bluuebunny/crossref_metadata_2025_split huggingface dataset:
Striatal precursors adopt cortical identities in response to local cues
Authors: Fishell Gord 
Published: April 2021

ABSTRACT
One of the early steps in the regionalization of the CNS is the subdivision of the forebrain into dorsal and basal telen-cephalic ventricular zones. These ventricular zones give rise to the cortex and striatum respectively, in the mature brain. Previous work suggests that while neural precursors are able to move within both the dorsal cortical and basal striatal ventricular zones, they are unable to cross the boundary area between them. To determine if the regional identities of the cells in these ventricular zones are restricted, cells from the basal striatal ventricular zone were either transplanted back into their original environ-ment or into the dorsally adjacent cortical ventricular zone. Use of in vitro explants of mouse telencephalon demon-strated that striatal precursors are able to integrate het-erotopically within 12 hours of being placed onto the surface of cortical ventricular zone. To examine whether heterotopically placed neural precursors have phenotypes appropriate to their host or donor environment, in vivo transplants in rats were performed. Striatal ventricular zone cells transplanted to a striatal environment adopt morphologies and axonal projections characteristic of striatal cells. In contrast, striatal ventricular zone cells transplanted in vivo to a cortical environment acquired morphologies and axonal projections specific to cortex. These findings suggest that within forebrain, position-specific cues play an instructive role in determining critical aspects of regional phenotype.
A role for HGF/SF in neural induction and its expression in Hensen’s node during gastrulation
Authors: Streit Andrea , Stern Claudio D. , Théry Clotilde , Ireland Grenham W. , Aparicio Samuel , Sharpe Melanie J. , Gherardi Ermanno 
Published: April 2021

ABSTRACT
It was previously shown (Roberts, C., Platt, N., Streit, A., Schachner, M. and Stern, C. D. (1991) Development 112, 959-970) that grafts of Hensen’s node into chick embryos enhance and maintain expression of the L5 carbohydrate in neighbouring epiblast cells, and that antibodies against L5 inhibit neural induction by such a graft. We now show that L5 is initially widely expressed in the epiblast, but as neural induction proceeds it gradually becomes confined to and up-regulated in the early neural plate. L5 can therefore be considered as a marker for cells that are competent to respond to neural induction.
We also show that Hepatocyte Growth Factor/Scatter Factor (HGF/SF) promotes the expression of L5 by extraembryonic epiblast in collagen gels after overnight culture. Explants cultured for several days in the presence of HGF/SF, as well as explants of prospective neural plate, can differentiate into cells with neuronal morphology expressing neuronal markers. To investigate whether HGF/SF is expressed in the chick embryo at appropriate stages of development, we produced specific cDNA probes and used them for in situ hybridization. We find that at the primitive streak stage, HGF/SF is expressed specifically in Hensen’s node. We therefore propose that HGF/SF plays a role during the early steps of neural induction, perhaps by inducing or maintaining the competence of the epiblast to respond to neural inducing signals.
A dominant inhibitory version of the small GTP-binding protein Rac disrupts cytoskeletal structures and inhibits developmental cell shape changes in Drosophila
Authors: Harden Nicholas , Loh Hui Yong , Chia William , Lim Louis 
Published: April 2021

ABSTRACT
The Rho subfamily of Ras-related small GTP-binding proteins is involved in regulation of the cytoskeleton. The cytoskeletal changes induced by two members of this subfamily, Rho and Rac, in response to growth factor stim-ulation, have dramatic effects on cell morphology. We are interested in using Drosophila as a system for studying how such effects participate in development. We have identified two Drosophila genes, DRacA and DRacB, encoding proteins with homology to mammalian Rac1 and Rac2. We have made transgenic flies bearing dominant inhibitory (N17DRacA), and wild-type versions of the DRacA cDNA under control of an Hsp70 promoter. Expression of the N17DRacA transgene during embryonic development causes a high frequency of defects in dorsal closure which are due to disruption of cell shape changes in the lateral epidermis. Embryonic expression of N17DRacA also affects germband retraction and head involution. The epidermal cell shape defects caused by expression of N17DRacA are accompanied by disruption of a localized accumulation of actin and myosin thought to be driving epidermal cell shape change. Thus the Rho subfamily may be generating localized changes in the cytoskeleton during Drosophila development in a similar fashion to that seen in mammalian and yeast cells. The Rho subfamily is likely to be partic-ipating in a wide range of developmental processes in Drosophila through its regulation of the cytoskeleton.
A conserved enhancer of the human and murine Hoxa-7 gene specifies the anterior boundary of expression during embryonal development
Authors: Knittel Thomas , Kessel Michael , Kim Myoung Hee , Gruss Peter 
Published: April 2021

ABSTRACT
The murine homeobox-containing gene Hoxa-7 is expressed in restricted patterns during embryogenesis and plays an important role in the control of region-specific differentiation. Previous studies have shown that separate elements specify lineage restriction and expression boundaries of Hoxa-7. In particular 3.6 kb of 5′ flanking sequences were sufficient to establish an anterior boundary of Hoxa-7 gene expression. To identify the minimal regulatory element specifying the anterior boundary of expression, transgenic mice were generated carrying chimeric constructs with deletions of 5′ flanking sequences fused to a thymidine kinase minimal promoter/E. coli lacZ reporter construct. By deletion analysis, a 470 bp long control element (AX 470) located 1.6 kb upstream of the transcription start site was identified that directed expression of the β-galactosidase protein in a pattern reflecting the anterior boundary of expression of the endogenous Hoxa-7 gene. This element was active in either orientation and conferred regionspecific expression to unrelated promoters, thereby behaving like an enhancer element. In contrast, transgenic mice carrying further 5′ and 3′ deletions of the 470 bp long element did not exhibit an anterior boundary of Hoxa-7 expression. Based on these results the minimal control element (AX 470) specifying the anterior boundary of Hox expression was designated as Hoxa-7 enhancer.
Furthermore, 3 kb of the human HOXA7 upstream region were sequenced and compared to its mouse homologue in order to identify conserved regions. Sequence comparison revealed motifs that were strongly conserved between both species. The human homologue of the mouse Hoxa-7 enhancer was 70% identical at the nucleotide level and was also capable of directing an anterior boundary in transgenic mice.
Using transgenic lines a detailed analysis of the Hoxa-7 enhancer-directed expression during embryogenesis was performed. lacZ expression was first detected in the allantois at day 7.5 p.c. and in mesoderm and ectoderm at day 8.5 of gestation. Between gestational ages E8.5 to E12.5 β-gal expression was observed in the somites, spinal cord, spinal ganglia and paraxial mesoderm as well as in mesenchymal layers of the kidney. A distinct anterior limit of expression was noted in transgenic lines at level C4 (neural tube) and C5 (spinal ganglia).
Our deletion experiments defined a minimal enhancer element specifying the anterior boundary of Hox gene expression in early and late phases of development. Further studies aim at characterizing the trans-acting factors that mediate the spatial and temporal expression of Hox genes in the developing embryo.
Vascular endothelial cell lineage-specific promoter in transgenic mice
Authors: Schlaeger Thorsten M. , Qin Ying , Fujiwara Yuko , Magram Jeanne , Sato Thomas N. 
Published: April 2021

ABSTRACT
Vascular endothelial cells play essential roles in the function and development of the cardiovascular system. However, due to the lack of lineage-specific markers suitable for molecular and biochemical analyses, very little is known about the molecular mechanisms that regulate endothelial cell differentiation. We report the first vascular endothelial cell lineage-specific (including angioblastic precursor cells) 1.2 kb promoter in transgenic mice. Moreover, deletion analysis of this promoter region in transgenic embryos revealed multiple elements that are required for the maximum endothelial cell lineage-specific expression. This is a powerful molecular tool that will enable us to identify factors and cellular signals essential for the establishment of vascular endothelial cell lineage. It will also allow us to deliver genes specifically into this cell type in vivo to test specifically molecules that have been implicated in cardiovascular development. Furthermore, we have established embryonic stem (ES) cells from the blastocysts of the transgenic mouse that carry the 1.2 kb promoter-LacZ reporter transgene. These ES cells were able to differentiate in vitro to form cystic embryoid bodies (CEB) that contain endothelial cells determined by PECAM immunohistochemistry. However, these in vitro differentiated endothelial cells did not express the LacZ reporter gene. This indicates the lack of factors and/or cellular interactions which are required to induce the expression of the reporter gene mediated by this 1.2 kb promoter in this in vitro differentiation system. Thus this system will allow us to screen for the putative inducers that exist in vivo but not in vitro. These putative inducers are presumably important for in vivo differentiation of vascular endothelial cells.
SpZ12-1, a negative regulator required for spatial control of the territory-specific CyIIIa gene in the sea urchin embryo
Authors: Wang David G.-W. , Kirchhamer Carmen V. , Britten Roy J. , Davidson Eric H. 
Published: April 2021

ABSTRACT
The CyIIIa cytoskeletal actin gene of the sea urchin Strongylocentrotus purpuratus is activated in late cleavage and expressed exclusively in the aboral ectoderm territory of the embryo. Previous gene transfer studies defined a 2.3 kb cis-regulatory region that is necessary and sufficient for correct temporal and spatial expression of a CyIIIa•CAT fusion gene. In this paper, a negative regulatory element within this region was identified that is required for repression of the CyIIIa gene in skeletogenic mesenchyme cells. The repression mediated by this regulatory element takes place after initial territorial specification. A cDNA clone encoding a DNA-binding protein with twelve Zn fingers (SpZ12-1) was isolated by probing an expression library with this cis-element. Deletion analysis of the SpZ12-1 protein confirmed that a DNA-binding domain is located within the Zn finger region. SpZ12-1 is the only DNAbinding protein in embryo nuclear extract that interacts with the specific cis-target sites required for repression of CyIIIa•CAT in skeletogenic mesenchyme and is likely to be the trans factor that mediates this repression.
The limbic system-associated membrane protein (LAMP) selectively mediates interactions with specific central neuron populations
Authors: Zhukareva Victoria , Levitt Pat 
Published: April 2021

ABSTRACT
The limbic system-associated membrane protein (LAMP) is a 64–68×103Mr glycoprotein that is expressed by subsets of neurons that are functionally interconnected. LAMP exhibits characteristics that are indicative of a developmentally significant protein, such as an early and restricted pattern of expression and the ability to mediate specific fiber-target interactions. A potential, selective adhesive mechanism by which LAMP may regulate the formation of specific circuits is investigated in the present experiments. LAMP is readily released from intact membranes by phosphatidyl inositol-specific phospholipase C. Purified, native LAMP, isolated by PI-PLC digestion and immunoaffinity chromatography, is capable of mediating fluorescent Covasphere aggregation via homophilic binding. To test the ability of LAMP to selectively facilitate substrate adhesion and growth of neurons from LAMP-positive, in contrast to LAMP-negative regions of the developing brain, purified LAMP was dotted onto nitrocellulose-coated dishes and test cells plated. Limbic neurons from perirhinal cortex bind specifically to substrate-bound LAMP within 4 hours, forming small cell aggregates with short neuritic processes that continue to grow through a 48 hour period of monitoring. Preincubation of cells with antiLAMP has a modest effect on cell binding but significantly reduces initiation of process growth. Non-limbic neurons from somatosensory cortex and olfactory bulb fail to bind or extend processes on the LAMP substrate to any significant extent. All cell populations bind equally well and form neurites on poly-D-lysine and laminin. The present results provide direct evidence that LAMP can specifically facilitate interactions with select neurons in the CNS during development. The data support the concept that patterned expression of unique cell adhesion molecules in functionally related regions of the mammalian brain can regulate circuit formation.
Sequential gene activation by ecdysone in Drosophila melanogaster: the hierarchical equivalence of early and early late genes
Authors: Huet François , Ruiz Claude , Richards Geoff 
Published: April 2021

ABSTRACT
Ecdysteroids are key regulators of insect development. In Drosophila melanogaster the late larval response to ecdysone is characterised by a precise sequential activation of members of the superfamily of nuclear receptors (DHR3, DHR39, EcR, E75, E78, FTZ-F1, usp). Many of these genes are localised in the polytene chromosome puffs of the salivary gland previously classified as intermoult, early or early-late puff loci. Ashburner et al. (Ashburner, M., Chihara, C., Meltzer, P. and Richards, G. (1974) Cold Spring Harbour Symp. Quant. Biol. 38, 655-662) proposed a formal model describing interactions between ecdysone, its receptor and the early and late puffs during this ecdysone response. To integrate transcripts from the intermoult and early-late puffs into this model, we have used a micro RT-PCR assay to study their hormonal regulation using salivary gland culture protocols first used in the puffing analyses. We show that transcripts from certain early-late puffs are induced in parallel with the early transcripts and are thus hierarchically equivalent. In vivo the profile of the increase in hormone titre, the sensitivity of different promoters to hormone and the rate of transcript accumulation must contribute to the temporal differences in expression observed between these two classes.
The cAMP Response Element Binding protein is involved in hydra regeneration
Authors: Galliot Brigitte , Welschof Martin , Schuckert Oliver , Hoffmeister Sabine , Schaller H. Chica 
Published: April 2021

ABSTRACT
Hydra provides an interesting developmental model system where pattern formation processes are easily accessible to experimentation during regeneration. Previous studies have shown that the neuropeptide head activator affects cellular growth and head-specific cellular differentiation during head regeneration and budding. In order to investigate the signal transduction pathway and the regulatory genes involved in these processes, we measured cAMP levels after head activator treatment and found that head activator leads to an increase in cAMP levels at concentrations where effects on nerve cell determination and differentiation are observed (10−11 to 10−9 M). Moreover, exposure of intact hydra to a permeable form of cAMP stimulates nerve-cell differentiation and thus mimicks the effect of endogenous head activator. Band-shift assays were performed to detect changes in hydra nuclear protein binding activity during regeneration or after head activator treatment. We found that the cAMP response element (CRE) promotes a specific and strong DNAbinding activity which is dramatically enhanced and modified during early regeneration or after HA treatment. We also identified a surprisingly highly conserved hydra gene encoding the cAMP Response Element Binding protein, which is involved in this CRE-binding activity. Initiation of regeneration upon wounding provokes an endogenous release of HA which leads to the final differentiation of determined nerve cells. We propose that the nerve-cell differentiation observed within the first 4-8 hours of regeneration relies on the agonist effect of head activator on the cAMP pathway, which would in turn modulate the CRE-binding activity of the hydra CREB protein and thus regulate the transcriptional activity of genes involved in regeneration processes.
LEUNIG regulates AGAMOUS expression in Arabidopsis flowers
Authors: Liu Zhongchi , Meyerowitz Elliot M. 
Published: April 2021

ABSTRACT
LEUNIG was identified in a genetic screen designed to isolate second-site enhancer mutations of the floral homeotic mutant apetala2-1. leunig mutations not only enhance apetala2, but by themselves cause a similar but less-pronounced homeotic transformation than apetala2 mutations. leunig flowers have sepals that are transformed toward stamens and carpels, and petals that are either staminoid or absent. In situ hybridization experiments with leunig mutants revealed altered expression pattern of the floral homeotic genes APETALA1, APETALA3, PISTIL-LATA, and AGAMOUS. Double mutants of leunig and agamous exhibited a phenotype similar to agamous single mutants, indicating that agamous is epistatic to leunig. Our analysis suggests that a key role of LEUNIG is to negatively regulate AGAMOUS expression in the first two whorls of the Arabidopsis flower.
The C. elegans neuronally expressed homeobox gene ceh-10 is closely related to genes expressed in the vertebrate eye
Authors: Svendsen Pia C. , McGhee James D. 
Published: April 2021

ABSTRACT
We describe the homeobox gene ceh-10 from the nematode Caenorhabditis elegans. The homeodomain of ceh-10 is closely related to the homeodomains of two genes recently cloned from the vertebrate retina, Chx10 from mice and Vsx-1 from goldfish. We show that the sequence conservation extends well beyond the homeodomain and includes a region (named the CVC domain) of roughly 60 amino acids immediately C-terminal to the homeodomain. As assayed in transgenic worms, the promoter region of ceh-10 directs expression of a lacZ reporter gene to a small number of neurons. We draw a parallel between the bipolar cells of the inner nuclear layer of the vertebrate retina, which express Chx10 and Vsx-1, and an interneuron in C. elegans called AIY, which expresses ceh-10. AIY receives synaptic input from a sensory cell, just as do bipolar cells of the vertebrate retina. In C. elegans, the sensory cell AFD is not known to be photosensitive but is known to be thermosensitive; moreover, a cell with similar position in the amphids of other nematodes has been suggested indeed to be photosensitive. Our results emphasize the highly conserved nature of sensory regulatory mechanisms and suggest one way in which photosensitive organelles might have originated in evolution.
Nonequivalent requirements for PS1 and PS2 integrin at cell attachments in Drosophila: genetic analysis of the αPS1 integrin subunit
Authors: Brower Danny L. , Bunch Thomas A. , Mukai Leona , Adamson Todd E. , Wehrli Marcel , Lam Suzanne , Friedlander Eric , Roote Carol E. , Zusman Susan 
Published: April 2021

ABSTRACT
We report on the generation and phenotype of mutant alleles of multiple edematous wings (mew), the gene encoding the αPS1 subunit of the PS1 integrin of Drosophila. None of the six alleles examined makes detectable protein, and one allele results from a chromosome break near the middle of the translated sequence, so we are confident that we have described the null phenotype. In contrast to if (αPS2) and mys (βPS) mutants, most mutant mew embryos hatch, to die as larvae. Mutant mew embryos display abnormal gut morphogenesis but, unlike mys or if embryos, there is no evidence of defects in the somatic muscles. Thus, the complementary distributions of PS1 (αPS1βPS) and PS2 (αPS2βPS) integrin on tendon cells and muscle, respectively, do not reflect equivalent requirements at the myotendinous junction. Dorsal herniation, characteristic of the mys lethal phenotype, is not observed in mew or in mew if embryos. Clonal analysis experiments indicate that eye morphogenesis is disrupted in mew clones, but if clones in the eye are relatively normal in morphology. Adult wings display blisters around large dorsal but not ventral mew clones. In contrast to dorsal mys clones, small mew patches do not necessarily display morphogenetic abnormalities. Thus, another integrin in addition to PS1 appears to function on the dorsal wing surface.
Neural crest cell-cell adhesion controlled by sequential and subpopulationspecific expression of novel cadherins
Authors: Nakagawa Shinichi , Takeichi Masatoshi 
Published: April 2021

ABSTRACT
We identified two cadherins, c-cad6B and c-cad7, expressed by neural crest cells at their premigratory and migratory stages, respectively, in chicken embryos. cDNA transfection experiments showed that both were homophilic adhesion molecules, endowing cells with specific adhesiveness. During development, c-cad6B appeared in the neural fold, localizing at the future neural crest area. This expression was maintained during neural tube closure, but disappeared after neural crest cells had left the neural tube, suggesting its role in neural fold fusion and/or in the formation and maintenance of the presumptive neural crest domain in the neural plate/tube. Crest cells emerging from the neural tube lost c-cad6B, and a subpopulation of them began to express c-cad7. This subpopulation-specific expression of c-cad7 persisted during their migration. The migrating c-cad7-positive cells clustered together, and eventually populated restricted regions including the dorsal and ventral roots but very little ganglia. The latter was populated with N-cadherin-positive crest cells. Migrating neural crest cells expressed αand βcatenin at cell-cell contacts, indicating that their cadherins are functioning. These results suggest that the migrating crest cells are grouped into subpopulations expressing different cadherins. The cadherin-mediated specific interaction between crest cells likely plays a role in intercellular signaling between homotypic cells as well as in sorting of heterotypic cells.