bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hoxa-2 expression in normal and transposed rhombomeres: independent regulation in the neural tube and neural crest
Authors: Prince Victoria , Lumsden Andrew 
Published: April 2021

ABSTRACT
In this study we have cloned the chick Hoxa-2 gene and analysed its expression during early development. We find that Hoxa-2 has a rostral limit of expression in the rhombencephalic neural tube corresponding precisely to the boundary between rhombomeres (r)1 and 2; a limit further rostral than any other Hox gene reported to date. Neural crest migrates from r2 to populate the first branchial arch, yet although Hoxa-2 is expressed down the full dorsoventral extent of r2 during the phase of neural crest emigration, there is no Hoxa-2 expression in either the emergent neural crest or in the first branchial arch. Conversely, at the level of r4, both the neural tube and the neural crest cells, which migrate out of this rhombomere to populate the second branchial arch, express Hoxa-2.
Other Hox genes expressed in the rhombencephalic neural tube demonstrate a transfer of expression from neural tube to neural crest at all axial levels of expression. Hoxa-2 is thus unusual in demonstrating separate anterior expression limits in neural tube and neural crest; this allowed us to test whether Hox gene expression patterns in neural crest are determined by migratory pathways or are prespecified by the site of origin in the neuroepithelium. Grafting experiments in which pairs of rhombomeres were transplanted to ectopic sites at the time of rhombomere boundary formation reveal a prepatterning of the neural crest with respect to Hoxa-2 expression. The decision to down-regulate Hoxa-2 expression in r2-derived neural crest, but to maintain Hoxa-2 expression in r4-derived neural crest is intrinsic to the premigratory crest cell population. Thus, following grafting of r4 to the r2 site and vice-versa, Hoxa-2 expression is maintained in r4-derived neural crest, but lost in r2-derived neural crest.
Differential response of embryonic and fetal myoblasts to TGFβ: a possible regulatory mechanism of skeletal muscle histogenesis
Authors: Angelis M. G. Cusella-De , Molinari S. , Donne A. Le , Coletta M. , Vivarelli E. , Bouche M. , Molinaro M. , Ferrari S. , Cossu G. 
Published: April 2021

ABSTRACT
Embryonic and fetal skeletal myoblasts were grown in culture in the presence of TGFβ. Under the conditions employed, TGFβ inhibited differentiation of fetal but not of embryonic myoblasts. To investigate the possible relevance of these data to skeletal muscle histogenesis in vivo, we studied the proliferation/differentiation state of mesodermal cells in the proximal region of the limb bud at the time of primary fiber formation. BrdU labeling and immunostaining for myosin heavy chains revealed that very few mesodermal cells enter the S phase of the cycle when differentiated primary fibers fist appear. However, a few hours later, many cells in S phase surround newly formed muscle fibers, suggesting that the latter may be a source of mitogens for undifferentiated myoblasts. Co-culture experiments supported this hypothesis, showing that medium conditioned by fiber-containing explants can stimulate myoblast proliferation.
Taken together these data suggested a possible mechanism for the regulation of muscle fiber formation. The model assumes that fibers form in the proximal region of the limb bud, where TGFβ is known to be present, and BrdU labeling experiments did not reveal cells in S phase.
It is conceivable that non-dividing embryonic myoblasts (which do not respond to TGFβ) can undergo differentiation, while fetal myoblasts are inhibited by TGFβ. Once formed, primary fibers may stimulate a new wave of proliferation in fetal myoblasts, in order to expand the pool of cells needed to form secondary fibers.
To test this model we developed an organ culture for limb buds which resulted in the production of myotubes with a phenotype similar to embryonic (primary) and fetal (secondary) fibers, roughly at the time when primary and secondary fibers form in vivo. When these cultures were treated with TGFβ embryonic myotubes did form (as expected), but fetal myotubes never appeared. Conversely, when these cultures were treated with anti-TGFβ neutralizing antibodies, fetal myotubes developed earlier than in control cultures, suggesting that endogenously produced TGFβ may repress differentiation of fetal cells in vitro and, possibly, in vivo.
Subcellular localization of the segment polarity protein patched suggests an interaction with the wingless reception complex in Drosophila embryos
Authors: Capdevila Javier , Pariente Félix , Sampedro Javier , Alonso José Luis , Guerrero Isabel 
Published: April 2021

ABSTRACT
The product of the segment polarity gene patched is a trans-membrane protein involved in the cell communication processes that establish polarity within the embryonic segments of Drosophila. Monoclonal antibodies have been raised against the patched protein, and by immunoelectron microscopy part of the patched staining is found associated with discrete regions of the lateral plasma membrane of the embryonic epidermal cells. Using a mutation affecting endocytosis (shibire) we find that patched is a membrane-bound protein, which is internalized by endocytosis, and that the preferential sites of accumulation resemble the described localizations of the cell-cell adhesive junctions of the epidermal cells. patched partially co-localizes with the wingless protein in the wingless-expressing and nearby cells, in structures that seem to be endocytic vesicles. These data suggest the interaction of patched protein with elements of the reception complex of wingless, as a way to control the wingless expression.
Violation of cell lineage restriction compartments in the chick hindbrain
Authors: Birgbauer Eric , Fraser Scott E. 
Published: April 2021

ABSTRACT
Previous cell lineage studies indicate that the repeated neuromeres of the chick hindbrain, the rhombomeres, are cell lineage restriction compartments. We have extended these results and tested if the restrictions are absolute. Two different cell marking techniques were used to label cells shortly after rhombomeres form (stage 9+ to 13) so that the resultant clones could be followed up to stage 25. Either small groups of cells were labelled with the lipophilic dye DiI or single cells were injected intracellularly with fluorescent dextran. The majority of the descendants labelled by either technique were restricted to within a single rhombomere. However, in a small but reproducible proportion of the cases (greater than 5%), the clones expanded across a rhombomere boundary. Neither the stage of injection, the stage of analysis, the dorsoventral position, nor the rhombomere identity correlated with the boundary crossing. Judging from the morphology of the cells, both neurons and non-neuronal cells were able to expand over a boundary. These results demonstrate that the rhombomere boundaries represent cell lineage restriction barriers which are not impenetrable in normal development.
Rat olfactory neurons can utilize the endogenous lectin, L-14, in a novel adhesion mechanism
Authors: Mahanthappa Nagesh K. , Cooper Douglas N. W. , Barondes Samuel H. , Schwarting Gerald A. 
Published: April 2021

ABSTRACT
L-14 is a divalent, lactosamine-binding lectin expressed in many vertebrate tissues. In the rat nervous system, L-14 expression has been observed previously in restricted neuronal subsets within the dorsal root ganglia and spinal cord. In this study we report that L-14 is expressed by non-neuronal cells in the rat olfactory nerve. We demonstrate that L-14 binds and co-localizes with two ligands in the rat olfactory system: a β-lactosamine-containing glycolipid, and a putative member of the laminin family. The former is expressed on the surfaces of nascent olfactory axons originating from neuron cell bodies in the olfactory epithelium. The latter is present in the extracellular matrix of the axonal path leading to synaptic targets in the olfactory bulb.
In vitro, we find that recombinant L-14 promotes primary olfactory neuron adhesion to two laminin family members, and promotes intercellular adhesion. Both activities are dose-dependent, and are independent of integrinmediated mechanisms. We have thus found that L-14 can serve two distinct adhesive functions in vitro, and propose that L-14 in vivo can promote olfactory axon fasciculation by crosslinking adjacent axons and promote axonal adhesion to the extracellular matrix.
lola encodes a putative transcription factor required for axon growth and guidance in Drosophila
Authors: Giniger Edward , Tietje Kathleen , Jan Lily Yeh , Jan Yuh Nung 
Published: April 2021

ABSTRACT
Mutations in the gene longitudinals lacking (lola) lead to defects in the development of axon tracts in the Drosophila embryonic central nervous system. We now show that lola mutations also cause defects of axon growth and guidance in the peripheral nervous system, and causes a particular cluster of embryonic sense organs (lch5) to be oriented improperly. Axonal aberrations caused by lola are similar to those caused by mutations of three other genes, logo, Notch and Delta, raising the possibility that lola works in the same genetic pathway as do these other molecules. The lola gene encodes at least two nuclear protein products, apparently by differential RNA splicing. The predicted proteins contain an amino-terminal motif similar to that recently described for a family of transcription factors, including the products of the Drosophila genes tramtrack and the Broad Complex. Like Ttk and BR-C, one of the two characterized products of the lola locus bears sequences similar to the zinc-finger motif, but the other (neuronal) form of the protein has no recognizable DNA-binding motif.
Axons arrest the migration of Schwann cell precursors
Authors: Bhattacharyya Anita , Brackenbury Robert , Ratner Nancy 
Published: April 2021

ABSTRACT
The neural crest gives rise to a variety of cell types including Schwann cells of the peripheral nervous system. Schwann cell precursors begin to differentiate early and migrate along specific pathways in the embryo before associating with nerve trunks. To determine whether motor axons direct the migration of Schwann cell precursors along specific pathways, we tested the effect of ablating the ventral half of the neural tube, which contains motor neuron cell bodies. The ventral neural tube was removed unilaterally from lumbar regions of chicken embryos at stage 17, when neural crest cells are just beginning to migrate and before motor axons have extended out of the neural tube. At several stages after ventral tube ablation, sections of the lumbar region of these embryos were stained with anti-acetylated tubulin to label developing axons, HNK-1 to label migrating neural crest cells and 1E8 to label Schwann cell precursors. In many embryos the ablation of motor neurons was incomplete. The staining patterns in these embryos support the idea that some Schwann cells are derived from the neural tube. In embryos with complete motor neuron ablation, at stage 18, HNK-1-positive neural crest cells had migrated to normal locations in both control and ablated sides of the embryo, suggesting that motor axons or the ventral neural tube are not required for proper migration of neural crest cells. However, by stage 19, cells that were positive for HNK-1 or 1E8 were no longer seen in the region of the ventral root, nor ventral to the ventral root region. Because Schwann cell precursors require neural-derived factors for their survival in vitro, we tested whether neural crest cells that migrate to the region of the ventral root in ventral neural tube-ablated embryos then die. Nile Blue staining for dead and dying cells in ventral neural tube-ablated embryos provided no evidence for cell death at stage 18. These results suggest that motor axons arrest the migration of Schwann cell precursors during neural crest migration.
Developmental control of a G1-S transcriptional program in Drosophila
Authors: Duronio Robert J. , O’Farrell Patrick H. 
Published: April 2021

ABSTRACT
We have defined a coordinate program of transcription of S-phase genes (DNA polymerase α, PCNA and the two ribonucleotide reductase subunits) that can be induced by the G1 cyclin, cyclin E. In Drosophila embryos, this program drives an intricate spatial and temporal pattern of gene expression that perfectly parallels the embryonic program of S-phase control. This dynamic pattern of expression is not disrupted by a mutation, string, that blocks the cell cycle. Thus, the transcriptional program is not a secondary consequence of cell cycle progression. We suggest that developmental signals control this transcriptional program and that its activation either directly or indirectly drives transition from G1 to S phase in the stereo-typed embryonic pattern.
Characterization of a novel Dictyostelium discoideum prespore-specific gene, PspB, reveals conserved regulatory sequences
Authors: Powell-Coffman Jo Anne , Firtel Richard A. 
Published: April 2021

ABSTRACT
While Dictyostelium discoideum has been studied as a developmental system for decades, and many regulatory proteins have been cloned, the molecular mechanisms of cell-type-specific gene expression are poorly understood. In this paper we characterize a novel prespore gene, PspB, and undertake a comparative analysis of the regulatory regions in prespore-specific D. discoideum promoters. Sequence alignment of the PSPB gene product with other prespore-specific proteins identifies a conserved, repeated 12 amino acid cysteine-containing motif that may be involved in spore coat function or assembly. Analysis of the PspB promoter identifies two domains essential for developmentally induced promoter activity. The first region includes two CA-rich elements (CAEs) that we show to be functionally homologous to the cAMP-inducible elements previously identified in the SP60 (cotC) promoter. The PspB CAEs compete with the SP60 (cotC) CAEs for binding in vitro to a developmentally regulated nuclear activity. We identify this activity as G-box Binding Factor, a developmentally induced transcription factor. The PspB CAEs and adjacent nucleotides direct a very low level of prespore-enriched expression, but high levels of cell-type-specific expression requires a second promoter region: a 46-bp AT-rich sequence that does not resemble the CAEs or any other previously described late gene promoter elements. Com-parison of the PspB AT element with regulatory regions of the SP60 (cotC), SP70 (cotB), and D19 (pspA) promoters reveals an extensive consensus sequence. We suggest that these AT-rich sequences may represent a common regulatory element (or elements) required for prespore gene activation.
Role of transforming growth factor-beta isoforms in regulating the expression of nerve growth factor and neurotrophin-3 mRNA levels in embryonic cutaneous cells at different stages of development
Authors: Buchman Vladimir L. , Sporn Michael , Davies Alun M. 
Published: April 2021

ABSTRACT
We have investigated if transforming growth factor-beta (TGF-β) isoforms influence the level of expression of nerve growth factor (NGF) mRNA and neurotrophin-3 (NT-3) mRNA in embryonic tissues innervated by neurons that depend on NGF and NT-3 for survival. Presumptive dermal and epidermal cells from the maxillary territory of the embryonic mouse trigeminal ganglion were cultured in defined medium during the early stages of innervation when trigeminal neurons switch their survival dependence from NT-3 to NGF. In E11 and E12 cultures, when the in vivo levels of NGF mRNA and NT-3 mRNA are increasing, TGF-β1, TGF-β2 and TGF-β3 each increased the level of NGF mRNA but had no effect on NT-3 mRNA. In E13 cultures, when the in vivo levels of NGF mRNA and NT-3 mRNA reach a peak (relative to actin mRNA) prior to a marked fall in the level of NT-3 mRNA and a gradual decrease in the level of NGF mRNA, TGF-βs promoted further increases in the level of NGF mRNA but caused a decrease in the level of NT-3 mRNA. All three TGF-β mRNAs were detected in the maxillary territory in vivo before the arrival of the earliest axons and their levels rose throughout the period in which sensory axons reach this territory. Our findings demonstrate age-related changes in the influence of TGF-βs on the expression of neurotrophins in developing cutaneous cells and raise the possibility that TGF-βs play a role in regulating the changing patterns of neurotrophin gene expression in sensory neuron target fields.
Characterisation of the second messenger pathway underlying neurite outgrowth stimulated by FGF
Authors: Williams Emma J. , Furness Josie , Walsh Frank S. , Doherty Patrick 
Published: April 2021

ABSTRACT
Cerebellar neurons, cultured on monolayers of 3T3 fibroblasts or on a polylysine/laminin-coated substratum, responded to recombinant basic FGF by extending longer neurites. The response was biphasic reaching a maximum at 5 ng/ml FGF, but desensitising at 100-200 ng/ml FGF. The response to FGF could be inhibited by a tyrosine kinase inhibitor (the erbstatin analogue), by a diacylglycerol lipase inhibitor (RHC-80267) and by a combination of N- and L-type calcium channel antagonists or other agents that negate the effects of calcium influx into neurons. The response to FGF could be fully mimicked by arachidonic acid added directly to the cultures, or generated via activation of phospholipase A2 with melittin. The response to melittin, but not to FGF or arachidonic acid, was inhibited by 4-bromophenacyl bromide, a phospholipase A2 inhibitor. The response to arachidonic acid was also biphasic and high concentrations of this agent could cross-desensitise the FGF response and vice versa. The response to arachidonic acid could be fully inhibited by the agents that block or negate the effects of calcium influx into neurons, but was not inhibited by the tyrosine kinase or diacylglycerol lipase inhibitors. These data suggest that FGF stimulates neurite outgrowth by activating a cascade that involves activation of phospholipase Cγ to produce diacylglycerol, conversion of diacylglycerol to arachidonic acid by diacylglycerol lipase and the activation of voltage-gated calcium channels by arachidonic acid.
Tiggrin, a novel Drosophila extracellular matrix protein that functions as a ligand for Drosophila αPS2βPS integrins
Authors: Fogerty Frances J. , Fessler Liselotte I. , Bunch Thomas A. , Yaron Yifah , Parker Carol G. , Nelson Robert E. , Brower Danny L. , Gullberg Donald , Fessler John H. 
Published: April 2021

ABSTRACT
Genetic and other studies of Drosophila integrins have implicated these extracellular matrix receptors in various morphogenetic events, but identification of their endogenous ligands has been elusive. We report the biochemical purification and cloning of tiggrin, a novel extracellular matrix protein from Drosophila. This 255 ×103Mr polypeptide contains the potential integrin recognition sequence Arg-Gly-Asp (RGD) and 16 repeats of a novel 73-77 amino acid motif. The tiggrin gene is at chromosome locus 26D12 and is expressed by embryonic hemocytes and fat body cells. Tiggrin protein is detected in matrices, especially at muscle attachment sites that also strongly express integrins. Tiggrin-coated surfaces support primary embryo cell culture and provide excellent substrates for αPS2βPS integrin-mediated cell spreading. Soluble RGD-peptides inhibit this cell spreading.
Developmental stage- and spermatogenic cycle-specific expression of transcription factor GATA-1 in mouse Sertoli cells
Authors: Yomogida Kentaro , Ohtani Haruo , Harigae Hideo , Ito Etsuro , Nishimune Yoshitake , Engel James Douglas , Yamamoto Masayuki 
Published: April 2021

ABSTRACT
GATA-1 is an essential factor for the transcriptional activation of erythroid-specific genes, and is also abundantly expressed in a discrete subset of cells bordering the seminiferous epithelium in tubules of the murine testis. In examining normal and germ-line defective mutant mice, we show here that GATA-1 is expressed only in the Sertoli cell lineage in mouse testis. GATA-1 expression in Sertoli cells is induced concomitantly with the first wave of spermatogenesis, and GATA-1-positive cells are uniformly distributed among all tubules during prepubertal testis development. However, the number of GATA-1-positive cells declines thereafter and were found only in the peripheral zone of seminiferous tubules in stages VII, VIII and IX of spermatogenesis in the adult mouse testis. In contrast, virtually every Sertoli cell in mutant W/Wv, jsd/jsd or cryptorchid mice (all of which lack significant numbers of germ cells) expresses GATA-1, thus showing that the expression of this transcription factor is negatively controlled by the maturing germ cells. These observations suggest that transcription factor GATA-1 is a developmental stage- and spermatogenic cycle-specific regulator of gene expression in Sertoli cells.
Neural selective activation and temporal regulation of a mammalian GAP-43 promoter in zebrafish
Authors: Reinhard Eva , Nedivi Elly , Wegner Jeremy , Skene J. H. Pate , Westerfield Monte 
Published: April 2021

ABSTRACT
Neurons throughout the vertebrate nervous system selectively activate the gene for a growth cone component, GAP-43, during embryonic development, and then decrease its expression abruptly as they form synapses. Distal interruption of mature axons in the central nervous system (CNS) of fish and amphibians, but not in the mammalian CNS reverses the developmental down-regulation of GAP-43 expression. To explore functional conservation and divergence of cis-acting elements that regulate expression of the GAP-43 gene, we studied activation, in transgenic zebrafish embryos, of mammalian GAP-43 genomic sequences fused to a marker gene. The DNA fragments containing the GAP-43 promoter, including a short fragment of 386 base pairs, were preferentially activated in the embryonic fish nervous system at times when extensive neuronal differentiation and neurite outgrowth take place.
After 2 days of development, expression of the mammalian transgenes was specifically downregulated in the fish spinal cord but increased in more rostral regions of the CNS. This expression pattern was well correlated with the regulation of the endogenous fish GAP-43 gene revealed by in situ hybridization. Elements of the mammalian gene located a substantial distance upstream of the minimal promoter directed additional expression of the marker gene in a specific set of non-neural cells in zebrafish embryos. Our results indicate that cis-acting elements of the GAP-43 gene, and signaling pathways controlling these elements during embryonic development, have been functionally conserved in vertebrate evolution.