bluuebunny/crossref_metadata_2025_split huggingface dataset:
Axogenesis in the embryonic brain of the grasshopper Schistocerca gregaria: an identified cell analysis of early brain development
Authors: Boyan George , Therianos Stavros , Williams J. Leslie D. , Reichert Heinrich 
Published: April 2021

ABSTRACT
Axogenesis in the embryonic brain was studied at the single cell level in the grasshopper Schistocerca gregaria. A small set of individually identifiable pioneer neurons establishes a primary axon scaffold during early embryogenesis. At the beginning of scaffold formation, pioneering axons navigate along and between glial borders that surround clusters of proliferating neuroblasts. In each brain hemisphere, an axonal outgrowth cascade involving a series of pioneer neurons establishes a pathway from the optic ganglia to the brain midline. At the midline the primary preoral commissural interconnection in the embryonic brain is pioneered by a pair of midline-derived pioneer neurons. A second preoral commissural connection is pioneered by two pairs of pars intercerebralis pioneer neurons. Descending tracts are pioneered by the progeny of identified neuroblasts in the pars intercerebralis, deutocerebrum and tritocerebrum; the postoral tritocerebral commissure is pioneered by a pair of tritocerebral neurons. All of the pioneering brain neurons express the cell adhesion molecule fasciclin I during initial axon outgrowth and fasciculation. Once established, the primary axon scaffold of the brain is used for fasciculation by subsequently differentiating neurons and, by the 40% stage of embryogenesis, axonal projections that characterize the mature brain become evident. The single cell analysis of grasshopper brain development presented here sets the stage for manipulative cell biological experiments and provides the basis for comparative molecular genetic studies of embryonic brain development in Drosophila.
The dorsal involuting marginal zone stiffens anisotropically during its convergent extension in the gastrula of Xenopus laevis
Authors: Moore Steven W. , Keller Raymond E. , Koehl M. A. R. 
Published: April 2021

ABSTRACT
Physically, the course of morphogenesis is determined by the distribution and timing of force production in the embryo and by the mechanical properties of the tissues on which these forces act. We have miniaturized a standard materials-testing procedure (the stress-relaxation test) to measure the viscoelastic properties of the dorsal involuting marginal zone, prechordal mesoderm, and vegetal endoderm of Xenopus laevis embryos during gastrulation. We focused on the involuting marginal zone, because it undergoes convergent extension (an important and wide-spread morphogenetic process) and drives involution, blastopore closure and elongation of the embryonic axis. We show that the involuting marginal zone stiffens during gastrulation, stiffening is a special property of this region rather than a general property of the whole embryo, stiffening is greater along the anteroposterior axis than the mediolateral axis and changes in the cytoskeleton or extra-cellular matrix are necessary for stiffening, although changes in cell-cell adhesions or cell-matrix adhesions are not ruled out. These findings provide a baseline of data on which future experiments can be designed and make specific, testable predictions about the roles of the cytoskeleton, extracellular matrix and intercellular adhesion in convergent extension, as well as predictions about the morphogenetic role of convergent extension in early development.
Formin isoforms are differentially expressed in the mouse embryo and are required for normal expression of gf-4 and shh in the limb bud
Authors: Chan David C. , Wynshaw-Boris Anthony , Leder Philip 
Published: April 2021

ABSTRACT
Mice homozygous for the recessive limb deformity (ld) mutation display both limb and renal defects. The limb defects, oligodactyly and syndactyly, have been traced to improper differentiation of the apical ectodermal ridge (AER) and shortening of the anteroposterior limb axis. The renal defects, usually aplasia, are thought to result from failure of ureteric bud outgrowth. Since the ld locus gives rise to multiple RNA isoforms encoding several different proteins (termed formins), we wished to understand their role in the formation of these organs. Therefore, we first examined the embryonic expression patterns of the four major ld mRNA isoforms. Isoforms I, II and III (all con-taining a basic amino terminus) are expressed in dorsal root ganglia, cranial ganglia and the developing kidney including the ureteric bud. Isoform IV (containing an acidic amino terminus) is expressed in the notochord, the somites, the apical ectodermal ridge (AER) of the limb bud and the developing kidney including the ureteric bud. Using a lacZ reporter assay in transgenic mice, we show that this differential expression of isoform IV results from distinct regulatory sequences upstream of its first exon. These expression patterns suggest that all four isoforms may be involved in ureteric bud outgrowth, while isoform IV may be involved in AER differentiation. To define further the developmental consequences of the ld limb defect, we analyzed the expression of a number of genes thought to play a role in limb development. Most signifi-cantly, we find that although the AERs of ld limb buds express several AER markers, they do not express detectable levels of fibroblast growth factor 4 (fgf-4), which has been proposed to be the AER signal to the mesoderm. Thus we conclude that one or more formins are necessary to initiate and/or maintain fgf-4 production in the distal limb. Since ld limbs form distal structures such as digits, we further conclude that while fgf-4 is capable of support-ing distal limb outgrowth in manipulated limbs, it is not essential for distal outgrowth in normal limb development. In addition, ld limbs show a severe decrease in the expression of several mesodermal markers, including sonic hedgehog (shh), a marker for the polarizing region and Hoxd-12, a marker for posterior mesoderm. We propose that incomplete differentiation of the AER in ld limb buds leads to reduction of polarizing activity and defects along the anteroposterior axis.
Modifications of cell fate specification in equal-cleaving nemertean embryos: alternate patterns of spiralian development
Authors: Martindale Mark Q. , Henry Jonathan Q. 
Published: April 2021

ABSTRACT
The nemerteans belong to a phylum of coelomate worms that display a highly conserved pattern of cell divisions referred to as spiral cleavage. It has recently been shown that the fates of the four embryonic cell quadrants in two species of nemerteans are not homologous to those in other spiralian embryos, such as the annelids and molluscs (Henry, J. Q. and Martindale, M. Q. (1994a) Develop. Genetics 15, 64-78). Equal-cleaving molluscs utilize inductive interactions to establish quadrant-specific cell fates and embryonic symmetry properties following fifth cleavage. In order to elucidate the manner in which cell fates are established in nemertean embryos, we have conducted cell isolation and deletion experiments to examine the developmental potential of the early cleavage blastomeres of two equal-cleaving nemerteans, Nemertopsis bivittata and Cerebratulus lacteus. These two species display different modes of development: N. bivittata develops directly via a non-feeding larvae, while C. lacteus develops to form a feeding pilidium larva which undergoes a radical metamorphosis to give rise to the juvenile worm. By examining the development of certain structures and cell types characteristic of quadrant-specific fates for each of these species, we have shown that isolated blastomeres of the indirect-developing nemertean, C. lacteus, are capable of generating cell fates that are not a consequence of that cell’s normal developmental program. For instance, dorsal blastomeres can form muscle fibers when cultured in isolation. In contrast, isolated blastomeres of the directdeveloping species, N. bivittata do not regulate their development to the same extent. Some cell fates are specified in a precocious manner in this species, such as those that give rise to the eyes. Thus, these findings indicate that equalcleaving spiralian embryos can utilize different mechanisms of cell fate and axis specification. The implications of these patterns of nemertean development are discussed in relation to experimental work in other spiralian embryos, and a model is presented that accounts for possible evolutionary changes in cell lineage and the process of cell fate specification amongst these protostome phyla.
Formation of lateral root meristems is a two-stage process
Authors: Laskowski Marta J. , Williams Mary E. , Nusbaum H. Chad , Sussex Ian M. 
Published: April 2021

ABSTRACT
In both radish and Arabidopsis, lateral root initiation involves a series of rapid divisions in pericycle cells located on the xylem radius of the root. In Arabidopsis, the number of pericycle cells that divide to form a primordium was estimated to be about 11. To determine the stage at which primordia are able to function as root meristems, primordia of different stages were excised and cultured without added hormones. Under these conditions, primordia that consist of 2 cell layers fail to develop while primordia that consist of at least 3-5 cell layers develop as lateral roots. We hypothesize that meristem formation is a two-step process involving an initial period during which a population of rapidly dividing, approximately isodiametric cells that constitutes the primordium is formed, and a sub-sequent stage during which meristem organization takes place within the primordium.
DPY-30, a nuclear protein essential early in embryogenesis for Caenorhabditis elegans dosage compensation
Authors: Hsu David R. , Chuang Pao-Tien , Meyer Barbara J. 
Published: April 2021

ABSTRACT
DPY-30 is an essential component of the C. elegans dosage compensation machinery that reduces X chromosome transcript levels in hermaphrodites (XX). DPY-30 is required for the sex-specific association of DPY-27 (a chromosome condensation protein homolog) with the hermaphrodite X chromosomes. Loss of dpy-30 activity results in XX-specific lethality. We demonstrate that dpy-30 encodes a novel nuclear protein of 123 amino acids that is present in both hermaphrodites and males (XO) throughout development. DPY-30 itself is not associated with the X chromosomes, nor is its pattern of expression perturbed by mutations in the gene hierarchy that controls dosage compensation. Therefore, DPY-30 is a ubiquitous factor that is likely to promote the hermaphrodite-specific association of DPY-27 with X by affecting the activity of a sex-specific dosage compensation gene. In XO animals, DPY-30 is required for developmental processes other than dosage compensation: coordinated movement, normal body size, correct tail morphology and mating behavior. We demonstrate that rescue of both the XX-specific lethality and the XO-specific morphological defects caused by dpy-30 mutations can be achieved by inducing dpy-30 transcripts either in the mother or in the embryo through the end of gastrulation. dpy-30 appears to be cotranscribed in an operon with a novel RNA-binding protein.
Overexpression of parathyroid hormone-related protein or parathyroid hormone in transgenic mice impairs branching morphogenesis during mammary gland development
Authors: Wysolmerski John J. , McCaughern-Carucci James F. , Daifotis Anastasia G. , Broadus Arthur E. , Philbrick William M. 
Published: April 2021

ABSTRACT
Parathyroid hormone-related protein (PTHrP) was originally discovered as the tumor product that causes humoral hypercalcemia of malignancy. PTHrP is now known to be widely expressed in many normal fetal tissues where it may participate in the regulation of organogenesis. In this report, we document that overexpression of PTHrP in myoepithelial cells in the mammary glands of transgenic mice resulted in a form of breast hypoplasia characterized by a profound defect in branching morphogenesis of the developing mammary duct system. In addition, transgenic mice manifested a defect in lobuloalveolar development during pregnancy that seemed to be, in part, the consequence of an impaired ability to form terminal ducts in response to estrogen and progesterone stimulation. The effects of PTHrP on branching morphogenesis during breast development appeared to be the result of aminoterminal PTH-like sequences that signal through the PTH/PTHrP receptor, since overexpression of parathyroid hormone itself in the mammary glands of transgenic mice caused a similar developmental phenotype, and delivery of PTHrP (1–36) via locally implanted slow-release pellets impaired breast development in normal mice. These results suggest that PTHrP, which is a native product of mammary epithelial and myoepithelial cells may participate in normal breast development, perhaps as a locally secreted growth inhibitor.
Specificity of CNS and PNS regulatory subelements comprising pan-neural enhancers of the deadpan and scratch genes is achieved by repression
Authors: Emery John F. , Bier Ethan 
Published: April 2021

ABSTRACT
The Drosophila pan-neural genes deadpan (dpn) and scratch (scrt) are expressed in most or all developing neural precursor cells of the central nervous system (CNS) and peripheral nervous system (PNS). We have identified a cisacting enhancer element driving full pan-neural expression of the dpn gene which is composed of independent CNSand PNS-specific subelements. We have also identified CNSand PNS-specific subelements of the scrt enhancer. Deletion analysis of the dpn and scrt PNS-specific subelements reveals that PNS specificity of these two evolutionarily unrelated enhancers is achieved in part by repression of CNS expression. We discuss the implications of the striking organizational similarities of the dpn, scrt, and sna pan-neural enhancers.
The division abnormally delayed (dally) gene: a putative integral membrane proteoglycan required for cell division patterning during postembryonic development of the nervous system in Drosophila
Authors: Nakato Hiroshi , Futch Tracy A. , Selleck Scott B. 
Published: April 2021

ABSTRACT
We have devised a genetic screen to obtain mutants affecting cell division patterning in the developing central nervous system of Drosophila. The division abnormally delayed (dally) locus was identified using a combination of “enhancer trap” and behavioral screening methods. The ordered cell cycle progression of lamina precursor cells, which generate synaptic target neurons for photoreceptors, is disrupted in dally mutants. The first of two lamina precursor cell divisions shows a delayed entry into mitosis. The second division, one that is triggered by an intercellular signal from photoreceptor axons, fails to take place. Similar to lamina precursors, cells that generate the ommatidia of the adult eye show two synchronized divisions found along the morphogenetic furrow in the eye disc and the first division cycle in dally mutants displays a delayed progression into M phase like that found in the first lamina precursor cell division. dally mutations also affect viability and produce morphological defects in several adult tissues, including the eye, antenna, wing and genitalia. Sequencing of a dally cDNA reveals a potential open reading frame of 626 amino acids with homology to a family of Glypican-related integral membrane proteoglycans. These heparan sulfate-containing proteins are attached to the external leaflet of the plasma membrane via a glycosylphosphatidylinositol linkage. Heparan sulfate proteoglycans may serve as co-receptors for a variety of secreted proteins including fibroblast growth factor, vascular endothelial growth factor, hepatocyte growth factor and members of the Wnt, TGF-β and Hedgehog families. The cell division defects found in dally mutants implicate the Glypican group of integral membrane proteoglycans in the control of cell division during development.
Translational control of oskar generates Short OSK, the isoform that induces pole plasm assembly
Authors: Markussen Finn-Hugo , Michon Anne-Marie , Breitwieser Wolfgang , Ephrussi Anne 
Published: April 2021

ABSTRACT
At the posterior pole of the Drosophila oocyte, oskar induces a tightly localized assembly of pole plasm. This spatial restriction of oskar activity has been thought to be achieved by the localization of oskar mRNA, since mislocalization of the RNA to the anterior induces anterior pole plasm. However, ectopic pole plasm does not form in mutant ovaries where oskar mRNA is not localized, suggesting that the unlocalized mRNA is inactive. As a first step towards understanding how oskar activity is restricted to the posterior pole, we analyzed oskar translation in wild type and mutants. We show that the targeting of oskar activity to the posterior pole involves two steps of spatial restriction, cytoskeleton-dependent localization of the mRNA and localization-dependent translation. Furthermore, our experiments demonstrate that two isoforms of Oskar protein are produced by alternative start codon usage. The short isoform, which is translated from the second in-frame AUG of the mRNA, has full oskar activity. Finally, we show that when oskar RNA is localized, accumulation of Oskar protein requires the functions of vasa and tudor, as well as oskar itself, suggesting a positive feedback mechanism in the induction of pole plasm by oskar.
Establishment of Drosophila imaginal precursor cells is controlled by the Arrowhead gene
Authors: Curtiss Jennifer , Heilig Joseph S. 
Published: April 2021

ABSTRACT
Metamorphosis in Drosophila melanogaster requires synchronization of numerous developmental events that occur in isolated imaginal precursor tissues. The imaginal primordia are established during embryonic stages and are quiescent for much of larval life. The Arrowhead gene is necessary for establishment of proper numbers of cells within a subset of imaginal precursor tissues. Loss-offunction mutations in Arrowhead reduce the number of abdominal histoblasts and salivary gland imaginal ring cells before the proliferative stages of their development. The number of abdominal histoblasts in mutant animals is approximately half that of wild-type, as might result from failure of a single early division of these cells. A neomorphic Arrowhead allele results in the specific loss of the retinal precursors by the early third instar, before they have begun to differentiate. Since Arrowhead mutations affect only subsets of imaginal tissue, there must be distinctions in the developmental regulation of different imaginal precursors. Arrowhead may be part of a regulatory pathway responsible for establishing the proper number of abdominal histoblasts and salivary gland imaginal ring cells. The neomorphic Arrowhead allele, which may cause misexpression of the Arrowhead gene in the eye-antenna imaginal disc, interferes with the establishment or proliferation of retinal precursor cells.
Targeted mutagenesis of the transcription factor GATA-4 gene in mouse embryonic stem cells disrupts visceral endoderm differentiation in vitro
Authors: Soudais Claire , Bielinska Malgorzata , Heikinheimo Markku , MacArthur Craig A. , Narita Naoko , Saffitz Jeffrey E. , Simon M. Celeste , Leiden Jeffrey M. , Wilson David B. 
Published: April 2021

ABSTRACT
Transcription factor GATA-4 belongs to a family of zinc finger proteins involved in lineage determination. GATA-4 is first expressed in yolk sac endoderm of the developing mouse and later in cardiac tissue, gut epithelium and gonads. To delineate the role of this transcription factor in differentiation and early development, we studied embryoid bodies derived from mouse embryonic stem (ES) cells in which both copies of the Gata4 gene were disrupted. Light and electron microscopy demonstrated that embryoid bodies formed from wild-type and heterozygous deficient ES cells were covered with a layer of visceral yolk sac endoderm, whereas no yolk sac endoderm was evident on the surface of the homozygous deficient embryoid bodies. Independently selected homozygous deficient cell lines displayed this distinctive phenotype, suggesting that it was not an artifact of clonal variation. Biochemical markers of visceral endoderm formation, such as α-feto-protein, hepatocyte nuclear factor-4 and binding sites for Dolichos biflorus agglutinin, were absent from the homozygous deficient embryoid bodies. Examination of other differentiation markers in the mutant embryoid bodies, studies of ES cell-derived teratocarcinomas and chimeric mouse analysis demonstrated that GATA-4-deficient ES cells have the capacity to differentiate along other lineages. We conclude that, under in vitro conditions, disruption of the Gata4 gene results in a specific block in visceral endoderm formation. These homozygous deficient cells should yield insights into the regulation of yolk sac endoderm development and the factors expressed by visceral endoderm that influence differentiation of adjoining ectoderm/mesoderm.
A role for En-2 and other murine homologues of Drosophila segment polarity genes in regulating positional information in the developing cerebellum
Authors: Millen Kathleen J. , Hui Chi-Chung , Joyner Alexandra L. 
Published: April 2021

ABSTRACT
To gain insight into the molecular genetic basis of cerebellar patterning, the expression patterns of many vertebrate homologues of Drosophila segment polarity genes were examined during normal and abnormal cerebellar development, including members of the En, Wnt, Pax, Gli and Dvl gene families. Five of these genes were found to show transient, spatially restricted patterns of expression. Strikingly, expression of En-2, En-1, Wnt-7B and Pax-2 defined eleven similar sagittal domains at 17.5 dpc, reminiscent of the transient sagittal domains of expression of Purkinje cell markers which have been implicated in cerebellar afferent patterning. Postnatally, transient anterior/posterior differences in expression were observed for En-2, En-1, Gli and Wnt-7B dividing the cerebellum into anterior and posterior regions. The expression patterns of these genes were altered in cerebella of En-2 homozygous mutant mice, which show a cerebellar foliation patterning defect. Strikingly, four of the Wnt-7B expression domains that are adjacent to the En-2 domains are lost in En-2 mutant embryonic cerebella. These studies provide the first evidence of a potential network of regulatory genes that establish spatial cues in the developing cerebellum by dividing it into a grid of positional information required for patterning foliation and afferents. Taken together with previous gene expression studies, our data suggests that eleven sagittal domains and at least two anterior/posterior compartments are the basic elements of spatial information in the cerebellum.