bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of ectopic expression of caudal during Drosophila development
Authors: Mlodzik Marek , Gibson Greg , Gehring Walter J. 
Published: April 2021

ABSTRACT
The effects of heat-shock-induced ectopic expression of the homeobox gene caudal (cad) at all stages of Drosophila development have been examined. Presence of cad protein (CAD) at the anterior end of cellular blastoderm embryos was found to disrupt head development and segmentation, due to alteration of the expression of segmentation genes such as fushi taraza and engrailed, as well as repression of head-determining genes such as Deformed. These results support the conclusion that, while CAD is probably required to activate transcription of fushi tarazu in the posterior half of the embryo, it should not be expressed in the anterior half prior to gastrulation, and thus suggest a role for the CAD gradient. Ectopic expression of CAD at later stages of development has no obvious effects on embryogenesis or imaginai disc development, suggesting that the homeotic genes of the Antennapedia and Bithorax Complexes are almost completely epistatic to caudal.
Structure and expression of the mouse Oct2a and Oct2b, two differentially spliced products of the same gene
Authors: Hatzopoulos Antonis K. , Stoykova Anastasia S. , R. Erselius Jörn , Goulding Martyn , Neuman Toomas , Gruss Peter 
Published: April 2021

ABSTRACT
A large family of tissue-specific nuclear proteins interact with the octamer motif ATTTGCAT, a transcriptional regulatory element found in the promoter and enhancer sequences of many genes. As a step towards elucidating the mechanism of this regulation, cDNA clones of the mouse Oct2 protein were isolated. One, called here Oct2b, encodes a larger variant of the previously described Oct2a proteins. The Oct2b cDNA has an insertion of 74 bp close to the 3 ′ end which creates an open reading frame distinct from Oct2a. As a result, the Oct2b protein has a carboxy end which is similar to that of the ubiquitous octamer-binding protein Oct1. Analysis of the Oct2 gene shows that Oct2a and Oct2b are differentially spliced products of the same gene. The insertion in the Oct2b cDNA results from the inclusion of an additional exon in the mRNA which would otherwise reside in an intron sequence of the Oct2a transcript.
RNA analysis demonstrates that both Oct2a and 2b mRNAs are most abundant in B-cells but they are also expressed in a variety of tissues including brain, intestine, testis, kidney, as well as in embryos. Interestingly, the ratio of Oct2a and 2b varies among tissues. In situ hybridization studies during mouse embryogenesis show that the Oct2 gene is widely expressed in the developing nervous system. In contrast, expression in the adult brain is confined to very specific areas which include the suprachiasmatic and medial mammillary nuclei, hippocampus, olfactory tract and the olfactory bulb. Oct2 proteins are present in both neuronal and oligodendroglial cells, although they are more abundant in glial cells.
Stimulatory effects of basic fibroblast growth factor on DNA synthesis in the human embryonic cornea
Authors: Hyldahl Louise , Schofield Paul N. , Engström Wilhelm 
Published: April 2021

ABSTRACT
First trimester human embryonic eye globes were micro dissected so that a passage was opened between the outer environment and the anterior chamber, which rendered free access of tissue culture medium to the endothelial cell monolayer. The dissected eye globes were main tained in organ culture for 24 h in the continuous presence of tritiated thymidine. Sections were cut through the whole eye globes and were subject to autoradiographic analysis in order to estimate the mitogenic response of human corneal endothelial cells to externally supplied growth factors and hormones.
It was found that the corneal endothelial cells could be stimulated to initiate DNA synthesis by exposure to basic fibroblast growth factor (bFGF). The thymidine label ling index nearly doubled after bFGF addition.
Northern blot analysis revealed the presence of bFGF transcripts in the embryonic eye. In contrast we were unable to trace any bFGF transcripts in other first trimester human embryonic organs. In an attempt to determine the topographical distribution of bFGF mRNA within the eye, we found that transcript levels were higher in the posterior regions of the eye globe. Immunostaining with the appropriate antibody showed conclusively that bFGF protein was present in both the anterior and posterior human eye. These results suggest that local production of bFGF may stimulate cell pro liferation in vivo.
The mechanics of notochord elongation, straightening and stiffening in the embryo of Xenopus laevis
Authors: Adams Dany Spencer , Keller Ray , Koehl M. A. R. 
Published: April 2021

Abstract
We have examined the biomechanical development of the notochord of Xenopus early tail-bud embryos by: (1) quantifying morphological and mechanical changes in the embryo during stages 20 – 28, and (2) conducting manipulative experiments to elucidate mechanical roles of various components of the notochord. The notochord, which is composed of a stack of flat cells surrounded by a connective tissue sheath, elongates dramatically and begins straightening between stages 21 and 25. At this time the fiber density in the notochord sheath goes up, the osmotic activity of the notochord cells increases, vacuoles within these cells swell, the internal pressure of the notochord increases 2- to 3-fold, and the flexural stiffness of the notochord rises by an order of magnitude. We suggest that the tendency of the notochord cells to osmotically swell is resisted by the sheath, thereby permitting the internal pressure to rise. This pressure increase results in the greater stiffness that permits the notochord to elongate and straighten without being buckled by the surrounding tissues.
The closely related Drosophila sry β and sry δ zinc finger proteins show differential embryonic expression and distinct patterns of binding sites on polytene chromosomes
Authors: Payre François , Noselli Stéphane , Lefrère Valérie , Vincent Alain 
Published: April 2021

Abstract
Serendipity (sry) beta (β) and delta (δ) are two finger protein genes resulting from a duplication event. Comparison of their respective protein products shows interspersed blocks of conserved and divergent amino-acid sequences. The most extensively conserved region corresponds to the predicted DNA-binding domain which includes 6 contiguous fingers; no significant sequence conservation is found upstream and downstream of the protein-coding region. We have analysed the evolutionary divergence of the sry β and δ proteins on two separate levels, their embryonic pattern of expression and their DNA-binding properties in vitro and in vivo. By using specific antibodies and transformant lines containing β -galactosidase fusion genes, we show that the sry β and sry δ proteins are maternally inherited and present in embryonic nuclei at the onset of zygotic transcription, suggesting that they are transcription factors involved in this process. Zygotic synthesis of the sry β protein starts during nuclear division cycles 12– 13, prior to cellularisation of the blastoderm, while the zygotic sry δ protein is not detectable before germ band extension (stage 10 embryos). Contrary to sry δ, the zygotic sry β protein constitutes only a minor fraction of the total embryonic protein. The sry δ and δ proteins made in E. coli bind to DNA, with partly overlapping specificities. Their in vivo patterns of binding to DNA, visualised by immunostaining polytene chromosomes, differ both in the number and position of their binding sites. Thus changes in expression pattern and DNA-binding specificity have contributed to the evolution of the sry β and δ genes.
Pattern of the insulin-like growth factor II gene expression during early mouse embryogenesis
Authors: Lee Jacqueline E. , Pintar John , Efstratiadis Argiris 
Published: April 2021

Abstract
The mouse insulin-like growth factor II (IGF-II) gene encodes a polypeptide that plays a role in embryonic growth. We have examined the temporal and spatial pattern of expression of this gene in sections of the mouse conceptus between embryonic days 4.0 and 8.5 by in situ hybridization. Abundant IGF-II transcripts were detected in all the trophectodermal derivatives, after implantation. Labeling was then observed in primitive endoderm, but was transient and disappeared after formation of the yolk sac. Expression was next detected in extraembryonic mesoderm at the early primitive streak stage. Labeling in the embryo proper appeared first at the late primitive streak/neural plate stage in lateral mesoderm and in anterior-proximal cells located between the visceral endoderm and the most cranial region of the embryonic ectoderm. The position of the latter cells suggests that their descendants are likely to participate in the formation of the heart and the epithelium of the ventral and lateral walls of the foregut, where intense labeling was observed at the neural fold stage. Hybridization was also detected in cranial mesenchyme, including neural crest cells. The intensity of hybridization signal increased progressively in paraxial (presomitic and somitic) mesoderm, while declining in the ectoplacental cone. The neuroectoderm and surface ectoderm did not exhibit hybridization at any stage. Immunohistochemical analysis indicated co-localization of IGF-II transcripts, translated pre-pro-IGF-II, and the cognate IGF-II/mannose-6-phosphate receptor. These correlations are consistent with the hypothesis that IGF-II has an autocrine function.
Ectoderm nuclei from sea urchin embryos contain a Spec–DNA binding protein similar to the vertebrate transcription factor USF
Authors: Tomlinson Craig R. , Kozlowski Mark T. , Klein William H. 
Published: April 2021

Abstract
The Spec gene family of Strongylocentrotus purpuratus is expressed exclusively in aboral ectoderm cells during embryogenesis. To investigate the regulation of Spec gene activity, the region around the Spec1 transcriptional initiation site was analyzed for sites of protein–DNA interaction. One high-affinity site bound a factor termed SpFl within the Spec1 5′ untranslated leader region at position +39 to +60. The core sequence recognized by SpFl, CACGTG, is the same as that of the upstream stimulatory factor (USF), a widely occurring vertebrate transcription factor containing a myc-HLH motif. A comparison of USF- and SpFl-binding activities suggested that SpFl was a sea urchin version of USF. SpFl activity was detectable only in ectoderm cells of the embryo, implying that it has a role as a cell type-specific transcription factor. SpFl-binding sites were also found upstream of the Spec2a and Spec2c genes in the same conserved sequence block as Spec1. Extracts from Lyte-chinus pictus embryos showed an SpFl-like activity, suggesting that SpFl is conserved in sea urchins. Surprisingly, changes in the Spec1, Spec2a, or Specie genes that removed or modified the SpFl-binding site had no effect on expression when reporter gene fusions containing these mutations were injected into sea urchin eggs and analyzed for expression during embryogenesis. We propose that, while SpFl may not be essential for expression of the exogenously introduced reporter genes, it may be required for proper regulation of the endogenous Spec genes.
Induction of a specialized muscle basal lamina at chimaeric synapses in culture
Authors: Swenarchuk Lauren E. , Champaneria Shashikant , Anderson M. John 
Published: April 2021

Abstract
To identify mechanisms that regulate the formation of the neuromuscular junction, we examined the cellular origin of a heparan sulfate proteoglycan (HSPG) that becomes highly concentrated within the synaptic cleft during the initial deposition of the junctional basal lamina. Using cultured nerve and muscle cells from anuran and urodele embryos, we prepared species-chimaeric synapses that displayed spontaneous cholinergic potentials, and eventually developed organized accumulations of acetylcholine receptors and HSPG at the sites of nerve-muscle contact. To determine the cellular origin of synaptic HSPG molecules, these chimaeric junctions were stained with both species-specific and cross-reactive monoclonal antibodies, labeled with contrasting fluorochromes. Our results demonstrate that synaptic HSPG is derived almost exclusively from muscle. Since it has already been shown that muscle cells can assemble virtually all of the known constituents of the junctional basal lamina into organized surface accumulations, without any input from nerve cells, we consider the possibility that the specialized synaptic basal lamina may be generated primarily by the myofibre, in response to another ‘inductive’ positional signal at the site of nerve-muscle contact.
Rotation of the tectal primordium reveals plasticity of target recognition in retinotectal projection
Authors: Ichijo Hiroyuki , Fujita Setsuya , Matsuno Toru , Nakamura Harukazu 
Published: April 2021

ABSTRACT
Retinotectal projection is precisely organized in a retinotopic manner. In normal projection, temporal retinal axons project to the rostral part of the tectum, and nasal axons to the caudal part of the tectum. The two-dimensional relationship between the retina and the tectum offers a useful experimental system for analysis of neuronal target recognition. We carried out rotation of the tectal primordium in birds at an early stage of development, around the 10-somite stage, to achieve a better understanding of the characteristics of target recognition, especially the rostrocaudal specificity of the tectum. Our results showed that temporal retinal axons projected to the rostral part of the rotated tectum, which was originally caudal, and that nasal axons projected to the caudal part of the rotated tectum, which was originally rostral. Therefore, the tectum that had been rotated at the 10-somite stage received normal topographic projection from the retinal ganglion cells. Rostrocaudal specificity of the tectum for target recognition is not determined by the 10-somite stage and is acquired through interactions between the tectal primordium and its surrounding structures.
Acrosin activation follows its surface exposure and precedes membrane fusion in human sperm acrosome reaction
Authors: Tesarik Jan , Drahorad Josef , Testart Jacques , Mendoza Carmen 
Published: April 2021

ABSTRACT
Evidence has accumulated suggesting multiple roles of acrosin in fertilization, including its participation in early steps of gamete recognition and binding. However, the implication of acrosin in many of these processes is not compatible with its presumptive sequestration within the sperm acrosome until a late phase of the acrosome reaction. In an earlier study (J. Tesarik, J. Drahorad, J. Peknicova, 1988, Fertil. Steril. 50, 133-141), we reported the binding of an anti-acrosin monoclonal antibody (M0-AKR.1) to the plasma membrane overlying the acrosome of human spermatozoa starting the acrosome reaction. In this study, we characterized further this antibody with regard to its reactivity with different forms of acrosin and found that it recognizes specifically an active form of this enzyme and does not react with its proenzyme form. MO-AKR.l was thus used as a probe for in situ analysis of acrosin activation during the acrosome reaction. When suspensions of living spermatozoa were incubated with MO-AKR.l and with another monoclonal antibody (T6) directed to an intra-acrosomal cytoskeletal protein, significantly more spermatozoa reacted with the former antibody than with the latter; this indicated that some of the spermatozoa showing acrosin immunoreactivity carried activated acrosin on the cell surface, while their acrosome was still impermeable to intra-acrosomal-directed probes. The size of this particular sperm subpopulation was increased by the action of follicular fluid (a natural acrosome reaction inducer), but not ionophore A23187 (an artificial acrosome reaction inducer); it corresponded to the proportion of spermatozoa showing acrosin immunoreactivity on the plasma membrane but neither intra-acrosomal staining nor perceptible membrane perturbations when examined by immunoelectron microscopy. When spermatozoa were pre-incubated with protease inhibitors before the addition of acrosome reaction-inducing agents, the percentage of cells binding MO-AKR.l was markedly reduced. These data suggest that limited acrosin activation on the sperm plasma membrane is an early event in the physiological acrosome reaction.
The embryonic development of larval muscles in Drosophila
Authors: Bate Michael 
Published: April 2021

Abstract
Each of the abdominal hemisegments A2–A7 in the Drosophila larva has a stereotyped pattern of 30 muscles. The pattern is complete by 13 h after egg laying, but the development of individual muscles has begun with the definition of precursors at least by the onset of germ band shortening, some 5.5 h earlier. The earliest signs of muscle differentiation are cell fusions, which occur in the ventralmost mesoderm overlying the CNS and at stereotyped positions in the rest of the mesoderm as the germ band shortens. At the end of shortening, the pattern of muscle precursors produced by these fusions is complete. Precursors filled with dye reveal extensive fine processes probably involved in itially in cell fusion and, subsequently, in navigation over the epidermis to form attachment points. The muscle pattern is formed before innervation and without cell death. Thus, neither of these processes is involved in determining the distribution of precursors. Evidence is presented for the view that the development of the larval muscle pattern in Drosophila depends on a prior segregation of founder cells at appropriate locations in the mesoderm with which other cells fuse to form the precursors.
Zygotic activity of the nullo locus is required to stabilize the actin-myosin network during cellularization in Drosophila
Authors: Simpson Lesilee , Wieschaus Eric 
Published: April 2021

Abstract
Cellularization of the Drosophila embryo requires the establishment of a hexagonal network of actin and myosin filaments that are interconnected around the nuclei in the cortex of the syncytial blastoderm. This cytoskeletal network provides the framework and possibly the contractile force for the membrane invaginations that synchronously subdivide the syncytial embryo into individual cells. Zygotic expression of the nullo locus is essential for the preservation of an intact actin-myosin network. Embryos deleted for the nullo locus have a disrupted network, resulting in the formation of many multinucleate cells. We show that nullo is not required for the initial formation of the actin-myosin network, but is necessary for the maintenanee of its hexagonal shape during cellularization. The phenotype of embryonic mosaics is nonautonomous, indicating that nullo does not have to be expressed in every nucleus for proper cellularization. Examination of nullo mutant clones in adults reveals that nullo activity is not required for cell division in imaginai discs. Furthermore, germline clone experiments suggest that maternal expression of the nullo locus is not essential for either germline proliferation or the cellularization of progeny. We propose a model in which nullo functions specifically at cellularization to stabilize the actinmyosin network during contraction.
A cytoplasmic determinant for dorsal axis formation in an early embryo of Xenopus laevis
Authors: Yuge M. , Kobayakawa Y. , Fujisue M. , Yamana K. 
Published: April 2021

Abstract
In Xenopus laevis, dorsal cells that arise at the future dorsal side of an early cleaving embryo have already acquired the ability to cause axis formation. Since the distribution of cytoplasmic components is markedly heterogeneous in an egg and embryo, it has been supposed that the dorsal cells are endowed with the activity to form axial structures by inheriting a unique cytoplasmic component or components localized in the dorsal region of an egg or embryo. However, there has been no direct evidence for this.
To examine the activity of the cytoplasm of dorsal cells, we injected cytoplasm (dorsal cytoplasm) from dorsal vegetal cells of a Xenopus 16-cell embryo into ventral vegetal cells of a simultaneous recipient. The cytoplasm caused secondary axis formation in 42 % of recipients. Histological examination revealed that well-developed secondary axes included notochord, as well as a neural tube and somites. However, injection of cytoplasm of ventral vegetal cells never caused secondary axis and most recipients became normal tailbud embryos. Furthermore, about two-thirds of ventral isolated halves injected with dorsal cytoplasm formed axial structures.
These results show that dorsal, but not ventral, cytoplasm contains the component or components responsible for axis formation. This can be the first step towards identifying the molecular basis of dorsal axis formation.
Dynamic changes in the distribution of cytoplasmic myosin during Drosophila embryogenesis
Authors: Young Paul E. , Pesacreta Thomas C. , Kiehart Daniel P. 
Published: April 2021

ABSTRACT
Dramatic changes in the localization of conventional non-muscle myosin characterize early embryogenesis in Drosophila melanogaster. During cellularization, myosin is concentrated around the furrow canals that form the leading margin of the plasma membrane as it plunges inward to package each somatic nucleus into a columnar epithelial cell. During gastrulation, there is specific antimyosin staining at the apical ends of those cells that change shape in regions of invagination.
Both of these localizations appear to result from a redistribution of a cortical store of maternal myosin. In the preblastoderm embryo, myosin is localized to the egg cortex, sub-cortical arrays of inclusions, and, diffusely, the yolk-free periplasm. At the syncytial blastoderm stage, myosin is found within cytoskeietal caps associated with the somatic nuclei at the embryonic surface. Following the final syncytial division, these myosin caps give rise to the myosin rings observed during cellularization.
These distributions are observed with both whole immune serum and affinity-purified antibodies directed against Drosophila non-muscle myosin heavy chain. They are not detected in embryos stained with antiDrosophila muscle myosin antiserum or with preimmune serum. Although immunolocalization can only suggest possible function, these myosin localizations and the coincident changes in cell morphology are consistent with a key role for non-muscle myosin in powering cellularization and gastrulation during embryogenesis.