bluuebunny/crossref_metadata_2025_split huggingface dataset:
The activity of Neurogenin1 is controlled by local cues in the zebrafish embryo
Authors: Blader Patrick , Fischer Nadine , Gradwohl Gerard , Guillemot François , Strähle Uwe 
Published: April 2021

ABSTRACT
Zebrafish neurogenin1 encodes a basic helix-loop-helix protein which shares structural and functional characteristics with proneural genes of Drosophila melanogaster. neurogenin1 is expressed in the early neural plate in domains comprising more cells than the primary neurons known to develop from these regions and its expression is modulated by Delta/Notch signalling, suggesting that it is a target of lateral inhibition. Misexpression of neurogenin1 in the embryo results in development of ectopic neurons. Markers for different neuronal subtypes are not ectopically expressed in the same patterns in neurogenin1-injected embryos suggesting that the final identity of the ectopically induced neurons is modulated by local cues. Induction of ectopic motor neurons by neurogenin1 requires coexpression of a dominant negative regulatory subunit of protein kinase A, an intracellular transducer of hedgehog signals. Moreover, the pattern of endogenous neurogenin1 expression in the neural plate is expanded in response to elevated levels of Hedgehog (Hh) signalling or abolished as a result of inhibition of Hh signalling. Together these data suggest that Hh signals regulate neurogenin1 expression and subsequently modulate the type of neurons produced by Neurogenin1 activity.
HSP70-2 is required for desynapsis of synaptonemal complexes during meiotic prophase in juvenile and adult mouse spermatocytes
Authors: Dix David J. , Allen James W. , Collins Barbara W. , Poorman-Allen Patricia , Mori Chisato , Blizard Deborah R. , Brown Paula R. , Goulding Eugenia H. , Strong Bradley D. , Eddy E. M. 
Published: April 2021

ABSTRACT
Spermatogenic cells synthesize a unique 70-kDa heat shock protein (HSP70-2) during prophase of meiosis I, and targeted disruption of the Hsp70-2 gene has shown that this protein is required for spermatogenic cell differentiation in adult mice. HSP70-2 is associated with synaptonemal complexes formed between paired homologous chromosomes during meiotic prophase. The present study focuses on the nearly synchronous first wave of spermatogenesis in 12-to 28-day old juvenile mice to determine more precisely when HSP70-2 is required and what meiotic processes are affected by its absence. Spermatogenesis in homozygous mutant mice (Hsp70-2−/−) proceeded normally until day 15 when increasing numbers of pachytene spermatocytes became apoptotic and differentiation of cells beyond the pachytene stage began to falter. Synaptonemal complexes assembled in Hsp70-2−/− mice and spermatocytes developed through the final pachytene substage. However, synaptonemal complexes failed to desynapse and normal diplotene spermatocytes were not observed. Metaphase spermatocytes were not seen in tissue sections from testes of Hsp70-2−/− mice, and expression of mRNAs and antigens characteristic of late pachytene spermatocytes (e.g., cyclin A1) and development of spermatids did not occur. Thus, HSP70-2 is required for synaptonemal complex desynapsis, and its absence severely impairs the transition of spermatogenic cells through the late meiotic stages and results in apoptosis beginning with the first wave of germ cell development in juvenile mice.
Essential roles of the winged helix transcription factor MFH-1 in aortic arch patterning and skeletogenesis
Authors: Iida Kiyoshi , Koseki Haruhiko , Kakinuma Hideaki , Kato Naoko , Mizutani-Koseki Yoko , Ohuchi Hideyo , Yoshioka Hidefumi , Noji Sumihare , Kawamura Koichi , Kataoka Yuki , Ueno Fukuko , Taniguchi Masaru , Yoshida Nobuaki , Sugiyama Toshihiro , Miura Naoyuki 
Published: April 2021

ABSTRACT
Mesenchyme Fork Head-1 (MFH-1) is a forkhead (also called winged helix) transcription factor defined by a common 100-amino acid DNA-binding domain. MFH-1 is expressed in non-notochordal mesoderm in the prospective trunk region and in cephalic neural-crest and cephalic mesoderm-derived mesenchymal cells in the prechordal region of early embryos. Subsequently, strong expression is localized in developing cartilaginous tissues, kidney and dorsal aortas. To investigate the developmental roles of MFH-1 during embryogenesis, mice lacking the MFH-1 locus were generated by targeted mutagenesis. MFH-1-deficient mice died embryonically and perinatally, and exhibited interrupted aortic arch and skeletal defects in the neurocranium and the vertebral column. Interruption of the aortic arch seen in the mutant mice was the same as in human congenital anomalies. These results suggest that MFH-1 has indispensable roles during the extensive remodeling of the aortic arch in neural-crest-derived cells and in skeletogenesis in cells derived from the neural crest and the mesoderm.
Sizzled: a secreted Xwnt8 antagonist expressed in the ventral marginal zone of Xenopus embryos
Authors: Salic Adrian N. , Kroll Kristen L. , Esvans Louise M. , Kirschner Marc W. 
Published: April 2021

ABSTRACT
An expression cloning screen was used to isolate a novel gene homologous to the extracellular cysteine-rich domain of frizzled receptors. The gene (which we called sizzled for secreted frizzled) was shown to encode a soluble secreted protein, containing a functional signal sequence but no transmembrane domains. Sizzled (szl) is capable of inhibiting Xwnt8 as assayed by (1) dose-dependent inhibition of siamois induction by Xwnt8 in animal caps, (2) rescue of embryos ventralized by Xwnt8 DNA and (3) inhibition of XmyoD expression in the marginal zone. Szl can dorsalize Xenopus embryos if expressed after the midblastula transition, strengthening the idea that zygotic expression of wnts and in particular of Xwnt8 plays a role in antagonizing dorsal signals. It also suggests that inhibiting ventralizing wnts parallels the opposition of BMPs by noggin and chordin. szl expression is restricted to a narrow domain in the ventral marginal zone of gastrulating embryos. szl thus encodes a secreted antagonist of wnt signaling likely involved in inhibiting Xwnt8 and XmyoD ventrally and whose restricted expression represents a new element in the molecular pattern of the ventral marginal zone.
Role of Dlx-1 and Dlx-2 genes in patterning of the murine dentition
Authors: Thomas Bethan L. , Tucker Abigail S. , Qiu Mensheng , Ferguson Christine A. , Hardcastle Zoë , Rubenstein John L. R. , Sharpe Paul T. 
Published: April 2021

ABSTRACT
The molecular events of odontogenic induction are beginning to be elucidated, but until now nothing was known about the molecular basis of the patterning of the dentition. A role for Dlx-1 and Dlx-2 genes in patterning of the dentition has been proposed with the genes envisaged as participating in an ‘odontogenic homeobox gene code’ by specifying molar development. This proposal was based on the restricted expression of the genes in molar ectomesenchyme derived from cranial neural crest cells prior to tooth initiation.
Mice with targeted null mutations of both Dlx-1 and Dlx-2 homeobox genes do not develop maxillary molar teeth but incisors and mandibular molars are normal. We have carried out heterologous recombinations between mutant and wild-type maxillary epithelium and mesenchyme and show that the ectomesenchyme underlying the maxillary molar epithelium has lost its odontogenic potential. Using molecular markers of branchial arch neural crest (Barxl) and commitment to chondrogenic differentiation (Sox9), we show that this population alters its fate from odontogenic to become chondrogenic. These results provide evidence that a subpopulation of cranial neural crest is specified as odontogenic by Dlx-1 and Dlx-2 genes. Loss of function of these genes results in reprogramming of this population of ectomesenchyme cells into chondrocytes. This is the first indication that the development of different shaped teeth at different positions in the jaws is determined by independent genetic pathways.
Oocyte determination and the origin of polarity in Drosophila: the role of the spindle genes
Authors: González-Reyes Acaimo , Elliott Heather , Johnston Daniel St 
Published: April 2021

ABSTRACT
The two main body axes in Drosophila become polarised as a result of a series of symmetry-breaking steps during oogenesis. Two of the sixteen germline cells in each egg chamber develop as pro-oocytes, and the first asymmetry arises when one of these cells is selected to become the oocyte. Anterior-posterior polarity originates when the oocyte then comes to lie posterior to the nurse cells and signals through the Gurken/Egfr pathway to induce the adjacent follicle cells to adopt a posterior fate. This directs the movement of the germinal vesicle and associated gurken mRNA from the posterior to an anterior corner of the oocyte, where Gurken protein signals for a second time to induce the dorsal follicle cells, thereby polarising the dorsal-ventral axis. Here we describe a group of five genes, the spindle loci, which are required for each of these polarising events. spindle mutants inhibit the induction of both the posterior and dorsal follicle cells by disrupting the localisation and translation of gurken mRNA. Moreover, the oocyte often fails to reach the posterior of mutant egg chambers and differentiates abnormally. Finally, double mutants cause both pro-oocytes to develop as oocytes, by delaying the choice between these two cells. Thus, these mutants reveal a novel link between oocyte selection, oocyte positioning and axis formation in Drosophila, leading us to propose that the spindle genes act in a process that is common to several of these events.
CNS midline cells in Drosophila induce the differentiation of lateral neural cells
Authors: Menne Thomas V. , Lüer Karin , Technau Gerhard M. , Klambt Christian 
Published: April 2021

ABSTRACT
Cells located at the midline of the developing central nervous system perform a number of conserved functions during the establishment of the lateral CNS. The midline cells of the Drosophila CNS were previously shown to be required for correct pattern formation in the ventral ectoderm and for the induction of specific mesodermal cells. Here we investigated whether the midline cells are required for the correct development of lateral CNS cells as well. Embryos that lack midline cells through genetic ablation show a 15% reduction in the number of cortical CNS cells. A similar thinning of the ventral nerve cord can be observed following mechanical ablation of the midline cells. We have identified a number of specific neuronal and glial cell markers that are reduced in CNS midline-less embryos (in single-minded embryos, in early heat-shocked Notchts1 embryos or in embryos where we mechanically ablated the midline cells). Genetic data suggest that both neuronal and glial midline cell lineages are required for differentiation of lateral CNS cells. We could rescue the lateral CNS phenotype of single-minded mutant embryos by transplantation of midline cells as well as by homotopic expression of single-minded, the master gene for midline development. Furthermore, ectopic midline cells are able to induce enhanced expression of some lateral CNS cell markers. We thus conclude that the CNS midline plays an important role in the differentiation or maintenance of the lateral CNS cortex.
ErbB3 is required for normal cerebellar and cardiac development: a comparison with ErbB2- and heregulin-deficient mice
Authors: Erickson Sharon L. , O’Shea K. Sue , Ghaboosi Nazli , Loverro Linda , Frantz Gretchen , Bauer Michelle , Lu Lucy H. , Moore Mark W. 
Published: April 2021

ABSTRACT
Heregulins bind directly to ErbB3 and ErbB4 receptors, leading to multiple dimerization possibilities including heterodimerization with the ErbB2 receptor. We have generated ErbB3-, ErbB2- and heregulin-deficient mice to assess their roles in development and differentiation. Heregulin-- and ErbB2−/− embryos died on E10.5 due to a lack of cardiac ventricular myocyte differentiation; ErbB3-- embryos survived until E13.5 exhibiting cardiac cushion abnormalities leading to blood reflux through defective valves. In ErbB3−/− embryos, the midbrain/hindbrain region was strikingly affected, with little differentiation of the cerebellar plate. Cranial ganglia defects, while present in all three nulls, were less severe in ErbB3−/− embryos. The cranial ganglia defects, along with a dramatic reduction in Schwann cells, enteric ganglia and adrenal chromaffin cells, suggests a generalized effect on the neural crest. Numerous organs, including the stomach and pancreas also exhibited anomalous development.
Genetic characterization of the role of the two HOX proteins, Proboscipedia and Sex Combs Reduced, in determination of adult antennal, tarsal, maxillary palp and proboscis identities in Drosophila melanogaster
Authors: Percival-Smith Anthony , Weber Jennifer , Gilfoyle Elaine , Wilson Peggy 
Published: April 2021

ABSTRACT
Both Proboscipedia (PB) and Sex Combs Reduced (SCR) activities are required for determination of proboscis identity. Here we show that simultaneous removal of PB and SCR activity results in a proboscis-to-antenna transformation. Dominant negative PB molecules inhibit the activity of SCR indicating that PB and SCR interact in a multimeric protein complex in determination of proboscis identity. These data suggest that the expression pattern of PB and SCR and the ability of PB and SCR to interact in a multimeric complex control the determination of four adult structures. The absence of PB and SCR expression leads to antennal identity; expression of only PB leads to maxillary palp identity; expression of only SCR leads to tarsus identity; and expression of both PB and SCR, which results in the formation of a PB-SCR-containing complex, leads to proboscis identity.
However, the PB-SCR interaction is not detectable in vitro and is not detectable genetically in the head region during embryogenesis, indicating the PB-SCR interaction may be regulated and indirect. This regulation may also explain why ectopic expression of SCRQ50K and SCR do not result in the expected transformation of the maxillary palp to an antennae and proboscis, respectively.
Previous analysis of the requirements of SCR activity for adult pattern formation has shown that ectopic expression of SCR results in an antenna-to-tarsus transformation, but removal of SCR activity in a clone of cells does not result in a tarsus-to-arista transformation. Here we show in five independent assays the reason for this apparent contradictory requirement of SCR activity in tarsus determination. SCR activity is required cell nonautonomously for tarsus determination. Specifically, we propose that SCR activity is required in the mesodermal adepithelial cells of all leg imaginal discs at late second/early third instar larval stage for the synthesis of a mesoderm-specific, tarsus-inducing, signaling factor, which after secretion from the adepithelial cells acts on the overlaying ectodermal cells determining tarsus identity.
This study characterizes a combinatorial interaction between two HOX proteins; a mechanism that may have a major role in patterning the anterior-posterior axis of other animals.
Misexpression of chick Vg1 in the marginal zone induces primitive streak formation
Authors: Shah Shailan B. , Skromne Isaac , Hume Clifford R. , Kessler Daniel S. , Lee Kevin J. , Stern Claudio D. , Dodd Jane 
Published: April 2021

ABSTRACT
In the chick embryo, the primitive streak is the first axial structure to develop. The initiation of primitive streak formation in the posterior area pellucida is influenced by the adjacent posterior marginal zone (PMZ). We show here that chick Vgl (cVgl), a member of the TGFβ family of signalling molecules whose homolog in Xenopus is implicated in mesoderm induction, is expressed in the PMZ of prestreak embryos. Ectopic expression of cVg1 protein in the marginal zone chick blastoderms directs the formation of a secondary primitive streak, which subsequently develops into an ectopic embryo. We have used cell marking techniques to show that cells that contribute to the ectopic primitive streak change fate, acquiring two distinct properties of primitive streak cells, defined by gene expression and cell movements. Furthermore, naive epiblast explants exposed to cVg1 protein in vitro acquire axial mesodermal properties. Together, these results show that cVg1 can mediate ectopic axis formation in the chick by inducing new cell fates and they permit the analysis of distinct events that occur during primitive streak formation.
Vitronectin is expressed in the ventral region of the neural tube and promotes the differentiation of motor neurons
Authors: Martinez-Morales Juan R. , Barbas Julio A. , Marti Elisa , Bovolenta Paola , Edgar David , Rodriguez-Tébar Alfredo 
Published: April 2021

ABSTRACT
The extracellular matrix protein vitronectin and its mRNA are present in the embryonic chick notochord, floor plate and in the ventral neural tube at the time position of motor neuron generation. When added to cultures of neural tube explants of developmental stage 9, vitronectin promotes the generation of motor neurons in the absence of either notochord or exogenously added Sonic hedgehog. Conversely, the neutralisation of endogenous vitronectin with antibodies inhibits over 90% motor neuron differentiation in co-cultured neural tube/notochord explants, neural tube explants cultured in the presence of Sonic hedgehog, and in committed (stage 13) neural tube explants. Furthermore, treatment of embryos with anti-vitronectin antibodies results in a substantial and specific reduction in the number of motor neurons generated in vivo. These results demonstrate that vitronectin stimulates the differentiation of motor neurons in vitro and in vivo. Since the treatment of stage 9 neural tube explants with Sonic hedgehog resulted in induction of vitronectin mRNA expression before the expression of floor plate markers, we conclude that vitronectin may act either as a downstream effector in the signalling cascade induced by Sonic hedhehog, or as a synergistic factor that increases Shh-induced motor neuron differentiation.
Characterization of a notochord-specific enhancer from the Brachyury promoter region of the ascidian, Ciona intestinalis
Authors: Corbo Joseph C. , Levine Michael , Zeller Robert W. 
Published: April 2021

ABSTRACT
We present evidence that the embryo of the ascidian, Ciona intestinalis, is an easily manipulated system for investigating the establishment of basic chordate tissues and organs. Ciona has a small genome, and simple, well-defined embyronic lineages. Here, we examine the regulatory mechanisms underlying the differentiation of the notochord. Particular efforts center on the regulation of a notochord-specific Ciona Brachyury gene (Ci-Bra). An electroporation method was devised for the efficient incorporation of transgenic DNA into Ciona embryos. This method permitted the identification of a minimal, 434 bp enhancer from the Ci-Bra promoter region that mediates the notochord-restricted expression of both GFP and lacZ reporter genes. This enhancer contains a negative control region that excludes Ci-Bra expression from inappropriate embryonic lineages, including the trunk mesenchyme and tail muscles. Evidence is presented that the enhancer is activated by a regulatory element which is closely related to the recognition sequence of the Suppressor of Hairless transcription factor, thereby raising the possibility that the Notch signaling pathway plays a role in notochord differentiation. We discuss the implications of this analysis with regard to the evolutionary conservation of integrative enhancers, and the subdivision of the axial and paraxial mesoderm in vertebrates.
Phase change and the regulation of trichome distribution in Arabidopsis thaliana
Authors: Telfer Abby , Bollman Krista M. , Poethig R. Scott 
Published: April 2021

ABSTRACT
Higher plants pass through several phases of shoot growth during which they may produce morphologically distinct vegetative structures. In Arabidopsis thaliana this phenomenon is apparent in the distribution of trichomes on the leaf surface. Leaves produced early in rosette development lack trichomes on their abaxial (lower) surface, leaves produced later have trichomes on both surfaces, and leaves in the inflorescence (bracts) may have few or no trichomes on their adaxial (upper) surface. Here we describe some of the factors that regulate this distribution pattern. We found that the timing of abaxial trichome production and the extent to which bracts lack adaxial trichomes varies in different ecotypes. The production of abaxial trichomes appears to be regulated by the age, rather than the size of the plant. This conclusion is based on the observation that mutations that affect either the rate (altered meristem programming1) or onset (paused) of leaf initiation respectively increase or decrease the number of leaves that lack abaxial trichomes, but have only a minor effect on the time at which the first leaf with abaxial trichomes is produced. The production of abaxial trichomes is coordinated with the reproductive development of the shoot as this trait is delayed by photoperiodic conditions and some mutations that delay flowering. The loss of adaxial trichomes is likely to be a consequence of floral induction, and is accelerated by terminal flower1-10, a mutation that accelerates inflorescence development. We demonstrate that gibberellins promote trichome production in Arabidopsis and present evidence indicating that abaxial trichome production is regulated by both the level of a trichome inducer and the competence of the abaxial epidermis to respond to this inducer.
Development of the Drosophila olfactory sense organs utilizes cell-cell interactions as well as lineage
Authors: Reddy G. Venugopala , Gupta Bhagwati , Ray Krishanu , Rodrigues Veronica 
Published: April 2021

ABSTRACT
We have examined the mechanisms underlying the development of the olfactory sense organs on the third segment of the antenna of Drosophila. Our studies suggest that a novel developmental strategy is employed. Specification of the founder or precursor cell is not governed by the genes of the achaete-scute complex. Another basic helix-loop-helix encoding gene, atonal, is essential for determination of only a subset of the sensilla types – the sensilla coel-oconica. Therefore, we predict the existence of additional proneural genes for the selection of sensilla trichoidea and sensilla basiconica. The choice of a founder cell from the presumed proneural domain is regulated by Notch activity. Soon after delamination of the founder cell, two to three additional neighboring cells also take on a sensory fate and these cells together form a presensillum cluster. The selection of neighbors does not occur when endocytosis is blocked using a temperature sensitive allele of shibire, thus suggesting that cell-cell communication is required for this step. The cells of the cluster divide once before terminal differentiation which is influenced by Notch activity. The final cell number within each sensillum is controlled by programmed cell death.