bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transforming growth factor-alpha (TGF-α) and insulin gene expression in human fetal pancreas
Authors: Miettine Pätvi J. , Heikinheimo Kristiina 
Published: April 2021

Abstract
Transforming growth factor-alpha (TGF-α) mRNA is expressed in several pancreatic cancer cell lines, but its expression during normal fetal pancreas development has not been studied. We investigated the expression of TGF-α, its receptor (EGF-R) and insulin mRNA and their corresponding peptides in human fetal pancreata (15–20 gestation weeks). Polymerase chain reaction (PCR) and RNAase protection analysis revealed that TGF-α and insulin mRNAs were detectable in pancreas during the developmental span studied. In northern blot analysis a single band of 4.8 kilobases (kb) corresponding to the TGF-α transcript and a 0.6 kb for the insulin mRNA were detected in the pancreas. Using in situ hybridization, TGF-α mRNA expression was seen in a low copy number in both the exo- and endocrine pancreas. By immunohistochemistry TGF-α-immuno-reactive cells were detected in the ducts, acini and islets showing that the mRNA was translated into protein. By contrast, insulin transcripts were detected in a high copy number, restricted to the islets of Langerhans. However, monoclonal insulin antibody detected less insulin containing cells than could be expected from the mRNA pattern suggesting that fetal β-cells rapidly secrete insulin instead of storing it in the secretory granules. Alternatively, the translation of insulin mRNA could be inefficient. By double labeling the pancreas sections with polyclonal TGF-α antiserum and monoclonal insulin antibody the TGF-α- and insulin-like immunoreactivity was localized to β-cells. Furthermore, mRNA for the TGF-α receptor, EGF-R, together with EGF-R-immu-noreactive cells were also present in pancreas. The results suggest that TGF-α may participate auto- and/or paracrinically in the development of human fetal pancreas.
Function of an Ultrabithorax minigene in imaginal cells
Authors: Castelli-Gair James , Müller Jürg , Bienz Mariann 
Published: April 2021

Abstract
An Ultrabithorax (Ubx) minigene constructed from three key Ubx control regions is capable of supporting development of Ubx null mutants throughout larval life and beyond to pharate flies, thereby rescuing the larval lethality due to the homeotic mutation. The cuticle of these flies shows that the minigene provides at least partial Ubx function in each of the four compartments whose morphogenetic pathways are determined by Ubx. We analyse β-galactosidase patterns in imaginal discs conferred by each individual Ubx control region. From the comparison of these patterns with Ubx expression in Cbx mutants, we infer that long-range repressor elements in the chromosomal Ubx gene play an important role in the generation of Ubx expression patterns in imaginal discs. Expression and function of our Ubx minigenes indicate that Ubx control regions are capable of functioning properly out of context and detached from their normal chromosomal location within the homeotic gene complex.
Diffusible rod-promoting signals in the developing rat retina
Authors: Watanabe Takashi , Raff Martin C. 
Published: April 2021

Abstract
We previously developed a reaggregate cell culture system in which embryonic rat retinal neuroepithelial cells proliferate and give rise to opsin-expressing rod photoreceptor cells (rods) on the same schedule in vitro as they do in vivo. We showed that the proportion of neuroepithelial cells in the embryonic day 15 (E15) retina that differentiated into opsin+ rods after 5 –6 days in such cultures increased by ∼40-fold when the E15 cells were cultured in the presence of an excess of postnatal day 1 (Pl) neural retinal cells. In the present study, we have further analyzed this rod-promoting activity of neonatal neural retinal cells. We show that the activity is mediated by a diffusible signal(s) that seems to act over a relatively short distance. Whereas neonatal (P1-P3) neural retina has rod-promoting activity, E15 and adult neural retina, neonatal thymus, cerebrum and cerebellum do not. Finally, we show that neonatal neural retina promotes rod but not amacrine cell development.
Regeneration of dopaminergic neurons in goldfish retina
Authors: Braisted Janet E. , Raymond Pamela A. 
Published: April 2021

Abstract
The conditions necessary to trigger regeneration of dopaminergic neurons were investigated in the goldfish retina. Intraocular injection of 6-hydroxydopamine (6-OHDA) was used to destroy dopaminergic neurons, and neuronal regeneration was monitored by injections of the thymidine analog bromodeoxyuridine (BUdR). Regenerated dopaminergic neurons, (identified by doublelabeling with anti-tyrosine hydroxylase and anti-BUdR antibodies) were found within 3 weeks after 2 injections of 0.6 mg/ml 6-OHDA (estimated intraocular concentration), but not after injection of lower doses. All retinas with regenerated dopaminergic neurons also contained other types of regenerated neurons, including cones and ganglion cells, consistent with nuclear counts which revealed non-selective cell loss (34 –36%) in both the outer and inner nuclear layers after exposure to the high dose, but not lower doses of 6-OHDA. Regenerated neurons were produced by clusters of dividing neuroepithelial cells probably derived from rod precursors in the outer nuclear layer. These results demonstrate that dopaminergic neurons will not regenerate after they are selectively ablated but only as part of a developmental process that involves generation of multiple cell types.
Evidence of a role for endogenous electrical fields in chick embryo development
Authors: Hotary Kevin B. , Robinson Kenneth R. 
Published: April 2021

Abstract
We have tested directly the hypothesis that the endogenous electrical field in the chick embryo plays a causal role in development. Conductive implants, which shunt currents out of the embryo and thus alter the internal held, were placed under the dorsal skin at the mid-trunk level of stage 11 – 15 embryos. Currents leaving the posterior intestinal portal (p.i.p.) of these embryos were reduced by an average of 30%. Control embryos receiving non-conductive implants showed no change in p.i.p. currents. In the group receiving current shunts, 92% of the embryos exhibited some developmental abnormality. Only 11% of the control group displayed defects. The most common defect in the experimental group (81%) was in tail development. Tail defects ranged from complete absence to the formation of a normal length, but morphologically abnormal tail. Internally, tail structures (neural tube, notochord and somites) were frequently absent or aberrantly formed. In 33% of the experimental embryos, the notochord continued lengthening in the absence of any other tail development. This led to the formation of ourenteric outgrowths from the hindgut. Defects in limb bud and head development were also found in experimentally treated embryos, but at a much lower frequency than tail defects.
The abnormalities observed in experimental embryos were very similar to those produced naturally in rumpless mutant chicks. A vibrating probe analysis of these mutants (from both dominant and recessive strains) showed that currents leaving the p.i.p. were significantly lower in phenotypically abnormal mutants than in wild-type and phenotypically normal mutant embryos from both strains. There was no apparent correlation between the average transepithelial potential (TEP) of these mutants and the development of tail abnormalities. The possible role of endogenous electrical fields in chick tail development is discussed.
Expression and functional involvement of N-cadherin in embryonic limb chondrogenesis
Authors: Oberlender Steven A. , Tuan Rocky S. 
Published: April 2021

ABSTRACT
Cell adhesion molecules have been shown to be important mediators of morphogenesis and pattern formation. In this study, we have shown that N-cadherin is expressed in a specific spatiotemporal manner in the developing limb bud during chondrogenesis in vivo and in cultured limb mesenchyme in vitro. The time period of maximal expression of N-cadherin corresponds to the period of active cellular condensation, an event believed to be a necessary prerequisite for chondrogenic differentiation. To directly assess the functional involvement of N-cadherin in cellular condensation, we have examined the effects of perturbing N-cadherin activity on both cell aggregation and chondrogenesis using NCD-2, a rat monoclonal antibody directed against the binding region of N-cadherin. Non-immune rat IgG was used as a control. Our results show that functional N-cadherin is necessary for chondrogenesis to proceed both in vivo and in vitro. Limb mesenchymal cells exhibited characteristic Ca2+-dependent cell aggregation in suspension, which was inhibited in the presence of exogenous NCD-2. In micromass cultures of limb mesenchymal cells, NCD-2 inhibited overt chondrogenesis in a dose-dependent manner. Furthermore, NCD-2 inhibition of chondrogenesis in micromass cultures was time-dependent, suggesting that N-cadherin is crucially involved during the latter half of the first 24 hours of culture, a time period most likely corresponding to active cellular condensation. NCD-2 also significantly influenced limb development when injected into embryonic limb buds in vivo. In addition to significant inhibition of chondrogenesis and developmental delays, gross developmental deformities and perturbation of overall pattern formation were also observed. Taken together, these results demonstrate that N-cadherin is functionally required in mediating the cell-cell interactions among mesenchymal cells important for chondrogenesis in micromass culture in vitro and in the intact limb bud in vivo.
engrailed-mediated repression of Ultrabithorax is necessary for the parasegment 6 identity in Drosophila
Authors: Mann Richard S. 
Published: April 2021

ABSTRACT
The homeotic genes of Drosophila are expressed in overlapping domains along the anterior-to-posterior axis and specify the distinct morphological patterns of each parasegment. Within single parasegments, the levels of homeotic gene expression are often modulated, in part because of cross-regulation by other homeotic gene products. However, the functional significance of different levels of homeotic gene expression is unclear. Here modulations in Ultrabithorax (Ubx) expression within parasegment 6 are examined. Specifically, Ubx is shown to be down-regulated in the posterior compartment of this parasegment by engrailed (en). The significance of Ubx repression by en was demonstrated by characterizing the expression of the Ubx target gene, Distal-less (Dll). In the posterior compartment of parasegment 6, Dll is normally expressed in a small cluster of cells. If Ubx is expressed uniformly via a heatshock promoter, Dll is inappropriately repressed in these posterior compartment cells. In the anterior compartment of parasegment 6, Dll is normally repressed by high levels of Ubx. However, if en is expressed uniformly via a heatshock promoter, Ubx is repressed and Dll is derepressed. Because Dll is required for the development of larval sensory structures, these results demonstrate that en-mediated repression of Ubx in the posterior compartment is necessary for the morphology of parasegment 6. Thus, different levels of homeotic gene expression can be important for their segmental patterning functions.
GATA factor activity is required for the trophoblast-specific transcriptional regulation of the mouse placental lactogen I gene
Authors: Ng Yuk-Kiu , George Kathleen M. , Engel James Douglas , Linzer Daniel I. H. 
Published: April 2021

ABSTRACT
The molecular determinants governing tissue-specific gene expression in the placenta are at present only poorly defined, particularly with respect to the regulation of specific hormone genes whose products are vital to embryonic development and the maintenance of a nurturing maternal environment. In continuing our analysis of the trophoblast-specific expression of the mouse placental lactogen I gene, we now demonstrate that the transcription factors GATA-2 and GATA-3 regulate the activity of this gene promoter. These factors are expressed in placental trophoblast cells, with peak levels of the GATA-2, GATA-3 and placental lactogen I mRNAs each accumulating at midgestation. Analysis of a region of the placental lactogen I gene promoter, previously shown to be sufficient for directing trophoblast-specific transcription, revealed the presence of three consensus binding sites for GATA-2 or GATA-3. Both GATA-2 and GATA-3 bind to these sites in vitro and mutation of these sites results in a significant decrease in promoter activity as assayed by transient transfection into the choriocarcinoma-derived cell line Rcho-1, which expresses endogenous GATA-2 and GATA-3. Furthermore, overexpression of GATA factors in Rcho-1 cells stimulates transcription from a co-transfected placental lactogen I gene promoter. Most significantly, expression of GATA-2 or GATA-3 was found to induce transcription from this promoter in transfected non-trophoblast (fibroblast) cells. These data indicate that GATA factors are both limiting and required transcriptional regulatory molecules in placental trophoblasts, and that the tissue specificity of the placental lactogen I gene is determined, at least in part, by GATA-2 and/or GATA-3.
Differential expression of Broad-Complex transcription factors may forecast tissue-specific developmental fates during Drosophila metamorphosis
Authors: Emery Ivette F. , Bedian Vahe , Guild Gregory M. 
Published: April 2021

ABSTRACT
The steroid hormone ecdysone initiates metamorphosis in Drosophila melanogaster by activating a cascade of gene activity that includes primary response transcriptional regulators and secondary response structural genes. The Broad-Complex (BR-C) primary response gene is composed of several distinct genetic functions and encodes a family of related transcription factor isoforms. Our objective was to determine whether BR-C isoforms were components of the primary ecdysone response in all tissues and whether tissue-specific isoform expression is associated with tissue-specific metamorphic outcomes. We used specific antibody reagents that recognize and distinguish among the Z1, Z2 and Z3 BR-C protein isoforms to study protein expression patterns during the initial stages of metamorphosis. Western blot analyses demonstrated that BR-C isoforms are induced at the onset of metamorphosis, each with unique kinetics of induction and repression. Whole-mount immunostaining showed that the BR-C proteins accumulate in the nuclei of all larval and imaginal tissues indicating that the BR-C is induced as a primary response in many tissues. Several tissues express different levels and combinations of the BR-C isoforms suggesting that the BR-C is important in determining the tissue-specific outcome of many parallel ecdysone response cascades. For example, prepupal salivary glands (destined for histolysis during metamorphosis) express Z1 isoforms while imaginal discs (destined for cell differentiation and morphogenesis) shift from the synthesis of Z2 isoforms to the synthesis of Z1 isoforms. The prepupal central nervous system (destined for tissue remodeling) expresses all isoforms, with Z3 pre-dominating. Salivary gland chromosome immunostaining indicated that BR-C proteins interact directly with numerous loci in the polytene genome. Finally, western blot analyses showed that distinct BR-C genetic functions can be correlated with single and specific BR-C protein isoforms.
Roles of heterotrimeric and monomeric G proteins in sperm-induced activation of mouse eggs
Authors: Moore Grace D. , Ayabe Takuya , Visconti Pablo E. , Schultz Richard M. , Kopf Gregory S. 
Published: April 2021

ABSTRACT
Results of several lines of experimentation suggest that sperm-induced egg activation has several features in common with G protein-coupled receptor signal transduction mechanisms. We report that microinjection of GDPβS into metaphase II-arrested mouse eggs blocks sperm-induced egg activation. Since GDPβS inactivates both het-erotrimeric and monomeric classes of G proteins, the involvement of members of each of these families in sperm-induced egg activation was evaluated. Neither pertussis toxin treatment of eggs nor microinjection of eggs with inhibitory antibodies toward Gαq blocked sperm-induced egg activation. Nevertheless, microinjection of phosducin, a protein that binds tightly to free G protein βγ subunits, specifically inhibited second polar body emission, the fertilization evoked decrease of H1 kinase activity and pronucleus formation. Microinjection of phosducin, however, did not inhibit the fertilization-induced modifications of the zona pellucida and microinjection of βγt did not result in egg activation in the absence of sperm. Inactivation of the monomeric Rho family of G proteins with C3 transferase from Clostridium botulinum inhibited emission of the second polar body and cleavage to the 2-cell stage, but did not affect the modifications of the zona pellucida or pronu-cleus formation. Microinjection of Rasval12, which is a constitutively active form of Ras, did not result in egg activation in the absence of sperm. Moreover, microinjection of either an anti-Ras neutralizing antibody (Y13-259) or a dominant negative form of Ras (RasT) did not affect events of sperm-induced egg activation. In contrast, microinjection of RasT inhibited embryo cleavage to the 2-cell stage. These results suggest that both heterotrimeric and monomeric G proteins are involved in various aspects of sperm-induced egg activation.
Combinatorial specification of blastomere identity by glp-1-dependent cellular interactions in the nematode Caenorhabditis elegans
Authors: Moskowitz Ivan P. G. , Gendreau Steven B. , Rothman Joel H. 
Published: April 2021

ABSTRACT
Most somatic cells in the nematode Caenorhabditis elegans arise from AB, the anterior blastomere of the 2-cell embryo. While the daughters of AB, ABa and ABp, are equivalent in potential at birth, they adopt different fates as a result of their unique positions. One such difference is that the distribution of epidermal precursors arising from ABp is reversed along the anterior-posterior axis relative to those arising from ABa. We have found that a strong mutation in the glp-1 gene eliminates this ABa/ABp difference. Furthermore, extensive cell lineage analyses showed that ABp adopts an ABa-like fate in this mutant. This suggests that glp-1 acts in a cellular interaction that makes ABp distinct from ABa. One ABp-specific cell type was previously shown to be induced by an interaction with a neighboring cell, P2. By removing P2 from early embryos, we have found that the widespread differences between ABa and ABp arise from induction of the entire ABp fate by P2. Lineage analyses of genetically and physically manipulated embryos further suggest that the identities of the AB greatgranddaughters (AB8 cells) are controlled by three regulatory inputs that act in various combinations. These inputs are: (1) induction of the ABp-specific fate by P2, (2) a previously described induction of particular AB8 cells by a cell called MS, and (3) a process that controls whether an AB8 cell is an epidermal precursor in the absence of either induction. When an AB8 cell is caused to receive a new combination of these regulatory inputs, its lineage pattern is transformed to resemble the lineage of the wild-type AB8 cell normally receiving that combination of inputs. These lineage patterns are faithfully reproduced irrespective of position in the embryo, suggesting that each combination of regulatory inputs directs a unique lineage program that is intrinsic to each AB8 cell.
Wingless can bring about a mesoderm-to-ectoderm induction in Drosophila embryos
Authors: Lawrence Peter A. , Johnston Paul , Vincent Jean-Paul 
Published: April 2021

ABSTRACT
By means of nuclear transplantations, we make mosaics in which largely wingless− embryos contain patches of wingless+ cells. In these genetic mosaics, using a standard assay for wingless function (the maintenance of engrailed expression), we uncover an induction across germ layers: Wingless made in the mesoderm can sustain engrailed expression in the ectoderm. This result makes clear that Wingless is expressed in the mesoderm until at least one hour after gastrulation and may function in this germ layer in the wild type.
Cardiovascular development in the zebrafish: II. Endocardial progenitors are sequestered within the heart field
Authors: Lee Robert K. K. , Stainier Didier Y. R. , Weinstein Brant M. , Fishman Mark C. 
Published: April 2021

ABSTRACT
We have examined the zebrafish embryo to ascertain the location of endocardial and myocardial progenitors prior to gastrulation, in an attempt to define the earliest stages of cardiac patterning. Currently there is uncertainty as to the spatial and lineage relationship of the progenitors for these two phenotypically distinct cell types that form the two concentric layers of the primitive heart tube. By single-cell injection and tracking, we distinguish a region in the early and midblastula which has the properties of a heart field, in that it defines a zone of cardiac progenitors within which there is a spatial gradient of propensity to generate heart cells, and which regulates, in the sense of adapting to the transplantation of pluripotential cells. This zone extends from the future ventral axis dorsally along the margin, with cardiogenic propensity tapering off laterally and dorsally. Myocardial progenitors are spread through-out this region, but endocardial precursors are restricted to the ventral marginal region. The cardiovascular progeny of the ventral cells include, in addition to endocardium and myocardium, cells in the endothelium and blood.
Micromere fate maps in leech embryos: lineage-specific differences in rates of cell proliferation
Authors: Smith Constance M. , Weisblat David A. 
Published: April 2021

ABSTRACT
Stereotyped early cleavages in glossiphoniid leech embryos yield 25 micromeres, along with 3 macromeres and 10 teloblasts. The micromeres generate prostomial tissues and also give rise to most of the squamous epithelium of a provisional integument that spreads epibolically from the animal pole, covering the rest of the embryo during germinal plate formation.
We systematically injected individual micromeres with fluorescent cell lineage tracers at the time of their birth and quantitatively mapped the contributions of all these cells to the late stage 7 embryo, a time in development that is early in the epibolic expansion. At this time, micromere derivatives comprise two types of cells: squamous epithelial (superficial) cells that cover the germinal bands and the region of the animal cap between the germinal bands; and underlying (deep) cells that are confined to the distal ends of the germinal bands and in the area between their distal ends. We find that individual micromeres contribute clones of deep and/or superficial progeny that are stereotyped with respect to both numbers and types of cells in the clone and the domains that they occupy. The N teloblasts also contribute cells to the squamous epithelium.
We find significant differences in the rate of cell proliferation between different micromere clones. These differences appear to reflect lineage-specific traits, since there is little or no regulation of cell number after ablation of individual micromeres.