bluuebunny/crossref_metadata_2025 huggingface dataset:
The induction of anterior and posterior neural genes in Xenopus laevis
Authors: Sharpe C. R. , Gurdon J. B.
Published: April 2021

We have investigated the interactions between mesoderm and ectoderm that result in the formation of a regionally differentiated nervous system in Xenopus embryos. We have used genes expressed at different positions along the neural tube as regional markers of neural induction in both whole, and in experimentally manipulated embryos. By comparing transcription from the anterior marker, XIF3, with that from the posterior marker, XIHbox6, and the general neural marker XIF6, we have shown that the normal induction process requires interactions between ectoderm and mesoderm that persist through gastrulation into the late neurula stages.

We have found that competence of the ectoderm to respond to induction is lost at the same early neurula stage for all three marker genes. Using rhodamine dextran-labelled mesoderm, we have established that the duration of contact between ectoderm and mesoderm required for gene activation in conjugates is the same for each of the markers. We have, however, identified regions of the mesoderm that can induce different combinations of neural marker gene expression. The anterior mesoderm induces expression of the anterior marker, XIF3, and the later migrating posterior mesoderm induces the ectoderm overlying it to express the posterior marker XIHbox6.

It has been proposed that neural inducing signals reach the ectoderm by two different routes: from mesoderm lying directly beneath the ectoderm or along the plane of the ectoderm. We have assessed the contribution of each route in respect of our three neural markers and find that a signal passing directly from mesoderm to ectoderm fully accounts for neural gene expression. We were unable to detect an inducing signal that passes along the plane of the ectoderm.
Single cell transplantation reveals interspecific cell communication in Drosophila chimeras
Authors: Becker Thomas , Technau Gerhard M.
Published: April 2021

Cell –cell communication is not only a common strategy for cell fate specification in vertebrates, but plays important roles in invertebrate development as well. We report here on experiments testing the compatibility of mechanisms specifying cell fate among six different Drosophila species. Following interspecific transplantation, the development of single ectodermal cells was traced in order to test their abilities to proliferate and differentiate in a heterologous environment. Despite considerable differences in cell size and length of cell cycle among some of the species, the transplants gave rise to fully differentiated clones that were integrated into the host tissue. Clones comprised cells of epidermal and/or neural histotypes, indicating that mechanisms mediating the epidermal/neural dichotomy in the ectoderm are conserved between the species. Cells of the neural lineages differentiated into neurones, glia, or both. Moreover, heterologous neurones sent out axons that followed major pathways along nerves and within the neuropile, demonstrating their ability to recognize positional cues in the heterologous CNS of the host.
Expression of the tyrosine kinase receptor gene trkB is confined to the murine embryonic and adult nervous system
Authors: Klein Rüdiger , Martin-Zanca Dionisio , Acid Mariano Barb , Parada Luis F.
Published: April 2021

We have examined the expression of the trkB gene, which encodes a member of the family of protein tyrosine kinase (TK) transmembrane receptors, during mouse embryogenesis using in situ hybridization and Northern analysis. Transcripts were first detected in the neuroepithelium and in the neural crest of 9.5 day embryos with regions of high expression in the neural folds and at the lateral neuroepithelium. However, during the process of cephalization and development of the peripheral nervous system, transcripts were detected in most neural tissues, including the brain, spinal cord, cranial and spinal ganglia, and along the pathways of axonal tracts extending peripherally. In the adult brain, expression continues in a complex pattern that is confined to specific regions or neuron types. The expression of trkB, a TK receptor, in early embryogenesis, and specifically in neural tissues, is consistent with the notion that this gene plays a role in the events that regulate the development of the nervous system.
Expression of the neuronal surface glycoprotein Thy-1 is under post-transcriptional control, and is spatially regulated, in the developing olfactory system
Authors: Xue G. P. , Calvert R. A. , Morris R. J.
Published: April 2021

Expression of the neuronal cell surface glycoprotein Thy-1 has been studied during the development of the olfactory bulb in mice and rats, using in situ hybridisation and immunohistochemistry to follow the appearance of Thy-1 mRNA and protein, respectively. The mRNA was first detected 4 days before birth on all mitral cells, the main projection neuron of the bulb, as they formed a distinct layer and grew dendrites. At no stage was any spatial gradient of expression of Thy-1 mRNA evident around the mitral cell layer. Thy-1 protein, on the other hand, was first detectable 2 days later on a group of mitral cells immediately adjacent the point of entry of the olfactory nerve. The numbers of immunoreactive cells spread, over the next 7 days, to include all mitral cells, those located rostrally and laterally in the bulb being slowest to express Thy-1 protein. Thus there was a spatiotemporal gradient of expression of Thy-1 protein, which was not apparent in the earlier general expression of its mRNA, suggesting that some further inductive signal was required after transcription in order to get effective production of protein. Analysis of the growth of the mitral cell axons in the lateral olfactory tract suggested this signal was related to the cessation of axonogenesis, as Thy-1 immunoreactivity became detectable on these axons only when their expression of the transient epitope detected by the GIO antibody, present on microtubule-associated protein (MAP)lx only during axonal growth, declined.

For the first week after Thy-1 protein appeared on mitral cells, it was not distributed uniformally on their surface. Immunoreaction was relatively weak on the somatic surface, and the molecule appeared to be entirely excluded from the distal regions of its main dendrite, above the outer plexiform layer. Here the dendrite reaches up to the synaptic glomeruli formed with the incoming olfactory nerve axons. These distal regions of the dendritic shaft became immunoreactive only after the periglomerular cells had first begun to express Thy-1 protein in the glomeruli. Immunolabelling of the somatic membrane then increased, to give the adult pattern of uniform Thy-1 labelling of the neuronal membrane by the end of the second postnatal week. It is suggested that some of the molecular features of Thy-1, and anatomical features of the main bulb, could interact to produce this initial restriction of Thy-1 to particular parts of the mitral cell suface.

Despite the mitral cells of the accessory olfactory bulb developing earlier than those of the main bulb, both Thy-1 mRNA and protein appeared 5 –7 days later on the cells of the accessory bulb. This may be related to the guidance role that the accessory axons are thought to play in respect of the later developing fibres of the main bulb.
Localization of the DER/flb protein in embryos: implications on the faint little ball lethal phenotype
Authors: Zak Naomi B. , Wides Ronald J. , Schejter Eyal D. , Raz Erez , Shilo Ben-Zion
Published: April 2021

Antibodies were raised against the Drosophila EGF receptor homolog (DER) and used for immunohistochemical analyses of Drosophila embryos. We found that DER is localized in a wide array of embryonic tissues, displaying a dynamic pattern of expression. DER appears to be expressed in all cells at the cellular blastoderm and gastrula stages. In extended-germ-band embryos, it is found predominantly in the mesoderm and the head. Finally, in retracted-germ-band embryos, DER immunoreactivity is most pronounced at sites of somatic muscle attachments and along the ventral midline of the CNS. We have thus observed that DER is expressed in the diverse tissues which are affected in the DER faint little ball (flb) embryonic lethal phenotype. The different pattern and extent of expression in each tissue suggests that the disparate aspects of the flb phenotype may result from different mechanisms of DER function. To understand the basis for the CNS phenotype of DER/flb mutants, we have closely followed the collapse of the CNS in mutant embryos. Our observations on the evolution of the final CNS phenotype, in combination with the temporo-spatial pattern of appearance of DER in the ventral neuroepithelium, suggest that this receptor participates in the second phase of neuron– glia interactions, namely in stabilization of the ladder-like CNS scaffolding formed by outgrowth of pioneer axonal processes along the glial pre-pattern.
The Notch locus of Drosophila is required in epidermal cells for epidermal development
Authors: Hoppe Pamela E. , Greenspan Ralph J.
Published: April 2021

The Notch locus of Drosophila plays an important role in cell fate decisions within the neurogenic ectoderm, a role thought to involve interactions at the cell surface. We have assayed the requirement for Notch gene expression in epidermal cells by two kinds of genetic mosaics. First, with gynandromorphs, we removed the wild-type gene long before the critical developmental events to produce large mutant clones. The genotype of cells in large clones was scored by means of an antibody to the Notch protein. Second, using mitotic recombination, we removed the gene at successively later times after completion of the mitotically active early cleavage stages, to produce small clones. These clones were detected by means of a linked mutation of cuticle pattern, armadillo. The results of both experiments demonstrate a requirement for Notch expression by epidermal cells, and thus argue against the model that the Notch product acts as a signal required only in the neuroblast to influence neighboring epidermal cells. The mitotic recombination experiment revealed that Notch product is required by epidermal cells subsequent to neuroblast delamination. This result implies that the Notch gene functions to maintain the determined state of epidermal cells, possibly by mediating cell surface interactions within the epidermis.
Tentacle morphogenesis in hydra: I. The role of head activator
Authors: Hobmayer Engelbert , Holstein Thomas W. , David Charles N.
Published: April 2021

Stimulation of tentacle-specific cell differentiation by the neuropeptide head activator was investigated in Hydra magnipapillata. Tentacle-specific sensory nerve cells were identified by a monoclonal antibody, NV1. Treatment of hydra with 1 pM head activator for 18 h stimulated differentiation of NV1+ nerve cells and tentacle epithelial cells in tissue from the distal gastric region. Head tissue and tissue from the proxmial gastric region did not respond to head activator treatment with increased NV1+ differentiation. Hence the distal gastric region appears to be the site of tentacle formation in hydra. Tentacle precursors in head tissue seem to be committed since they fail to respond to head activator or to changes in tissue size with altered amounts of tentacle formation. We suggest that NV1 precursors form a complex with tentacle epithelial cell precursors, which then moves distally through the head region into the tentacles. The signal for NV1+ differentiation appears to be formation of this complex.
Interaction between satellite cells and skeletal muscle fibers
Authors: Bischoff Richard
Published: April 2021

Single myofibers with attached satellite cells isolated from adult rats were used to study the influence of the mature myofiber on the proliferation of satellite cells. The satellite cells remain quiescent when cultured in serum containing medium but proliferate when exposed to mitogen from an extract of crushed adult muscle. The response of satellite cells to mitogen was measured under three situations with respect to cell contact: (1) in contact with a viable myofiber and its basal lamina, (2) detached from the myofiber by centrifugal force and deposited on the substratum and (3) beneath the basal lamina of a Marcaine killed myofiber. The results show that satellite cells in contact with the plasmalemma of a viable myofiber have reduced mitogenic response. Since inhibiting growth may induce differentiation, I tested whether satellite cells proliferating on the surface of a myofiber would fuse. Although the satellite cell progeny were fusion competent, they did not fuse with the myofiber. To determine whether fusion competence of the myofiber changes with time in culture, embryonic myoblasts were challenged to fuse with myofibers that had been stripped of satellite cells and cultured for several days. The myoblasts fused with pseudopodia! sprouts growing from the ends of the myofiber, but did not fuse with the original myofiber surface. These results indicate that contact with the surface of a mature myofiber suppresses proliferation of myogenic cells but the cells do not fuse with the myofiber.
Double anterior chick limb buds and models for cartilage rudiment specification
Authors: Wolpert Lewis , Hornbruch Amata
Published: April 2021

Most models for the specification of the skeletal elements in the developing limb bud are based on a chemical specification well before overt cartilage differentiation. By contrast, a physico-mechanical model proposes that the process of condensation – an early feature of cartilage differentiation – is itself the basis for patterning the elements. The models thus make quite different predictions as to when the rudiments are specified. Double anterior limb buds have been constructed at stages earlier than condensation, with the expectation that, if specification of the humerus occurs before cartilage condensation, then limbs containing two humeri should develop, since the presumptive humerus lies largely in the anterior region. The development of anterior and posterior parts, on their own, was in general, consistent with the fate map; both developed a humerus that was thinner than normal. Double anterior limbs developed two humeri in 28 % of cases and a much thicker humerus in 39 %. These results strongly support models based on an early specification of limb rudiments and cannot be accounted for by the physical model. Double anterior limbs in which the two parts were from different stages, developed such that a digit 3 could lie adjacent to the radius, giving further striking evidence for early specification and local autonomy of development.
Identification in Xenopus of a structural homologue of the Drosophila gene Snail
Authors: Sargent Michael G. , Bennett Michael F.
Published: April 2021

We have cloned a Xenopus cDNA that is related to snail, a gene that is required for mesoderm formation in Drosophila. The cDNA encodes a protein that contains five zine-fingers that closely resemble those of snail. In the non-canonical parts of the DNA-binding loop, there is almost 90 % homology between snail and xsna. The corresponding mRNA (xsna) is expressed strongly at the start of zygotic transcription simultaneously with the transcription factor EFla. In early gastrulae, xsna is equally distributed between the dorsal and ventral halves of the equatorial zone. The possibility that the capacity to synthesise xsna is more localised before the start of zygotic transcription has been investigated by culturing fragments of stage 8 embryos until xsna is synthesised. The capacity to synthesise xsna at stage 8 is located principally in the dorsal half of the equatorial zone. A small amount of maternal xsna is localised in the vegetal hemisphere before zygotic transcription starts. xsna is not present in isolated animal caps but can be induced by the mesoderm-inducing factors XTC-MIF and bFGF. Synthesis of xsna does not occur autonomously in dispersed cells but is restored when cells reaggregate in the presence of calcium and magnesium.
Expression and function of aneven-skippedhomolog in the leechHelobdella robusta
Authors: Song Mi Hye , Huang Françoise Z. , Chang Gwendolen Y. , Weisblat David A.
Published: April 2021

We have identified homologs of the Drosophila pair-rule gene even-skipped in the glossiphoniid leeches Helobdella robusta and Theromyzon trizonare. In leech embryos, segments arise sequentially from five pairs of embryonic stem cells (teloblasts) that undergo iterated divisions to generate columns (bandlets) of segmental founder cells (primary blast cells), which in turn generate segmentally iterated sets of definitive progeny. In situ hybridization revealed that Hro-eve is expressed in the teloblasts and primary blast cells, and that these transcripts appear to be associated with mitotic chromatin. In more advanced embryos, Hro-eve is expressed in segmentally iterated sets of cells in the ventral nerve cord. Lineage analysis revealed that neurons expressing Hro-eve arise from the N teloblast. To assess the function of Hro-eve, we examined embryos in which selected blastomeres had been injected with antisense Hro-eve morpholino oligonucleotide (AS-Hro-eve MO), concentrating on the primary neurogenic (N teloblast) lineage. Injection of AS-Hro-eve MO perturbed the normal patterns of teloblast and blast cell divisions and disrupted gangliogenesis. These results suggest that Hro-eve is important in regulating early cell divisions through early segmentation, and that it also plays a role in neuronal differentiation.
Diverse dependencies of developing Merkel innervation on the trkA and both full-length and truncated isoforms of trkC
Authors: Cronk Katharine M. , Wilkinson George A. , Grimes Rachel , Wheeler Esther F. , Jhaveri Sonal , Fundin Bengt T. , Silos-Santiago Immaculada , Tessarollo Lino , Reichardt Louis F. , Rice Frank L.
Published: April 2021

This study demonstrates that innervation dependent on two different neurotrophin tyrosine kinase (trk) receptors can form the same types of sensory endings (Merkel endings) in the same target (Merkel cells of vibrissa follicles). Some endings transiently express trkA during their initial development, whereas others express trkC throughout their development. Consequently, elimination of kinase domains of either trkA or trkC each result in a partial loss of Merkel endings, whereas absence of kinase domains of both receptors results in a total loss. At the onset of Merkel ending development, at least one kinase-lacking trkC isoform is transiently expressed on all the follicle cells, while neurotrophin 3 is transiently expressed only in the cells at the middle third of the follicle where the Merkel endings and cells develop. This transient non-neuronal expression of truncated trkC is essential for development of any Merkel endings, whereas some Merkel endings and cells still begin to develop in the absence of neurotrophin 3. Therefore, truncated trkC plays a more important role in the development of this innervation than kinase forms of trkA or trkC or of NT3, the only known ligand for trkC receptors.
pax2.1is required for the development of thyroid follicles in zebrafish
Authors: Wendl Thomas , Lun Klaus , Mione Marina , Favor Jack , Brand Michael , Wilson Stephen W. , Rohr Klaus B.
Published: April 2021

The thyroid gland is an organ primarily composed of endoderm-derived follicular cells. Although disturbed embryonic development of the thyroid gland leads to congenital hypothyroidism in humans and mammals, the underlying principles of thyroid organogenesis are largely unknown. In this study, we introduce zebrafish as a model to investigate the molecular and genetic mechanisms that control thyroid development. Marker gene expression suggests that the molecular pathways of early thyroid development are essentially conserved between fish and mammals. However during larval stages, we find both conserved and divergent features of development compared with mammals. A major difference is that in fish, we find evidence for hormone production not only in thyroid follicular cells, but also in an anterior non-follicular group of cells.

We show that pax2.1 and pax8, members of the zebrafish pax2/5/8 paralogue group, are expressed in the thyroid primordium. Whereas in mice, only Pax8 has a function during thyroid development, analysis of the zebrafish pax2.1 mutant no isthmus (noi–/–) demonstrates that pax2.1 has a role comparable with mouse Pax8 in differentiation of the thyroid follicular cells. Early steps of thyroid development are normal in noi–/–, but later expression of molecular markers is lost and the formation of follicles fails. Interestingly, the anterior non-follicular site of thyroid hormone production is not affected in noi–/–. Thus, in zebrafish, some remaining thyroid hormone synthesis takes place independent of the pathway leading to thyroid follicle formation. We suggest that the noi–/– mutant serves as a new zebrafish model for hypothyroidism.
Patterning of the embryo: the first spatial decisions in the life of a mouse
Authors: Zernicka-Goetz Magdalena
Published: April 2021

Although in most species the polarity of the embryo takes its roots from the spatial patterning of the egg, mammals were viewed as an exception. This was because the anteroposterior polarity of the mouse embryo could not be seen until gastrulation, and no developmental cues were known that could define polarity at earlier stages. Why should we now re-consider this view? While mechanisms of axis formation in mammals could, in principle, be unique, the evolutionary conservation of numerous other developmental processes raises the question of why mammals would have evolved a different way or timing of organising their embryonic polarity. Indeed, recent evidence shows that well before the onset of gastrulation, the mouse embryo initiates asymmetric patterns of gene expression in its visceral endoderm. Although this extra-embryonic tissue does not contribute to the body itself, it is involved in axis formation. Other recent work has revealed that spatial distribution of cells in the visceral endoderm can be traced back to polarity present at the blastocyst stage. These insights have raised the possibility that embryonic polarity might also originate early during development of mammalian embryos. Indeed it now appears that there are at least two spatial cues that operate in the mouse egg to shape polarity of the blastocyst. One of these is at the animal pole, which is defined by the site of female meiosis, and another is associated with the position of sperm entry. In this review I discuss these recent findings, which have led to the recognition that mouse embryos initiate development of their polarity at the earliest stages of their life. This novel perspective raises questions about the nature of cellular and molecular mechanisms that could convert developmental cues in the zygote to axes of the blastocyst, and hence into polarity of the post-implantation embryo. It also brings to light the need to understand how such mechanisms could enable early mouse development to be so regulative.
The chicken β-globin insulator element conveys chromatin boundary activity but not imprinting at the mouseIgf2/H19domain
Authors: Szabó Piroska E. , Tang Shih-Huey E. , Reed Michael R. , Silva Francisco J. , Tsark Walter M. K. , Mann Jeffrey R.
Published: April 2021

Imprinting of the mouse insulin-like growth factor 2 (Igf2) and H19 genes is regulated by an imprinting control region (ICR). The hypomethylated maternal copy functions as a chromatin insulator through the binding of CTCF and prevents Igf2 activation in cis, while hypermethylation of the paternal copy inactivates insulator function and leads to inactivation of H19 in cis. The specificity of the ICR sequence for mediating imprinting and chromatin insulation was investigated by substituting it for two copies of the chicken β-globin insulator element, (ChβGI)2, in mice. This introduced sequence resembles the ICR in size, and in containing CTCF-binding sites and CpGs, but otherwise lacks homology. On maternal inheritance, the (ChβGI)2 was hypomethylated and displayed full chromatin insulator activity. Monoallelic expression of Igf2 and H19 was retained and mice were of normal size. These results suggest that the ICR sequence, aside from CTCF-binding sites, is not uniquely specialized for chromatin insulation at the Igf2/H19 region. On paternal inheritance, the (ChβGI)2 was also hypomethylated and displayed strong insulator activity – fetuses possessed very low levels of Igf2 RNA and were greatly reduced in size, being as small as Igf2-null mutants. Furthermore, the paternal H19 allele was active. These results suggest that differential ICR methylation in the female and male germ lines is not acquired through differential binding of CTCF. Rather, it is likely to be acquired through a separate or downstream process.
Mathematical modeling of the interaction between yolk utilization and fish growth in zebrafish,Danio rerio
Authors: Schwartz Ashley V. , Sant Karilyn E. , Navarrete Julian , George Uduak Z.
Published: April 2021

Optimal embryonic development plays a major role in the health of an individual beyond the developmental stage. Nutritional perturbation during development is associated with cardiovascular and metabolic disease later in life. With both nutritional uptake and overall growth being risk factors for eventual health, it is necessary to understand not only the behavior of the processes during development but also their interactions. In this study, we used differential equations, image analyses, curve fittings, parameter estimation and laboratory experiments to quantify the rate of yolk absorption and its effect on early development of a vertebrate model (Danio rerio). Findings from this study establish a nonlinear functional relationship between nutrient absorption and early fish growth. We found that the rate of change in fish length and yolk utilization is logistic, that is the yolk decays rapidly for a period of time before leveling out. An interesting finding from this study is that yolk utilization reaches its maximum at 84 h post-fertilization. We validated our mathematical models against experimental observations, making them powerful tools for replication and future simulations.
Cis-regulatory dissection of cone development reveals a broad role for Otx2 and Oc transcription factors
Authors: Lonfat Nicolas , Wang Su , Lee ChangHee , Garcia Mauricio , Choi Jiho , Park Peter J. , Cepko Connie
Published: April 2021

The vertebrate retina is generated by retinal progenitor cells (RPCs), which produce >100 cell types. Although some RPCs produce many cell types, other RPCs produce restricted types of daughter cells, such as a cone photoreceptor and a horizontal cell (HC). We used genome-wide assays of chromatin structure to compare the profiles of a restricted cone/HC RPC and those of other RPCs in chicks. These data nominated regions of regulatory activity, which were tested in tissue, leading to the identification of many cis-regulatory modules (CRMs) active in cone/HC RPCs and developing cones. Two transcription factors, Otx2 and Oc1, were found to bind to many of these CRMs, including those near genes important for cone development and function, and their binding sites were required for activity. We also found that Otx2 has a predicted autoregulatory CRM. These results suggest that Otx2, Oc1 and possibly other Onecut proteins have a broad role in coordinating cone development and function. The many newly discovered CRMs for cones are potentially useful reagents for gene therapy of cone diseases.
A multi-gene knockdown approach reveals a new role for Pax6 in controlling organ number in Drosophila
Authors: Ordway Alison J. , Teeters Gary M. , Weasner Bonnie M. , Weasner Brandon P. , Policastro Robert , Kumar Justin P.
Published: April 2021

Genetic screens are designed to target individual genes for the practical reason of establishing a clear association between a mutant phenotype and a single genetic locus. This allows for a developmental or physiological role to be assigned to the wild-type gene. We previously observed that the concurrent loss of Pax6 and Polycomb epigenetic repressors in Drosophila leads the eye to transform into a wing. This fate change is not seen when either factor is disrupted separately. An implication of this finding is that standard screens may miss the roles that combinations of genes play in development. Here, we show that this phenomenon is not limited to Pax6 and Polycomb but rather applies more generally. We demonstrate that in the Drosophila eye-antennal disc, the simultaneous downregulation of Pax6 with either the NURF nucleosome remodeling complex or the Pointed transcription factor transforms the head epidermis into an antenna. This is a previously unidentified fate change that is also not observed with the loss of individual genes. We propose that the use of multi-gene knockdowns is an essential tool for unraveling the complexity of development.
WNT signaling in pre-granulosa cells is required for ovarian folliculogenesis and female fertility
Authors: Habara Okiko , Logan Catriona Y. , Kanai-Azuma Masami , Nusse Roeland , Takase Hinako M.
Published: April 2021

In mammalian ovaries, immature oocytes are reserved in primordial follicles until their activation for potential ovulation. Precise control of primordial follicle activation (PFA) is essential for reproduction, but how this is achieved is unclear. Here, we show that canonical wingless-type MMTV integration site family (WNT) signaling is pivotal for pre-granulosa cell (pre-GC) activation during PFA. We identified several WNT ligands expressed in pre-GCs that act in an autocrine manner. Inhibition of WNT secretion from pre-GCs/GCs by conditional knockout (cKO) of the wntless (Wls) gene led to female infertility. In Wls cKO mice, GC layer thickness was greatly reduced in growing follicles, which resulted in impaired oocyte growth with both an abnormal, sustained nuclear localization of forkhead box O3 (FOXO3) and reduced phosphorylation of ribosomal protein S6 (RPS6). Constitutive stabilization of β-catenin (CTNNB1) in pre-GCs/GCs induced morphological changes of pre-GCs from a squamous into a cuboidal form, though it did not influence oocyte activation. Our results reveal that canonical WNT signaling plays a permissive role in the transition of pre-GCs to GCs, which is an essential step to support oocyte growth.
An immunofluorescent study of the haemoglobinsin metamorphosing Xenopus laevis
Authors: Jurd Richard D. , Maclean Norman
Published: April 2021

It has long been known that in many vertebrates different haemoglobins exist in foetal and adult animals, and that during development the circulating foetal haemoglobin is gradually replaced by haemoglobin of the adult type, (reviewed by Gratzer & Allison, 1960). The phenomenon is well established in the bullfrog, Rana catesbiana (McCutcheon, 1936; Riggs, 1951; Baglioni & Sparks, 1963; Moss & Ingram, 1968a, b). Our studies on haemoglobin from the South African clawed toad, Xenopus laevis, employing column chromatography on carboxymethylcellulose, and polyacrylamide-gel disc electrophoresis, demonstrate a similar situation. Column chromatography reveals two tadpole haemoglobin peaks and three adult peaks, with no peaks common to the tadpole and the adult (Maclean, Brooks & Jurd, 1969; Jurd & Maclean, 1969).
Electrical properties of the slime mould grex
Authors: Garrod D. R. , Palmer J. F. , Wolpert L.
Published: April 2021

An electrophysiological investigation of the migrating grex of the slime mould, Dictyostelium discoideum, has been carried out with two aims in view. It was hoped to obtain information which would be relevant to, first, the formation and regulation of cellular pattern in the grex, and secondly, the problem of grex movement.
Desynchronization of cell divisions in the course of egg cleavage and an attempt at experimental shift of its onset
Authors: Chulitskaia E. V.
Published: April 2021

There is considerable current interest in the study of regularities and modes of regulation of cell cycles in the course of development (Dettlaff, 1964; Graham, Arms & Gurdon, 1966; Chulitskaia, 1967 a). The period of cleavage divisions is a very suitable object for such investigations. It consists of two different periods known as periods of synchronous and asynchronous cell divisions (Syngayewskaya, 1931; Balinsky, 1931; Costello, 1955; Sirakami, 1958; Neyfakh & Rott, 1959; Dan, 1960; Pankova, 1963; Agrell, 1964; Engelberg, 1964; Skoblina, 1965; Chulitskaia, 1967 ó ; Rott & Sheveleva, 1968). Peculiarities of these two periods are known rather well but regularities of the transition from synchronous to asynchronous divisions are still imperfectly understood (Rückert, 1899; Hoff-Jorgensen & Zeuthen, 1952; Agrell & Person, 1956; Neyfakh & Rott, 1959; Neyfakh, 1961; Agrell, 1961, 1962; Pankova, 1963; Brown, 1965; Bachvarova, Davidson, Allfrey & Mirsky, 1966; Timofeeva, Kafiani & Neyfakh, 1967; Chulitskaia, 1967a, b; Rott & Sheveleva, 1968).
Cleavage delay and abnormal morphogenesis in Lymnaea eggs after pulse treatment with azide of successive stages in a cleavage cycle
Authors: Camey Toshie , Geilenkirchen W. L. M.
Published: April 2021

Heat treatments of short duration of successive stages in a cleavage cycle of Lymnaea eggs differentially affect the division cycle and morphogenesis. Effects on the division cycle are most pronounced after a treatment during actual cleavage, at the end of interphase and during prometaphase. Abnormal morphogenesis is only found when a heat shock is applied during metaphase-anaphase stages; after treatment development proceeds up to the blastula stage. Development after the blastula stage, however, may be disturbed, leading to death, exogastrulation or malformations of the embryo.
Stimulation of germ cell proliferation in the planarian Dugesia tigrina (Girard)
Authors: Vowinckel C.
Published: April 2021

Sexual strains of Dugesia tigrina display a seasonal development of sex organs in late summer or autumn and lay cocoons in the suceeding spring. This is followed by a period of asexual reproduction in mid-summer. Such a seasonal alternation of reproductive pathways makes this flatworm an ideal subject of inquiry into the inductive mechanisms controlling reproduction and its ultimate coupling to changes in the environment. Asexual strains of this species reproduce by fission only.
Neurulation in Xenopus laevis. An analysis and model based upon light and electron microscopy
Authors: Schroeder Thomas E.
Published: April 2021

It is a matter of general knowledge that neurulation, as it occurs in most chordate embryos, proceeds by longitudinal in-folding of the neural plate. Lovtrup (1965) ably described such morphogenetic movements as they occur in several neurulating amphibians. The mechanical causes of these movements are not clearly understood, however. In his review of the prominent theories of neurulation, Curtis (1967) points to their various inadequacies and concludes that ‘possibly the solution of this problem is to search for contractile movements in the cells involved in neurulation’ (p. 310).
Experiments on β-mercaptoethanol as an inhibitor of neurulation movements in amphibian larvae
Authors: Jacobson Carl-Olof
Published: April 2021

The morphogenetic movements of the ectoderm during neurulation include: (1) the movements taking place within the neural plate, which becomes longer and more concentrated in a medio-lateral direction (Jacobson, 1962); and (2) those found in the lateral epidermis layer which, in an epibolic way, moves in a dorsal direction, thus exerting a pushing effect on the lateral edges of the neural plate (Lewis, 1947). The former is, to a great extent, realized by a change of form of the neuroepithelium cells, from cuboidal in early neurulae to the high columnar cells observed during later phases of neural-tube closure. In the epidermis, on the other hand, the case is the reverse. The dorsal spreading of the layer is made possible by a flattening of the cells.
L’action de l’actinomycine D sur le pouvoir inducteur du nœud de Hensen et la compétence neurogène de l’ectoblaste de poulet
Authors: Gallera Par J.
Published: April 2021

Chez les Bactéries, l’actinomycine D se fixe sur l’ADN et empêche la formation de l’ARN messager, ce qui se traduit presque instantanément (après quelques minutes au maximum) par le blocage de la synthèse des protéines spécifiques. L’action de l’actinomycine sur les cellules animales est plus complexe. Employée à doses très faibles, elle semble affecter surtout la formation de l’ARN messager, mais elle peut aussi agir directement sur les composants cytoplasmiques. Administrée à une concentration plus forte, elle se révèle nettement toxique. D’autre part, le cytoplasme des cellules animales contient toujours un stock important de divers ARN messagers plus ou moins stables dont l’action ne peut se manifester qu’au moment ou les autres composants cytoplasmiques atteignent un état déterminé de maturation. Par conséquent, l’arrêt de la production de l’ARN messager ne se répercute sur la synthèse des protéines qu’après un délai plus ou moins long. Chez les Oursins, l’actinomycine naltère pas le développement embryonnaire jusqu’au stade de la blastula (Giudice, Mutolo & Donatuti, 1968). Chez les Urodèles (Brachet & Denis, 1963) et chez la Truite (Hagenmaier, 1969), le développement se poursuit normalement jusquau début de la gastrulation. Selon Flickinger (1963), Heilporn-Pohl (1964), Leani Collini & Ranzi (1967), l’ARN spécifique de chaque tissu embryonnaire serait synthétisé, chez les Anoures et les Oiseaux, juste avant sa différenciation. Ajoutons encore quil est souvent impossible de préciser la nature de l’ARN dont la synthèse a été inhibée par l’actinomycine (Denis, 1966). 11 est d’ailleurs probable que les anomalies graves résultent d’une action toxique de cet antibiotique (Harris, 1968). Toutefois, l’emploi d’un matériel, qui se prête particulièrement bien à létude de la synthèse massive des protéines spécifiques, a permis à Soriano (1968) de démontrer que l’epithélium œsophagien de Souris cultivé in vitro sur un milieu additionné d’actinomycine D à raison de 0,05 μg/ml empêche entièrement la kératinisation, sans que cet épithélium, retransplanté sur le milieu normal après 24 h, montre le moindre signe de dégénérescence et que lincorporation de leucine tritiée soit diminuée.
Recent findings on oogenesis of Drosophila melanogaster: II. Further evidence on the origin of yolk platelets
Authors: Giorgi F. , Jacob J.
Published: April 2021

Vitellogenic ovaries from Drosophila melanogaster flies have been exposed, either in in vivo or in vitro conditions, to various extracellular tracers in an attempt to determine the possible route of entry of the yolk precursors.

Ruthenium red and lanthanum nitrate have been shown to gain access to the oocyte surface by initially passing through the intercellular spaces of the follicle layer. Both these tracers, however, never attain an intracellular location within any of the cells forming the ovarian chamber.

Colloidal Thorotrast when injected into adult females has never been detected within any of the ovarian chambers examined, irrespective of their stage.

Vitellogenic oocytes exposed to peroxidase in in vivo conditions exhibit the oolemma and all the structural elements present in the cortical ooplasm well labelled within a very short time after the injection. Moreover, with gradually increasing exposure times to peroxidase, the labelled yolk platelets increase progressively in number. At each time interval after the injection, the label over the yolk platelets remains restricted to the superficial layer and never gets into the associated body.

The pattern of tritiated lysine incorporation into vitellogenic oocytes has been studied over a period of 20 h. A few hours after injection of the radioactive tracer, the silver grains located over the ooplasm appear distributed at random. A predominant labelling of the yolk platelets as compared to the rest of the ooplasm, becomes evident only with a 6 h delay since the time of injection.

When analysed by electrophoresis and isolectrofocusing, the vitellogenic ovary is seen to exhibit a number of protein bands which are common to those of other tissues as, for instance, haemolymph and fat body.

The evidence obtained in the present study is discussed in relation to the hypothesis of an extraovarian origin of the yolk precursors and their sequestration into forming yolk platelets.
Le matériel extracellulaire au cours du développement du chondrocrâne des amphibiens: Mise en place et constitution
Authors: Corsin Jacqueline
Published: April 2021

Changes in the extracellular matrix of the cranial cartilages of amphibians

During the differentiation of cranial cartilages the composition of perichordal and perineural extracellular matrix changes: at first only collagen and hyaluronic acid can be detected, later chondroitin-sulphates 4 and 6 appear and their concentrations progressively increase while the concentration of hyaluronic acid is decreasing.

The possible effects of these substances not only on the chondrogenetic cells but also between themselves are discussed.
Importance des associations de tissus du membre dans le développement des membres surnuméraires induits par déviation de nerf chez le Triton Pleurodeles waltlii Michah
Authors: Lheureux Emile
Published: April 2021

Importance of limb tissue associations in the development of nerve-induced supernumerary limbs in the newt Pleurodeles waltlii Michah.

Brachial nerve tip deviation has been carried out at various points in the upper arm and close to the limb. Some associations of cutaneous or muscular tissue from two opposite sides - dorsal and ventral or anterior and posterior - of the upper arm were made at these points. Various degrees of development of the nerve-induced supernumerary limbs were observed. When a nerve deviation was not followed by grafting of tissue from the opposite side, the supernumerary limbs did not develop or were strongly hypomorphic. A normal limb development can occur when tissues from the opposite side are associated with the ones located at the nerve tip. Such associations allow a harmonious nerve-induced supernumerary limb to develop and consequently allow all transverse axes to be established. Orientation of nerve-induced supernumerary limbs is determined by the orientation of the tissues in the area of nerve deviation.

In terms of positional information, since an absence of contact between tissues from two opposite sides results in a lack of normal development, we can conclude that positional values located on either side of, the centre of, at least, one transverse axis should be in contact to allow limb development, i.e. a regenerated limb or nerve-induced supernumerary limbs or supernumerary limbs. It appears that contact between such values along any transverse axis, under sufficient nervous stimulation may give rise to a supernumerary limb.
In vitrodevelopment of haploid mouse embryos produced by bisection of one-cell fertilized eggs
Authors: Tarkowski Andrzej K.
Published: April 2021

F1(CBA × C57BL/10) mouse eggs originating from spontaneous or induced ovulation and fertilized by CBA-T6T6 or PO spermatozoa were bisected with a glass needle into halves each containing a pronucleus. This technique offers a unique opportunity of producing both andro-genetic and gynogenetic haploid embryos from one egg.

Out of 600 operated eggs, in 406 (67·7%) both halves survived. During 96 h of culture in vitro the fragments were inspected once daily and finally examined in air-dried preparations. Eighty-seven per cent of halves underwent first cleavage but their further development was to a large extent affected by extrinsic factors connected with experimental procedure (mainly by suboptimal and variable culture conditions) and by the origin of eggs (those from spontaneous ovulation being superior). For this reason developmental capabilities of egg halves were assessed in a selected group of pairs in which at least one partner reached the stage of four or more blastomeres. The observed ratio between pairs with both or only one sister embryo developing successfully suggests that androgenetic embryos carrying Y rather than X chromosome can cleave twice but do not survive beyond 4-cell stage. None of the metaphase plates from older embryos contained a Y chromosome. These observations imply that the X chromosome is genetically active during early cleavage and that a full haploid set is required for preimplantation development to be completed.

Formation of blastocysts varied from batch to batch, with an average of 12-8% and maximal incidence of 29·5%. In 34 pairs both fragments developed beyond the 4-cell stage but in only one case did both form blastocysts. Haploid blastocysts were composed of 27 cells on average which was about a half of the number of cells in control diploid zona-free whole eggs. Ten out of 51 embryos with metaphase plates proved to be haploid/diploid mosaics.
In vitrodevelopment of palatal tissues from embryonic mice: II. Tissue isolation and recombination studies
Authors: Tyler Mary S. , Koch William E.
Published: April 2021

The epithelial and mesenchymal tissues of the secondary palate from 12-, 13-, and 14-day embryonic mice were enzymatically separated and cultured in isolation and in homochronic and heterochronic recombinations. In both homochronic and heterochronic recombinations, epithelial differentiation was similar to that in vivo. In heterochronic recombinations, epithelium differentiated according to a schedule appropriate for the age of the epithelium rather than for the age of the mesenchyme, suggesting that differentiation of palatal epithelium is temporally ‘determined’ as early as 12 days of gestation. Palatal epithelium cultured in isolation was capable of limited differentiation. Potential for differentiation therefore exists within the isolated palatal epithelium at an early stage of palatal development, and epithelial-mesenchymal interactions are required during palatal development to support full epithelial differentiation.
Blood formation in a clonal cell line of mouse teratocarcinoma
Authors: Cudennec Claude A. , Nicolas Jean-Francois
Published: April 2021

Pluripotent cells of a teratocarcinoma clonal line differentiate into various tissues when they are cultivated in submerged cultures. We describe here the formation of endodermal vesicles and blood islands in organotypic cultures of such cells. These are the first macroscopically visible tissues to appear in organ culture and they give rise to megalocytes, the ultimate stage of blood cell evolution in the normal mouse embryo yolk-sac. As in the normal embryo yolk-sac, the formation of haemoglobin-containing cells stops after a while, but it is not replaced by adult haemopoiesis in culture.
Studies on the development of F1 embryos from inter-strain crosses involving DDK mice
Authors: Wakasugi Noboru , Morita Mitsuyo
Published: April 2021

The development of the early mouse embryos was investigated from 36 to 84 h after the presumed time of fertilization. The mean number of cells constituting the embryo from the intra-strain crosses of three strains at 84 h of development was as follows: DDK, 22·7; BS, 43-1 and ITES, 62·0. A significant difference was observed in the cleavage rate of the embryo between DDK and the other two strains.

The F1 embryos from the crosses of BS females × DDK males and ITES females x DDK males showed almost the same progress of development as BS and ITES embryos, respectively. Therefore, it is concluded that the early development of the F1 embryos is regulated mainly by the factors from the mother.

The morulae from the semi-sterile cross, DDK females x BS males, showed conspicuously small cell numbers as compared with their litter-mates that developed to the blastocyst stage. It is inferred that the discrimination is already made during cleavage between the fortunate survivors and the lethal embryos due to the incompatibility between the cytoplasmic factor of DDK eggs and alien spermatozoa.