bluuebunny/crossref_metadata_2025_split huggingface dataset:
Functional analysis of Wingless reveals a link between intercellular ligand transport and dorsal-cell-specific signaling
Authors: Dierick Herman A. , Bejsovec Amy 
Published: April 2021

ABSTRACT
The Drosophila segment polarity gene wingless (wg) is essential for cell fate decisions in the developing embryonic epidermis. Wg protein is produced in one row of cells near the posterior of every segment and is secreted and distributed throughout the segment to generate wild-type pattern elements. Ventrally, epidermal cells secrete a diverse array of anterior denticle types and a posterior expanse of naked cuticle; dorsally, a stereotyped pattern of fine hairs is secreted. We describe three new wg alleles that promote naked cuticle cell fate but show reduced denticle diversity and dorsal patterning. These mutations cause single amino acid substitutions in a cluster of residues that are highly conserved throughout the Wnt family. By manipulating expression of transgenic proteins, we demonstrate that all three mutant molecules retain the intrinsic capacity to signal ventrally but fail to be distributed across the segment. Thus, movement of Wg protein through the epidermal epithelium is essential for proper ventral denticle specification and this planar movement is distinct from the apical-basal transcytosis previously described in polarized epithelia. Furthermore, ectopic overexpression of the mutant proteins fails to rescue dorsal pattern elements. Thus we have identified a region of Wingless that is required for both the transcytotic process and signal transduction in dorsal cell populations, revealing an unexpected link between these two aspects of Wg function.
Caenorhabditis elegans lin-25: cellular focus, protein expression and requirement for sur-2 during induction of vulval fates
Authors: Nilsson Lars , Li Xiajun , Tiensuu Teresa , Auty Roy , Greenwald Iva , Tuck Simon 
Published: April 2021

ABSTRACT
Induction of vulval fates in the C. elegans hermaphrodite is mediated by a signal transduction pathway involving Ras and MAP kinase. Previous genetic analysis has suggested that two potential targets of this pathway in the vulva precursor cells are two novel proteins, LIN-25 and SUR-2. In this report, we describe further studies of lin-25. The results of a genetic mosaic analysis together with those of experiments in which lin-25 was expressed under the control of an heterologous promoter suggest that the major focus of lin-25 during vulva induction is the vulva precursor cells themselves. We have generated antisera to LIN-25 and used these to analyse the pattern of protein expression. LIN-25 is present in all six precursor cells prior to and during vulva induction but later becomes restricted to cells of the vulval lineages. Mutations in genes in the Ras/MAP kinase pathway do not affect the pattern of expression but the accumulation of LIN-25 is reduced in the absence of sur-2. Overexpression of LIN-25 does not rescue sur-2 mutant defects suggesting that LIN-25 and SUR-2 may function together. LIN-25 is also expressed in the lateral hypodermis. Overexpression of LIN-25 disrupts lateral hypodermal cell fusion, suggesting that lin-25 may play a role in regulating cell fusions in C. elegans.
pos-1 encodes a cytoplasmic zinc-finger protein essential for germline specification in C. elegans
Authors: Tabara Hiroaki , Hill Russell J. , Mello Craig C. , Priess James R. , Kohara Yuji 
Published: April 2021

ABSTRACT
Germ cells arise during early C. elegans embryogenesis from an invariant sequence of asymmetric divisions that separate germ cell precursors from somatic precursors. We show that maternal-effect lethal mutations in the gene pos-1 cause germ cell precursors to inappropriately adopt somatic cell fates. During early embryogenesis, pos-1 mRNA and POS-1 protein are present predominantly in the germ precursors. POS-1 is a novel protein with two copies of a CCCH finger motif previously described in the germline proteins PIE-1 and MEX-1 in C. elegans, and in the mammalian TIS11/Nup475/TTP protein. However, mutations in pos-1 cause several defects in the development of the germline blastomeres that are distinct from those caused by mutations in pie-1 or mex-1. The earliest defect detected in pos-1 mutants is the failure to express APX-1 protein from maternally provided apx-1 mRNA, suggesting that POS-1 may have an important role in regulating the expression of maternal mRNAs in germline blastomeres.
Control of early cardiac-specific transcription of Nkx2-5 by a GATA-dependent enhancer
Authors: Lien Ching-Ling , Wu Chuanzhen , Mercer Brian , Webb Robert , Richardson James A. , Olson Eric N. 
Published: April 2021

ABSTRACT
The homeobox gene Nkx2-5 is the earliest known marker of the cardiac lineage in vertebrate embryos. Nkx2-5 expression is first detected in mesodermal cells specified to form heart at embryonic day 7.5 in the mouse and expression is maintained throughout the developing and adult heart. In addition to the heart, Nkx2-5 is transiently expressed in the developing pharynx, thyroid and stomach. To investigate the mechanisms that initiate cardiac transcription during embryogenesis, we analyzed the Nkx2-5 upstream region for regulatory elements sufficient to direct expression of a lacZ transgene in the developing heart of transgenic mice. We describe a cardiac enhancer, located about 9 kilobases upstream of the Nkx2-5 gene, that fully recapitulates the expression pattern of the endogenous gene in cardiogenic precursor cells from the onset of cardiac lineage specification and throughout the linear and looping heart tube. Thereafter, as the atrial and ventricular chambers become demarcated, enhancer activity becomes restricted to the developing right ventricle. Transcription of Nkx2-5 in pharynx, thyroid and stomach is controlled by regulatory elements separable from the cardiac enhancer. This distal cardiac enhancer contains a high-affinity binding site for the cardiac-restricted zinc finger transcription factor GATA4 that is essential for transcriptional activity. These results reveal a novel GATA-dependent mechanism for activation of Nkx2-5 transcription in the developing heart and indicate that regulation of Nkx2-5 is controlled in a modular manner, with multiple regulatory regions responding to distinct transcriptional networks in different compartments of the developing heart.
Comparison of early nerve cord development in insects and vertebrates
Authors: Arendt Detlev , Nübler-Jung Katharina 
Published: April 2021

ABSTRACT
It is widely held that the insect and vertebrate CNS evolved independently. This view is now challenged by the concept of dorsoventral axis inversion, which holds that ventral in insects corresponds to dorsal in vertebrates. Here, insect and vertebrate CNS development is compared involving embryological and molecular data. In insects and vertebrates, neurons differentiate towards the body cavity. At early stages of neurogenesis, neural progenitor cells are arranged in three longitudinal columns on either side of the midline, and NK-2/NK-2.2, ind/Gsh and msh/Msx homologs specify the medial, intermediate and lateral columns, respectively. Other pairs of regional specification genes are, however, expressed in transverse stripes in insects, and in longitudinal stripes in the vertebrates.
There are differences in the regional distribution of cell types in the developing neuroectoderm. However, within a given neurogenic column in insects and vertebrates some of the emerging cell types are remarkably similar and may thus be phylogenetically old: NK-2/NK-2.2-expressing medial column neuroblasts give rise to interneurons that pioneer the medial longitudinal fascicles, and to motoneurons that exit via lateral nerve roots to then project peripherally. Lateral column neuroblasts produce, among other cell types, nerve rootglia and peripheral glia. Midline precursors give rise to glial cells that enwrap outgrowing commissural axons. The midline glia also express netrin homologs to attract commissural axons from a distance.
Expression of ptc and gli genes in talpid
3 suggests bifurcation in Shh pathway*
Authors: Lewis K. E. , Drossopoulou G. , Paton I. R. , Morrice D. R. , Robertson K. E. , Burt D. W. , Ingham P. W. , Tickle C. 
Published: April 2021

ABSTRACT
talpid 3 is an embryonic-lethal chicken mutation in a molecularly un-characterised autosomal gene. The recessive, pleiotropic phenotype includes polydactylous limbs with morphologically similar digits. Previous analysis established that hox-D and bmp genes, that are normally expressed posteriorly in the limb bud in response to a localised, posterior source of Sonic Hedgehog (Shh) are expressed symmetrically across the entire anteroposterior axis in talpid3 limb buds. In contrast, Shh expression itself is unaffected. Here we examine expression of patched (ptc), which encodes a component of the Shh receptor, and is probably itself a direct target of Shh signalling, to establish whether talpid3 acts in the Shh pathway. We find that ptc expression is significantly reduced in talpid3 embryos. We also demonstrate that talpid3 function is not required for Shh signal production but is required for normal response to Shh signals, implicating talpid3 in transduction of Shh signals in responding cells. Our analysis of expression of putative components of the Shh pathway, gli1, gli3 and coupTFII shows that genes regulated by Shh are either ectopically expressed or no longer responsive to Shh signals in talpid3 limbs, suggesting possible bifurcation in the Shh pathway. We also describe genetic mapping of gli1, ptc, shh and smoothened in chickens and confirm by co-segregation analysis that none of these genes correspond to talpid3.
The type I serine/threonine kinase receptor ActRIA (ALK2) is required for gastrulation of the mouse embryo
Authors: Gu Zhenyu , Reynolds Ellen M. , Song Jihwan , Lei Hong , Feijen Alie , Yu Lian , He Weiwu , MacLaughlin David T. , Raaij Janny van den Eijnden-van , Donahoe Patricia K. , Li En 
Published: April 2021

ABSTRACT
ActRIA (or ALK2), one of the type I receptors of the transforming growth factor-β (TGF-β) superfamily, can bind both activin and bone morphogenetic proteins (BMPs) in conjunction with the activin and BMP type II receptors, respectively. In mice, ActRIA is expressed primarily in the extraembryonic visceral endoderm before gastrulation and later in both embryonic and extraembryonic cells during gastrulation. To elucidate its function in mouse development, we disrupted the transmembrane domain of ActRIA by gene targeting. We showed that embryos homozygous for the mutation were arrested at the early gastrulation stage, displaying abnormal visceral endoderm morphology and severe disruption of mesoderm formation. To determine in which germ layer ActRIA functions during gastrulation, we performed reciprocal chimera analyses. (1) Homozygous mutant ES cells injected into wild-type blastocysts were able to contribute to all three definitive germ layers in chimeric embryos. However, a high contribution of mutant ES cells in chimeras disrupted normal development at the early somite stage. (2) Consistent with ActRIA expression in the extraembryonic cells, wild-type ES cells failed to rescue the gastrulation defect in chimeras in which the extraembryonic ectoderm and visceral endoderm were derived from homozygous mutant blastocysts. Furthermore, expression of HNF4, a key visceral endoderm-specific transcription regulatory factor, was significantly reduced in the mutant embryos. Together, our results indicate that ActRIA in extraembryonic cells plays a major role in early gastrulation, whereas ActRIA function is also required in embryonic tissues during later development in mice.
Regulation of the spalt/spalt-related gene complex and its function during sensory organ development in the Drosophila thorax
Authors: de Celis José F. , Barrio Rosa , Kafatos Fotis C. 
Published: April 2021

ABSTRACT
The nuclear proteins Spalt and Spalt-related belong to a conserved family of transcriptional regulators characterised by the presence of double zinc-finger domains. In the wing, they are regulated by the secreted protein Decapentaplegic and participate in the positioning of the wing veins. Here, we identify regulatory regions in the spalt/spalt-related gene complex that direct expression in the wing disc. The regulatory sequences are organised in independent modules, each of them responsible for expression in particular domains of the wing imaginal disc. In the thorax, spalt and spalt-related are expressed in a restricted domain that includes most proneural clusters of the developing sensory organs in the notum, and are regulated by the signalling molecules Wingless, Decapentaplegic and Hedgehog. We find that spalt/spalt-related participate in the development of sensory organs in the thorax, mainly in the positioning of specific proneural clusters. Later, the expression of at least spalt is eliminated from the sensory organ precursor cells and this is a requisite for the differentiation of these cells. We postulate that spalt and spalt-related belong to a category of transcriptional regulators that subdivide the thorax into expression domains (prepattern) required for the localised activation of proneural genes.
Patterning mechanisms in the body trunk and the appendages of Drosophila
Authors: Morata Ginés , Sánchez-Herrero Ernesto 
Published: April 2021

ABSTRACT
During evolution, many animal groups have developed specialised outgrowths of the body wall, limbs or appendages. The type of appendage depends on the identity of the segment where they appear, indicating that the Hox genes contribute to appendage specification. Moreover, work carried out principally in Drosophila has identified the gene products and the mechanisms involved in pattern formation in the appendages. In this essay, we compare the morphogenetic processes in the appendages and the body wall; the function of the Hox genes and the response to the signalling molecules involved in local patterning. We speculate that, although the basic mechanisms are similar, there are significant differences in the manner the body trunk and appendages respond to them.
Mesonephric cell migration induces testis cord formation and Sertoli cell differentiation in the mammalian gonad
Authors: Tilmann Christopher , Capel Blanche 
Published: April 2021

ABSTRACT
In mammals a single gene on the Y chromosome, Sry, controls testis formation. One of the earliest effects of Sry expression is the induction of somatic cell migration from the mesonephros into the XY gonad. Here we show that mesonephric cells are required for cord formation and male-specific gene expression in XY gonads in a stage- specific manner. Culturing XX gonads with an XY gonad at their surface, as a ‘sandwich’, resulted in cell migration into the XX tissue. Analysis of sandwich gonads revealed that in the presence of migrating cells, XX gonads organized cord structures and acquired male-specific gene expression patterns. From these results, we conclude that mesonephric cell migration plays a critical role in the formation of testis cords and the differentiation of XY versus XX cell types.
Xenopus nodal-related signaling is essential for mesendodermal patterning during early embryogenesis
Authors: Osada Shin-Ichi , Wright Christopher V. E. 
Published: April 2021

ABSTRACT
Previously, we showed that Xenopus nodal-related factors (Xnrs) can act as mesoderm inducers, and that activin induces Xnr transcription, suggesting that Xnrs relay or maintain induction processes initiated by activin-like molecules. We used a dominant negative cleavage mutant Xnr2 (cmXnr2) to carry out loss-of-function experiments to explore the requirement for Xnr signaling in early amphibian embryogenesis, and the relationship between activin and Xnrs. cmXnr2 blocked mesoderm induction caused by Xnr, but not activin, RNA. In contrast, cmXnr2 did suppress mesoderm and endoderm induction by activin protein, while Xnr transcript induction was unaffected by cmXnr2, consistent with an interference with the function of Xnr peptides that were induced by activin protein treatment. The severe hyperdorsalization and gastrulation defects caused by Xnr2 in whole embryos were rescued by cmXnr2, establishing a specific antagonistic relationship between the normal and cleavage mutant proteins. Expression of cmXnr2 resulted in delayed dorsal lip formation and a range of anterior truncations that were associated with delayed and suppressed expression of markers for dorsoanterior endoderm, in which the recently recognized head organizer activity resides. Reciprocally, Xnr2 induced dorsoanterior endodermal markers, such as cerberus, Xhex-1 and Frzb, in animal cap ectoderm. The migratory behavior of head mesendoderm explanted from cmXnr2 RNA-injected embryos was drastically reduced. These results indicate that Xnrs play crucial roles in initiating gastrulation, probably by acting downstream of an activin-like signaling pathway that leads to dorsal mesendodermal specification, including setting up the head organizer.
Direct action of the Nodal-related signal Cyclops in induction of sonic hedgehog in the ventral midline of the CNS
Authors: Müller Ferenc , Albert Stephanie , Blader Patrick , Fischer Nadine , Hallonet Marc , Strähle Uwe 
Published: April 2021

ABSTRACT
The secreted molecule Sonic hedgehog (Shh) is crucial for floor plate and ventral brain development in amniote embryos. In zebrafish, mutations in cyclops (cyc), a gene that encodes a distinct signal related to the TGFβ family member Nodal, result in neural tube defects similar to those of shh null mice. cyc mutant embryos display cyclopia and lack floor plate and ventral brain regions, suggesting a role for Cyc in specification of these structures. cyc mutants express shh in the notochord but lack expression of shh in the ventral brain. Here we show that Cyc signalling can act directly on shh expression in neural tissue. Modulation of the Cyc signalling pathway by constitutive activation or inhibition of Smad2 leads to altered shh expression in zebrafish embryos. Ectopic activation of the shh promoter occurs in response to expression of Cyc signal transducers in the chick neural tube. Furthermore an enhancer of the shh gene, which controls ventral neural tube expression, is responsive to Cyc signal transducers. Our data imply that the Nodal related signal Cyc induces shh expression in the ventral neural tube. Based on the differential responsiveness of shh and other neural tube specific genes to Hedgehog and Cyc signalling, a two-step model for the establishment of the ventral midline of the CNS is proposed.
Distribution of polarizing activity and potential for limb formation in mouse and chick embryos and possible relationships to polydactyly
Authors: Tanaka Mikiko , Cohn Martin J. , Ashby Peter , Davey Megan , Martin Paul , Tickle Cheryll 
Published: April 2021

ABSTRACT
A central feature of the tetrapod body plan is that two pairs of limbs develop at specific positions along the head-to-tail axis. However, the potential to form limbs in chick embryos is more widespread. This could have implications for understanding the basis of limb abnormalities. Here we extend the analysis to mouse embryos and examine systematically the potential of tissues in different regions outside the limbs to contribute to limb structures. We show that the ability of ectoderm to form an apical ridge in response to FGF4 in both mouse and chick embryos exists throughout the flank as does ability of mesenchyme to provide a polarizing region signal. In addition, neck tissue has weak polarizing activity. We show, in chick embryos, that polarizing activity of tissues correlates with the ability either to express Shh or to induce Shh expression. We also show that cells from chick tail can give rise to limb structures. Taken together these observations suggest that naturally occurring polydactyly could involve recruitment of cells from regions adjacent to the limb buds. We show that cells from neck, flank and tail can migrate into limb buds in response to FGF4, which mimics extension of the apical ectodermal ridge. Furthermore, when we apply simultaneously a polarizing signal and a limb induction signal to early chick flank, this leads to limb duplications.
Positional cues specify and maintain aleurone cell fate in maize endosperm development
Authors: Becraft Philip W. , Asuncion-Crabb Yvonne 
Published: April 2021

ABSTRACT
A genetic analysis of maize aleurone development was conducted. Cell lineage was examined by simultaneously marking cells with C1 for anthocyanin pigmentation in the aleurone and wx1 for amylose synthesis in the starchy endosperm. The aleurone and starchy endosperm share a common lineage throughout development indicating that positional cues specify aleurone fate. Mutants in dek1 block aleurone formation at an early stage and cause peripheral endosperm cells to develop as starchy endosperm. Revertant sectors of a transposon-induced dek1 allele showed that peripheral endosperm cells remain competent to differentiate as aleurone cells until late in development. Ds-induced chromosome breakage was used to generate Dek1 loss-of-function sectors. Events occurring until late development caused aleurone cells to switch fate to starchy endosperm indicating that cell fate is not fixed. Thus, positional cues are required to specify and maintain aleurone fate and Dek1 function is required to respond to these cues. An analysis of additional mutants that disrupt aleurone differentiation suggests a hierarchy of gene functions to specify aleurone cell fate and then control aleurone differentiation. These mutants disrupt aleurone differentiation in reproducible patterns suggesting a relationship to endosperm pattern formation.
A GATA-dependent right ventricular enhancer controls dHAND transcription in the developing heart
Authors: McFadden David G. , Charité Jeroen , Richardson James A. , Srivastava Deepak , Firulli Anthony B. , Olson Eric N. 
Published: April 2021

ABSTRACT
Heart formation in vertebrates is believed to occur in a segmental fashion, with discreet populations of cardiac progenitors giving rise to different chambers of the heart. However, the mechanisms involved in specification of different chamber lineages are unclear. The basic helix-loop-helix transcription factor dHAND is expressed in cardiac precursors throughout the cardiac crescent and the linear heart tube, before becoming restricted to the right ventricular chamber at the onset of looping morphogenesis. dHAND is also expressed in the branchial arch neural crest, which contributes to craniofacial structures and the aortic arch arteries. Using a series of dHAND-lacZ reporter genes in transgenic mice, we show that cardiac and neural crest expression of dHAND are controlled by separate upstream enhancers and we describe a composite cardiac-specific enhancer that directs lacZ expression in a pattern that mimics that of the endogenous dHAND gene throughout heart development. Deletion analysis reduced this enhancer to a 1.5 kb region and identified subregions responsible for expression in the right ventricle and cardiac outflow tract. Comparison of mouse regulatory elements required for right ventricular expression to the human dHAND upstream sequence revealed two conserved consensus sites for binding of GATA transcription factors. Mutation of these sites abolished transgene expression in the right ventricle, identifying dHAND as a direct transcriptional target of GATA factors during right ventricle development. Since GATA factors are not chamber-restricted, these findings suggest the existence of positive and/or negative coregulators that cooperate with GATA factors to control right ventricular-specific gene expression in the developing heart.