bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of postembryonic G1 cell cycle progression in Caenorhabditis elegans by a cyclin D/CDK-like complex
Authors: Park Morgan , Krause Michael W. 
Published: April 2021

Abstract
In many organisms, initiation and progression through the G1 phase of the cell cycle requires the activity of G1-specific cyclins (cyclin D and cyclin E) and their associated cyclin-dependent kinases (CDK2, CDK4, CDK6). We show here that the Caenorhabditis elegans genes cyd-1 and cdk-4, encoding proteins similar to cyclin D and its cognate cyclin-dependent kinases, respectively, are necessary for proper division of postembryonic blast cells. Animals deficient for cyd-1 and/or cdk-4 activity have behavioral and developmental defects that result from the inability of the postembryonic blast cells to escape G1 cell cycle arrest. Moreover, ectopic expression of cyd-1 and cdk-4 in transgenic animals is sufficient to activate a S-phase reporter gene. We observe no embryonic defects associated with depletion of either of these two gene products, suggesting that their essential functions are restricted to postembryonic development. We propose that the cyd-1 and cdk-4 gene products are an integral part of the developmental control of larval cell proliferation through the regulation of G1 progression.
Anteroposterior patterning of the epidermis by inductive influences from the vegetal hemisphere cells in the ascidian embryo
Authors: Wada Shuichi , Katsuyama You , Saiga Hidetoshi 
Published: April 2021

Abstract
Patterning along the anteroposterior axis is a critical step during animal embryogenesis. Although mechanisms of anteroposterior patterning in the neural tube have been studied in various chordates, little is known about those of the epidermis. To approach this issue, we investigated patterning mechanisms of the epidermis in the ascidian embryo. First we examined expression of homeobox genes (Hrdll-1, Hroth, HrHox-1 and Hrcad) in the epidermis. Hrdll-1 is expressed in the anterior tip of the epidermis that later forms the adhesive papillae, while Hroth is expressed in the anterior part of the trunk epidermis. HrHox-1 and Hrcad are expressed in middle and posterior parts of the epidermis, respectively. These data suggested that the epidermis of the ascidian embryo is patterned anteroposteriorly.
In ascidian embryogenesis, the epidermis is exclusively derived from animal hemisphere cells. To investigate regulation of expression of the four homeobox genes in the epidermis by vegetal hemisphere cells, we next performed hemisphere isolation and cell ablation experiments. We showed that removal of the vegetal cells before the late 16- cell stage results in loss of expression of these homeobox genes in the animal hemisphere cells. Expression of Hrdll-1 and Hroth depends on contact with the anterior-vegetal (the A-line) cells, while expression of HrHox-1 and Hrcad requires contact with the posterior-vegetal (the B-line) cells. We also demonstrated that contact with the vegetal cells until the late 32-cell stage is sufficient for animal cells to express Hrdll-1, Hroth and Hrcad, while longer contact is necessary for HrHox-1 expression. Contact with the A-line cells until the late 32-cell stage is also sufficient for formation of the adhesive papillae.
Our data indicate that the epidermis of the ascidian embryo is patterned along the anteroposterior axis by multiple inductive influences from the vegetal hemisphere cells and provide the first insight into mechanisms of epidermis patterning in the chordate embryos.
Anterior patterning by synergistic activity of the early gastrula organizer and the anterior germ layer tissues of the mouse embryo
Authors: Tam Patrick P. L. , Steiner Kirsten A. 
Published: April 2021

Abstract
Fragments of the germ layer tissues isolated from the early-primitive-streak (early-streak) stage mouse embryos were tested for axis induction activity by transplantation to late-gastrula (late-streak to early-bud) stage host embryos. The posterior epiblast fragment that contains the early gastrula organizer was able to recruit the host tissues to form an ectopic axis. However, the most anterior neural gene that was expressed in the ectopic axis was Krox20 that marks parts of the hindbrain, but markers of the mid-and forebrain (Otx2 and En1) were not expressed. Anterior visceral endoderm or the anterior epiblast alone did not induce any ectopic neural tissue. However, when these two anterior germ layer tissues were transplanted together, they can induce the formation of ectopic host-derived neural tissues but these tissues rarely expressed anterior neural genes and did not show any organization of an ectopic axis. Therefore, although the anterior endoderm and epiblast together may display some inductive activity, they do not act like a classical organizer. Induction of the anterior neural genes in the ectopic axis was achieved only when a combination of the posterior epiblast fragment, anterior visceral endoderm and the anterior epiblast was transplanted to the host embryo. The formation of anterior neural structures therefore requires the synergistic interaction of the early gastrula organizer and anterior germ layer tissues.
Mutations in the Rho1 small GTPase disrupt morphogenesis and segmentation during early Drosophila development
Authors: Magie Craig R. , Meyer Michael R. , Gorsuch Michael S. , Parkhurst Susan M. 
Published: April 2021

Abstract
Rho GTPases play an important role in diverse biological processes such as actin cytoskeleton organization, gene transcription, cell cycle progression and adhesion. They are required during early Drosophila development for proper execution of morphogenetic movements of individual cells and groups of cells important for the formation of the embryonic body plan. We isolated loss-of-function mutations in the Drosophila Rho1 (Rho1) gene during a genetic screen for maternal-effect mutations, allowing us to investigate the specific roles Rho1 plays in the context of the developing organism. Here we report that Rho1 is required for many early events: loss of Rho1 function results in both maternal and embryonic phenotypes. Embryos homozygous for the Rho1 mutation exhibit a characteristic zygotic phenotype, which includes severe defects in head involution and imperfect dorsal closure. Two phenotypes are associated with reduction of maternal Rho1 activity: the actin cytoskeleton is disrupted in egg chambers, especially in the ring canals and embryos display patterning defects as a result of improper maintenance of segmentation gene expression. Despite showing imperfect dorsal closure, Rho1 does not activate downstream genes or interact genetically with members of the JNK signaling pathway, used by its relatives dRac and dCdc42 for proper dorsal closure. Consistent with its roles in regulating actin cytoskeletal organization, we find that Rho1 interacts genetically and physically with the Drosophila formin homologue, cappuccino. We also show that Rho1 interacts both genetically and physically with concertina, a Gα protein involved in cell shape changes during gastrulation.
spen encodes an RNP motif protein that interacts with Hox pathways to repress the development of head-like sclerites in the Drosophila trunk
Authors: Wiellette Elizabeth L. , Harding Katherine W. , Mace Kimberly A. , Ronshaugen Matthew R. , Wang Fawn Y. , McGinnis William 
Published: April 2021

Abstract
Drosophila has eight Hox proteins, and they require factors acting in parallel to regulate different segmental morphologies. Here we find that the Drosophila gene split ends (spen), has a homeotic mutant phenotype, and appears to encode such a parallel factor. Our results indicate that spen plays two important segment identity roles. One is to promote sclerite development in the head region, in parallel with Hox genes; the other is to cooperate with Antennapedia and teashirt to suppress head-like sclerite development in the thorax. Our results also indicate that without spen and teashirt functions, Antennapedia loses its ability to specify thoracic identity in the epidermis. spen transcripts encode extraordinarily large protein isoforms (approx. 5,500 amino acids), which are concentrated in embryonic nuclei. Both Spen protein isoforms and Spen-like proteins in other animals possess a clustered repeat of three RNP (or RRM) domains, as well as a conserved motif of 165 amino acids (SPOC domain) at their C-termini. Spen is the only known homeotic protein with RNP binding motifs, which indicates that splicing, transport, or other RNA regulatory steps are involved in the diversification of segmental morphology. Previous studies by Dickson and others (Dickson, B. J., Van Der Straten, A., Dominguez, M. and Hafen, E. (1996). Genetics 142, 163-171) identified spen as a gene that acts downstream of Raf to suppress Raf signaling in a manner similar to the ETS transcription factor Aop/Yan. This raises the intriguing possibility that the Spen RNP protein might integrate signals from both the Raf and Hox pathways.
Recombination and disjunction in female germ cells of Drosophila depend on the germline activity of the gene Sex-lethal
Authors: Bopp Daniel , Schütt Corina , Puro Jaakko , Huang He , Nöthiger Rolf 
Published: April 2021

Abstract
Gametogenesis in males and females differs in many ways. An important difference in Drosophila is that recombination between homologous chromosomes occurs only in female meiosis. Here, we report that this process relies on the correct functioning of Sex-lethal (Sxl) which is primarily known as the master gene in somatic sex determination. Certain alleles of this gene (Sxlfs) disrupt the germline, but not the somatic function of Sxl and cause an arrest of germ cell development during cystocyte proliferation. Using dominant suppressor mutations that relieve this early block in Sxlfs mutant females, we discovered additional requirements of Sxl for normal meiotic differentiation of the oocyte. Females mutant for Sxlfs and carrying a suppressor become fertile, but pairing of homologous chromosomes and formation of chiasmata is severely perturbed, resulting in an almost complete lack of recombinants and a high incidence of non-disjunction events. Similar results were obtained when germline expression of wild-type Sxl was compromised by mutations in virilizer (vir), a positive regulator of Sxl. Ectopic expression of a Sxl transgene in premeiotic stages of male germline development, on the other hand, is not sufficient to allow recombination to take place, which suggests that Sxl does not have a discriminatory role in this female-specific process. We propose that Sxl performs at least two tasks in oogenesis: an ‘early’ function in formation of the egg chamber, and a ‘late’ function in progression of the meiotic cell cycle, suggesting that both events are coordinated by a common mechanism.
A role for PS integrins in morphological growth and synaptic function at the postembryonic neuromuscular junction of Drosophila
Authors: Beumer Kelly J. , Rohrbough Jeffrey , Prokop Andreas , Broadie Kendal 
Published: April 2021

Abstract
A family of three position-specific (PS) integrins are expressed at the Drosophila neuromuscular junction (NMJ): a beta subunit (βPS), expressed in both presynaptic and postsynaptic membranes, and two alpha subunits (αPS1, αPS2), expressed at least in the postsynaptic membrane. PS integrins appear at postembryonic NMJs coincident with the onset of rapid morphological growth and terminal type-specific differentiation, and are restricted to type I synaptic boutons, which mediate fast, excitatory glutamatergic transmission. We show that two distinctive hypomorphic mutant alleles of the β subunit gene myospheroid (mysb9 and mysts1), differentially affect βPS protein expression at the synapse to produce distinctive alterations in NMJ branching, bouton formation, synaptic architecture and the specificity of synapse formation on target cells. The mysb9 mutation alters βPS localization to cause a striking reduction in NMJ branching, bouton size/number and the formation of aberrant ‘mini-boutons’, which may represent a developmentally arrested state. The mysts1 mutation strongly reduces βPS expression to cause the opposite phenotype of excessive synaptic sprouting and morphological growth. NMJ function in these mutant conditions is altered in line with the severity of the morphological aberrations. Consistent with these mutant phenotypes, transgenic overexpression of the βPS protein with a heat-shock construct or tissue-specific GAL4 drivers causes a reduction in synaptic branching and bouton number. We conclude that βPS integrin at the postembryonic NMJ is a critical determinant of morphological growth and synaptic specificity. These data provide the first genetic evidence for a functional role of integrins at the postembryonic synapse.
Mash1regulates neurogenesis in the ventral telencephalon
Authors: Casarosa Simona , Fode Carol , Guillemot François 
Published: April 2021

ABSTRACTPrevious studies have shown that mice mutant for the gene Mash1 display severe neuronal losses in the olfactory epithelium and ganglia of the autonomic nervous system, demonstrating a role for Mash1 in development of neuronal lineages in the peripheral nervous system. Here, we have begun to analyse Mash1 function in the central nervous system, focusing our studies on the ventral telencephalon where it is expressed at high levels during neurogenesis. Mash1 mutant mice present a severe loss of progenitors, particularly of neuronal precursors in the subventricular zone of the medial ganglionic eminence. Discrete neuronal populations of the basal ganglia and cerebral cortex are subsequently missing. An analysis of candidate effectors of Mash1 function revealed that the Notch ligands Dll1 and Dll3, and the target of Notch signaling Hes5, fail to be expressed in Mash1 mutant ventral telencephalon. In the lateral ganglionic eminence, loss of Notch signaling activity correlates with premature expression of a number of subventricular zone markers by ventricular zone cells. Therefore, Mash1 is an important regulator of neurogenesis in the ventral telencephalon, where it is required both to specify neuronal precursors and to control the timing of their production.
Genetic evidence for cell death mediated by nerve growth factor and the neurotrophin receptor p75 in the developing mouse retina and spinal cord
Authors: MarÍa Frade José , Barde Yves-Alain 
Published: April 2021

Abstract
The role of nerve growth factor (NGF) and of the neurotrophin receptor p75 (p75NTR) in programmed cell death was investigated in the retina and the spinal cord of mouse embryos. Large numbers of cells express p75NTR in and along the developing optic nerve and in the mantle zone of the spinal cord. In embryos carrying deletions in the ngf or the p75NTR gene, cell death was reduced in the retina and in the spinal cord. Increased numbers of Islet-1-immunoreactive cells were detected in the dorsal spinal cord, and the mantle zone was enlarged in both mutants. These results indicate that NGF/p75NTR-dependent mechanisms are used to remove cells when axonal tracts elongate in developing neuroepithelia.
Stromal cells mediate retinoid-dependent functions essential for renal development
Authors: Mendelsohn Cathy , Batourina Ekatherina , Fung Suquin , Gilbert Thierry , Dodd Jane 
Published: April 2021

ABSTRACT
The essential role of vitamin A and its metabolites, retinoids, in kidney development has been demonstrated in vitamin A deficiency and gene targeting studies. Retinoids signal via nuclear transcription factors belonging to the retinoic acid receptor (RAR) and retinoid X receptor (RXR) families. Inactivation of RARα and RARβ2 receptors together, but not singly, resulted in renal malformations, suggesting that within a given renal cell type, their concerted function is required for renal morphogenesis. At birth, RARαβ2−mutants displayed small kidneys, containing few ureteric bud branches, reduced numbers of nephrons and lacking the nephrogenic zone where new nephrons are continuously added. These observations have prompted us to investigate the role of RARα and RARβ2 in renal development in detail. We have found that within the embryonic kidney, RARα and RARβ2 are colocalized in stromal cells, but not in other renal cell types, suggesting that stromal cells mediate retinoid-dependent functions essential for renal development. Analysis of RARαβ2− mutant kidneys at embryonic stages revealed that nephrons were formed and revealed no changes in the intensity or distribution of molecular markers specific for different metanephric mesenchymal cell types. In contrast the development of the collecting duct system was greatly impaired in RARαβ2− mutant kidneys. Fewer ureteric bud branches were present, and ureteric bud ends were positioned abnormally, at a distance from the renal capsule. Analysis of genes important for ureteric bud morphogenesis revealed that the proto-oncogene c-ret was downregulated. Our results suggest that RARα and RARβ2 are required for generating stromal cell signals that maintain c-ret expression in the embryonic kidney. Since c-ret signaling is required for ureteric bud morphogenesis, loss of c-ret expression is a likely cause of impaired ureteric bud branching in RARαβ2− mutants.
Shoot apical meristem and cotyledon formation during Arabidopsis embryogenesis: interaction among the CUP-SHAPED COTYLEDON and SHOOT MERISTEMLESS genes
Authors: Aida Mitsuhiro , Ishida Tetsuya , Tasaka Masao 
Published: April 2021

Abstract
The shoot apical meristem and cotyledons of higher plants are established during embryogenesis in the apex. Redundant CUP-SHAPED COTYLEDON 1 (CUC1) and CUC2 as well as SHOOT MERISTEMLESS (STM) of Arabidopsis are required for shoot apical meristem formation and cotyledon separation. To elucidate how the apical region of the embryo is established, we investigated genetic interactions among CUC1, CUC2 and STM, as well as the expression patterns of CUC2 and STM mRNA. Expression of these genes marked the incipient shoot apical meristem as well as the boundaries of cotyledon primordia, consistent with their roles for shoot apical meristem formation and cotyledon separation. Genetic and expression analyses indicate that CUC1 and CUC2 are redundantly required for expression of STM to form the shoot apical meristem, and that STM is required for proper spatial expression of CUC2 to separate cotyledons. A model for pattern formation in the apical region of the Arabidopsis embryo is presented.
Mouse primordial germ cells lacking β1 integrins enter the germline but fail to migrate normally to the gonads
Authors: Anderson Robert , Fässler Reinhard , Georges-Labouesse Elisabeth , Hynes Richard O. , Bader Bernhard L. , Kreidberg Jordan A. , Schaible Kyle , Heasman Janet , Wylie Christopher 
Published: April 2021

Abstract
Primordial germ cells are the founder cells of the gametes. They are set aside at the initial stages of gastrulation in mammals, become embedded in the hind-gut endoderm, then actively migrate to the sites of gonad formation. The molecular basis of this migration is poorly understood. Here we sought to determine if members of the integrin family of cell surface receptors are required for primordial germ cell migration, as integrins have been implicated in the migration of several other motile cell types. We have established a line of mice which express green fluorescent protein in germline cells that has enabled us to efficiently purify primordial germ cells at different stages by flow cytometry. We have catalogued the spectrum of integrin subunit expression by primordial germ cells during and after migration, using flow cytometry, immunocytochemistry and RT-PCR. Through analysis of integrin β1−/−→wild-type chimeras, we show that embryonic cells lacking β1 integrins can enter the germline. However, integrin β1−/− primordial germ cells do not colonize the gonad efficiently. Embryos with targeted deletion of integrin subunit α3, α6, or αV show no major defects in primordial germ cell migration. These results demonstrate a role for β1-containing integrins in the development of the germline, although an equivalent role for α integrin subunit(s) has yet to be established.
Mice lacking HSP90β fail to develop a placental labyrinth
Authors: Voss Anne K. , Thomas Tim , Gruss Peter 
Published: April 2021

ABSTRACT
The 90 kDa heat-shock proteins (HSP90s) play important roles during stress situations as general chaperones and under physiological conditions in the conformational activation of specific protein substrates. Vertebrates express two cytosolic HSP90s (HSP90α and HSP90β) ubiquitously. We have mutated the Hsp90β gene in murine embryonic stem cells and generated Hsp90β mutant mice. Heterozygous animals were phenotypically normal. Interestingly, homozygous embryos developed normally until embryonic day 9.0/9.5. Then, although Hsp90β is expressed ubiquitously, they exhibited phenotypic abnormalities restricted to the placenta. The mutant concepti failed to form a fetal placental labyrinth and died a day later. Fusion between the allantois and the chorionic plate occurred, allantoic blood vessels invaded the chorion, but then did not expand. Mutant trophoblast cells failed to differentiate into trilaminar labyrinthine trophoblast.
Despite conspicuous similarities between HSP90α and HSP90β at the molecular level, our data suggest that HSP90β has a key role in placenta development that cannot be performed by the endogenous HSP90α alone. Analysis of chimeric concepti consisting of mutant embryos and tetraploid embryos or ES cells revealed that wild-type allantois was able to induce mutant trophoblast to differentiate. In contrast, trophoblast wild type at the Hsp90β locus was unable to differentiate when in contact with mutant allantois. Therefore, the primary defect caused by the Hsp90β mutation resided in the allantois. The allantois mesoderm is thought to induce trophoblast differentiation. Our results show that Hsp90β is a necessary component of this induction process.
SHH-N upregulates Sfrp2 to mediate its competitive interaction with WNT1 and WNT4 in the somitic mesoderm
Authors: Lee Catherine S. , Buttitta Laura A. , May Noah R. , Kispert Andreas , Fan Chen-Ming 
Published: April 2021

ABSTRACT
Dorsoventral polarity of the somitic mesoderm is established by competitive signals originating from adjacent tissues. The ventrally located notochord provides the ventralizing signals to specify the sclerotome, while the dorsally located surface ectoderm and dorsal neural tube provide the dorsalizing signals to specify the dermomyotome. Noggin and SHH-N have been implicated as the ventralizing signals produced by the notochord. Members of the WNT family of proteins, on the other hand, have been implicated as the dorsalizing signals derived from the ectoderm and dorsal neural tube. When presomitic explants are confronted with cells secreting SHH-N and WNT1 simultaneously, competition to specify the sclerotome and dermomyotome domains within the naive mesoderm can be observed. Here, using these explant cultures, we provide evidence that SHH-N competes with WNT1, not only by upregulating its own receptor Ptc1, but also by upregulating Sfrp2 (Secreted frizzled-related protein 2), which encodes a potential WNT antagonist. Among the four known Sfrps, Sfrp2 is the only member expressed in the sclerotome and upregulated by SHH-N recombinant protein. We further show that SFRP2-expressing cells can reduce the dermomyotome-inducing activity of WNT1 and WNT4, but not that of WNT3a. Together, our results support the model that SHH-N at least in part employs SFRP2 to reduce WNT1/4 activity in the somitic mesoderm.