bluuebunny/crossref_metadata_2025_split huggingface dataset:
EST analysis of gene expression in early cleavage-stage sea urchin embryos*
Authors: Lee Youn-Ho , Huang Guyang Matthew , Cameron R. Andrew , Graham Geoffrey , Davidson Eric H. , Hood Leroy , Britten Roy J. 
Published: April 2021

Abstract
A set of 956 expressed sequence tags derived from 7-hour (mid-cleavage) sea urchin embryos was analyzed to assess biosynthetic functions and to illuminate the structure of the message population at this stage. About a quarter of the expressed sequence tags represented repetitive sequence transcripts typical of early embryos, or ribosomal and mitochondrial RNAs, while a majority of the remainder contained significant open reading frames. A total of 232 sequences, including 153 different proteins, produced significant matches when compared against GenBank. The majority of these identified sequences represented ‘housekeeping’ proteins, i.e., cytoskeletal proteins, metabolic enzymes, transporters and proteins involved in cell division. The most interesting finds were components of signaling systems and transcription factors not previously reported in early sea urchin embryos, including components of Notch and TGF signal transduction pathways. As expected from earlier kinetic analyses of the embryo mRNA populations, no very prevalent protein-coding species were encountered; the most highly represented such sequences were cDNAs encoding cyclins A and B. The frequency of occurrence of all sequences within the database was used to construct a sequence prevalence distribution. The result, confirming earlier mRNA population analyses, indicated that the poly(A) RNA of the early embryo consists mainly of a very complex set of low-copy-number transcripts.
The Drosophila chiffon gene is required for chorion gene amplification, and is related to the yeast Dbf4 regulator of DNA replication and cell cycle
Authors: Landis Gary , Tower John 
Published: April 2021

ABSTRACT
The Drosophila chorion genes encode the major protein components of the chorion (eggshell) and are arranged in two clusters in the genome. To meet the demand for rapid chorion synthesis, Drosophila ovary follicle cells amplify the chorion gene clusters ∼80-fold. Amplification proceeds through repeated firing of one or more DNA replication origins located near the center of each gene cluster. Hypomorphic mutant alleles of the chiffon gene cause thin, fragile chorions and female sterility, and were found to eliminate chorion gene amplification. Null alleles of chiffon had the additional phenotypes of rough eyes and thin thoracic bristles: phenotypes often associated with disruption of normal cell cycle. The chiffon locus was cloned by chromosomal walking from the nearby cactus locus. A 6.5 kb transcript was identified and confirmed to be chiffon by sequencing of mutant alleles and by phenotypic rescue with genomic transformation constructs. The protein predicted by translation of the 5.1 kb chiffon ORF contains two domains related to the S. cerevisiae Dbf4 regulator of DNA replication origin firing and cell cycle progression: a 44 residue domain designated CDDN1 (43% identical) and a 41 residue domain designated CDDN2 (12% identical). The CDDN domains were also found in the S. pombe homolog of Dbf4, Dfp1, as well as in the proteins predicted by translation of the Aspergillus nimO gene and specific human and mouse clones. The data suggest a family of eukaryotic proteins related to Dbf4 and involved in initiation of DNA replication.
Directionality of Wingless protein transport influences epidermal patterning in the Drosophila embryo
Authors: Moline Melissa M. , Southern Cozumel , Bejsovec Amy 
Published: April 2021

ABSTRACT
Active endocytotic processes are required for the normal distribution of Wingless (Wg) protein across the epidermal cells of each embryonic segment. To assess the functional consequences of this broad Wg distribution, we have devised a means of perturbing endocytosis in spatially restricted domains within the embryo. We have constructed a transgene expressing a dominant negative form of shibire (shi), the fly dynamin homologue. When this transgene is expressed using the GAL4-UAS system, we find that Wg protein distribution within the domain of transgene expression is limited and that Wg-dependent epidermal patterning events surrounding the domain of expression are disrupted in a directional fashion. Our results indicate that Wg transport in an anterior direction generates the normal expanse of naked cuticle within the segment and that movement of Wg in a posterior direction specifies diverse denticle cell fates in the anterior portion of the adjacent segment. Furthermore, we have discovered that interfering with posterior movement of Wg rescues the excessive naked cuticle specification observed in naked (nkd) mutant embryos. We propose that the nkd segment polarity phenotype results from unregulated posterior transport of Wg protein and therefore that wild-type Nkd function may contribute to the control of Wg movement within the epidermal cells of the segment.
Lis1, the Drosophila homolog of a human lissencephaly disease gene, is required for germline cell division and oocyte differentiation
Authors: Liu Zhao , Xie Ting , Steward Ruth 
Published: April 2021

Abstract
Lissencephaly is a severe congenital brain malformation resulting from incomplete neuronal migration. One causal gene, LIS1, is homologous to nudF, a gene required for nuclear migration in A. nidulans. We have characterized the Drosophila homolog of LIS1 (Lis1) and show that Lis1 is essential for fly development. Analysis of ovarian Lis1 mutant clones demonstrates that Lis1 is required in the germline for synchronized germline cell division, fusome integrity and oocyte differentiation. Abnormal packaging of the cysts was observed in Lis1 mutant clones. Our results indicate that LIS1 is important for cell division and differentiation and the function of the membrane cytoskeleton. They support the notion that LIS1 functions with the dynein complex to regulate nuclear migration or cell migration.
The homeobox gene, Xanf-1, can control both neural differentiation and patterning in the presumptive anterior neurectoderm of the Xenopus laevis embryo
Authors: Ermakova Galina V. , Alexandrova Eugenia M. , Kazanskaya Olga V. , Vasiliev Oleg L. , Smith Maria W. , Zaraisky Andrey G. 
Published: April 2021

Abstract
From the onset of neurectoderm differentiation, homeobox genes of the Anf class are expressed within a region corresponding to the presumptive telencephalic and rostral diencephalic primordia. Here we investigate functions of the Xenopus member of Anf, Xanf-1, in the differentiation of the anterior neurectoderm. We demonstrate that ectopic Xanf-1 can expand the neural plate at expense of adjacent non-neural ectoderm. In tadpoles, the expanded regions of the plate developed into abnormal brain outgrowths. At the same time, Xanf-1 can inhibit terminal differentiation of primary neurones. We also show that, during gastrula/ neurula stages, the exogenous Xanf-1 can downregulate four transcription regulators, XBF-1, Otx-2, Pax-6 and the endogenous Xanf-1, that are expressed in the anterior neurectoderm. However, during further development, when the exogenous Xanf-1 was presumably degraded, re-activation of XBF-1, Otx-2 and Pax-6 was observed in the abnormal outgrowths developed from blastomeres microinjected with Xanf-1 mRNA. Other effects of the ectopic Xanf-1 include cyclopic phenotype and inhibition of the cement gland, both by Otx-2-dependent and -independent mechanisms. Using fusions of Xanf-1 with the repressor domain of Drosophila engrailed or activator domain of herpes virus VP16 protein, we showed that most of the observed effects of Xanf-1 were probably elicited by its functioning as a transcription repressor. Altogether, our data indicate that the repressor function of Xanf-1 may be necessary for regulation of both neural differentiation and patterning in the presumptive anterior neurectoderm.
Spatially discrete FGF-mediated signalling directs glial morphogenesis
Authors: Condron Barry 
Published: April 2021

Abstract
Neurons provide critical signals that regulate both the number and differentiation of glia. In addition, glia are attracted to and enwrap neuronal axonal processes. FGF-like signalling is thought to be one of the many potential axon-derived morphogenetic signals, however, the multiple roles of FGFs have made experimental tests of these signals difficult in vivo. In the Drosophila FGF receptor mutant heartless, glia migrate to axons, but fail to elongate around them. This study shows that in the similar but larger grasshopper CNS, FGF signalling is likely to mediate one step in the close interaction between glia and axons. FGF2-coated beads attract glia in the CNS and compete with axons for their resident, enwrapped glia. In addition, bath applied FGF2 causes mature axonal glia, which normally enwrap axon tracts, to round up. FGF2 activates the product of the grasshopper heartless FGF receptor gene and probably interferes with the normal function of an endogenous axon-associated FGF-like molecule. It is proposed that insect axons provide a critical spatially restricted FGF-like signal that induces glia to enwrap them.
Gap junction-mediated transfer of left-right patterning signals in the early chick blastoderm is upstream of Shh asymmetry in the node
Authors: Levin Michael , Mercola Mark 
Published: April 2021

Abstract
Invariant patterning of left-right asymmetry during embryogenesis depends upon a cascade of inductive and repressive interactions between asymmetrically expressed genes. Different cascades of asymmetric genes distinguish the left and right sides of the embryo and are maintained by a midline barrier. As such, the left and right sides of an embryo can be viewed as distinct and autonomous fields. Here we describe a series of experiments that indicate that the initiation of these programs requires communication between the two sides of the blastoderm. When deprived of either the left or the right lateral halves of the blastoderm, embryos are incapable of patterning normal left-right gene expression at Hensen’s node. Not only are both flanks required, suggesting that there is no single signaling source for LR pattern, but the blastoderm must be intact. These results are consistent with our previously proposed model in which the orientation of LR asymmetry in the frog, Xenopus laevis, depends on large-scale partitioning of LR determinants through intercellular gap junction channels (M. Levin and M. Mercola (1998) Developmental Biology 203, 90-105). Here we evaluate whether gap junctional communication is required for the LR asymmetry in the chick, where it is possible to order early events relative to the well-characterized left and right hierarchies of gene expression. Treatment of cultured chick embryos with lindane, which diminishes gap junctional communication, frequently unbiased normal LR asymmetry of Shh and Nodal gene expression, causing the normally left-sided program to be recapitulated symmetrically on the right side of the embryo. A survey of early expression of connexin mRNAs revealed that Cx43 is present throughout the blastoderm at Hamburger-Hamilton stage 2–3, prior to known asymmetric gene expression. Application of antisense oligodeoxynucleotides or blocking antibody to cultured embryos also resulted in bilateral expression of Shh and Nodal transcripts. Importantly, the node and primitive streak at these stages lack Cx43 mRNA. This result, together with the requirement for an intact blastoderm, suggests that the path of communication through gap junction channels circumvents the node and streak. We propose that left-right information is transferred unidirectionally throughout the epiblast by gap junction channels in order to pattern left-sided Shh expression at Hensen’s node.
Development of erythroid and myeloid progenitors in the yolk sac and embryo proper of the mouse
Authors: Palis James , Robertson Scott , Kennedy Marion , Wall Charles , Keller Gordon 
Published: April 2021

Abstract
In this study, we have mapped the onset of hematopoietic development in the mouse embryo using colony-forming progenitor assays and PCR-based gene expression analysis. With this approach, we demonstrate that commitment of embryonic cells to hematopoietic fates begins in proximal regions of the egg cylinder at the mid-primitive streak stage (E7.0) with the simultaneous appearance of primitive erythroid and macrophage progenitors. Development of these progenitors was associated with the expression of SCL/tal-1 and GATA-1, genes known to be involved in the development and maturation of the hematopoietic system. Kinetic analysis revealed the transient nature of the primitive erythroid lineage, as progenitors increased in number in the developing yolk sac until early somite-pair stages of development (E8.25) and then declined sharply to undetectable levels by 20 somite pairs (E9.0). Primitive erythroid progenitors were not detected in any other tissue at any stage of embryonic development. The early wave of primitive erythropoiesis was followed by the appearance of definitive erythroid progenitors (BFU-E) that were first detectable at 1-7 somite pairs (E8.25) exclusively within the yolk sac. The appearance of BFU-E was followed by the development of later stage definitive erythroid (CFU-E), mast cell and bipotential granulocyte/macrophage progenitors in the yolk sac. C-myb, a gene essential for definitive hematopoiesis, was expressed at low levels in the yolk sac just prior to and during the early development of these definitive erythroid progenitors. All hematopoietic activity was localized to the yolk sac until circulation was established (E8.5) at which time progenitors from all lineages were detected in the bloodstream and subsequently in the fetal liver following its development. This pattern of development suggests that definitive hematopoietic progenitors arise in the yolk sac, migrate through the bloodstream and seed the fetal liver to rapidly initiate the first phase of intraembryonic hematopoiesis. Together, these findings demonstrate that commitment to hematopoietic fates begins in early gastrulation, that the yolk sac is the only site of primitive erythropoiesis and that the yolk sac serves as the first source of definitive hematopoietic progenitors during embryonic development.
flex, an X-linked female-lethal mutation in Drosophila melanogaster controls the expression of Sex-lethal
Authors: Bhattacharya Ananya , Sudha S. , Chandra H. Sharat , Steward Ruth 
Published: April 2021

Abstract
The Sex-lethal (Sxl) gene is required in Drosophila females for sexual differentiation of the soma, for gem cell differentiation and dosage compensation. We have isolated three new alleles of female-lethal-on-X (flex), an X-linked female-lethal mutation and have characterized its function in sex determination. SXL protein is missing in flex/flex embryos, however transcription from both SxlPe, the early Sxl promoter and SxlPm, the late maintenance promoter, is normal in flex homozygotes. In flex/flex embryos, Sxl mRNA is spliced in the male mode. Analysis of flex germline clones shows that it also functions in oogenesis, but in contrast to Sxl mutants that show an early arrest tumorous phenotype, flex mutant egg chambers develop to stage 10. In flex ovarian clones, Sxl RNA is also spliced in the male form. Hence, flex is a sex-specific regulator of Sxl functioning in both the soma and the germline. Genetic interaction studies show that flex does not enhance female lethality of Sxl loss-of-function alleles but it rescues the male-specific lethality of both of the gain-of-function Sxl mutations, SxlM1 and SxlM4. In contrast to mutations in splicing regulators of Sxl, the female lethality of flex is not rescued by either SxlM1 or SxlM4. Based on these observations, we propose that flex regulates Sxl at a post- splicing stage and regulates either its translation or the stability of the SXL protein.
The development of the pattern of retinal ganglion cells in the chick retina: mechanisms that control differentiation
Authors: McCabe Kathryn L. , Gunther Erik C. , Reh Thomas A. 
Published: April 2021

Abstract
Neurons in both vertebrate and invertebrate eyes are organized in regular arrays. Although much is known about the mechanisms involved in the formation of the regular arrays of neurons found in invertebrate eyes, much less is known about the mechanisms of formation of neuronal mosaics in the vertebrate eye. The purpose of these studies was to determine the cellular mechanisms that pattern the first neurons in vertebrate retina, the retinal ganglion cells. We have found that the ganglion cells in the chick retina develop as a patterned array that spreads from the central to peripheral retina as a wave front of differentiation. The onset of ganglion cell differentiation keeps pace with overall retinal growth; however, there is no clear cell cycle synchronization at the front of differentiation of the first ganglion cells. The differentiation of ganglion cells is not dependent on signals from previously formed ganglion cells, since isolation of the peripheral retina by as much as 400 μm from the front of ganglion cell differentiation does not prevent new ganglion cells from developing. Consistent with previous studies, blocking FGF receptor activation with a specific inhibitor to the FGFRs retards the movement of the front of ganglion cell differentiation, while application of exogenous FGF1 causes the precocious development of ganglion cells in peripheral retina. Our observations, taken together with those of previous studies, support a role for FGFs and FGF receptor activation in the initial development of retinal ganglion cells from the undifferentiated neuroepithelium peripheral to the expanding wave front of differentiation.
The novel signal peptides, Pedibin and Hym-346, lower positional value thereby enhancing foot formation in hydra
Authors: Grens Ann , Shimizu Hiroshi , Hoffmeister Sabine A. H. , Bode Hans R. , Fujisawa Toshitaka 
Published: April 2021

Abstract
Signaling molecules affecting patterning processes are usually proteins and rarely peptides. Two novel peptides, pedibin and Hym-346, that are closely related to one another have been isolated from Hydra vulgaris and Hydra magnipapillata. Several experiments indicate that both cause a reduction in the positional value gradient, the principle patterning process governing the maintenance of form in the adult hydra. The peptides cause an increase in the rate of foot regeneration following bisection of the body column. Treatment of animals with either peptide for an extended period of time resulted in an apical extension of the range of expression of CnNk-2 along the body column. Such an extension is correlated with a decrease in positional value. Transplantation of tissue treated with Hym-346 results in an increase in the fraction forming feet, and aggregates derived from Hym-346 tissue form more feet and fewer heads. The latter two experiments provide a direct measure of the lowering of positional value in the treated tissue. These results suggest that peptides play signaling roles in patterning processes in cnidaria and, plausibly, in more complex metazoans as well.
Extrinsic and intrinsic factors control the genesis of amacrine and cone cells in the rat retina
Authors: Belliveau Michael J. , Cepko Constance L. 
Published: April 2021

ABSTRACT
The seven major classes of cells of the vertebrate neural retina are generated from a pool of multipotent progenitor cells. Recent studies suggest a model of retinal development in which both the progenitor cells and the environment change over time (Cepko, C. L., Austin, C. P., Yang, X., Alexiades, M. and Ezzeddine, D. (1996). Proc. Natl. Acad. Sci. USA 93, 589-595). We have utilized a reaggregate culture system to test this model. A labeled population of progenitors from the embryonic rat retina were cultured with an excess of postnatal retinal cells and then assayed for their cell fate choices. We found that the postnatal environment had at least two signals that affected the embryonic cells’ choice of fate; one signal inhibited the production of amacrine cells and a second affected the production of cone cells. No increase in cell types generated postnatally was observed. The source of the inhibitor of the amacrine cell fate appeared to be previously generated amacrine cells, suggesting that amacrine cell number is controlled by feedback inhibition. The progenitor cell lost its ability to be inhibited for production of an amacrine cell as it entered M phase of the cell cycle. We suggest that postmitotic cells influence progenitor cell fate decisions, but that they do so in a manner restricted by the intrinsic biases of progenitor cells.
Patterning of the R7 and R8 photoreceptor cells of Drosophila: evidence for induced and default cell-fate specification
Authors: Chou Wen-Hai , Huber Armin , Bentrop Joachim , Schulz Simone , Schwab Karin , Chadwell Linda V. , Paulsen Reinhard , Britt Steven G. 
Published: April 2021

Abstract
Opsin gene expression in the R7 and R8 photoreceptor cells of the Drosophila compound eye is highly coordinated. We have found that the R8 cell specific Rh5 and Rh6 opsins are expressed in non-overlapping sets of R8 cells, in a precise pairwise fashion with Rh3 and Rh4 in the R7 cells of individual ommatidia. Removal of the R7 cells in sevenless, boss or sina mutants, disrupts Rh5 expression and dramatically increases the number of Rh6-expressing R8 cells. This suggests that the expression of Rh5 may be induced by an Rh3-expressing R7 cell, whereas Rh6 expression is most likely a default state of the R8 cell. We found that the paired expression of opsin genes in the R7 and R8 cells occurs in a sevenless and boss independent manner. Furthermore, we found that the generation of both Rh3- and Rh4-expressing R7 cells can occur in the absence of an R8 cell. These results suggest that the specification of opsin expression in the R7 cells may occur autonomously, whereas the R7 photoreceptor cell may be responsible for regulating a binary developmental switch between induced and default cell-fates in the R8 cell.
Membrane-tethered Drosophila Armadillo cannot transduce Wingless signal on its own
Authors: Cox Rachel T. , Pai Li-Mei , Miller Jeffrey R. , Orsulic Sandra , Stein Joel , McCormick Carol Ann , Audeh Yara , Wang Wei , Moon Randall T. , Peifer Mark 
Published: April 2021

ABSTRACT
Drosophila Armadillo and its vertebrate homolog β-catenin are key effectors of Wingless/Wnt signaling. In the current model, Wingless/Wnt signal stabilizes Armadillo/β-catenin, which then accumulates in nuclei and binds TCF/LEF family proteins, forming bipartite transcription factors which activate transcription of Wingless/Wnt responsive genes. This model was recently challenged. Overexpression in Xenopus of membrane-tethered β-catenin or its paralog plakoglobin activates Wnt signaling, suggesting that nuclear localization of Armadillo/β-catenin is not essential for signaling. Tethered plakoglobin or β-catenin might signal on their own or might act indirectly by elevating levels of endogenous β-catenin. We tested these hypotheses in Drosophila by removing endogenous Armadillo. We generated a series of mutant Armadillo proteins with altered intracellular localizations, and expressed these in wild-type and armadillo mutant backgrounds. We found that membrane-tethered Armadillo cannot signal on its own; however it can function in adherens junctions. We also created mutant forms of Armadillo carrying heterologous nuclear localization or nuclear export signals. Although these signals alter the subcellular localization of Arm when overexpressed in Xenopus, in Drosophila they have little effect on localization and only subtle effects on signaling. This supports a model in which Armadillo’s nuclear localization is key for signaling, but in which Armadillo intracellular localization is controlled by the availability and affinity of its binding partners.