bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tail formation as a continuation of gastrulation: the multiple cell populations of the Xenopus tailbud derive from the late blastopore lip
Authors: Gont Linda K. , Steinbeisser Herbert , Blumberg Bruce , De Robertis Eddy M. 
Published: April 2021

ABSTRACT
Three lines of evidence suggest that tail formation in Xenopus is a direct continuation of events initiated during gastrulation. First, the expression of two gene markers, Xbra and Xnot2, can be followed from the blastopore lip into distinct cell populations of the developing tailbud. Second, the tip of the tail retains Spemann’s tail organizer activity until late stages of development. Third, lineage studies with the tracer DiI indicate that the cells of the late blastopore are fated to form specific tissues of the tailbud, and that intercalation of dorsal cells continues during tail elongation. In particular, the fate map shows that the tip of the tail is a direct descendant of the late dorsal blastopore lip. Thus, the tailbud is not an undifferentiated blastema as previously thought, but rather consists of distinct cell populations which arise during gastrulation.
The kit-ligand (steel factor) and its receptor c-kit/W: pleiotropic roles in gametogenesis and melanogenesis
Authors: Besmer Peter , Manova Katia , Duttlinger Regina , Huang Eric J. , Packer Alan , Gyssler Corina , Bachvarova Rosemary F. 
Published: April 2021

ABSTRACT
The c-kit receptor tyrosine kinase belongs to the PDGF/CSF-l/c-kit receptor subfamily. The kit ligand, KL, also called steel factor, is synthesized from two alternatively spliced mRNAs as transmembrane proteins that can either be proteolytically cleaved to produce soluble forms of KL or can function as cell-associated molecules. The c-kit receptor kinase and KL are encoded at the white spotting (IV) and steel (SI) loci of the mouse, respectively. Mutations at both the W and the SI locus cause deficiencies in gametogenesis, melanogenesis and hematopoiesis. The c-kit receptor is expressed in the cellular targets of IF and SI mutations, while KL is expressed in their microenvironment. In melanogenesis, c-kit is expressed in melanoblasts from the time they leave the neural crest and expression continues during embryonic development and in the melanocytes of postnatal animals. In gametogenesis c-kit is expressed in primordial germ cells, in spermatogonia, and in primordial and growing oocytes, implying a role at three distinct stages of gametogenesis.
Many mutant alleles are known at W and SI loci and their phenotypes vary in the degree of severity in the different cellular targets of the mutations. While many W and SI alleles severely affect primordial germ cells (PGC), several mild SI alleles have weak effects on PGCs and exhibit differential male or female sterility. Steel Panda (SlPan) is a KL expression mutation in which KL RNA transcript levels are reduced in most tissues analyzed. In female SlPan / SlPan mice, ovarian follicle development is arrested at the one layered cuboidal stage as a result of reduced KL expression in follicle cells, indicating a role for c-kit in oocyte growth.
W sh is a c-kit expression mutation, which affects mast cells and melanogenesis. While the mast cell defect results from lack of c-kit expression, the pigmentation deficiency appears to stem from ectopic c-kit receptor expression in the somitic dermatome at the time of migration of melanoblasts from the neural crest to the periphery. It is proposed that the ectopic c-kit expression in mice affects early melanogenesis in a dominant fashion. The “sash” or white belt of Wsh/+ animals and some other mutant mice is explained by the varying density of melanoblasts along the body axis of wild-type embryos.
Developmental expression of the syndecans: possible function and regulation
Authors: Bernfield Merton , Hinkes Michael T. , Gallo Richard L. 
Published: April 2021

ABSTRACT
Recent work has made clear that heparan sulfate at the cell surface is essential for a wide variety of interactions of cells with their microenvironment, including the action of growth factors, extracellular matrix, proteases and protease inhibitors. A major source of this cell surface heparan sulfate is a multigene family of proteoglycans, the syndecans, that are expressed developmentally in association with changes in tissue organization and morphology and induced during wound repair. In this review, we describe mechanisms underlying the differential expression of the syndecans, focusing on syndecan-1. The induction of syndecan-1 can result from soluble extracellular factor(s) acting at multiple levels of cellular regulation. At the transcriptional level, the promoter of the murine syndecan-1 gene contains potential recognition sites for several well-known regulatory genes, including Hox and MyoD family members. Because changes in syndecan expression enable cells to become more or less responsive to their microenvironment, understanding these regulatory mechanisms can lead to an improved understanding of how cellular behavior is controlled during development and wound repair.
crumbs and stardust, two genes of Drosophila required for the development of epithelial cell polarity
Authors: Knust Elisabeth , Tepaß Ulrich , Wodarz Andreas 
Published: April 2021

ABSTRACT
Loss-of-function mutations in the Drosophila genes crumbs and stardust are embryonic lethal and cause a breakdown of ectodermally derived epithelia during organogenesis, leading to formation of irregular cell clusters and extensive cell death in some epithelia. The mutant phenotype develops gradually and affects the various epithelia to different extents, crumbs encodes a large transmembrane protein with 30 EGF-like repeats and four laminin A G-domain-like repeats in its extra- cellular domain, suggesting its participation in protein- protein interactions. The CRUMBS protein is exclusively expressed on the apical membrane of all ectodermally derived epithelia, the tissues affected in crumbs and stardust mutant embryos. The gene function is com- pletely abolished by a crumbs mutation that causes pro- duction of a protein with a truncated cytoplasmic domain. Instead of being apically localized as in wild- type, the mutant CRUMBS protein is diffusely distributed in the cytoplasm; this occurs before any morphologically detectable cellular phenotype is visible, suggesting that targeting of proteins is affected in crumbs mutant embryos. Later, the protein can be detected on the apical and basolateral membranes. Mutations in stardust produce a phenotype nearly identical to that associated with crumbs mutations, suggesting that both genes are functionally related. Double imitant combinations and gene dosage studies suggest that both genes are part of a common genetic pathway, in which stardust acts down- stream of crumbs.
Dissecting Wnt signalling pathways and Wnf-sensitive developmental processes through transient misexpression analyses in embryos of Xenopus laevis
Authors: Moon Randall T. , Christian Jan L. , Campbell Robert M. , McGrew L. Lynn , DeMarais Alyce A. , Torres Monica , Lai Cheng-Jung , Olson Daniel J. , Kelly Gregory M. 
Published: April 2021

ABSTRACT
We review evidence that Xenopus Wnts (Xwnts) have activities consistent with their hypothesized roles as secreted signalling factors involved in multiple developmental processes. Transient misexpression of different Xwnts has distinct effects upon early development, and upon the formation of tissues in UV-irradiated embryos. Misexpression of Xwnts also has distinct effects on the in vitro differentiation of blastula cap expiants. Cellular responses to Xwnt signals include changes in gap junctional permeability, altered responsiveness to growth factors, and possibly changes in cell adhesion. Current data suggest that a maternal Xwnt- or noggin-like activity is involved in the Nieuwkoop center activity during mesoderm induction, that Xwnt-8 participates in a pathway of differentiation as ventral mesoderm, and that Xwnt-5A is a potential modulator of morphogenetic movements.
Analysis of the formation of the animal pole plasm in the eggs of Limnaea stagnalis
Authors: Raven Chr. P. , Wal U. P. Van Der 
Published: April 2021

ABSTRACT
The animal pole plasm in the eggs of Limnaea stagnalis becomes visible about 1 hr. before the first cleavage. At this time the male pronucleus is on its way toward the animal pole, while the female pronucleus is being formed by the fusion of karyomeres resulting from the swelling of the egg chromosomes after the completion of the second maturation division.
Periodic sensitivity of mechanisms of cytodifferentiation in cleaving eggs of Limnaea stagnalis
Authors: Geilenkirchen W. L. M. 
Published: April 2021

ABSTRACT
Eggs of Limnaea stagnalis, of ages differing by 15-min. intervals between oviposition and the third cleavage division, have been centrifuged at 640 g. for 10 min. Centrifugation before first cleavage did not have any effect on development. Centrifugation at first, second and third cleavage caused a strong morphogenetic effect. Centrifugation during prophase of second and third division caused delay of cleavage. The mitotic figure is disrupted. It is suggested that the morphogenetic effect of centrifugation can be ascribed to a disturbance of the normal distribution of morphogenetic ‘substance’ at or in the cell surface, by random insertion or resorption of membrane after stretching the cell.
The effect of plucking hairs during different phases of the follicular cycle
Authors: Johnson Elizabeth , Ebling F. J. 
Published: April 2021

ABSTRACT
Hair growth is intermittent; periods of activity when the follicle is producing the hair alternating with periods of rest when the dead hair is retained. In the rat, hair growth occurs in a series of waves which start ventrally and pass over the flanks to the back (Dry, 1926; Butcher, 1934; Johnson, 1958).
Lactate dehydrogenase isoenzymes in foetal and neonatal tissues
Authors: Latner A. L. , Skillen A. W. 
Published: April 2021

ABSTRACT
The Existence of isoenzymes, one class of the multiple molecular forms of enzymes, is now well recognized. Isoenzyme distribution patterns, particularly those of lactate dehydrogenase (LDH), have been extensively studied and are often tissue and species specific (Markert & Møller, 1959; Wieland, Pfleiderer, Haupt & Wörner, 1959; Plagemann, Gregory & Wroblewski, 1960; Tsao, 1960). Various techniques, such as zone electrophoresis and column chromatography, have been used to separate isoenzymes of lactate dehydrogenase. Using starch-gel electrophoresis combined with visual demonstration of the isoenzyme patterns, we have detected the usual five zones of activity in human tissues (Latner & Skillen, 1961). They are termed LD1 LD2, LD3, LD4 and LD5 where, according to the terminology we use, the latter is the isoenzyme which migrates furthest towards the anode and is most prominent in heart muscle.
Cell movements, cell division and growth in the hydroid Clytia johnstoni
Authors: Hale L. J. 
Published: April 2021

ABSTRACT
In Clytia johnstoni, mitosis is almost exclusively a function of the ectoderm cells; only very rarely does an endoderm cell divide. Thus new endoderm cells must be produced by the ectoderm cells. Cell divisions may occur anywhere in the stolonic ectoderm except for approximately the first 0·3 mm. from a growing tip. During the development of a hydranth mitoses are rare except for a local wave of ectodermal cell division contributing to the formation of the tentacles and buccal region. Growth only takes place in the first 6–12 mm. of a stolon. The ectoderm cells in the first 2–3 mm. move towards the tip; those on the ‘top’ of a stolon (i.e. away from the substratum) are concerned in the initiation of hydranths and those at the sides and bottom with stolon growth. In the remainder of this region ectoderm cells on the top of the stolon migrate into and form the ectoderm of the hydranths. The hydroplasm contains cells, mostly endoderm, which are derived from non-growing regions of the stolon and from regressing parts of the animal. During the ebb and flow of the hydroplasm, such cells are transported to, and adhere to the growing regions of stolons and to growing hydranths. The endoderm of hydranths is almost entirely supplied by this means. Cells differentiate into the various regions of the hydranth and stolon according to their positions relative to the growing tip.
Patterns of pigmentation in experimentally produced mouse chimaerae
Authors: Tarkowski Andrzej K. 
Published: April 2021

ABSTRACTDistribution of pigment-forming cells has been analysed in sixteen individuals (six embryos, nine newborn young, one adult animal) developed from fused eggs differing in genotype for pigmentation (pink eye dilution versus agouti). The following structures were examined: the outer layer of the retina (all individuals), choroid and Harderian gland and skin from various regions of the body (postnatal individuals). In the six embryos, pigment was revealed in their retinae but since the development of pigmentation was still in progress at that age the genotype of non-pigmented cells could not be identified. In seven out of the nine newborn young the outer layer of the retina was a mosaic with pigmented and non-pigmented cells intermingled. In the two other animals the outer layer of the retina was homogenous, being of’pink’ type in one animal and of ‘agouti’ type in the other. In the adult animal the outer layer of the retina of one eye seems to be composed of two types of cells. The difference of pigmentation between them is quantitative only, the colour and shape of the granules being the same and typical for the agouti (hybrid) component. To postulate the chimaeric constitution it would be necessary to assume, therefore, that the cells derived from the LAB Grey component (pink-eyed) have been in some way induced by the neighbouring hybrid cells to synthesize pigment typical of the latter. In all newborn animals, except the one with non-pigmented eyes, melanocytes from the agouti component were detected in the choiroid, Harderian gland and the samples of skin examined. However, the presence of melanocytes of the other genotype could be neither proved nor rejected. On the basis of the composition of the retinae and the distribution of pigmented melanocytes in the skin it is inferred that the majority of animals developed from fused eggs are real chimaeras, at least as far as the neural derivatives are concerned. Since pigmentation does not reveal the genetic constitution of structures of different developmental history and derivation, the chimaeric character of animals with homogenous retinae cannot be excluded.
The lin-3/let-23 pathway mediates inductive signalling during male spicule development in Caenorhabditis elegans
Authors: Chamberlin Helen M. , Sternberg Paul W. 
Published: April 2021

ABSTRACT
During Caenorhabditis elegans male spicule development, four pairs of precursor cells respond to multiple positional cues and establish a pattern of fates that correlates with relative anterior-posterior cell position. One of the extracellular cues is provided by the F and U cells, which promote anterior fates. We show that the genes in the lin-3/let-23 signalling pathway required for hermaphrodite vulval induction also mediate this F/U signal. Reduction-of-function mutations in lin-3, let-23, sem-5, let-60 or lin-45 disrupt the fate of anterior cells. Likewise, activation of the pathway with ubiquitously produced signal results in posterior cells inappropriately adopting the anterior fates even in the absence of F and U. We have further used this genetic pathway to begin to understand how multiple posi-tional cues are integrated to specify cell fate. We demon-strate that lin-15 acts in spicule development as it does in vulval induction, as a negative regulator of let-23 receptor activity. A second extracellular cue, from Y.p, also acts antagonistically to the lin-3/let-23 pathway. However, this signal is apparently integrated into the lin-3/let-23 pathway at some step after lin-45 raf and is thus functionally distinct from lin-15. We have also investigated the role of lin-12 in forming the anterior/posterior pattern of fates. A lin-12 gain-of-function defect is masked by redundant positional information from F and U.
Role of the teashirt gene in Drosophila midgut morphogenesis: secreted proteins mediate the action of homeotic genes
Authors: Mathies Laura D. , Kerridge Stephen , Scott Matthew P. 
Published: April 2021

ABSTRACT
Homeotic genes control the development of embryonic structure by coordinating the activities of downstream ‘target’ genes. The identities and functions of target genes must be understood in order to learn how homeotic genes control morphogenesis. Drosophila midgut development is regulated by homeotic genes expressed in the visceral mesoderm, where two of their target genes have been identified. Both encode secreted proteins. The Ultrabithorax (Ubx) homeotic gene activates transcription of the decapentaplegic (dpp) gene, which encodes a TGFβ class protein, while in adjacent mesoderm cells the abdominal-A (abd-A) homeotic gene activates transcription of the wingless (wg) gene, which encodes a Wnt class protein. The homeotic genes Antennapedia (Antp) and Sex combs reduced (Scr) act in more anterior midgut regions. Here we report the identification of another homeotic gene target in the midgut mesoderm, the teashirt (tsh) gene, which encodes a protein with zinc finger motifs. tsh is necessary for proper formation of anterior and central midgut structures. Antp activates tsh in anterior midgut mesoderm. In the central midgut mesoderm Ubx, abd-A, dpp, and wg are required for proper tsh expression. The control of tsh by Ubx and abd-A, and probably also by Antp, is mediated by secreted signaling molecules. By responding to signals as well as localized transcription regulators, the tsh transcription factor is produced in a spatial pattern distinct from any of the homeotic genes.
Soma-germline asymmetry in the distributions of embryonic RNAs in Caenorhabditis elegans
Authors: Seydoux Geraldine , Fire Andrew 
Published: April 2021

ABSTRACT
Early embryogenesis in Caenorhabditis elegans is characterized by a series of unequal cleavages that mark the stepwise separation of somatic and germ lineages. We have developed an in situ hybridization protocol to examine the localization of specific maternal and embryonically transcribed messenger RNAs during these early cleavages. We detected three classes of maternal RNAs: RNAs that are maintained in all cells, RNAs that are maintained in germline cells but are lost from somatic cells, and a population of RNAs that are associated with the germlinespecific P granules. We observed embryonically transcribed RNAs in somatic cells as early as the 4-cell stage. These transcripts were not detected in germline cells. These observations suggest that mechanisms which distinguish between soma and germline cause asymmetries in mRNA stability and transcription within the first few cleavages of C. elegans embryogenesis.
GLP-1 is localized to the mitotic region of the C. elegans germ line
Authors: Crittenden Sarah L. , Troemel Emily R. , Evans Thomas C. , Kimble Judith 
Published: April 2021

ABSTRACT
In C. elegans, germline mitosis depends on induction by the somatic distal tip cell (DTC) and on activity of the glp-1 gene. Using antibodies to GLP-1 protein, we have examined GLP-1 on western blots and by immunocytochemistry. GLP-1 is tightly associated with membranes of mitotic germline cells, supporting its identification as an integral membrane protein. Furthermore, GLP-1 is localized within the germ line to the mitotic region, consistent with the model that GLP-1 acts as a membrane receptor for the distal tip cell signal. Unexpectedly, GLP-1 and the zone of mitosis extend further than the DTC processes. We present three models by which the DTC may influence GLP-1 activity and thereby determine the zone of mitosis. The spatial restriction of GLP-1 appears to be controlled at the translational level in hermaphrodites. We suggest that down-regulation of GLP-1 may be required to effect the transition from mitosis into meiosis.
RK2, a glial-specific homeodomain protein required for embryonic nerve cord condensation and viability in Drosophila
Authors: Campbell Gerard , Göring Harald , Lin Tina , Spana Eric , Andersson Siv , Doe Chris Q. , Tomlinson Andrew 
Published: April 2021

ABSTRACT
We report the identification of RK2, a glial-specific home-odomain protein. RK2 is localized to the nucleus of virtually all embryonic and imaginal glial cells, with the exception of midline glia. Embryos mutant for the gene encoding RK2 are embryonic lethal but normal for early gliogenesis (birth, initial divisions and migration of glia) and axonogenesis (neuronal pathfinding and fasciculation). However, later in development, there are significantly fewer longitudinal glia that are spatially disorganized; in addition, there is a slight disorganization of axon fascicles and a defective nerve cord condensation. This suggests that RK2 is not required for early glial determination, but rather for aspects of glial differentiation or function that are required for embryonic viability.
Genesis of an organ: molecular analysis of the pha-1 gene
Authors: Granato Michael , Schnabel Heinke , Schnabel Ralf 
Published: April 2021

ABSTRACT
The organisation of organ formation is still an unsolved problem. Mutations in the zygotic lethal gene pha-1 affect a late step during organ development in the nematode C. elegans. In mutant embryos all tissues in the pharynx fail to undergo terminal differentiation and morphogenesis. The expression of an early differentiation marker in pharyngeal muscle precursors is not impaired in mutant embryos, which suggests that pharynx cells still acquire their identity. Therefore the gene defines an organ-specific terminal differentiation function. We cloned and sequenced the pha-1 gene and found that the deduced protein sequence contains features characteristic of the bZIP family of transcription factors. During embryogenesis a transgenic pha-1 reporter construct is expressed transiently in all pharynx precursor cells at the time when these cells become restricted to form the pharynx organ. A mosaic analysis of the requirement of pha-1 activity during pharynx formation is consistent with the notion that pha-1 acts cell-autonomously in all cells of the pharynx primordium. The data suggest that pha-1 initiates and coordinates programs required for cytodifferentiation and morphogenesis in all cell types of the entire organ on the transcriptional level. We propose that organs are independent developmental units whose identity is reflected on the gene regulatory level.