bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three genes of the MAP kinase cascade, mek-2, mpk-1/sur-1 and let-60 ras, are required for meiotic cell cycle progression in Caenorhabditis elegans
Authors: Church Diane L. , Guan Kun-Liang , Lambie Eric J. 
Published: April 2021

ABSTRACT
In the germline of Caenorhabditis elegans hermaphrodites, meiotic cell cycle progression occurs in spatially restricted regions. Immediately after leaving the distal mitotic region, germ cells enter meiosis and thereafter remain in the pachytene stage of first meiotic prophase for an extended period. At the dorsoventral gonadal flexure, germ cells exit pachytene and subsequently become arrested in diakinesis. We have found that exit from pachytene is dependent on the function of three members of the MAP kinase signaling cascade. One of these genes, mek-2, is a newly identified C. elegans MEK (MAP kinase kinase). The other two genes, mpk-1/sur-1 (MAP kinase) and let-60 ras, were previously identified based on their roles in vulval induction and are shown here to act in combination with mek-2 to permit exit from pachytene. Through genetic mosaic analysis, we demonstrate that the expression of mpk-1/sur-1 is required within the germline to permit exit from pachytene.
The Drosophila 63F early puff contains E63-1, an ecdysone-inducible gene that encodes a novel Ca2+-binding protein
Authors: Andres Andrew J. , Thummel Carl S. 
Published: April 2021

ABSTRACT
Pulses of ecdysone at the end of Drosophila larval development dramatically reprogram gene expression as they signal the onset of metamorphosis. Ecdysone directly induces several early puffs in the salivary gland polytene chromosomes that, in turn, activate many late puffs. Three early puffs, at 2B5, 74EF, and 75B, have been studied at the molecular level. Each contains a single ecdysone primary-response gene that encodes a family of widely expressed transcription factors. We report here a molecular characterization of the 63F early puff. Unexpectedly, we have found this locus to be significantly different from the previously characterized early puff loci. First, the 63F puff contains a pair of ecdysone-inducible genes that are transcribed in the larval salivary glands: E63-1 and E63-2. Second, E63-1 induction in late third instar larvae appears to be highly tissue-specific, restricted to the salivary gland. Third, E63-1 encodes a novel Ca2+-binding protein related to calmodulin. The discovery of an ecdysone-inducible Ca2+-binding protein provides a foundation for integrating steroid hormone and calcium second messenger signaling pathways and generates an additional level for potential regulation of the ecdysone response.
A sea urchin homologue of the chordate Brachyury (T) gene is expressed in the secondary mesenchyme founder cells
Authors: Harada Yoshito , Yasuo Hitoyoshi , Satoh Noriyuki 
Published: April 2021

ABSTRACT
Chordates are thought to have emerged from some common ancestor of deuterostomes by organizing shared anatomical and embryological features including a notochord, a dorsal nerve cord and pharyngeal gill slits. Because the notochord is the most prominent feature of chordates and because the Brachyury (T) gene is essential for notochord formation, the T gene is a key molecular probe with which to explore the origin and evolution of chordates. We investigated whether the sea urchin (echin- oderm) conserves the T gene and, if so, where the sea urchin T gene is expressed.
A cDNA clone for the sea urchin T (HpTa) gene contained a long open reading frame that encodes a polypeptide of 434 amino acids. Although the overall degree of amino acid identity was not very high (52%, sea urchin/mouse), in the T domain of the N terminus the amino acid identity was 73% (sea urchin/mouse). The HpTa gene is present as a single copy per haploid genome. As with the chordate T gene, the expression of HpTa is transient, being first detected in the swimming blastula, maximally transcribed in the gastrula, decreasing at the prism larval stage and barely detectable at the pluteus larval stage. HpTa tran- scripts were found in the secondary mesenchyme founder cells, vegetal plate of the mesenchyme blastula, extending tip of the invaginating archenteron and, finally, the secondary mesenchyme cells at the late-gastrula stage. The results suggest that the T gene was organized prior to the branching of a lineage leading to chordates from that leading to echinoderms and that, during sea urchin development, the T gene is utilized to specify the developmental fate of embryonic cells to the secondary mesenchyme.
Expression of the unc-4 homeoprotein in Caenorhabditis elegans motor neurons specifies presynaptic input
Authors: Miller David M. , Niemeyer Charles J. 
Published: April 2021

ABSTRACT
In the nematode, Caenorhabditis elegans, VA and VB motor neurons arise from a common precursor cell but adopt different morphologies and synapse with separate sets of interneurons in the ventral nerve cord. A mutation that inactivates the unc-4 homeodomain gene causes VA motor neurons to assume the VB pattern of synaptic input while retaining normal axonal polarity and output; the disconnection of VA motor neurons from their usual presynaptic partners blocks backward locomotion. We show that expression of a functional unc-4-β-galactosidase chimeric protein in VA motor neurons restores wild-type movement to an unc-4 mutant. We propose that unc-4 controls a differentiated characteristic of the VA motor neurons that distinguishes them from their VB sisters, thus dictating recognition by the appropriate interneurons. Our results show that synaptic choice can be controlled at the level of transcription in the post-synaptic neuron and identify a homeoprotein that defines a subset of cell-specific traits required for this choice.
Targeted mutation of the murine goosecoid gene results in craniofacial defects and neonatal death
Authors: Yamada Gen , Mansouri Ahmed , Torres Miguel , Stuart Edward T. , Blum Martin , Schultz M. , Robertis Eddy M. De , Gruss Peter 
Published: April 2021

ABSTRACT
The goosecoid gene encodes a homeodomain-containing protein that has been identified in a number of species and has been implicated in a variety of key developmental processes. Initially suggested to be involved in organizing the embryo during early development, goosecoid has since been demonstrated to be expressed during organogenesis – most notably in the head, the limbs and the ventrolateral body wall. To investigate the role of goosecoid in embryonic development, we have inactivated the gene by gene targeting to generate mice mutant for the goosecoid gene. Mice that are homozygous for the goosecoid mutation do not display a gastrulation phenotype and are born; however, they do not survive more than 24 hours. Analysis of the homozygotes revealed numerous developmental defects affecting those structures in which goosecoid is expressed during its second (late) phase of embryonic expression. Predominantly, these defects involve the lower mandible and its associated musculature including the tongue, the nasal cavity and the nasal pits, as well as the components of the inner ear (malleus, tympanic ring) and the external auditory meatus. Although the observed phenotype is in accordance with the late expression domains of goosecoid in wild-type embryos, we suggest that the lack of an earlier phenotype is the result of functional compensation by other genes.
Origin and specification of type II sensory neurons in Drosophila
Authors: Brewster Rachel , Bodmer Rolf 
Published: April 2021

ABSTRACT
The peripheral nervous system (PNS) of Drosophila is a preferred model for studying the genetic basis of neuro-genesis because its simple and stereotyped pattern makes it ideal for mutant analysis. Type I sensory organs, the external (bristle-type) sensory organs (es) and the internal (stretch-receptive) chordotonal organs (ch), have been postulated to derive from individual ectodermal precursor cells that undergo a stereotyped pattern of cell division. Little is known about the origin and specification of type II sensory neurons, the multiple dendritic (md) neurons. Using the flp/FRT recombinase system from yeast, we have determined that a subset of md neurons derives from es organ lineages, another subset derives from ch organ lineages and a third subset is unrelated to sensory organs. We also provide evidence that the genes, numb and cut, are both required for the proper differentiation of md neurons.
Posterior stripe expression of hunchback is driven from two promoters by a common enhancer element
Authors: Margolis Jonathan S. , Borowsky Mark L. , SteingrÍmsson EirÍkur , Shim Chung Wha , Lengyel Judith A. , Posakony James W. 
Published: April 2021

ABSTRACT
The gap gene hunchback (hb) is required for the formation and segmentation of two regions of the Drosophila embryo, a broad anterior domain and a narrow posterior domain. Accumulation of hb transcript in the posterior of the embryo occurs in two phases, an initial cap covering the terminal 15% of the embryo followed by a stripe at the anterior edge of this region. By in situ hybridization with transcript-specific probes, we show that the cap is composed only of mRNA from the distal transcription initiation site (P1), while the later posterior stripe is composed of mRNA from both the distal and proximal (P2) transcription initiation sites. Using a series of genomic rescue constructs and promoter-lacZ fusion genes, we define a 1.4 kb fragment of the hb upstream region that is both necessary and sufficient for posterior expression. Sequences within this fragment mediate regulation by the terminal gap genes tailless (tll) and huckebein, which direct the formation of the posterior hb stripe. We show that the tll protein binds in vitro to specific sites within the 1.4 kb posterior enhancer region, providing the first direct evidence for activation of gene expression by tll. We propose a model in which the anterior border of the posterior hb stripe is determined by tll concentration in a manner analogous to the activation of anterior hb expression by bicoid.
Defective bone formation in Krox-20 mutant mice
Authors: Levi Giovanni , Topilko Piotr , Schneider-Maunoury Sylvie , Lasagna Marco , Mantero Stefano , Cancedda Ranieri , Charnay Patrick 
Published: April 2021

ABSTRACT
Endochondral ossification is the prevalent mode of vertebrate skeleton formation; it starts during embryogenesis when cartilage models of long bones develop central regions of hypertrophy which are replaced by bony trabeculae and bone marrow. Although several transcription factors have been implicated in pattern formation in the limbs and axial skeleton, little is known about the transcriptional regulations involved in bone formation. We have created a null allele in the mouse Krox-20 gene, which encodes a zinc finger transcription factor, by in frame insertion of the E. coli lacZ gene and shown that hindbrain segmentation and peripheral nerve myelination are affected in Krox-20−/− embryos. We report here that Krox-20 is also activated in a subpopulation of growth plate hypertrophic chondrocytes and in differentiating osteoblasts and that its disruption severely affects endochondral ossification. Krox-20−/− mice develop skeletal abnormalities including a reduced length and thickness of newly formed bones, a drastic reduction of calcified trabeculae and severe porosity. The periosteal component to bone formation and calcification does not appear to be affected in the homozygous mutant suggesting that the major role for Krox-20 is to be found in the control of the hypertrophic chondrocyte-osteoblast interactions leading to endosteal bone formation.
Retinoic acid establishes ventral retinal characteristics
Authors: Hyatt G. A. , Schmitt E. A. , Marsh-Armstrong N. , McCaffery P. , Dräger U. C. , Dowling J. E. 
Published: April 2021

ABSTRACT
The developing eye is known to be rich in retinoic acid (RA), and perturbations in RA levels during formation of the optic primordia, as well as RA receptor mutations, cause retinal malformations, especially in ventral eye regions. To test the hypothesis that RA plays a role in the establishment of ventral retinal characteristics, we examined several dorsal and ventral ocular markers in RA-treated zebrafish. The optic stalk represents the ventral-most region of the early eye field. During normal development, the optic stalks constrict, decreasing in width and are gradually replaced by the optic nerve. Systemic high RA levels cause an expansion in the optic stalk with an increased cell content and a patent lumen. In addition, the stalks do not constrict and persist into later stages of development indicating an enhancement of early ventral eye characteristics. Expression of the transcription factor pax[b], normally confined to the ventral retina, expands into the dorsal retina following RA treatment, whereas msh[c], normally expressed in the dorsal retinal pole, disappears. Activity of an aldehyde dehydrogenase that normally occupies the dorsal third of the retina is reduced or abolished following high systemic RA. When a localized RA source, an RA-soaked bead, is placed next to the developing eye, a fissure resembling the choroid fissure appears in the eye facing the bead. Taken together, these observations suggest that RA is involved in the determination of the ventral retina.
A targeted mouse Otx2 mutation leads to severe defects in gastrulation and formation of axial mesoderm and to deletion of rostral brain
Authors: Ang Siew-Lan , Jin Ou , Rhinn Muriel , Daigle Nathalie , Stevenson Lois , Rossant Janet 
Published: April 2021

ABSTRACT
Mouse Otx2 is a bicoid-class homeobox gene, related to the Drosophila orthodenticle (otd) gene. Expression of this gene is initially widespread in the epiblast at embryonic day 5.5 but becomes progressively restricted to the anterior end of the embryo at the headfold stage. In flies, loss of function mutations in otd result in deletion of pre-antennal and antennal segments; which leads to the absence of head structures derived from these segments. To study the function of Otx2 in mice, we have generated a homeobox deletion mutation in this gene. Mice homozygous for this mutation show severe defects in gastrulation and in formation of axial mesoderm and loss of anterior neural tissues. These results demonstrate that Otx2 is required for proper development of the epiblast and patterning of the anterior brain in mice, and supports the idea of evolutionary conservation of the function of Otd/Otx genes in head development in flies and mice.
The establishment of the hepatic architecture is a prerequisite for the development of a lobular pattern of gene expression
Authors: Notenboom Robbert G. E. , de Boer Piet A. J. , Moorman Antoon F. M. , Lamers Wouter H. 
Published: April 2021

ABSTRACT
We have studied the expression patterns of ammonia-metabolising enzymes and serum proteins in intraspleni-cally transplanted embryonic rat hepatocytes by in situ hybridisation and immunohistochemical analysis. The enzymic phenotype of individually settled hepatocytes was compared with that of hepatocytes being organised into a three-dimensional hepatic structure. Our results demon-strate that development towards the terminally differenti-ated state with zonal differences in enzyme content requires the incorporation of hepatocytes into lobular structures. Outside such an architectural context, phenotypic matura-tion becomes arrested and hepatocytes linger in the pro-todifferentiated state. These features identify the foetal period as a crucial time for normal liver development and show that the establishment of the terminally differentiated hepatocellular phenotype, beginning with the differen-tiation of hepatocytes from the embryonic foregut, is realised via a multistep process.
The alignment of the axis of asymmetry in regenerating protoplasts of the moss, Ceratodon purpureus, is determined independently of axis polarity
Authors: Cove D. J. , Quatrano R. S. , Hartmann E. 
Published: April 2021

ABSTRACT
Ceratodon protoplasts regenerate by polar outgrowth to form cell filaments. The kinetics of regeneration show that some cellular event has to be completed before regenera-tion can be initiated. The development of the regeneration axis is strongly influenced by light, with axis alignment and axis polarity being fixed independently. We define axis alignment as the relationship of the regeneration axis to the incident light, independent of polarity. Thus protoplasts regenerating directly towards, or directly away from the light source are defined as being similarly aligned but with opposite polarity. Protoplasts that regenerate in unidirec-tional red light form axes that are aligned parallel to the light direction, with about 70% being polarised towards the light and about 30% away. In unidirectional blue or white light, almost all protoplasts regenerate towards the light but axis alignment is determined less stringently. Re- ori-entation of protoplasts regenerating in unidirectional light shows that axis alignment is fixed between 8 and 9 hours before protoplasts regenerate and that axis polarity is fixed later. When protoplasts are removed from directional light to either non-directional light or to darkness, regeneration axes continue to be aligned by the earlier directional stimulus for at least 24 hours. Thus although axis alignment is fixed only about 8 hours before regeneration, in the absence of contradictory information about direc-tionality in the light environment, protoplasts retain a memory of light direction for much longer. However, both reorientation and removal from a directional light field have profound effects on axis polarity; the pattern observed in undisturbed protoplasts being lost. To account for these observations, we propose that separate gradients are established independently to determine the alignment and polarity of the regeneration axis respectively. The alignment gradient is established rapidly and is steeper in red than in blue or white light, the polarity gradient is established slowly and is steeper in white or blue light than in red. These studies will now allow a genetic dissection of these processes in moss.
Rpx: a novel anterior-restricted homeobox gene progressively activated in the prechordal plate, anterior neural plate and Rathke’s pouch of the mouse embryo
Authors: Hermesz Edit , Mackem Susan , Mahon Kathleen A. 
Published: April 2021

ABSTRACT
We have isolated a new murine homeobox gene, Rpx (for Rathke’s pouch homeobox), that is dynamically expressed in the prospective cephalic region of the embryo during gastrulation. Early expression is seen in the anterior midline endoderm and prechordal plate precursor. Expression is subsequently activated in the overlying ectoderm of the cephalic neural plate, suggesting that inductive contact with Rpx-expressing mesendoderm is required for this expression. Subsequently, Rpx expression is extinguished in the mesendoderm while remaining in the prospective prosencephalic region of the neural plate ectoderm. Ultimately, transcripts become restricted to Rathke’s pouch, the primordium of the pituitary, which is known to be derived from the most anterior ectoderm of the early embryo. Down regulation of Rpx in the pouch coincides with the differentiation of pituitary-specific cell types. Rpx is the earliest known marker for the pituitary primordium, suggestive of a role in the early determination or differentiation of the pituitary. Since Rpx is expressed so dynamically and so early in the anterior region of the embryo, and since its early expression domain is much more extensive than the region fated to form the pituitary, it is likely that Rpx is involved in the initial determination of the anterior (prechordal) region of the embryo.
Clones in the chick diencephalon contain multiple cell types and siblings are widely dispersed
Authors: Golden Jeffrey A. , Cepko Constance L. 
Published: April 2021

ABSTRACT
The thalamus, hypothalamus and epithalamus of the vertebrate central nervous system are derived from the embryonic diencephalon. These regions of the nervous system function as major relays between the telencephalon and more caudal regions of the brain. Early in development, the diencephalon morphologically comprises distinct units known as neuromeres or prosomeres. As development proceeds, multiple nuclei, the functional and anatomical units of the diencephalon, derive from the neuromeres. It was of interest to determine whether progenitors in the diencephalon give rise to daughters that cross nuclear or neuromeric boundaries. To this end, a highly complex retroviral library was used to infect diencephalic progenitors. Retrovirally marked clones were found to contain neurons, glia and occasionally radial glia. The majority of clones dispersed in all directions, resulting in sibling cells populating multiple nuclei within the diencephalon. In addition, several distinctive patterns of dispersion were observed. These included clones with siblings distributed bilaterally across the third ventricle, clones that originated in the lateral ventricle, clones that crossed neuromeric boundaries, and clones that crossed major boundaries of the developing nervous system, such as the diencephalon and mesencephalon. These findings demonstrate that progenitor cells in the diencephalon are multipotent and that their daughters can become widely dispersed.
Mutations in the 8 kDa dynein light chain gene disrupt sensory axon projections in the Drosophila imaginal CNS
Authors: Phillis R. , Statton D. , Caruccio P. , Murphey R. K. 
Published: April 2021

ABSTRACT
Mutations in an 8 kDa (8 ×103Mr) cytoplasmic dynein light chain disrupt sensory axon trajectories in the imaginal nervous system of Drosophila. Weak alleles are behaviorally mutant, female-sterile and exhibit bristle thinning and bristle loss. Null alleles are lethal in late pupal stages and alter neuronal anatomy within the imaginal CNS. We utilized P[Gal4] inserts to examine the axon projections of stretch receptor neurons and an engrailed-lacZ construct to characterize the anatomy of tactile neurons. In mutant animals both types of sensory neurons exhibited altered axon trajectories within the CNS, suggesting a defect in axon pathfinding. However, the alterations in axon trajec-tory did not prevent these axons from reaching their normal termination regions. In the alleles producing these neuronal phenotypes, expression of the cytoplasmic dynein 8 kDa light chain gene is completely absent. These results demonstrate a new function for the cytoplasmic dynein light chain in the regulation of axonogenesis and may provide a point of entry for studies of the role of cellular motors in growth cone guidance.
Discrete developmental stages during teliospore formation in the corn smut fungus, Ustilago maydis
Authors: Banuett Flora , Herskowitz Ira 
Published: April 2021

ABSTRACT
Ustilago maydis is a dimorphic fungus with a yeast-like non-pathogenic form and a filamentous (hyphal) pathogenic form that induces tumor formation in maize. Within mature tumors’ hyphae give rise to teliospores’ which are round’ diploid cells surrounded by a specialized cell wall. Here we describe the time course of fungal development in the plant with a focus on the morphological changes in the hyphae and the pathway of teliospore formation. We confirm and extend earlier observations that U. maydis hyphae branch extensively on the leaf surface and intra-cellularly before induction of tumors. We observe that at later stages the filaments undergo a series of discrete morphogenetic changes leading to teliospore formation. In particular’ we show that the hyphae become embedded in a mucilaginous matrix within the tumor cells and the hyphal tips become modified. The hyphae then undergo fragmentation to release individual cells that exhibit a variety of shapes on their way to becoming rounded. Finally’ a specialized cell wall is deposited. Support for the existence of such a pathway comes from analysis of a mutant defective in the fuz1 gene: inactivation of fuz1 blocks production of the mucilaginous matrix and fragmentation of the hyphae’ leading to a defect in teliospore formation. The different morphological changes that occur while in the plant but not in culture suggest that plant inputs play a key role in fungal development.