bluuebunny/crossref_metadata_2025_split huggingface dataset:
Segmental expression of Hoxa-2 in the hindbrain is directly regulated by Krox-20
Authors: Nonchev Stefan , Vesque Christine , Maconochie Mark , Seitanidou Tania , Ariza-McNaughton Linda , Frain Monique , Marshall Heather , Sham Mai Har , Krumlauf Robb , Charnay Patrick 
Published: April 2021

ABSTRACT
The hindbrain is a segmented structure divided into repeating metameric units termed rhombomeres (r). The Hox family, vertebrate homologs of the Drosophila HOM-C homeotic selector genes, are expressed in rhombomere-restricted patterns and are believed to participate in regulating segmental identities. Krox-20, a zinc finger gene, has a highly conserved pattern of expression in r3 and r5 and is functionally required for their maintenance in mouse embryos. Krox-20 has been shown to directly regulate the Hoxb-2 gene and we wanted to determine if it was involved in regulating multiple Hox genes as a part of its functional role. Hoxa-2 is the only known paralog of Hoxb-2, and we examined the patterns of expression of the mouse Hoxa-2 gene with particular focus on r3 and r5 in wild type and Krox-20−/− mutant embryos. There was a clear loss of expression in r3, which indicated that Hoxa-2 was downstream of Krox-20. Using transgenic analysis with E. coli lacZ reporter genes we have identified and mapped an r3/r5 enhancer in the 5′ flanking region of the Hoxa-2 gene. Deletion analysis narrowed this region to an 809 bp BglII fragment, and in vitro binding and competition assays with bacterially expressed Krox-20 protein identified two sites within the enhancer. Mutation of these Krox-20 sites in the regulatory region specifically abolished r3/r5 activity, but did not affect neural crest and mesodermal components. This indicated that the two Krox-20 sites are required in vivo for enhancer function. Furthermore, ectopic expression of Krox-20 in r4 was able to transactivate the Hoxa-2/lacZ reporter in this rhombomere. Together our findings suggest that Krox-20 directly participates in the transcriptional regulation of Hoxa-2 during hindbrain segmentation, and is responsible for the upregulation of the r3 and r5 domains of expression of both vertebrate group 2 Hox paralogs. Therefore, the segmental phenotypes in the Krox-20 mutants are likely to reflect the role of Krox-20 in directly regulating multiple Hox genes.
REGA-1 is a GPI-linked member of the immunoglobulin superfamily present on restricted regions of sheath cell processes in grasshopper
Authors: Seaver Elaine C. , Carpenter Ellen M. , Bastiani Michael J. 
Published: April 2021

ABSTRACT
REGA-1 is a glycoprotein localized to sheath cell processes in the developing CNS when NBs are producing progeny and neurons are maturing and extending processes. It is also present on a subset of muscles and on the lumenal surface of the ectoderm in the embryonic appendages when pioneer neurons are growing into the CNS. REGA-1 is associated with the extracellular side of the cell membrane by a glycosyl-phosphatidylinositol linkage. We have identified a cDNA clone encoding REGA-1 using a sequence from purified protein. Sequence analysis defines REGA-1 as a novel member of the immunoglobulin superfamily containing three immunoglobulin domains and one fibronectin type III repeat. Each Ig domain has distinct sequence characteristics that suggest discrete functions. REGA-1 is similar to other Ig superfamily members involved in cell adhesion events and neurite outgrowth.
Autonomous and nonautonomous Notch functions for embryonic muscle and epidermis development in Drosophila
Authors: Baker Rob , Schubiger Gerold 
Published: April 2021

ABSTRACT
The Notch (N) gene encodes a cell signaling protein that mediates neuronal and epidermal determination in Drosophila embryos. N also regulates several aspects of myogenic development; embryos lacking N function have too many muscle founder cells and fail to properly differentiate somatic muscle. To identify cell-autonomous requirements for Notch function during muscle development, we expressed a Notch minigene in the mesoderm, but not in the ectoderm, of amorphic N− embryos. In these embryos, muscle founder hypertrophy is rescued, indicating that Notch is autonomously required by mesoderm cells to regulate the proper number of muscle founders. However, somatic muscle differentiation is only partially normalized, suggesting that Notch is also required in the ectoderm for proper muscle development.
Additionally, mesodermal expression of Notch partially rescues epidermal development in overlying neurogenic ectoderm. This is unexpected, since previous studies suggest that Notch is autonomously required by proneural ectoderm cells for epidermal development. Mesodermal expression of a truncated Notch protein lacking the extracellular domain does not rescue ventral epidermis, suggesting that the extracellular domain of Notch can non-autonomously rescue epidermal development across germ layers.
An extracellular matrix molecule that is selectively expressed during development is important for gastrulation in the sea urchin embryo
Authors: Berg Linnea K. , Chen Siming W. , Wessel Gary M. 
Published: April 2021

ABSTRACT
The extracellular matrix is important in the regulation of many cellular events of early development including migration, shape change, proliferation and gene expression. In the sea urchin embryo, disruption of the extracellular matrix results in selective defects in each of these events during gastrulation. Here we describe a new molecule of the extracellular matrix in Lytechinus variegatus, referred to as ECM 18, that has several important features. First, antibody interference of ECM 18 results in a profound but reversible inhibition of primary mesenchyme cell organization and endoderm morphogenesis during gastrulation. Second, during gastrulation, ECM 18 mRNA accumulates to highest levels in the invaginating endoderm and the ECM 18 protein is deposited in the basal lamina surrounding the archenteron as well as in other areas of the blastocoel wall. Immunolocalization by fluorescence and electron microscopy demonstrates the selective accumulation of ECM 18 in the extracellular matrix. Third, although the mRNA encoding ECM 18 is present throughout development, the protein accumulates only during gastrulation. ECM 18 protein is not detected in eggs or early embryos and analysis of polysome-associated mRNA suggests that at least part of the translational regulation of ECM 18 is at the level of ECM 18 mRNA-polysome formation. Finally, sequence analysis of ECM 18 shows that the protein contains a repeat sequence with a conserved cysteine motif, suggestive of involvement in proteinprotein interactions. Thus, ECM 18 appears to be important in mediating select morphogenetic changes during gastrulation and the pattern of its expression in the embryo is unique among the extracellular matrix molecules known in this embryo.
The Caenorhabditis elegans LIN-26 protein is required to specify and/or maintain all non-neuronal ectodermal cell fates
Authors: Labouesse Michel , Hartwieg Erika , Horvitz H. Robert 
Published: April 2021

ABSTRACT
The C. elegans gene lin-26, which encodes a presumptive zinc-finger transcription factor, is required for hypodermal cells to acquire their proper fates. Here we show that lin26 is expressed not only in all hypodermal cells but also in all glial-like cells. During asymmetric cell divisions that generate a neuronal cell and a non-neuronal cell, LIN-26 protein is symmetrically segregated and then lost from the neuronal cell. Expression in glial-like cells (socket and sheath cells) is biologically important, as some of these neuronal support cells die or seem sometimes to be transformed to neuron-like cells in embryos homozygous for strong loss-of-function mutations. In addition, most of these glial-like cells are structurally and functionally defective in animals carrying the weak loss-of-function mutation lin-26(n156). lin-26 mutant phenotypes and expression patterns together suggest that lin-26 is required to specify and/or maintain the fates not only of hypodermal cells but also of all other non-neuronal ectodermal cells in C. elegans. We speculate that lin-26 acts by repressing the expression of neuronal-specific genes in non-neuronal cells.
Genetic analysis of Laminin A in Drosophila: extracellular matrix containing laminin A is required for ocellar axon pathfinding
Authors: García-Alonso Luis , Fetter Richard D. , Goodman Corey S. 
Published: April 2021

ABSTRACT
Genetic analysis of the Laminin A (LamA) gene in Drosophila reveals that distinct classes of sensory axons have different requirements for extracellular matrix (ECM) containing laminin A versus epithelial cell surfaces. In the eye-antenna imaginal disc, the nerve from the three simple eyes (ocelli) to the brain is pioneered by a population of transient ocellar neurons whose axons extend on an ECM that covers and connects the disc epithelium and brain. Axons from neighboring mechanosensory (bristle) neurons extend under the ECM in direct contact with the surface of the disc cells, and pioneer a different axon pathway that enters the brain in a different location. In LamA mutants, the ocellar pioneer axons display striking pathfinding defects, while neighboring bristle axons appear normal; the ocellar pioneers usually extend in the proper direction, adhering to the epithelium and sometimes fasciculating with mechanosensory axons, but they invariably fail to reach the brain.
Evidence in the mouse for self-renewing stem cells in the formation of a segmented longitudinal structure, the myotome
Authors: Nicolas J. F. , Mathis L. , Bonnerot C. 
Published: April 2021

ABSTRACT
A novel method of clonal analysis has been used in the mouse to define the cellular events that lead to the formation of a segmented longitudinal structure, the myotome. Progenitor cells of the myotome were randomly marked during development by intragenic homologous recombination in transgenic mice expressing a reporter laacZ gene. 153 clones corresponding to 7829 cells, that is 20% of the myotomal population of one embryo, were obtained from 3000 E11.5 embryos. Their analysis leads to the hypothesis that, at E11.5, the 41 segments of the myotome have been mainly produced from a unique, spatially organised pool of self-renewing stem cells that accompanies the formation of the anterior-posterior axis.
Switching the in vivo specificity of a minimal Hox-responsive element
Authors: Chan Siu-Kwong , Ryoo Hyung-Don , Gould Alex , Krumlauf Robb , Mann Richard S. 
Published: April 2021

ABSTRACT
The homeodomain proteins encoded by the Hox complex genes do not bind DNA with high specificity. In vitro, Hox specificity can be increased by binding to DNA cooperatively with the homeodomain protein extradenticle or its vertebrate homologs, the pbx proteins (together, the PBC family). Here we show that a two basepair change in a Hox-PBC binding site switches the Hox-dependent expression pattern generated in vivo, from labial to Deformed. The change in vivo correlates with an altered Hox binding specificity in vitro. Further, we identify similar Deformed-PBC binding sites in the Deformed and Hoxb-4 genes and show that they generate Deformed or Hoxb-4 expression patterns in Drosophila and mouse embryos, respectively. These results suggest a model in which Hox-PBC binding sites play an instructive role in Hox specificity by promoting the formation of different Hox-PBC heterodimers in vivo. Thus, the choice of Hox partner, and therefore Hox target genes, depends on subtle differences between Hox-PBC binding sites.
The C. elegans gene pag-3 is homologous to the zinc finger proto-oncogene gfi-1
Authors: Jia Yiwen , Xie Guofeng , McDermott Joan B. , Aamodt Eric 
Published: April 2021

ABSTRACT
Mutations in the Caenorhabditis elegans gene pag-3 result in misexpression of touch receptor-specific genes in the BDU interneurons and in motility defects. We cloned pag-3 and found that the gene encodes a C2H2-type zinc finger protein related to the mammalian GFI-1 protein. Sequencing of the three pag-3 alleles showed that two apparent null alleles encode a nonsense mutation before the zinc fingers and a missense mutation in the fourth zinc finger that changes a coordinating histidine to a tyrosine. The third allele contains a nonsense mutation in the N-terminal region but is not a null allele. Northern analysis showed that a single pag-3 transcript of about 1.6 kb is present in embryos and L1, L2 and L3 larvae. pag-3 message levels were about twofold higher in pag-3 mutants than in wildtype animals, which suggested that pag-3 may negatively regulate its own expression. pag-3lacZ fusion genes were expressed in the BDU interneurons, the touch neurons, 11 VA and 11 VB ventral cord motor neurons, two AVF interneurons and in unidentified neurons of the retrovesicular ganglion. The BDU neurons and the ALM touch neurons are lineal sister cells in the AB.a lineage and the VA and VB motor neurons are lineal sister cells in the AB.p lineage. The VA motor neurons are required for backward movement and the VB motor neurons are required for forward movement. Mosaic analysis showed that the wildtype pag-3 gene is required in the AB.p lineage for coordinated movement and in the AB.a lineage to suppress touch neuron gene expression in the BDU neurons. Because pag-3 is expressed in both the BDU neurons and in the touch neurons, another protein(s) not expressed in the touch neurons may interact with pag-3 to repress touch neuron gene expression in the BDU neurons. Alternatively, another protein in the touch receptor cells may inactivate PAG-3 and allow expression of the touch receptor program. These results show that pag-3 is a temporally regulated gene that is expressed early in development and functions in multiple types of neurons. They also strongly suggest that the PAG-3 protein is a DNA-binding protein with properties similar to the mammalian proto-oncogene product GFI-1.
Xmsx-1 modifies mesodermal tissue pattern along dorsoventral axis in Xenopus laevis embryo
Authors: Maeda Ryu , Kobayashi Ako , Sekine Ryo , Lin Jih-Jing , Kung Hsiang-fu , Maéno Mitsugu 
Published: April 2021

ABSTRACT
This study analyzes the expression and the function of Xenopus msx-1(Xmsx-1) in embryos, in relation to the ventralizing activity of bone morphogenetic protein-4 (BMP-4). Expression of Xmsx-1was increased in UV-treated ventralized embryos and decreased in LiCl-treated dorsalized embryos at the neurula stage (stage 14). Whole-mount in situ hybridization analysis showed that Xmsx-1is expressed in marginal zone and animal pole areas, laterally and ventrally, but not dorsally, at mid-gastrula (stage 11) and late-gastrula (stage 13) stages. Injection of BMP-4 RNA, but not activin RNA, induced Xmsx-1 expression in the dorsal marginal zone at the early gastrula stage (stage 10+), and introduction of a dominant negative form of BMP-4 receptor RNA suppressed Xmsx-1expression in animal cap and ventral marginal zone explants at stage 14. Thus, Xmsx-1 is a target gene specifically regulated by BMP-4 signaling. Embryos injected with Xmsx-1 RNA in dorsal blastomeres at the 4-cell stage exhibited a ventralized phenotype, with microcephaly and swollen abdomen. Histological observation and immunostaining revealed that these embryos had a large block of muscle tissue in the dorsal mesodermal area instead of notochord. On the basis of molecular marker analysis, however, the injection of Xmsx-1RNA did not induce the expression of α-globin, nor reduce cardiac α-actin in dorsal marginal zone explants. Furthermore, a significant amount of α-actin was induced and α-globin was turned off in the ventral marginal zone explants injected with Xmsx-1. These results indicated that Xmsx-1 is a target gene of BMP-4 signaling, but possesses a distinct activity on dorsal-ventral patterning of mesodermal tissues.
A role for Siamois in Spemann organizer formation
Authors: Fan Melinda J. , Sokol Sergei Y. 
Published: April 2021

ABSTRACT
The vertebrate body plan is specified in the early embryo through the inductive influence of the organizer, a special region that forms on the dorsalmost side of the embryo at the beginning of gastrulation. In Xenopus, the homeobox gene Siamois is activated prior to gastrulation in the area of organizer activity and is capable of inducing a secondary body axis when ectopically expressed. To elucidate the function of endogeneous Siamois in dorsoventral axis formation, we made a dominant repressor construct (SE) in which the Siamois homeodomain was fused to an active repression domain of Drosophila engrailed. Overexpression of 1-5 pg of this chimeric mRNA in the early embryo blocks axis development and inhibits activation of dorsal, but not ventrolateral, marginal zone markers. At similar expression levels, SE proteins with altered DNA-binding specificity do not have the same effect. Coexpression of mRNA encoding wild-type Siamois, but not a mutated Siamois, restores dorsal development to SE embryos. Furthermore, SE strongly blocks axis formation triggered by β-catenin but not by the organizer product noggin. These results suggest that Siamois function is essential for β-catenin-mediated formation of the Spemann organizer, and that Siamois acts prior to noggin in specifying dorsal development.
Limb proprioceptive deficits without neuronal loss in transgenic mice overexpressing neurotrophin-3 in the developing nervous system
Authors: Ringstedt Thomas , Kucera Jan , Lendahl Urban , Ernfors Patrik , Ibáñez Carlos F. 
Published: April 2021

ABSTRACT
The role of neurotrophin-3 (NT3) during sensory neuron development was investigated in transgenic mice overex-pressing NT3 under the control of the promoter and enhancer regions of the nestin gene, an intermediate filament gene widely expressed in the developing nervous system. Most of these mice died during the first postnatal day, and all showed severe limb ataxia suggestive of limb propriocep-tive dysfunction. Tracing and histological analyses revealed a complete loss of spindles in limb muscles, absence of peripheral and central Ia projections, and lack of cells immunoreactive to parvalbumin in the dorsal root ganglion (DRG). Despite these deficits, there was no neuronal loss in the DRG of these mice. At birth, transgenic DRG showed increased neuron numbers, and displayed a normal propor-tion of neurons expressing substance P, calcitonin gene-related peptide and the NT3 receptor trkC. Transgenic dorsal roots exhibited an increased number of axons at birth, indicating that all sensory neurons in transgenic mice projected to the dorsal spinal cord. Despite the absence of central Ia afferents reaching motorneurons, several sensory fibers were seen projecting towards ectopic high levels of NT3 in the midline of transgenic spinal cords. These findings suggest novel roles for NT3 in differentiation of propriocep-tive neurons, target invasion and formation of Ia projections which are independent from its effects on neuronal survival.
Regulation of cone cell formation by Canoe and Ras in the developing Drosophila eye
Authors: Matsuo Takashi , Takahashi Kuniaki , Kondo Shunzo , Kaibuchi Kozo , Yamamoto Daisuke 
Published: April 2021

ABSTRACT
Cone cells are lens-secreting cells in ommatidia, the unit eyes that compose the compound eye of Drosophila. Each ommatidium contains four cone cells derived from precursor cells of the R7 equivalence group which express the gene sevenless (sev). When a constitutively active form of Ras1 (Ras1V12) is expressed in the R7 equivalence group cells using the sev promoter (sev-Ras1V12), additional cone cells are formed in the ommatidium. Expression of Ras1N17, a dominant negative form of Ras1, results in the formation of 1-3 fewer cone cells than normal in the ommatidium. The effects of Ras1 variants on cone cell formation are modulated by changing the gene dosage at the canoe (cno) locus, which encodes a cytoplasmic protein with Ras-binding activity. An increase or decrease in gene dosage potentiates the sevRas1V12 action, leading to marked induction of cone cells. A decrease in cno+ activity also enhances the sev-Ras1N17 action, resulting in a further decrease in the number of cone cells contained in the ommatidium. In the absence of expression of sev-Ras1V12 or sev-Ras1N17, an overdose of wild-type cno (cno+) promotes cone cell formation while a significant reduction in cno+ activity results in the formation of 1-3 fewer cone cells than normal in the ommatidium. We propose that there are two signaling pathways in cone cell development, one for its promotion and the other for its repression, and Cno functions as a negative regulator for both pathways. We also postulate that Cno predominantly acts on a prevailing pathway in a given developmental context, thereby resulting in either an increase or a decrease in the number of cone cells per ommatidium. The extra cone cells resulting from the interplay of Ras1V12 and Cno are generated from a pool of undifferentiated cells that are normally fated to develop into pigment cells or undergo apoptosis.
The PDGFα receptor is required for neural crest cell development and for normal patterning of the somites
Authors: Soriano Philippe 
Published: April 2021

ABSTRACT
Platelet-derived growth factors (PDGFs) have been implicated in the control of cell proliferation, survival and migration. Patch mutant mice harbor a deletion including the PDGFα receptor gene and exhibit defects of neural crest origin which affect pigmentation in heterozygotes and cranial bones in homozygotes. To verify the role of the PDGFαR gene during development, mice carrying a targeted null mutation were generated. No pigmentation phenotype was observed in heterozygotes. Homozygotes die during embryonic development and exhibit incomplete cephalic closure similar to that observed in a subset of Patch mutants. In addition, increased apoptosis was observed on pathways followed by migrating neural crest cells. However, alterations in mutant vertebrae, ribs and sternum were also observed, which appear to stem from a deficiency in myotome formation. These results indicate that PDGFs may exert their functions during early embryogenesis by affecting cell survival and patterning.