bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regional specification of muscle progenitors in Drosophila: the role of the msh homeobox gene
Authors: Nose Akinao , Isshiki Takako , Takeichi Masatoshi 
Published: April 2021

ABSTRACT
The somatic musculature in the abdominal hemisegments of Drosophila consists of 30 uniquely identifiable muscle fibers. Previous studies have suggested that the muscle diversity originates in a special class of myoblasts, called muscle founders, that are formed by the division of muscle progenitors. However, the mechanisms that locate and specify the muscle progenitors/founders are largely unknown. In this study, we first used a novel marker, rP298-LacZ, to chart the development of muscle progenitors/founders during the formation of distinct groups of mature muscles. We then determined the function of the muscle segment homeobox (msh) gene in myogenesis. msh encodes a homeobox-containing protein, vertebrate homologues of which are known as Msxs. We show that msh is expressed in the dorsal and lateral domains of muscle progenitors and is required for the specification of the progenitor cells. Ectopic expression of msh in the entire mesoderm inhibits the proper development of the normally msh-negative muscle progenitors in the dorsolateral domain. These results suggest that msh plays a role in regional specification of muscle progenitors/founders.
Balancing division and expansion during maize leaf morphogenesis: analysis of the mutant, warty-1
Authors: Reynolds James O. , Eisses John F. , Sylvester Anne W. 
Published: April 2021

ABSTRACT
Cell division and expansion are growth events that contribute to the developing shape, or morphogenesis, of a plant. Division and expansion are coordinated to the extent that plant organs, such as leaves, generally portray a predictable cellular pattern. To dissect the relationship between division and expansion, and to test for the role of each during morphogenesis, we have identified a recessive mutation warty-1 that produces a primary defect in cell size and shape in mutant leaves. Warty-1 mutant plants are similar to non-mutant siblings in terms of flowering time, overall plant size and leaf shape. Mature adult leaves have raised warts, consisting of excessively enlarged cells, that appear in patchy distribution throughout the blade. Cell wall deposition is abnormal or incomplete, suggesting cytokinesis is also affected, either directly or indirectly. Cells first increase in size at specific positions, which correspond to predictable cell dimensions of a developing 1 cm leaf. Once mutant cells exceed 133% normal size, cytokinesis becomes abnormal. As differentiation progresses, cells that appear normal in the mutant are actually dividing faster and are smaller than comparable cells in non-mutant siblings. These results suggest that (1) cells may compensate for growth defects by altering their cell cycle and that (2) proper execution of cytokinesis may require that cell size ratios are properly maintained.
Specification of first quartet micromeres in Ilyanassa involves inherited factors and position with respect to the inducing D macromere
Authors: Sweet Hyla C. 
Published: April 2021

ABSTRACT
In the embryos of the gastropod Ilyanassa obsoleta, the development of several ectodermal structures requires an inductive interaction between the micromeres and the D macromere. The first quartet micromeres (1a, 1b, 1c and 1d) contribute to the head of the larva and descendants of 1a and 1c normally develop the eyes. The eyes do not develop if 1a and 1c are removed at the eight-cell stage. However, regulative eye development may occur if the precursors of 1a and 1c are removed at the two- or four-cell stage. One purpose of this study was to demonstrate which cells of the cleavage-stage embryo have the potential to develop an eye. The results of blastomere deletion experiments suggest that only the first quartet micromeres have this ability. In addition, the 1b micromere was found to be equivalent to 1a and 1c, but 1d was found to have a poorer eye-forming ability. A second purpose of this study was to examine how eye development is normally restricted to the 1a and 1c micromeres. Cell transplantation experiments demonstrate that the proximity of a first quartet micromere relative to the inducing D macromere is important for determining whether or not it will go on to develop an eye. The 1b micromere may not develop an eye during normal development because it is too far from the D macromere. However, the eye-forming ability of the 1d micromere is not influenced by its close position to the D macromere, but is restricted by its polar lobe lineage.
Injection of sperm extract mimics spatiotemporal dynamics of Ca2+ responses and progression of meiosis at fertilization of ascidian oocytes
Authors: Kyozuka Keiichiro , Deguchi Ryusaku , Mohri Tatsuma , Miyazaki Shunichi 
Published: April 2021

ABSTRACT
Sperm extract (SE) of the ascidian, Ciona savignyi, injected into oocytes induced repetitive intracellular Ca2+ increases with kinetics consistent with those at fertilization and caused reinitiation and progression of meiosis as in fertilized oocytes with the formation of polar bodies. The Ca2+ response comprised two sets of Ca2+ oscillations separated by 5 minutes and correlated with the first and second meiotic metaphase. The effects of SE were dose dependent and the critical dose corresponded roughly to a single spermatozoon. In the first Ca2+ transient observed by confocal microscopy, a Ca2+ wave started from the SE injection site at the peripheral region of the oocyte and propagated across the ooplasm. The similar wave was produced by injection at the central region, starting from an arbitrary cortical area after 30 seconds, probably after SE had diffused to the cortex. The sensitivity to SE is thought to be preferentially higher in the cortex. The effective component of SE was heat-unstable, and its molecular weight was estimated as in the range between 10×104 and 3×104 using membrane filters. These results suggest that, in ascidian fertilization, a cytosolic sperm protein factor is introduced to the oocyte cortex and induces Ca2+ waves and thereby meiotic resumption, leading to cell-cycle-correlated Ca2+ oscillations.
Neurofibromin modulation of ras activity is required for normal endocardial-mesenchymal transformation in the developing heart
Authors: Lakkis Maha M. , Epstein Jonathan A. 
Published: April 2021

ABSTRACT
Endocardial cushions are the precursors of the cardiac valves and form by a process of epithelial-mesenchymal transformation. Secreted growth factors from myocardium induce endocardial cells to transform into mesenchyme and invade the overlying extracellular matrix. Here, we show that the product of the Nf1 neurofibromatosis gene is required to regulate this event. In the absence of neurofibromin, mouse embryo hearts develop overabundant endocardial cushions due to hyperproliferation and lack of normal apoptosis. Neurofibromin deficiency in explant cultures is reproduced by activation of ras signaling pathways, and the Nf1−/− mutant phenotype is prevented by inhibiting ras in vitro. These results indicate that neurofibromin normally acts to modulate epithelial-mesenchymal transformation and proliferation in the developing heart by down regulating ras activity.
Determination of the zebrafish forebrain: induction and patterning
Authors: Grinblat Yevgenya , Gamse Joshua , Patel Mukesh , Sive Hazel 
Published: April 2021

ABSTRACT
We report an analysis of forebrain determination and patterning in the zebrafish Danio rerio. In order to study these events, we isolated zebrafish homologs of two neural markers, odd-paired-like (opl), which encodes a zinc finger protein, and fkh5, which encodes a forkhead domain protein. At mid-gastrula, expression of these genes defines a very early pattern in the presumptive neurectoderm, with opl later expressed in the telencephalon, and fkh5 in the diencephalon and more posterior neurectoderm. Using in vitro explant assays, we show that forebrain induction has occurred even earlier, by the onset of gastrulation (shield stage). Signaling from the early gastrula shield, previously shown to be an organizing center, is sufficient for activation of opl expression in vitro. In order to determine whether the organizer is required for opl regulation, we removed from late blastula stage embryos either the presumptive prechordal plate, marked by goosecoid (gsc) expression, or the entire organizer, marked by chordin (chd) expression. opl was correctly expressed after removal of the presumptive prechordal plate and consistently, opl was correctly expressed in one-eyed pinhead (oep) mutant embryos, where the prechordal plate fails to form. However, after removal of the entire organizer, no opl expression was observed, indicating that this region is crucial for forebrain induction. We further show that continued organizer function is required for forebrain induction, since beads of BMP4, which promotes ventral fates, also prevented opl expression when implanted during gastrulation. Our data show that forebrain specification begins early during gastrulation, and that a wide area of dorsal mesendoderm is required for its patterning.
Vascularization in the murine allantois occurs by vasculogenesis without accompanying erythropoiesis
Authors: Downs Karen M. , Gifford Shannon , Blahnik Melanie , Gardner Richard L. 
Published: April 2021

ABSTRACT
The aim of this study was to determine whether the blood vessels of the murine allantois are formed by vasculogenesis or angiogenesis. Morphological analysis revealed that differentiation of allantoic mesoderm into an outer layer of mesothelium and an inner vascular network begins in the distal region of the allantois, which is most remote from other tissues, as early as the late neural plate stage (approximately 7.75 days postcoitum). Nascent blood vessels were not found in the base of the allantois until 4-somite pairs had formed in the fetus (approximately 8.25 days postcoitum), and vascular continuity with the yolk sac and fetus was not present until the 6-somite-pair stage (approximately 8.5 days postcoitum). Immunohistochemical analysis demonstrated that flk-1, a molecular marker of early endothelial cells, is expressed in significantly more distal than basal core cells in the early allantois and never in mesothelium. Furthermore, synchronous grafting of donor yolk sac containing blood islands into blood islands of headfold-stage host conceptuses provided no evidence that the yolk sac contributes endothelial cells to the allantois. Finally, when removed from conceptuses and cultured in isolation, neural plate and headfold-stage allantoises formed a conspicuous vascular network that was positive for Flk-1. Hence, the vasculature of the allantois is formed intrinsically by vasculogenesis rather than extrinsically via angiogenesis from the adjacent yolk sac or fetus.
Whether allantoic vasculogenesis is associated with erythropoiesis was also investigated. Benzidine-staining in situ revealed that primitive erythroid cells were not identified in the allantois until 6-somite pairs when continuity between its vasculature and that of the yolk sac was first evident. Nevertheless, a small number of allantoises removed from conceptuses at a considerably earlier stage were found to contain erythroid precursor cells following culture in isolation. To determine whether such erythroid cells could be of allantoic origin, host allantoises were made chimeric with lacZ-expressing donor allantoises that were additionally labeled with [3H]methyl thymidine. Following culture and autoradiography, many lacZ-expressing benzidine-stained cells were observed in donor allantoises, but none contained silver grains above background. Moreover, no cells of donor allantoic origin were found in the fetus or yolk sac. Hence, vasculogenesis seems to be independent of erythropoiesis in the allantois and to involve a distal-to-proximal gradient in differentiation of allantoic mesoderm into the endothelial cell lineage. Furthermore, this gradient is established earlier than reported previously, being present at the neural plate stage.
Drosophila engrailed can substitute for mouse Engrailed1 function in mid-hindbrain, but not limb development
Authors: Hanks Mark C. , Loomis Cynthia A. , Harris Esther , Tong Chung-Xiang , Anson-Cartwright Lynn , Auerbach Anna , Joyner Alexandra 
Published: April 2021

ABSTRACT
The Engrailed-1 gene, En1, a murine homologue of the Drosophila homeobox gene engrailed (en), is required for midbrain and cerebellum development and dorsal/ventral patterning of the limbs. In Drosophila, en is involved in regulating a number of key patterning processes including segmentation of the epidermis. An important question is whether, during evolution, the biochemical properties of En proteins have been conserved, revealing a common underlying molecular mechanism to their diverse developmental activities. To address this question, we have replaced the coding sequences of En1 with Drosophila en. Mice expressing Drosophila en in place of En1 have a near complete rescue of the lethal En1 mutant brain defect and most skeletal abnormalities. In contrast, expression of Drosophila en in the embryonic limbs of En1 mutants does not lead to repression of Wnt7a in the embryonic ventral ectoderm or full rescue of the embryonic dorsal/ventral patterning defects. Furthermore, neither En2 nor en rescue the postnatal limb abnormalities that develop in rare En1 null mutants that survive. These studies demonstrate that the biochemical activity utilized in mouse to mediate brain development has been retained by Engrailed proteins across the phyla, and indicate that during evolution vertebrate En proteins have acquired two unique functions during embryonic and postnatal limb development and that only En1 can function postnatally.
Requirement of the MADS-box transcription factor MEF2C for vascular development
Authors: Lin Qing , Lu Jianrong , Yanagisawa Hiromi , Webb Robert , Lyons Gary E. , Richardson James A. , Olson Eric N. 
Published: April 2021

ABSTRACT
The embryonic vasculature develops from endothelial cells that form a primitive vascular plexus which recruits smooth muscle cells to form the arterial and venous systems. The MADS-box transcription factor MEF2C is expressed in developing endothelial cells and smooth muscle cells (SMCs), as well as in surrounding mesenchyme, during embryogenesis. Targeted deletion of the mouse MEF2C gene resulted in severe vascular abnormalities and lethality in homozygous mutants by embryonic day 9.5. Endothelial cells were present and were able to differentiate, but failed to organize normally into a vascular plexus, and smooth muscle cells did not differentiate in MEF2C mutant embryos. These vascular defects resemble those in mice lacking the vascular-specific endothelial cell growth factor VEGF or its receptor Flt-1, both of which are expressed in MEF2C mutant embryos. These results reveal multiple roles for MEF2C in vascular development and suggest that MEF2-dependent target genes mediate endothelial cell organization and SMC differentiation.
Equivalence in the genetic control of hindbrain segmentation in fish and mouse
Authors: Moens C. B. , Cordes S. P. , Giorgianni M. W. , Barsh G. S. , Kimmel C. B. 
Published: April 2021

ABSTRACT
The vertebrate hindbrain is subdivided into a series of rhombomeres whose segmental organization serves to pattern the architecture and innervation of the developing head. The zebrafish gene valentino is required cell-autonomously in the development of rhombomeres 5 and 6, and valentino mutants lack visible hindbrain segmentation caudal to the r3/4 boundary (Moens, C. B., Yan, Y.-L., Appel, B., Force, A. G., and Kimmel, C. B. (1996) Development 122, 3981-3990). Here we show that valentino is the zebrafish homologue of the mouse segmentation gene kreisler, which encodes a bZip transcription factor. The valentino gene is expressed in a manner consistent with its proposed role in subdividing rhombomeres 5 and 6 from their common precursor ‘proto-segment’ in the presumptive hindbrain, a process that we also demonstrate is reflected in the normal order of appearance of rhombomere boundaries. As well as having similar phenotypes with respect to visible hindbrain segmentation and patterns of marker gene expression, valentino and kreisler mutants have similar pharyngeal arch and inner ear defects, consistent with a conserved role for this gene in hindbrain segmentation and in patterning of the head periphery.
Zebrafish hox genes: genomic organization and modified colinear expression patterns in the trunk
Authors: Prince Victoria E. , Joly Lucille , Ekker Marc , Ho Robert K. 
Published: April 2021

ABSTRACT
The Hox genes are implicated in conferring regional identity to the anteroposterior axis of the developing embryo. We have characterized the organization and expression of hox genes in the teleost zebrafish (Danio rerio), and compared our findings with those made for the tetrapod vertebrates. We have isolated 32 zebrafish hox genes, primarily via 3′RACE-PCR, and analyzed their linkage relationships using somatic cell hybrids. We find that in comparison to the tetrapods, zebrafish has several additional hox genes, both within and beyond the expected 4 hox clusters (A-D). For example, we have isolated a member of hox paralogue group 8 lying on the hoxa cluster, and a member of hox paralogue group 10 lying on the b cluster, no equivalent genes have been reported for mouse or human. Beyond the 4 clusters (A-D) we have isolated a further 3 hox genes (the hoxx and y genes), which according to their sequence homologies lie in paralogue groups 4, 6, and 9. The hoxx4 and hoxx9 genes occur on the same set of hybrid chromosomes, hinting at the possibility of an additional hox cluster for the zebrafish.
Similar to their tetrapod counterparts, zebrafish hox genes (including those with no direct tetrapod equivalent) demonstrate colinear expression along the anteroposterior (AP) axis of the embryo. However, in comparison to the tetrapods, anterior hox expression limits are compacted over a short AP region; some members of adjacent paralogue groups have equivalent limits. It has been proposed that during vertebrate evolution, the anterior limits of Hox gene expression have become dispersed along the AP axis allowing the genes to take on novel patterning roles and thus leading to increased axial complexity. In the teleost zebrafish, axial organization is relatively simple in comparison to that of the tetrapod vertebrates; this may be reflected by the less dispersed expression domains of the zebrafish hox genes.
XBMPRII, a novel Xenopus type II receptor mediating BMP signaling in embryonic tissues
Authors: Frisch Amanda , Wright Christopher V. E. 
Published: April 2021

ABSTRACT
Bone Morphogenetic Proteins (BMPs) are potent regulators of embryonic cell fate that are presumed to initiate signal transduction in recipient cells through multimeric, transmembrane, serine/threonine kinase complexes made up of type I and type II receptors. BMPRII was identified previously in mammals as the only type II receptor that binds BMPs, but not activin or TGFβ? in vitro. We report the cloning and functional analysis in vivo of its Xenopus homolog, XBMPRII. XBMPRII is expressed maternally and zygotically in an initially unrestricted manner. Strikingly, XBMPRII transcripts then become restricted to the mesodermal precursors during gastrulation. Expression is lower in the dorsal organizer region, potentially providing a mechanism to suppress the actions of BMP4 on dorsally fated tissues. Similar to the results seen for a truncated type I BMP receptor (tBR), a dominant-negative form of XBMPRII (tBRII) can dorsalize ventral mesoderm, induce extensive secondary body axes, block mesoderm induction by BMP4 and directly neuralize ectoderm, strongly suggesting that XBMPRII mediates BMP signals in vivo. However, although both tBRII and tBR can induce partial secondary axes, marker analysis shows that tBRII-induced axes are more anteriorly extended. Additionally, coinjection of tBRII and tBR synergistically increases the incidence of secondary axis formation.
A truncated activin type II receptor (ΔXAR1) is knownto block both activin and BMP signaling in vivo. Here we show that such crossreactivity does not occur for tBRII, in that it does not affect activin signaling. Furthermore, our studies indicate that the full-length activin type II receptor (XAR1) overcomes a block in BMP4 signaling imposed by tBRII, implicating XAR1 as a common component of BMP and activin signaling pathways in vivo. These data implicate XBMPRII as a type II receptor with high selectivity for BMP signaling, and therefore as a critical mediator of the effects of BMPs as mesodermal patterning agents and suppressors of neural fate during embryogenesis.
Xenopus Zic-related-1 and Sox-2, two factors induced by chordin, have distinct activities in the initiation of neural induction
Authors: Mizuseki Kenji , Kishi Masashi , Matsui Masaru , Nakanishi Shigetada , Sasai Yoshiki 
Published: April 2021

ABSTRACT
In a differential screen for downstream genes of the neural inducers, we identified two extremely early neural genes induced by Chordin and suppressed by BMP-4: Zic-related-1 (Zic-r1), a zinc finger factor related to the Drosophila pair-rule gene odd-paired, and Sox-2, a Sry-related HMG factor. Expression of the two genes is first detected widely in the prospective neuroectoderm at the beginning of gastrulation, following the onset of Chordin expression and preceding that of Neurogenin (Xngnr-1). Zic-r1 mRNA injection activates the proneural gene Xngnr-1, and initiates neural and neuronal differentiation in isolated animal caps and in vivo. In contrast, Sox-2 alone is not sufficient to cause neural differentiation, but can work synergistically with FGF signaling to initiate neural induction. Thus, Zic-r1 acts in the pathway bridging the neural inducer with the downstream proneural genes, while Sox-2 makes the ectoderm responsive to extracellular signals, demonstrating that the early phase of neural induction involves simultaneous activation of multiple functions.
Inner ear and maternal reproductive defects in mice lacking the Hmx3 homeobox gene
Authors: Wang Weidong , Water Thomas Van De , Lufkin Thomas 
Published: April 2021

ABSTRACT
The Hmx homeobox gene family is of ancient origin, being present in species as diverse as Drosophila, sea urchin and mammals. The three members of the murine Hmx family, designated Hmx1, Hmx2 and Hmx3, are expressed in tissues that suggest a common functional role in sensory organ development and pregnancy. Hmx3 is one of the earliest markers for vestibular inner ear development during embryogenesis, and is also upregulated in the myometrium of the uterus during pregnancy. Targeted disruption of the Hmx3 gene results in mice with abnormal circling behavior and severe vestibular defects owing to a depletion of sensory cells in the saccule and utricle, and a complete loss of the horizontal semicircular canal crista, as well as a fusion of the utricle and saccule endolymphatic spaces into a common utriculosaccular cavity. Both the sensory and secretory epithelium of the cochlear duct appear normal in the Hmx3 null animals. The majority of Hmx3 null females have a reproductive defect. Hmx3 null females can be fertilized and their embryos undergo normal preimplantation development, but the embryos fail to implant successfully in the Hmx3 null uterus and subsequently die. Transfer of preimplantation embryos from mutant Hmx3 uterine horns to wild-type pseudopregnant females results in successful pregnancy, indicating a failure of the Hmx3 null uterus to support normal post-implantation pregnancy. Molecular analysis revealed the perturbation of Hmx, Wnt and LIF gene expression in the Hmx3 null uterus. Interestingly, expression of both Hmx1 and Hmx2 is downregulated in the Hmx3 null uterus, suggesting a hierarchical relationship among the three Hmx genes during pregnancy.