horseradish peroxidase and ferritin and these proteins subsequently were found to be localized in coated pits, caveolae and secondary lysosomes of the trophoblast. Comparison of the uptake of [3H]dextran and of 125I-labelled bovine serum albumin indicated that proteins could be taken up by cultured tissue by mechanisms in addition to simple fluid phase endocytosis. During culture of explants of blastocyst with l2SI-labelled bovine serum albumin, a large fraction of the radioactivity taken up by the tissue appeared in the TCA-soluble fraction of the culture medium indicating that cultured trophoblast hydrolysed proteins. That amino acids released from captured protein could be used for protein synthesis by the trophoblast was indicated by the labelling of tissue and medium proteins after culturing explants with β-lactamase labelled with [14C]leucine. A major product (Mr approximately 17X103) present in the medium was likely to have been ovine trophoblast protein-1. It is concluded that, during the expansion of the ovine blastocyst, the trophoblast has the ability to take up proteins, transport them to lysosomes and degrade them to amino acids which are used for protein synthesis. Thus proteins, as well as free amino acids, present in the histotrophe may be an important source of nitrogen for the sheep conceptus in the critical period just prior to implantation.
Spatiotemporal expression of murine carcinoembryonic antigen (CEA) gene family members during mouse embryogenesis
Authors: Huang Jing Qi , Turbide Claire , Daniels Eugene , Jothy Serge , Beauchemin Nicole
Published: April 2021

Carcinoembryonic antigen is a glycosylated protein used as a human tumor marker to assess recurrences of gastrointestinal, breast and lung cancers. This protein is a member of the immunoglobulin supergene family and has been shown to function as a homophilic and heterophilic cell adhesion molecule. We have studied the spatial and temporal expression of two cloned mouse CEA gene family members during development using Northern analyses and in situ hybridization. Transcripts detected by the mouse CEA probes are expressed from 10.5 days post coitum (p.c.) to birth in mouse embryos and fetuses and are present from 16.5 days p.c. to adulthood in intestine and colon as evaluated by Northern analyses. The RNA is also present in many other tissues including meninges, cartilage and bone, blood vessel walls, placenta, dermis, muscle layers of the stomach and intestine and bronchioles of developing mouse embryos and fetuses. This expression pattern is similar to that of proteins of the Transforming Growth Factor β gene family. The role of mouse CEA gene • family members is unclear; however, the localizations of these CEA family members in the mouse embryo and fetus suggest an important functional role during active morphogenesis, a complex process in which cell adhesion molecules are significantly involved.
Pattern formation under the control of the terminal system in the Drosophila embryo
Authors: Casanova Jordi
Published: April 2021

The specification of the most anterior and posterior domains of the Drosophila embryo depends on the activity of the torso protein, a putative tyrosine kinase receptor. Localized torso activity at the poles of the embryo generates graded information that specifies distinct portions of the body. The primary response to the terminal signal in the posterior end of the embryo is likely to be the activation of the gap genes huckebein and tailless. Here I address the question of how the graded maternal signal generates different elements of the pattern at the posterior end of the embryo and what role huckebein and tailless activities may play in this process. These experiments show that distinctly localized activities of huckebein and tailless are responsible for the appropriate expression of other genes known to be under the control of the terminal system. Moreover, they suggest that different elements of the terminal pattern can be specified in response to distinct levels of graded tailless activity.
The pattern of transcription of the neurogenic gene Delta of Drosophila melanogaster
Authors: Haenlin Marc , Kramatschek Bernd , Campos-Ortega José A.
Published: April 2021

The function of the Delta locus of Drosophila melanogaster is required for the correct separation of neural and epidermal cell lineages. We describe here the transcriptional organization of this locus and the spatial pattern of mRNA accumulation during embryogenesis. Delta produces three mRNAs with protein-coding capacity, which differ only at their untranslated 3′ ends and thus encode the same protein; other minor RNAs from the locus are shown not to have any protein-coding capacity and to correspond to introns. No indications were obtained for multiple translational products of the locus. In situ hybridization using digoxigenin-labelled probes confirms that Delta RNA is present at high concentration in all presumptive neurogenic territories of the embryo. Since all the constituent cells of these territories contain Delta RNA, a differential distribution of the protein among the derivatives of the neuroectodermal cells is improbable. Some time after segregation of lineages, Delta RNA reappears in neuroblasts. The possible significance of these observations with respect to the function of the Delta product during lineage segregation is discussed.
Post-transcriptional regulation of ornithine decarboxylase in Xenopus laevis oocytes
Authors: Bassez Therèse , Paris Jeannie , Omilli Francis , Dorel Corine , Osborne H. Beverley
Published: April 2021

The level at which ornithine decarboxylase expression is regulated in growing oocytes has been investigated. Immunoprecipitation of the in vivo labelled proteins showed that ornithine decarboxylase accumulated less rapidly in stage IV oocytes than in previtellogenic stage I+II oocytes. Quantitative Northern analysis showed that ornithine decarboxylase mRNA is abundant in oocytes (about 8×l08 transcripts/cell) and this number does not significantly change during oogenesis. Polysome analysis showed that this mRNA is present in polysomes in stage I+II oocytes but has passed into puromycin-insensitive mRNP particles by stage IV of oogenesis.

Therefore, during the growth phase of oogenesis, ornithine decarboxylase expression is regulated at a translational level. These results are discussed relative to the temporal expression of ornithine decarboxylase and of other proteins whose expression also decreases during oogenesis. In order to perform these experiments, the cDNA (XLODC1) corresponding to Xenopus laevis ornithine decarboxylase mRNA was cloned and sequenced.
Gradients of homeoproteins in developing feather buds
Authors: Chuong Cheng-Ming , Oliver Guillermo , Ting Sheree A. , Jegalian Beatrice G. , Chen Hai Ming , Robertis Eddy M. De
Published: April 2021

Homeoproteins are functionally involved in pattern formation. Recently, homeoproteins have been shown to be distributed in a graded fashion in developing limb buds. Here we examine the expression of homeoproteins in chicken feather development by immunocytochemical localization. We find that XlHbox 1 antigen is present in cell nuclei and is distributed in a gradient in the mesoderm of developing feather buds, with strongest expression in the anterior-proximal region. The gradient is most obvious in feather buds from the mid-trunk level. Feather buds from the scapular level express very high levels of XlHbox 1 and feather buds from the caudal region express no XlHbox 1, suggesting that a broad gradient along the body axis is superimposed on a smaller gradient within each individual feather bud. Feather ectoderm also expresses XlHbox 1 antigen but without an obvious graded pattern. Another homeoprotein, Hox 5.2, is also expressed in developing feather buds in a graded way, and its distribution pattern is partially complementary to that of XlHbox 1. These observations suggest that homeoproteins may be involved in setting up the anteroposterior polarity of cell fields at different levels, first for the body axis, then for the limb axis and finally for the feather axis.
Organotypic arrangement of mouse embryonic lung cells on a basement membrane extract: involvement of laminin
Authors: Schuger Lucia , O’shea K. Sue , Nelson Bradley B. , Varani James
Published: April 2021

The behavior of embryonic murine lung cells on a basement membrane extract (Matrigel) was investigated. Single cell suspensions generated by trypsinization of lungs removed from day 12 embryos were plated on Matrigel and cultured for up to one week. The basement membrane extract was used as a gel, and as a wet or dried him. In all of these instances, organotypic arrangement of the embryonic lung cells was observed. This process consisted of cell aggregation, sorting, polarization and formation of a tridimensional organization resembling embryonic lung. The maximal degree of organotypic development was obtained by using a thick gel; minimal reorganization was observed using a dried Flim. A rabbit polyclonal serum to laminin inhibited organotypic pattern formation while normal rabbit serum did not. Culture of lung cells on laminin gels promoted epithelial cyst formation but poor mesenchymal organization. By studying the behavior of epithelial and/or mesenchymal enriched cell populations on Matrigel, it was concluded that organotypic pattern formation on Matrigel required the presence of both cell populations. Cultivation of dissociated lung cells on a gel consisting of a mixture of collagens type I and III (Vitrogen-100) produced only cell aggregation. Cultivation of lung cells on a thin film of Vitrogen-100 or on uncoated tissue culture plastic produced monolayers of mesenchymal cells alone. Cultivation of lung cells in suspension also failed to induce organotypic arrangement even at maximal cell densities. The present study strongly supports a role for the basement membrane in the organotypic rearrangement of embryonic lung cells and subsequent in vitro cyst formation and budding of the reestablished epithelium. This, in turn, reinforces the concept of the basement membrane as a major regulator of organogenesis.
Galactosyl transferase-dependence of neurita outgrowth on substratumbound laminin
Authors: Thomas William A. , Schaefer Andrew W. , Treadway R. Morris
Published: April 2021

The cell surface enzyme β 1–4 galactosyl transferase (galtase) has been implicated in a number of cellular events involving adhesion and recognition, among them migration of neural crest and mesenchymal cells as well as initiation and elongation of neurites from PC 12 cells. Results presented here demonstrate that reagents that specifically alter galtase activity modulate the rate of neurite outgrowth from chick dorsal root ganglia on substrata coated with the large extracellular matrix glycoprotein, laminin (LN), a known substrate for galtase activity. Not all neurites responded equally to reagent addition, and in every experiment a subset of neurites was ostensibly unaffected by reagent, even at the highest concentration tested. Those neurites that were affected demonstrated an ability to adapt to the continued presence of reagent and resume normal elongation. These results support the hypothesis that cell surface galtase activity plays an important role in mediating neurite elongation and suggest further that differential expression of galtase at the nerve growth cone might contribute to axonal guidance through glycoconjugate-rich environments in vivo.
Time course of opsin expression in developing rod photoreceptors
Authors: Knight Jennifer K. , Raymond Pamela A.
Published: April 2021

We have investigated the time course of rod photoreceptor determination in the goldfish retina. Rod precursor cells located in the outer nuclear layer of the mature retina continuously generate rod photoreceptors. In this study, we asked when rod precursor cells begin to express opsin, which would signal their commitment to the rod pathway of differentiation. There are three possibilities: a rod precursor could express opsin while still mitotic, at or shortly after the terminal mitosis but before differentiation, or during differentiation.

We used immunocytochemistry with antibodies against bromodeoxyuridine, BrdU (a thymidine analogue) and against opsin to determine when during the mitotic history of a cell the expression of opsin first occurred, taking a double labelled cell to be evidence of commitment to the rod cell fate. We found that the first double labelled cells appeared at 4 days after BrdU injection. The number of double labelled cells increased to peak at 10 days, and then fell. These results support the hypothesis that dividing rod precursor cells are probably multipotent stem cells not committed to the rod cell fate.
Expression and regulation of the abd-A gene of Drosophila
Authors: Macias Ana , Casanova Jordi , Morata Gines
Published: April 2021

We have developed a specific polyclonal antibody that recognizes the protein products of the abdominal-A (abdA) gene, a member of the bithorax complex of Drosophila. The normal expression domain extends from parasegments 7 to 13, in good correspondence with previous genetic and molecular results. However, while the anterior border of expression is precisely demarcated by a parasegmental boundary, the posterior border does not coincide with a lineage boundary. Within the normal domain, the expression of abd-A shows intrametameric modulation; the amount of product is higher in posterior compartments and in the most anterior cells of the anterior compartments and then gradually decreases. We have examined the effect on abd-A expression of a number of mutations, some mapping within and others outside the abd-A transcription unit. Those mapping to the transcription unit eliminate or severely reduce the amount of abd-A antigen, while those mapping outside produce an abnormal distribution of abd-A protein. Finally, we show that the abd-A gene is down-regulated in part of the Abdominal-B (Abd-B) domain, precisely in those regions where the Abd-B gene is expressed at high levels.
Somatostatin receptors are restricted to a subpopulation of osteoblast-like cells during endochondral bone formation
Authors: Mackie Eleanor J. , Trechsel Ulrich , Bruns Christian
Published: April 2021

Specific binding sites for the peptide hormone somatostatin have previously been demonstrated in long bones from neonatal rats. In the present study, the distribution of somatostatin receptors during embryonic bone formation has been investigated using the stable radio-iodinated somatostatin analogue, SDZ 204–090. Somatostatin receptors in rat long bones were first detectable at the time of invasion of the cartilage model by osteogenic cells. Initially, receptors were detectable throughout the region occupied by osteogenic cells. As bone growth proceeded, however, receptors were restricted to the region of most recent invasion of the hypertrophic cartilage, where osteoid had not yet been deposited. In vivo labelling studies in neonatal rats were carried out to identify the cells bearing somatostatin receptors. Receptors were present in a restricted region of the metaphysis, immediately adjacent to the hypertrophic cartilage. Chondrocytes, osteoclasts and mature osteoblasts were not labelled by the radioligand. The labelled cells were often apposed to remnants of cartilage matrix and stained positively for the osteoblast marker, alkaline phosphatase. Thus the cells with specific somatostatin-binding sites were probably osteoblast precursor cells. Specific binding was detectable in all endochondral bones examined, including those of the skull, but no specific binding was found in the membrane bones of the skull. These data suggest that somatostatin is involved in the regulation of osteoblast differentiation during endochondral bone formation.
Epithelial scatter factor and development of the chick embryonic axis
Authors: Stern Claudio D. , Ireland Grenham W. , Herrick Sarah E. , Gherardi Ermanno , Gray Julia , Perryman Marion , Stoker Michael
Published: April 2021

Scatter factor, a recently characterised protein secreted by certain embryonic fibroblasts, affects cultured epithelia by increasing cell motility, the breakdown of cell junctions and cell scattering. The process of gastrulation in higher vertebrate embryos, during which the primitive streak forms, involves an epithelial-to-mesenchymal transformation resembling the effects of the factor on cultured cells. The factor was applied locally to chick embryos, using both scatter-factorsecreting cell lines and inert carriers. We found that scatter factor can generate local supernumerary axial structures resembling primitive streak and/or neural plate and conclude that it may have primitive-streak- and/or neural-inducing activity in chick embryos.
Growth-factor-related proteins that are inducers in early amphibian development may mediate similar steps in amniote (bird) embryogenesis
Authors: Cooke Jonathan , Wong Adeline
Published: April 2021

Xenopus and murine activin A homologues (XTC-MIF and WEHI-MIF) and Xenopus and bovine basic fibroblast growth factor (bFGFs) are potent inducers of mesodermal and endodermal pathways of development in amphibian blastular animal cap cells. Porcine transforming growth factor β2 (TGF β2) is a weaker inducer in the same assay but human platelet-derived growth factor (PDGF) is inactive. We have assayed these factors for evidence of homologous effects in bird development. Unlike amphibians, bird embryos never exhibit a clean segregation of a cell layer that has a uniform specification when uninduced, and can be cultured in isolation as an assay after exposure to soluble factors. We have therefore performed less direct experiments, of three types. We have briefly cultured early chick epiblast cells with and without factors and then assayed their capacity to attach and spread upon fibronectin, in comparison with young streak and substreak hypoblast cells. We have asked whether similar microculture with factors alters the ability of quail epiblast cells to disrupt morphogenesis, and to integrate into the structure, of host chick blastoderms into which they are seeded. Finally, whole early chick blastoderms have been preincubated with or without factors for a brief period before setting them up to develop in vitro under circumstances usually permitting successful formation of axial pattern. Strong effects of the activin-like factors, of bFGF and of TGF β2 were seen in all three procedures, while PDGF was essentially inactive. In epiblast cells, effective factors at picomolar concentrations induced stable spreading upon fibronectin, and a capacity to adhere and spread upon basal epiblast surface and prevent morphogenesis in host blastoderms. Preincubation of whole early blastoderms with these factors led to characteristic deviation from normal development over the subsequent 24 h. We therefore suggest that peptides from the particular families that are active as inducers in amphibian blastula ectoderm may mediate homologous or closely related steps in respecification throughout vertebrates.