bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differential H4 acetylation of paternal and maternal chromatin precedes DNA replication and differential transcriptional activity in pronuclei of 1-cell mouse embryos
Authors: Adenot Pierre G. , Mercier Yvan , Renard Jean-Paul , Thompson Eric M. 
Published: April 2021

ABSTRACT
In the mouse embryo, transcriptional activation begins during S/G2 phase of the first cell cycle when paternal and maternal chromatin are still in separate nuclear entities within the same cytoplasm. At this time, the male pronucleus exhibits greater transcriptional activity than the female pronucleus. Since acetylation of histones in the nucleosome octamer exerts a regulatory influence on gene expression, we investigated changes in histone acetylation during the remodeling of paternal and maternal chromatin from sperm entry through to minor genome activation and mitosis. We found (1) neither mature sperm nor metaphase II maternal chromatin stained for hyperacetylated histone H4; (2) immediately following fertilization, hyperacetylated H4 was associated with paternal but not maternal chromatin while, in parthenogenetically activated oocytes, maternal chromatin became hyperacetylated; (3) in zygotes, differential levels and patterns of hyperacetylated H4 between male and female pronuclei persisted throughout most of G1 with histone deacetylases and acetyltransferases already active at this time; (4) when transcriptional differences are observed in S/G2, male and female pronuclei have equivalent levels of H4 hyperacetylation and DNA replication was not required to attain this equivalence and (5) in contrast to the lack of H4 hyperacetylation on gametic chromatin, chromosomes at the first mitosis showed distinct banding patterns of H4 hyperacetylation. These results suggest that sperm chromatin initially out-competes maternal chromatin for the pool of hyperacetylated H4 in the oocyte, that hyperacetylated H4 participates in the process of histone-protamine exchange in the zygote, and that differences in H4 acetylation in male and female pronuclei during G1 are translated across DNA replication to transcriptional differences in S/G2. Prior to fertilization, neither paternal nor maternal chromatin show memory of H4 hyperacetylation patterns but, by the end of the first cell cycle, before major zygotic genome activation at the 2-cell stage, chromosomes already show hyperacetylated H4 banding patterns.
Two copies of a subelement from the Vg1 RNA localization sequence are sufficient to direct vegetal localization in Xenopus oocytes
Authors: Gautreau Denise , Cote Colette A. , Mowry Kimberly L. 
Published: April 2021

ABSTRACT
Localization of mRNA has emerged as a fundamental mechanism for generating polarity during development. In vertebrates, one example of this phenomenon is Vg1 RNA, which is localized to the vegetal cortex of Xenopus oocytes. Vegetal localization of Vg1 RNA is directed by a 340-nt sequence element contained within its 3′ untranslated region. To investigate how such cis-acting elements function in the localization process, we have undertaken a detailed analysis of the precise sequence requirements for vegetal localization within the 340-nt localization element. We present evidence for considerable redundancy within the localization element and demonstrate that critical sequences lie at the ends of the element. Importantly, we show that a subelement from the 5′ end of the Vg1 localization element is, when duplicated, sufficient to direct vegetal localization. We suggest that the Vg1 localization element is composed of smaller, redundant sequence motifs and identify one such 6-nt motif as essential for localization. These results allow insight into what constitutes an RNA localization signal and how RNA sequence elements may act in the localization process.
Novel regulatory interactions revealed by studies of murine limb pattern in Wnt-7a and En-1 mutants
Authors: Cygan Jennifer A. , Johnson Randy L. , McMahon Andrew P. 
Published: April 2021

ABSTRACT
Classical embryological experiments have demonstrated that dorsal-ventral patterning of the vertebrate limb is dependent upon ectodermal signals. One such factor is Wnt-7a, a member of the Wnt family of secreted proteins, which is expressed in the dorsal ectoderm. Loss of Wnt-7a results in the appearance of ventral characteristics in the dorsal half of the distal limb. Conversely, En-1, a homeo-domain transcription factor, is expressed exclusively in the ventral ectoderm, where it represses Wnt-7a. En-1 mutants have dorsal characteristics in the ventral half of the distal limb. Experiments in the chick suggest that the dorsalizing activity of Wnt-7a in the mesenchyme is mediated through the regulation of the LIM-homeodomain transcription factor Lmx-1. Here we have examined the relationship between Wnt-7a, En-1 and Lmx-1b, a mouse homolog of chick Lmx-1, in patterning the mammalian limb. We find that Wnt-7a is required for Lmx-1b expression in distal limb mesenchyme, and that Lmx-1b activation in the ventral mesenchyme of En-1 mutants requires Wnt-7a. Consistent with Lmx-1b playing a primary role in dorsal-ization of the limb, we find a direct correlation between regions of the anterior distal limb in which Lmx-1b is misregulated during limb development and the localization of dorsal-ventral patterning defects in Wnt-7a and En-1 mutant adults. Thus, ectopic Wnt-7a expression and Lmx-1b activation underlie the dorsalized En-1 phenotype, although our analysis also reveals a Wnt-7a-independent activity for En-1 in the repression of pigmentation in the ventral epidermis. Finally, we demonstrate that ectopic expression of Wnt-7a in the ventral limb ectoderm of En-1 mutants results in the formation of a second, ventral apical ectodermal ridge (AER) at the junction between Wnt-7a-expressing and nonexpressing ectoderm. Unlike the normal AER, ectopic AER formation is dependent upon Wnt-7a activity, indicating that distinct genetic mechanisms may be involved in primary and secondary AER formation.
Deficient development and maintenance of postsynaptic specializations in mutant mice lacking an ‘adult’ acetylcholine receptor subunit
Authors: Missias Andrea C. , Mudd Jacqueline , Cunningham Jeanette M. , Steinbach Joseph H. , Merlie John P. , Sanes Joshua R. 
Published: April 2021

ABSTRACT
At many synapses, ‘fetal’ neurotransmitter receptor subunits are replaced by ‘adult’ subunits as development proceeds. To assess the significance of such transitions, we deleted the gene encoding the adult acetylcholine receptor (AChR) ε subunit, which replaces its fetal counterpart, the γ subunit, at the skeletal neuromuscular junction during early postnatal life. Several aspects of postnatal maturation, including synapse elimination, proceeded normally in the absence of the adult AChR, but structural development of the endplate was compromised. Later, inadequate compensation by the γ subunit led to severely reduced AChR density in mutant endplates relative to controls. This decreased density led to a profound reorganization of AChR-associated components of the postsynaptic membrane and cytoskeleton. Together, these results suggest novel roles for AChRs in assembly of the postsynaptic apparatus.
Analysis of Hoxd-13 and Hoxd-11 misexpression in chick limb buds reveals that Hox genes affect both bone condensation and growth
Authors: Goff Deborah J. , Tabin Clifford J. 
Published: April 2021

ABSTRACT
Hox genes are important regulators of limb pattern in vertebrate development. Misexpression of Hox genes in chicks using retroviral vectors provides an opportunity to analyze gain-of-function phenotypes and to assess their modes of action. Here we report the misexpression phenotype for Hoxd-13 and compare it to the misexpression phenotype of Hoxd-11. Hoxd-13 misexpression in the hindlimb results in a shortening of the long bones, including the femur, the tibia, the fibula and the tarsometatarsals. Mutations in an alanine repeat region in the N-terminus of Hoxd-13 have recently been implicated in human synpolydactyly (Muragaki, Y., Mundlos, S., Upton, J. and Olsen, B. R. (1996) Science 272, 548-551). N-terminal truncations of Hoxd-13 which lack this repeat were constructed and were found to produce a similar, although slightly milder, mis-expression phenotype than the full-length Hoxd-13.
The stage of bone development regulated by Hox genes has not previously been examined. The changes in bone lengths caused by Hoxd-13 misexpression are late phenotypes that first become apparent during the growth phase of the bones. Analysis of tritiated thymidine uptake by the tibia and fibula demonstrates that Hox genes can pattern the limb skeleton by regulating the rates of cell division in the proliferative zone of growing cartilage. Hoxd-11, in contrast to Hoxd-13, acts both at the initial cartilage condensation phase in the foot and during the later growth phase in the lower leg.
Ectopic Hoxd-13 appears to act in a dominant negative manner in regions where it is not normally expressed. We propose a model in which all Hox genes are growth promoters, regulating the expression of the same target genes, with some Hox genes being more effective promoters of growth than other Hox genes. According to this model, the overall rate of growth in a given region is the result of the combined action of all of the Hox genes expressed in that region competing for the same target genes.
Mutations in lottchen cause cell fate transformations in both neuroblast and glioblast lineages in the Drosophila embryonic central nervous system
Authors: Buescher Marita , Chia William 
Published: April 2021

ABSTRACT
The Drosophila embryonic central nervous system (CNS) develops from a stereotyped pattern of neuronal progenitor cells called neuroblasts (NB). Each NB has a unique identity that is defined by the time and position of its formation and a characteristic combination of genes it expresses. Each NB generates a specific lineage of neurons and/or glia. Here we describe the genetic and phenotypic analysis of lottchen (ltt), a novel gene whose loss of function causes a change in the identity of at least one NB as well as cell fate transformations within the lateral glioblast lineage. In wildtype embryos the parental NB of the motoneuron RP2 is NB4-2. ltt embryos are distinguished by an additional RP2-like neuron which appears later in development. We show that the two RP2 neurons are derived from two distinct GMC4-2a-like cells that do not share the same parental NB, indicating that a second NB has acquired the potential to produce a GMC and a neuron which is normally restricted to the NB4-2 lineage. Moreover, the ltt mutations lead to a loss of correctly specified longitudinal glia; this coincides with severely defective longitudinal connectives. Therefore, lottchen plays a role in specifying the identity of both neuroblast and glioblast lineages in the Drosophila embryonic CNS. We discuss the possibility that ltt may act to differentiate NB identity along the medial lateral axis.
Notochord alters the permissiveness of myotome for pathfinding by an identified motoneuron in embryonic zebrafish
Authors: Beattie Christine E. , Eisen Judith S. 
Published: April 2021

ABSTRACT
During zebrafish development, identified motoneurons innervate cell-specific regions of each trunk myotome. One motoneuron, CaP, extends an axon along the medial surface of the ventral myotome. To learn how this pathway is established during development, the CaP axon was used as an assay to ask whether other regions of the myotome were permissive for normal CaP pathfinding. Native myotomes were replaced with donor myotomes in normal or reversed dorsoventral orientations and CaP pathfinding was assayed. Ventral myotomes were permissive for CaP axons, even when they were taken from older embryos, suggesting that the CaP pathway remained present on ventral myotome throughout development. Dorsal myotomes from young embryos were also permissive for CaP axons, however, older dorsal myotomes were non-permissive, showing that permissiveness of dorsal myotome for normal CaP pathfinding diminished over time. This process appears to depend on signals from the embryo, since dorsal myotomes matured in vitro remained permissive for CaP axons. Genetic mosaics between wild-type and floating head mutant embryos revealed notochord involvement in dorsal myotome change of permissiveness. Dorsal and ventral myotomes from both younger and older floating head mutant embryos were permissive for CaP axons. These data suggest that initially both dorsal and ventral myotomes are permissive for CaP axons but as development proceeds, there is a notochord-dependent decrease in permissiveness of dorsal myotome for CaP axonal outgrowth. This change participates in restricting the CaP pathway to the ventral myotome and thus to neuromuscular specificity.
Nucleocytoplasmic localisation of extradenticle protein is spatially regulated throughout development in Drosophila
Authors: Aspland Simon E. , White Robert A. H. 
Published: April 2021

ABSTRACT
The extradenticle protein is a homeodomain transcription factor which has an important role regulating the DNA-binding specificity of homeotic selector proteins. We have made a monoclonal antibody against extradenticle and have studied the expression of the protein in the embryo and in imaginal discs. We find that extradenticle is initially uniformly distributed as expected but strikingly is excluded from nuclei until gastrulation. During the extended germ band stage the protein remains predominantly cytoplasmic and does not accumulate in nuclei until germ band retraction. Nuclear accumulation occurs in a highly spatially regulated pattern. In the imaginal discs the nuclear accumulation of extradenticle is also spatially regulated and, in the wing and leg discs, distal regions exhibit cytoplasmic extradenticle whereas proximally the protein is nuclear. We suggest that this regulation of the sub-cellular localisation of extradenticle is important for the interactions between extradenticle and the homeotic selector proteins and that extradenticle is not simply a ubiquitously available cofactor.
Cell-cell association directed mitotic spindle orientation in the early development of the marine shrimp Sicyonia ingentis
Authors: Wang Steven W. , Griffin Fred J. , Clark Wallis H. 
Published: April 2021

ABSTRACT
During early cleavages of Sicyonia ingentis embryos, mitotic spindle orientations differ between blastomeres and change in a predictable manner with each successive mitosis. From 2nd through 7th cleavages, spindles orient at a 90° angle with respect to the spindle of the parent blastomere. Thus, spindle orientation is parallel to the cleavage plane that formed the blastomere. To determine if specific spindle orientations were intrinsic properties of individual blastomeres, we altered blastomere associations and asked how mitotic spindle orientation was affected in successive cleavages using laser scanning confocal microscopy. Linear embryos were constructed by dissociating 4-cell embryos and recombining the blastomeres in a linear array. The ensuing cleavage (3rd embryonic cleavage) of these linear embryos was parallel to the long axis of the embryo, resulting in four parallel pairs of blastomeres which lay in a common plane that was parallel to the substratum. The 4th cleavage produced a linear embryo with the 16 blastomeres arranged in four parallel quartets. Then, in preparation for 5th cleavage, spindles oriented at a 45° angle (not parallel as in normal development) with respect to the previous cleavage plane. When 8-cell linear embryos were separated into linear half-embryos, subsequent spindle orientations were not like those observed for intact 8-cell linear embryos, but rather regressed to the orientation seen in 4-cell linear embryos. We suggest that the reorientation of mitotic spindles during early cleavage of S. ingentis is neither an intrinsic property nor age dependent, but rather is cell contact related. Further, these results in conjunction with observations of non-manipulated embryos suggest that spindle poles (centrosomes) avoid cytoplasmic regions adjacent to where there is cell-cell contact during early development.
Expression and function of decapentaplegic and thick veins during the differentiation of the veins in the Drosophila wing
Authors: de Celis Jose F. 
Published: April 2021

ABSTRACT
The differentiation of the veins in the Drosophila wing involves the coordinate activities of several signal transduction pathways, including those mediated by the transmembrane receptors Torpedo and Notch. In this report, the role of the signalling molecule Decapentaplegic during vein differentiation has been analysed. It is shown that decapentaplegic is expressed in the pupal veins under the control of genes that establish vein territories in the imaginal disc. Decapentaplegic, acting through its receptor Thick veins, activates vein differentiation and restricts expression of both veinlet and the Notch-ligand Delta to the developing veins. Genetic combinations between mutations that increase or reduce Notch, veinlet and decapentaplegic activities suggest that the maintenance of the vein differentiation state during pupal development involves cross-regulatory interactions between these pathways.
SDC-3 coordinates the assembly of a dosage compensation complex on the nematode X chromosome
Authors: Davis Tamara L. , Meyer Barbara J. 
Published: April 2021

ABSTRACT
X chromosome expression in C. elegans is controlled by a chromosome-wide regulatory process called dosage compensation that specifically reduces by half the level of transcripts made from each hermaphrodite X chromosome. This process equalizes X expression between the sexes (XX hermaphrodites and XO males), despite their two-fold difference in X chromosome dose, and thereby prevents sex- specific lethality. Dosage compensation is achieved by a protein complex that associates with X in a sex-specific fashion to modulate gene expression. SDC-3, a protein that coordinately controls both sex determination and dosage compensation, activates dosage compensation by directing the dosage compensation protein complex to the hermaphrodite X chromosomes. We show that SDC-3 coordinates this assembly through its own sex-specific association with X. SDC-3 in turn requires other members of the dosage compensation gene hierarchy for its stability and its X localization. In addition, SDC-3 requires its own zinc finger motifs and an amino-terminal region for its X association. Our experiments suggest the possible involvement of zinc finger motifs in X chromosome recognition and the amino- terminal region in interactions with other dosage compensation proteins.
SHAGGY and DISHEVELLED exert opposite effects on wingless and decapentaplegic expression and on positional identity in imaginal discs
Authors: Heslip Tim R. , Theisen Heidi , Walker Heli , Marsh J. Lawrence 
Published: April 2021

ABSTRACT
The finding that Wingless (WG) and Decapentaplegic (DPP) suppress each others transcription provides a mechanism for creating developmental territories in fields of cells. Here, we address the mechanism of that antagonism. The dishevelled (dsh) and shaggy (sgg) genes encode intracellular proteins generally thought of as downstream of WG signaling. We have investigated the effects of changing either DSH or SGG activity on both cell fate and wg and dpp expression. At the level of cell fate in discs, DSH antagonizes SGG activity. At the level of gene expression, SGG positively regulates dpp expression and negatively regulates wg expression while DSH activity suppresses dpp expression and promotes wg expression. Sharp borders of gene expression correlating precisely with clone boundaries suggest that the effects of DSH and SGG on transcription of wg and dpp are not mediated by secreted factors but rather act through intracellular effectors. The interactions described here suggest a model for the antagonism between WG and DPP that is mediated via SGG. The model incorporates autoactivation and lateral inhibition, which are properties required for the production of stable patterns. The regulatory interactions described exhibit extensive ability to organize new pattern in response to manipulation or injury.
Subsets of retinal progenitors display temporally regulated and distinct biases in the fates of their progeny
Authors: Alexiades Macrene R. , Cepko Constance L. 
Published: April 2021

ABSTRACT
Cell fate determination in the developing vertebrate retina is characterized by the sequential generation of seven classes of cells by multipotent progenitor cells. Despite this order of genesis, more than one cell type is generated at any time; for example, in the rat, several cell types are born during the prenatal period, while others are born postnatally. In order to examine whether there are classes of progenitor cells with distinct developmental properties contributing to this developmental progression, we examined antigen expression in progenitor cells during rat retinal development. Two markers of amacrine and horizontal cells, the VC1.1 epitope and syntaxin, were found to be expressed on a subset of progenitors in a temporally regulated manner that closely paralleled the birthdays of these cell types. In order to investigate which cell types were produced by the progenitors expressing these markers, fluorescent latex microspheres covalently coupled to VC1.1 antibodies were used to indelibly label VC1.1+ progenitor cells and their progeny. Early in retinal development, VC1.1+ progenitors generated a high percentage of amacrine and horizontal cells, but no cone photoreceptors. During this same period, a comparable number of cone photoreceptors were generated by VC1.1- progenitors. In the late embryonic and early postnatal period, VC1.1+ progenitors continued to generate predominantly amacrine cells, but also gave rise to an increasing number of rod photoreceptors. These findings demonstrate that expression of these two markers by progenitors is highly correlated with a bias towards the production of amacrine and horizontal cells. The fact that subsets of progenitors with temporally regulated and distinct biases are intermingled within the retinal neuroepithelium provides a basis for understanding how different cell types are generated both simultaneously and in a particular order by multipotent progenitors during retinal development.