bluuebunny/crossref_metadata_2025 huggingface dataset:
A role for the Drosophila segment polarity gene armadillo in cell adhesion and cytoskeletal integrity during oogenesis
Authors: Peifer Mark , Orsulic Sandra , Sweeton Dari , Wieschaus Eric
Published: April 2021

The epithelial sheet is a structural unit common to many tissues. Its organization appears to depend on the function of the multi-protein complexes that form adherens junctions. Elegant cell biological experiments have provided support for hypotheses explaining the function of adherens junctions and of their components. These systems, however, lack the ability to test function within an entire organism during development. The realization that the product of the Drosophila segment polarity gene armadillo is related to the vertebrate adhesive junction components plakoglobin and β-catenin led to the suggestion that armadillo might provide a genetic handle to study adhesive junction structure and function. An examination of the potential function of Armadillo in cell-cell adhesive junctions was initiated using the Drosophila ovary as the model system. We examined the distribution of Armadillo in the Drosophila ovary and demonstrated that this localization often parallels the location of cell-cell adhesive junctions. The consequences of removing armadillo function from the germ-line cells of the ovary were also examined. Germ-line armadillo mutations appear to disrupt processes requiring cell adhesion and integrity of the actin cytoskeleton, consistent with a role for Armadillo in cell-cell adhesive junctions. We have also used armadillo mutations to examine the effects on ovarian development of altering the stereotyped cell arrangements of the ovary. The implications of these results for the role of adhesive junctions during development are discussed.
Sperm require β-N-acetylglucosaminidase to penetrate through the egg zona pellucida
Authors: Miller David J. , Gong Xiaohai , Shur Barry D.
Published: April 2021

Fertilization in the mouse is initiated by sperm 1,4-galactosyltransferase (GalTase) binding to terminal N-acetylglucosamine residues on the zona pellucida glyco-protein ZP3. Binding of ZP3 induces exocytosis of the sperm acrosome, whose contents are believed to digest a penetration slit in the zona matrix through which sperm reach the egg. As a consequence of acrosomal exocytosis, GalTase is redistributed to the lateral aspect of the sperm head, where its function remains unknown. In this location, GalTase could conceivably impede zona penetration by binding to N-acetylglucosamine residues exposed on zona pellucida glycoproteins. Therefore, in this study we investigated the presence and function of acrosomal glycosidases capable of removing the GalTase-binding site from zona pellucida glycoproteins. β-N-acetylglucosaminidase was found at very high levels in sperm, being more than 20-fold higher than other glycosidases assayed. The specific isozymic variant was identified as -hexosaminidase B. β-N-acetylglucosaminidase was localized to sperm acrosomes by bio-chemical and indirect immunofluorescence studies and was released during the acrosome reaction, as expected for an enzyme involved in zona penetration. To determine if, in fact, acrosomal β-N-acetylglu-cosaminidase facilitated penetration through the zona, an assay was developed using eggs that were rendered incapable of triggering the block to polyspermy. A specific competitive inhibitor of β-N-acetylglu-cosaminidase activity, PUGNAC, inhibited sperm penetration of the zona in a dose-dependent manner, whereas a closely related β-glucosidase inhibitor, PUGLU, had no effect on zona penetration or on β-N-acetylglu-cosaminidase activity. Neither glycosidase inhibitor affected sperm motility or induction of the acrosome reaction. These results demonstrate that β-N-acetylglu-cosaminidase is found in sperm acrosomes and is released during the acrosome reaction, at which time it facilitates sperm penetration through the zona. These results also imply that sperm have developed mechanisms to prevent the formation of stable interactions between surface receptors and their zona pellucida ligands during penetration.
ES cells have only a limited lymphopoietic potential after adoptive transfer into mouse recipients
Authors: Müller Albrecht M. , Dzierzak Elaine A.
Published: April 2021

While hematopoietic stem cells from adult and fetal stages of murine development are capable of long term reconstitution of all mature blood lineages in vivo, embryonic hematopoietic stem cell repopulation in vivo has proved difficult. It is thought that there are many fewer hematopoietic stem cells in the embryo than in the fetal/adult stages of mouse development and that these cells possess a different developmental potential. One source of such cells are embryonic stem (ES) cells which can differentiate into most mature blood lineages in vitro. We have therefore used transplantation of differentiated ES cells to assess the hematopoietic potential of embryonic hematopoietic cells in vivo. We demonstrate here that precursors obtained from in vitro cultures of normal ES cells can contribute only to restricted and limited hematopoiesis in a mouse without leading to tumour formation. Repopulation occurs for greater than 6.5 months at levels ranging from 0.1% to 6% in B and T cell lineages in peripheral blood. In contrast to in vitro colony data demonstrating the myeloid lineage developmental potential of ES cells, no donor-derived myeloid repopulation was observed in CFU-S assays and no macrophage and mast cells were found in long term repopulated recipients. Thus, the hematopoietic potential of ES cells in vivo is limited to low levels of repopulation and is restricted to the lymphoid lineage.
Multiple RNA regulatory elements mediate distinct steps in localization of oskar mRNA
Authors: Kim-Ha Jeongsil , Webster Philippa J. , Smith Jeffrey L. , Macdonald Paul M.
Published: April 2021

Pattern formation in the early development of many organisms relies on localized cytoplasmic proteins, which can be prelocalized as mRNAs. The Drosophila oskar gene, required both for posterior body patterning and germ cell determination, encodes one such mRNA. Localization of oskar mRNA is an elaborate process involving movement of the transcript first into the oocyte from adjacent interconnected nurse cells and then across the length of the oocyte to its posterior pole. We have mapped RNA regulatory elements that direct this localization. Using a hybrid lacZ/oskar mRNA, we identify several elements within the oskar 3 untranslated region that affect different steps in the process: the early movement into the oocyte, accumulation at the anterior margin of the oocyte and finally localization to the posterior pole. This use of multiple cis-acting elements suggests that localization may be orchestrated in a combinatorial fashion, thereby allowing localized mRNAs with ultimately different destinations to employ common mechanisms for shared intermediate steps.
Asymmetric patterns of gap junctional communication in developing chicken skin
Authors: Serras Florenci , Fraser Scott , Chuong Cheng-Ming
Published: April 2021

To study the pattern of gap junctional communication in chicken skin and feather development, we injected Lucifer Yellow into single cells and monitored the transfer of the fluorescent dye through gap junctions. Dye coupling is present between cells of the epithelium as well as between cells of the mesoderm. However, dye transfer did not occur equally in all directions and showed several consistent patterns and asymmetries, including: (1) no dye coupling between mesoderm and epithelium, (2) partial restriction of dye coupling at the feather bud/interbud boundary during early feather bud development, (3) preferential distribution of Lucifer Yellow along the anteroposterior axis of the feather placode and (4) absence of dye coupling in some epithelial cells. These results suggest the presence of preferential pathways of communication that may play a role in the patterning of chicken skin.
Xwnt-5A: a maternal Wnt that affects morphogenetic movements after overexpression in embryos of Xenopus laevis
Authors: Moon Randall T. , Campbell Robert M. , Christian Jan L. , McGrew L. Lynn , Shih John , Fraser Scott
Published: April 2021

To contribute to an understanding of the roles and mechanisms of action of Wnts in early vertebrate development, we have characterized the normal expression of Xenopus laevis Wnt-5A, and investigated the consequences of misexpression of this putative signalling factor. Xwnt-5A transcripts are expressed throughout development, and are enriched in both the anterior and posterior regions of embryos at late stages of development, where they are found primarily in ectoderm, with lower levels of expression in mesoderm. Overexpression of Xwnt-5A in Xenopus embryos leads to complex mal-formations distinct from those achieved by ectopic expression of Xwnts -1, -3A, or -8. This phenotype is unlikely to result from Xwnt-5A acting as an inducing agent, as overexpression of Xwnt-5A does not rescue dorsal structures in UV-irradiated embryos, does not induce mesoderm in blastula caps, and Xwnt-5A does not alter the endogenous patterns of expression of goosecoid, Xbra, or Xwnt-8. To pursue whether Xwnt-5A has the capacity to affect morphogenetic movements, we investigated whether overexpression of Xwnt-5A alters the normal elongation of blastula cap explants induced by activin. Intriguingly, Xwnt-5A blocks the elongation of blastula caps in response to activin, without blocking the differentiation of either dorsal or ventral mesoderm within these explants. The data are consistent with Xwnt-5A having the potential activity of modifying the morphogenetic movements of tissues.
Defective lens fiber differentiation and pancreatic tumorigenesis caused by ectopic expression of the cellular retinoic acid-binding protein I
Authors: Perez-Castro Ana V. , Tran Vinh T. , Nguyen-Huu M. Chi
Published: April 2021

All-trans retinoic acid, a metabolite of retinol, is a possible morphogen in vertebrate development. Two classes of cellular proteins, which specifically bind all-trans retinoic acid, are thought to mediate its action: the nuclear retinoic acid receptors (RAR α, β, γ), and the cytoplasmic binding proteins known as cellular retinoic acid-binding proteins I and II (CRABP I and II). The function of the retinoic acid receptors is to regulate gene transcription by binding to DNA in conjunction with the nuclear retinoid X receptors (RXR α, β, γ), which in turn have 9-cis retinoic acid as a ligand. Several lines of evidence suggest that the role of the cellular retinoic acid-binding proteins is to control the concentration of free retinoic acid reaching the nucleus in a given cell. Here, we have addressed the role of the cellular retinoic acid-binding protein I in development by ectopically expressing it in the mouse lens, under the control of the A-crystallin promoter. We show that this ectopic expression interferes with the development of the lens and with the differentiation of the secondary lens fiber cells, causing cataract formation. These results suggest that correct regulation of intracellular retinoic acid concentration is required for normal eye development. In addition, the generated transgenic mice also present expression of the transgene in the pancreas and develop pancreatic carcinomas, suggesting that overexpression of the cellular retinoic acid-binding protein is the cause of the tumors. These results taken together provide evidence for a role of the cellular retinoic acid-binding protein in development and cell differentiation. The relevance of these findings to the possible role of the cellular retinoic acid-binding proteins in the transduction of the retinoic acid signal is discussed.
Distribution of swallow protein in egg chambers and embryos of Drosophila melanogaster
Authors: Hegdé Jay , Stephenson Edwin C.
Published: April 2021

The Drosophila maternal effect gene swallow has a role in localizing bicoid mRNA at the anterior margin of the oocyte during oogenesis, and a poorly characterized role in nuclear divisions in early embryogenesis. We have examined the distribution of swallow protein during oogenesis and embryogenesis using anti-swallow antibodies. During oogenesis, high levels of swallow protein are present in basal nurse cell cytoplasm, although small amounts are also present at the anterior oocyte margin, the site of bicoid RNA localization. Only a small fraction of swallow protein is in a position to interact directly with bicoid RNA during localization. The asymmetric distribution of swallow protein is disrupted in swallow ovaries, in which bicoid RNA becomes unlocalized late in oogenesis. swallow protein is uniformly distributed in eggs, but becomes localized to nuclei during early mitotic divisions in early embryogenesis. swallow protein enters each nucleus at the beginning of mitosis, occupies a position complementary to that of condensed chromatin, and leaves each nucleus at the end of mitosis. We show examples of nuclear division defects in swallow mutant embryos, and suggest that the abnormal nuclear divisions in early swallow embryos reflect a second function for swallow protein that contributes to abdominal segmentation defects common in swallow embryos.
Defects in heart and lung development in compound heterozygotes for two different targeted mutations at the N-myc locus
Authors: Moens Cecilia B. , Stanton Brian R. , Parada Luis F. , Rossant Janet
Published: April 2021

Two types of mutant allele, one leaky and one null, have been generated by gene targeting at the N-myc locus in embryonic stem cells and the phenotypes of mice homozygous for these mutations have been described. These mutations have shown that N-myc has a number of functions during development, including a role in branching morphogenesis in the lung, which manifests itself at birth in mice homozygous for the leaky allele, and roles in the development of the mesonephric tubules, the neuroepithelium, the sensory ganglia, the gut and the heart, which become evident at midgestation in embryos homozygous for the null allele. In an attempt to define roles for N-myc at other stages of development, we have combined the two types of N-myc mutant allele in a compound heterozygote that as a result contains approximately 15% of normal levels of N-Myc protein. Compound heterozygotes died during gestation at a time intermediate to the times of death of embryos homozygous for either mutation individually, and their death appeared to result from cardiac failure stemming from hypoplasia of the compact subepicardial layer of the myocardium. Investigation of the expression pattern of N-myc and various markers of differentiation in wild-type and compound heterozygote mutant hearts has suggested that N-myc may function in maintaining the proliferation and/or preventing the differentiation of compact layer myocytes. This study illustrates the importance of generating different mutations at a given locus to elucidate fully the function of a particular gene during development.
Muscle development is independent of innervation during Drosophila embryogenesis
Authors: Broadie Kendal , Bate Michael
Published: April 2021

We have examined the role of innervation in directing embryonic myogenesis, using a mutant (prospero), which delays the pioneering of peripheral motor nerves of the Drosophila embryo. In the absence of motor nerves, myoblasts fuse normally to form syncytial myotubes, myotubes form normal attachments to the epidermis, and a larval musculature comparable to the wild-type pattern is generated and maintained. Likewise, the twist-expressing myoblasts that prefigure the adult musculature segregate normally in the absence of motor nerves, migrate to their final embryonic positions and continue to express twist until the end of embryonic development. In the absence of motor nerves, myotubes uncouple at the correct developmental stage to form single cells. Subsequently, uninnervated myotubes develop the mature electrical and contractile properties of larval muscles with a time course indistinguishable from normally innervated myotubes. We conclude that innervation plays no role in the patterning, morphogenesis, maintenance or physiological development of the somatic muscles in the Drosophila embryo.
Mice homozygous for a targeted disruption of Hoxd-3 (Hox-4.1) exhibit anterior transformations of the first and second cervical vertebrae, the atlas and the axis
Authors: Condie Brian G. , Capecchi Mario R.
Published: April 2021

Gene targeting in embryo-derived stem (ES) cells was used to generate mice with a disruption in the homeobox-containing gene Hoxd-3 (Hox-4.1). Mice homozygous for this mutation show a radically remodeled craniocervical joint. The anterior arch of the atlas is transformed to an extension of the basioccipital bone of the skull. The lateral masses of the atlas also assume a morphology more closely resembling the exoccipitals and, to a variable extent, fuse with the exoccipitals. Formation of the second cervical vertebra, the axis, is also affected. The dens and the superior facets are deleted, and the axis shows ‘atlas-like’ characteristics. An unexpected observation is that different parts of the same vertebra are differentially affected by the loss of Hoxd-3 function. Some parts are deleted, others are homeotically transformed to more anterior structures. These observations suggest that one role of Hox genes may be to differentally control the proliferation rates of the mesenchymal condensations that give rise to the vertebral cartilages. Within the mouse Hox complex, paralogous genes not only encode very similar proteins but also often exhibit very similar expression patterns. Therefore, it has been postulated that paralogous Hox genes would perform similar roles. Surprisingly, however, no tissues or structures are affected in common by mutations in the two paralogous genes, Hoxa-3 and Hoxd-3.
A Drosophila GATA family member that binds to Adh regulatory sequences is expressed in the developing fat body
Authors: Abel Ted , Michelson Alan M. , Maniatis Tom
Published: April 2021

We have identified a Drosophila transcription factor that binds a sequence element found in the larval promoters of all known alcohol dehydrogenase (Adh) genes. DNA sequence analysis of cDNA clones encoding this protein, box A-binding factor (ABF), reveals that it is a member of the GATA family of transcriptional regulatory factors. ABF-binding sites within the D. mulleri and D. melanogaster larval Adh promoters function as positive regulatory elements and in cotransfection experiments, ABF functions as a transcriptional activator. In further support of a role for ABF in the regulation of Adh expression, ABF mRNA is expressed in the embryonic fat body, a tissue that contains high levels of Adh mRNA.

Our studies demonstrate that the fat body develops from segmentally repeated clusters of mesodermal cells, which later expand and coalesce to form the mature fat body. These observations establish ABF as the earliest known fat body precursor marker in the Drosophila embryo. Together with the established role of GATA factors during mammalian development, these results suggest that ABF may play a key role in the organogenesis of the fat body.
Regulation of expression of mRNAs encoding the nerve growth factor receptors p75 and trkA in developing sensory neurons
Authors: Wyatt Sean , Davies Alun M.
Published: April 2021

We have used a quantitative reverse transcription/polymerase chain reaction amplification technique to study the regulation of p75 mRNA and trkA mRNA expression in developing NGF-dependent trigeminal neurons. Before becoming NGF dependent, these neurons express low levels of p75 and trkA mRNAs in vivo. At this stage in vitro, the level of p75 mRNA is maintained and upregulated by BDNF, whereas the level of trkA mRNA is sustained independently of neurotrophins and is down regulated by BDNF. With the acquisition of NGF dependence, p75 and trkA mRNA levels increase markedly in vivo. At this stage in vitro, the level of p75 mRNA is up regulated by NGF, but this response is lost at later stages.

The level of trkA mRNA is sustained in neurons grown with NGF but is not up-regulated by concentrations of NGF above those required to support survival. At no stage during the early development of trigeminal neurons do depolarising levels of potassium ions affect the expression of either p75 mRNA or trkA mRNA. These findings suggest that the expression of p75 and trkA mRNAs are differentially regulated by BDNF and NGF at successive early stages of neuronal development.
A role for Pax-1 as a mediator of notochordal signals during the dorsoventral specification of vertebrae
Authors: Koseki Haruhiko , Wallin Johan , Wilting Jörg , Mizutani Yoko , Kispert Andreas , Ebensperger Cecilia , Herrmann Bernhard G. , Christ Bodo , Balling Rudi
Published: April 2021

The notochord plays an important role in the differentiation of the paraxial mesoderm and the neural tube. We have analyzed the role of the notochord in somite differentiation and subsequent formation of the vertebral column using a mouse mutant, Danforth’s short-tail (Sd). In this mutant, the skeletal phenotype is most probably a result of degeneration and subsequent loss of the notochord. The Sd gene is known to interact with undulated (un), a sclerotome mutant. Double mutants between Sd and un alleles show an increase in the severity of the defects, mainly in the ventral parts of the vertebrae. We also show that part of the Sd phenotype is strikingly similar to that of the un alleles. As un is known to be caused by a mutation in the Pax-1 gene, we analyzed Pax-1 expression in Sd embryos. In Sd embryos, Pax-1 expression is reduced, providing a potential molecular basis for the genetic interaction observed. A complete loss of Pax-1 expression in morphologically intact mesenchyme was found in the lower thoracic-lumbar region, which is phenotypically very similar to the corresponding region in a Pax-1 null mutant, Undulated short-tail. The sclerotome developmental abnormalities in Sd coincide closely, both in time and space, with notochordal changes, as determined by whole-mount T antibody staining. These findings indicate that an intact notochord is necessary for normal Pax-1 expression in sclerotome cells, which is in turn required for the formation of the ventral parts of the vertebrae. The observed correlation among structural changes of the notochord, Pax-1 expression levels and skeletal phenotypes, suggests that Pax-1 might be an intrinsic mediator of notochordal signals during the dorsoventral specification of vertebrae.
Distinct elements of the xsna promoter are required for mesodermal and ectodermal expression
Authors: Mayor Roberto , Essex Linda J. , Bennett Michael F. , Sargent Michael G.
Published: April 2021

Xsna, the Xenopus homologue of Drosophila snail, is expressed in both mesoderm and ectoderm. Expression occurs in all mesoderm initially but is down regulated in a tissue-specific fashion at the end of gastrulation in a way that reveals the subdivision of the mesoderm before its derivatives are overtly differentiated. Xsna is also expressed in the ectoderm of the prospective neural fold from stage 11, in a distinct band of cells surrounding the prospective neural plate, which we designate the neural plate border. The deep and superficial ectoderm compartments labelled by Xsna represent the prospective neural crest and the prospective roof of the neural tube, respectively. Xsna expression persists in neural crest cells during their subsequent migration.

The role of the Xsna promoter in creating this pattern of expression has been investigated by injecting fertilised eggs with constructs containing the 5 upstream sequence of the gene fused to a reporter. An element of 115 base pairs ( 160 to 45 relative to the transcriptional start) is sufficient to drive appropriate reporter gene expression. The promoter does not contain a TATA or CAAT box and does not have a high GC content, but RNA synthesis starts precisely at 33 bases upstream to the translational start. The start sequence can be deleted so that transcription is initiated elsewhere without affecting the expression pattern. The distribution of Xsna promoter activity within the embryo, examined using -galactosidase ( -gal) fusions, is similar to that of the endogenous mRNA seen by in situ hybridisation. The contribution of elements within the 5 sequence have been assessed by comparing the expression patterns of constructs that have deletions in this region. Sequences from 112 to 97 are required for mesodermal expression and sequences from 96 to 44 are required for ectodermal expression. The behaviour of the injected promoter constructs differ in one important respect from the endogenous gene in that expression in an animal cap assay is not inducible by mesoderm-inducing factors but is inducible by cells of the vegetal pole.
Combinatorial control of touch receptor neuron expression in Caenorhabditis elegans
Authors: Mitani Shohei , Du Hongping , Hall David H. , Driscoll Monica , Chalfie Martin
Published: April 2021

Six touch receptor neurons with distinctive morphological features sense gentle touch in Caenorhabditis elegans. Previous studies have identified three genes (lin-32, unc-86 and mec-3) that regulate touch cell development. However, since other cell types also require these genes, we suspected that other genes help restrict the expression of touch cell characteristics to the six neurons seen in the wild type. To identify such genes, we have examined mutants defective in genes required for the development of other C. elegans cells for changes in the pattern of touch cell-specific features. Mutations in seven genes either reduce (lin-14) or increase (lin-4, egl-44, egl-46, sem-4, ced-3 and ced-4) the number of touch receptor-like cells. The combinatorial action of these genes, all of which are required for the production of many cell types, restrict the number of cells expressing touch receptor characteristics in wild-type animals by acting as positive and negative regulators and by removing cells by programmed cell death.
Formation of the shoot apical meristem in Arabidopsis thaliana: an analysis of development in the wild type and in the shoot meristemless mutant
Authors: Barton M. Kathryn , Poethig R. Scott
Published: April 2021

The primary shoot apical meristem of Arabidopsis is initiated late in embryogenesis, after the initiation of the cotyledons. We have identified a gene, called SHOOT MERISTEMLESS, which is critical for this process. shoot meristemless mutant seedlings lack a shoot apical meristem but are otherwise healthy and viable. The anatomy of mutant embryos demonstrates that the shoot meristemless-1 mutation completely blocks the initiation of the shoot apical meristem, but has no other obvious effects on embryo development. The failure of shoot meristemless tissue to regenerate shoots in tissue culture suggests that this gene regulates adventitious shoot meristem formation, as well as embryonic shoot meristem formation.
glp-1 can substitute for lin-12 in specifying cell fate decisions in Caenorhabditis elegans
Authors: Fitzgerald Kevin , Wilkinson Hilary A. , Greenwald Iva
Published: April 2021

Members of the lin-12/Notch gene family encode receptors for intercellular signals and are found throughout the animal kingdom. In many animals, the presence of at least two lin-12/Notch genes raises the issue of the significance of this duplication and divergence. In Caenorhabditis elegans, two lin-12/Notch genes, lin-12 and glp-1, encode proteins that are 50% identical, with different numbers of epidermal growth factor-like motifs in their extracellular domains. Many of the cell fate decisions mediated by lin-12 and glp-1 are distinct. Here, we express glp-1 protein under the control of lin12 regulatory sequences in animals lacking endogenous lin-12 activity and find that glp-1 can substitute for lin12 in mediating cell fate decisions. These results imply that the lin-12 and glp-1 proteins are biochemically interchangeable, sharing common ligand and effector proteins, and that the discrete lin-12 and glp-1 mutant phenotypes result from differential gene expression. In addition, these results suggest that the duplicate lin12/Notch genes found in vertebrates may also be biochemically interchangeable.
pipsqueak, an early acting member of the posterior group of genes, affects vasa level and germ cell-somatic cell interaction in the developing egg chamber
Authors: Siegel Vivian , Jongens Thomas A. , Jan Lily Yeh , Jan Yuh Nung
Published: April 2021

We have identified a new member of the posterior group of genes, which we call pipsqueak. We show that pipsqueak acts after the establishment of the oskar posterior anchor but before the localization of vasa protein during oogenesis. Characterization of multiple alleles at the pipsqueak locus shows that pipsqueak, like vasa, is required for early stages of oogenesis, including but not limited to formation of the egg chamber and progression through Stage 6 of oogenesis. Genetic interaction studies suggest that pipsqueak acts at least partially through vasa; molecular studies indicate that pipsqueak affects vasa level in the ovary. We compare vasa and pipsqueak mutant phenotypes in order to determine whether pipsqueak acts solely through vasa, and present a model for the role of pipsqueak in posterior pattern formation.
Cell patterning in the Drosophila segment: engrailed and wingless antigen distributions in segment polarity mutant embryos
Authors: van de Heuvel Marcel , Klingensmith John , Perrimon Norbert , Nusse Roel
Published: April 2021

By a complex and little understood mechanism, segment polarity genes control patterning in each segment of the Drosophila embryo. During this process, cell to cell communication plays a pivotal role and is under direct control of the products of segment polarity genes. Many of the cloned segment polarity genes have been found to be highly conserved in evolution, providing a model system for cellular interactions in other organisms. In Drosophila, two of these genes, engrailed and wingless, are expressed on either side of the parasegment border. wingless encodes a secreted molecule and engrailed a nuclear protein with a homeobox. Maintenance of engrailed expression is dependent on wingless and vice versa. To investigate the role of other segment polarity genes in the mutual control between these two genes, we have examined wingless and engrailed protein distribution in embryos mutant for each of the segment polarity genes.

In embryos mutant for armadillo, dishevelled and porcupine, the changes in engrailed expression are identical to those in wingless mutant embryos, suggesting that their gene products act in the wingless pathway. In embryos mutant for hedgehog, fused, cubitus inter- ruptus Dominant and gooseberry, expression of engrailed is affected to varying degrees. However wingless expression in the latter group decays in a similar way earlier than engrailed expression, indicating that these gene products might function in the maintenance of wingless expression. Using double mutant embryos, epistatic relationships between some segment polarity genes have been established. We present a model showing a current view of segment polarity gene interactions.
Cell fate patterning during C. elegans vulval development
Authors: Hill Russell J. , Sternberg Paul W.
Published: April 2021

Precursor cells of the vulva of the C. elegcuis hermaphrodite choose between two vulval cell fates (1°and 2°) and a non-vulval epidermal fate (3°) in response to three intercellular signals. An inductive signal produced by the anchor cell induces the vulval precursors to assume the 1 and 2 vulval fates. This inductive signal is an EGF-like growth factor encoded by the gene lin-3. An inhibitory signal mediated by lin-/5, and which may originate from the surrounding epidermis, prevents the vulval precursors from assuming vulval fates in the absence of the inductive signal. A short range lateral signal, which acts through the gene lin-12, regulates the pattern of 1°and 2° fates assumed by the induced vulval precursors.

The combined action of the three signals precisely directs the six vulval precursors to adopt a 3° 3° 2° 1° 2° 3° pattern of fates. The amount of inductive signal produced by the anchor cell appears to determine the number of vulval precursors that assume vulval fates. The three induced vulval precursors most proximal to the anchor cell are proposed to adopt the 2° 1° 2° pattern of fates in response to a gradient of the inductive signal and also in response to lateral signalling that inhibits adjacent vulval precursor cells from both assuming the 1°fate.
Dry mass, lipid content and protein content of the intact and zona-free mouse ovum
Authors: Loewenstein Joseph E. , Cohen Adolph I.
Published: April 2021

Intact and zona-free single-celled mouse ova were analyzed for total protein and were dried and weighed on a quartz fiber fishpole balance before and after lipid extraction. The zona pellucida was found to contribute 19 per cent, of the dry mass of the intact ovum. It was estimated to be 96 per cent, water and 4 per cent, solid matter, of which 30 per cent, was protein. No statistically significant amount of lipid was found. The cytoplasm was estimated to be 85 per cent, water and 15 per cent, solid matter, of which 12·5 per cent, was lipid and 71 per cent, protein. The lipid content was no greater than that of protoplasm from other sources, indicating the presence of only a small amount of yolk. The cytoplasm was found to be less variable in mass than the zona pellucida.
Developmental abnormalities in the head region of the talpid3 mutant of the fowl
Authors: Ede D. A. , Kelly W. A.
Published: April 2021

The inherited abnormality talpid3 in the fowl causes embryonic death on or before the 14th day of incubation, and developmental defects have been observed to appear on the 2nd day. Abnormalities in the head region include a tendency for the eyes to be drawn together in the mid-line, and absence of the upper beak. Rathke’s pouch is abnormal or absent, and in some cases ectopic lenses are produced within the head. Multiple epiphyseal structures are produced from the roof and abnormal ventral evaginations from the floor of the diencephalon. The developmental interrelations of these abnormalities are described, and the possible nature of the basic developmental disturbance isdiscussed. The production of extraocular lens tissue is discussed in the light of information on lens induction in normal embryos.
Effect of various inhibitors on several enzymes and other biochemical substances in chick embryo explants
Authors: Newburgh R. W. , Clark Alice , Wilson Audrey , Scholz Marion
Published: April 2021

Earlier studies in our laboratory indicated the predominance of pentose cycle activity in early embryos (Jolley, Cheldelin & Newburgh, 1959; Coffey, 1963). In addition a correlation was demonstrated between enzymes generating reduced triphosphopyridine nucleotide and lipid synthesis (Bieber, Cheldelin & Newburgh, 1962; Baker & Newburgh, 1963). Since several of the biosynthetic pathways involve this compound, it is conceivable that in a rapidly growing system such as the early chick embryo enzymes generating TPNH may play a major röle. We have chosen to use explants of chick embryos in an attempt to gain insight into the relation of changes of these enzymes with other chemical changes which may more directly relate to differentiation. These latter changes include synthesis of such macromolecules as DNA, RNA, hemoglobin, collagen and myosin. This method permits the addition of certain chemicals to the media such as substrates or inhibitors (Hayashi et al., 1959), allowing easy manipulation of the environment. Prior to studying the above macromolecules it seemed appropriate to study the effect of certain inhibitors on glucose-6-phosphate, 6-phosphogluconic acid and isocitric dehydrogenase. It was hoped that such information might be useful for purposes of establishing base lines of biochemical activity. The inhibitors chosen were fluorouracil, chloramphenicol and acetyl pyridine, and it will be shown that these had several rather specific effects on the enzymes studied. The first two inhibitors were chosen because of their relation to RNA or protein biosynthesis and the latter since it is an analogue of the pyridine moiety of TPN.
The ultrastructure of germ cells in foetal and neonatal male rats
Authors: Franchi L. L. , Mandl Anita M.
Published: April 2021

Male germ cells of foetal and neonatal rats (14 · 5 days p.c. to 7 days p.p.) were examined with the electron microscope. Female germ cells of young specimens (14 · 5 to 16 · 5 days p.c.) were re-examined for comparison. Shortly after sex differentiation, male and female germ cells have many features in common. The endoplasmic reticulum in oögonia, however, is the more highly developed, while the outline of gonocytes becomes markedly more angular as development proceeds. Between 15-5 and 18-5 days p.c., mitochondria in the male aggregate at one pole of the cell; those of the female remain randomly distributed. The significance of mitochondrial ‘polarization’ is obscure, but it is possible that the process is in some way related to cessation of mitotic activity. From 18 · 5 days p.c. onwards, when mitochondria become re-distributed evenly, groups of specific organelles (A- and B-bodies) appear in the cytoplasm. Three types of B-bodies have been identified. Of these, one type resembles lysosomes. The incidence of B-bodies increases during late intra-uterine life and reaches its peak between birth and 2 days p.p. Thereafter, they become rarer, as do germ cells situated in the centre of the seminiferous cord. At this time, a high proportion of gonocytes grow cytoplasmic extensions establishing contact with the basement membrane; their nucleus and nucleolus change their shape, while their mitochondria contain more regularly arranged parallel cristae than do those of ‘unattached’ gonocytes. Cells showing these signs of ‘streaming’ or migration are believed to correspond to the ‘transitional’ cells identified under the light microscope, and to be the immediate precursors of the first generation of spermatogonia type-A. After 2 days p.p., B-bodies appear to persist almost only in those gonocytes that have failed to establish contact with the basement membrane. The possible significance of B-bodies in spontaneous degeneration and high radiosensitivity of gonocytes is discussed. A few isolated germ cells show degenerative changes during the first 3 days after birth. These frequently show swollen endoplasmic reticulum, abnormal mitochondria and an abundance of B-bodies. Widespread degeneration does not set in until about 5 days, and largely affects ‘unattached’ gonocytes at inter-phase; a few degenerating cells undergoing mitosis have been observed. Degeneration takes the form of lysis: the cell membrane ruptures, the cytoplasm streams out over a wide area, and the nucleus becomes distorted. The process by which lysing germ cells are eliminated from the testis has not been fully established. The ultrastructure of spermatogonia type-A is essentially similar to that of their precursors. Most of the small germ cells corresponding to spermatogonia type-A seen under the light microscope lie with their long axis parallel to the basement membrane.
Developmental abnormalities in the trunk and limbs of the talpid3 mutant of the fowl
Authors: Ede D. A. , Kelly W. A.
Published: April 2021

Three talpid mutants have been described in the fowl, all of which are characterized by lethal embryonic abnormalities. As explained in a previous paper (Ede & Kelly, 1964), Cole’s talpid and talpid3 are similar in all essential respects and show striking abnormalities in the head region, whereas talpid2 has a relatively normal head. In all three, embryos surviving to 11 days and over show the following abnormalities in the trunk region: (1) The vertebral column is shortened. (2) The limbs are extremely short and the number of digits on each is greater than normal. (3) The viscera are ectopic, i.e. they protrude through the ventral body wall, which remains open. (4) Feather development is incomplete. (5) There is much subcutaneous oedema and haemorrhage. Instances of inherited polydactyly have always excited interest on account of the light they may throw on the origins and production of the pentadactyl limb pattern in typical vertebrate embryos. The talpid mutants are particularly interesting in this respect since the effect on limb development is much more drastic than in other cases of inherited polydactyly in the fowl, producing a totally different pattern rather than simply duplicating one of the digits as in polydactyly (Po), duplicate (Pod) and diplopodia (dp) (reviewed by Hutt, 1949). Also, unlike these other mutants in which other structures are affected only to a very minor degree, the effect of the talpid genes is extremely pleiotropic, producing widespread developmental disturbances. The unravelling of complex pleiotropic patterns of damage has long been established as a powerful technique of embryological investigation, especially by Grüneberg in many studies on mouse mutants (reviewed by Grüneberg, 1963). In these studies it is postulated that gene action is unitary, and that by establishing a ‘pedigree of causes’ the primary action of the gene, producing the primary defect from which all the others ultimately arise, is revealed. In this paper the development of the abnormalities in the trunk and limbs of talpid3 is analysed with a view to discovering the connexions between them and relating them to the abnormalities of the head region. The basic defect appears to lie in some disturbance of the mesenchyme, affecting its segregation into mesenchymal condensations, and later the formation within it of cartilage and bone. It is hoped that further work will test this hypothesis, and give more precise information about the fundamental developmental disturbances.
The rôle of tissue organization in the differentiation of embryonic chick neural retina
Authors: Peck D.
Published: April 2021

Neural retina from chick embryos 6 to 14 day incubation was cultured either as intact fragments or as populations of dispersed cells following enzymatic dissociation into a suspension of single cells. Within 10 to 24 hr., 95 to 100 per cent, of the cells cultured as populations of dispersed cells transformed into pigmented cells reminiscent of, but not identical to, those of pigmented retina. This transformation did not occur in intact fragments of neural retina similarly cultured. The nature of the mechanism by which the transformation occurs has been experimentally investigated. The results indicate that some unstable inhibitor of tyrosinase may be responsible for the unorthodox differentiation of these cells.
The rôle of neurohumours in early embryogenesis. : I. Serotonin content of developing embryos of sea urchin and loach
Authors: Buznikov G. A. , Chudakova I. V. , Zvezdina N. D.
Published: April 2021

Serotonin (5-hydroxytryptamine, 5-HT) is shown to be present in early embryos of Deuterostomia, in the sea urchin Strongylocentrotus dröbachiensis, and in a teleost—the loach Misgurnus fossilis. 5-HT is found in mature unfertilized eggs of S. dröbachiensis’, soon after fertilization the concentration of this substance rises sharply, while the first four cleavage divisions are accompanied by rhythmical rises in 5-HT content. In the early blastula 5-HT concentration is low, it rises somewhat in the mid- and late blastula and at the beginning of gastrulation, dropping again in the late gastrula to zero. Pluteus formation is accompanied by the resumption of 5-HT synthesis. 5-HT seems to appear in the loach eggs within the first minutes of fertilization. The first three cleavage divisions are accompanied by sharp fluctuations of 5-HT content, although no distinct synchrony could be found between the 5-HT rises and divisions in this case. Up to the stage of the late blastula no 5-HT is found. Two high 5-HT peaks are observed during gastrulation. From this and earlier work the suggestion is put forward that 5-HT is a universal participant in the processes of early embryogenesis both in Protostomia and Deuterostomia. The elucidation of the rôle of this embryonic hormone requires further investigation.
Control of muscle differentiation by embryonic neural tissues
Authors: Muchmore William B.
Published: April 2021

Previous work has suggested that in the salamander embryonic spinal cord enhances and embryonic brain suppresses differentiation of muscle from somitic mesoderm. These results have been confirmed by means of transplantation and explantation experiments performed on early neurulae of Ambystoma maculatum. Transplantation of presumptive spinal cord into the hind-brain region results in increased size of post-otic myotomes. On the other hand, transplantation of presumptive forebrain into the trunk neural plate usually results in a striking decrease in size of trunk myotomes. Orthotopic transplants of neural plate have little or no effect upon the development of myotomes. Ventral ectoderm transplanted into the neural plate at stage is incorporated into the host spinal cord and adjacent myotomes are usually normal. Transplants of trunk neural plate over lateral mesoderm often results in increased size of myotomes without affecting the pronephros. Explants of large amounts of somite mesoderm in an ectodermal envelope readily differentiate into muscle. Inclusion of presumptive brain cells in such explants results in a conspicuous decrease in frequency of occurrence of muscle differentiation and in quantity of muscle actually formed. The control of muscle differentiation in the early embryo is considered in the light of the known influences exerted by the neural tissues.
Studies on kidney tubulogenesis. I. The effect of actinomycin D on tubulogenesis in vitro
Authors: Jainchill John , Saxén Lauri , Vainio Tapani
Published: April 2021

The effects of actinomycin D upon the induction of tubulogenesis in mouse metanephrogenic mesenchyme by dorsal spinal cord have been studied. A drug concentration of 0 · 05 μg./c.c. was found to be optimal for inhibiting differentiation without being lethal for the cells. Treatment of both spinal cord and mesenchyme, or of mesenchyme only, for 30 min. just prior to recombination, inhibited tubulogenesis. Treatment of the spinal cord (inducer) only, either just prior to or up to 8 hr. before recombina-tion had no effect. Treatment of the spinal cord and mesenchyme for 30 min. with 0 · 05 μg./c.c. actinomycin at any time up to 20 hr. after recombination inhibited tubulogenesis. If 24 or more hours elapsed between recombination and treatment with the drug, however, differentiation could no longer be inhibited. In all cases exposure to actinomycin reduced tissue viability, but both spinal cord and liver (dummy inducer) protected the mesenchyme and increased cell viability in the latter, measured by neutral red uptake. In the discussion the significance of the change in the effect of exposure to actinomycin between 20 and 24 hr. after recombination is considered with reference both to other studies of this time period in the mesenchyme induction system, and to analogous results achieved with actinomycin in other systems.
Induction de l’endoderme pré-hépatique par le mésoderme de l’aire cardiaque chez l’embryon de poulet
Authors: Douarin par Nicole Le
Published: April 2021

Dans des travaux antérieurs (Le Douarin, 1961, 1962) j’ai localisé les territoires présomptifs du foie chez l’embryon de Poulet de 9 à 15 somites. Ces territoires s’étendent de part et d’autre de l’axe somitique jusqu’au niveau du 15ème somite environ et se réunissent sur la ligne médioventrale dans le repli cardiaque. L’étude des potentialités histogénétiques des différentes régions de ces aires hépatiques a montré que seules les parties contenant le repli cardiaque peuvent fournir du foie lorsqu’elles sont isolées et transplantées en greffes coelomiques (Le Douarin, 1964). Il est apparu ainsi que le territoire présomptif endodermique du foie n’est pas aussi étendu que le territoire mésodermique. Il est localisé dès un stade précoce dans la lèvre antérieure de l’ombilic intestinal (Text-fig. 1).