bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of proneural gene expression and cell fate during neuroblast segregation in the Drosophila embryo
Authors: Skeath James B. , Carroll Sean B. 
Published: April 2021

Abstract
The Drosophila embryonic central nervous system develops from sets of progenitor neuroblasts which segregate from the neuroectoderm during early embryogenesis. Cells within this region can follow either the neural or epidermal developmental pathway, a decision guided by two opposing classes of genes. The proneural genes, including the members of the achaete-scute complex (AS-C), promote neurogenesis, while the neurogenic genes prevent neurogenesis and facilitate epidermal development. To understand the role that proneural gene expression and regulation play in the choice between neurogenesis and epidermogenesis, we examined the temporal and spatial expression pattern of the achaete (ac) regulatory protein in normal and neurogenic mutant embryos. The ac protein is first expressed in a repeating pattern of four ectodermal cell clusters per hemisegment. Even though 5 –7 cells initially express ac in each cluster, only one, the neuroblast, continues to express ac. The repression of ac in the remaining cells of the cluster requires zygotic neurogenic gene function. In embryos lacking any one of five genes, the restriction of ac expression to single cells does not occur; instead, all cells of each cluster continue to express ac, enlarge, delaminate and become neuroblasts. It appears that one key function of the neurogenic genes is to silence proneural gene expression within the nonsegregating cells of the initial ectodermal clusters, thereby permitting epidermal development.
Expression of the two mannose 6-phosphate receptors is spatially and temporally different during mouse embryogenesis
Authors: Matzner U. , Figura K. Von , Pohlmann R. 
Published: April 2021

Abstract
Mammalian cells express two mannose 6-phosphate receptors, MPR46 and MPR300, both of which mediate the targeting of lysosomal enzymes to lysosomes. Additionally the receptors mediate the secretion (MPR46) and the endocytosis (MPR300) of lysosomal enzymes and the binding of IGFH (MPR300). We have analyzed the distribution of MPR46 and MPR300 transcripts during mouse embryogenesis by in situ hybridization. Up to day 15.5 of embryonic development we found a non-overlapping distribution of the transcripts for the two receptors. High expression of MPR46 was observed at sites of hemopoiesis and in the thymus while MPR300 was highly expressed in the cardiovascular system. Late in embryogenesis (day 17.5) a wide variety of tissues expressed the receptors, but still the expression pattern was almost non-overlapping. This unexpected complementary expression pattern points to specific functions of the two mannose 6-phosphate receptors during mouse embryogenesis.
Interactions between primordial germ cells play a role in their migration in mouse embryos
Authors: Gomperts Miranda , Garcia-Castro Martin , Wylie Chris , Heasman Janet 
Published: April 2021

ABSTRACT
Primordial germ cells (PGCs) are the founder cell population of the gametes which form during the sexually mature stage of the life cycle. In the mouse, they arise early in embryogenesis, first becoming visible in the extraembryonic mesoderm, posterior to the primitive streak, at 7.5 days post coitum (d.p.c.). They subsequently become incorporated into the epithelium of the hind gut, from which they emigrate (9.5 d.p.c.) and move first into the dorsal mesentery (10.5 d.p.c.), and then into the genital ridges that lie on the dorsal body wall (11.5 d.p.c.). We have used confocal microscopy to study PGCs stained with an antibody that reacts with a carbohydrate antigen (Stage-Specific Embryonic Antigen-1, SSEA-1) carried on the PGC surface. This allows the study of the whole PGC surface, at different stages of their migration.
The appearance of PGCs in tissue sections has given rise to the conventional view that they migrate as individuals, each arriving in turn at the genital ridge. In this paper, we show that PGCs leave the hind gut independently, but then extend long (up to 40 μm) processes, with which they link up to each other to form extensive networks. During the 10.5 – 11.5 d.p.c. period, these networks of PGCs aggregate into groups of tightly apposed cells in the genital ridges. As this occurs, their processes are lost, and their appearance suggests they are now non-motile. Furthermore, we find that PGCs taken from the dorsal mesentery at 10.5 d.p.c. perform the same sequence of movements in culture. At first they are actively locomotory. They become linked to other PGCs via long processes and form clusters of non-motile cells. This aggregation together into closely apposed masses may be an important component of PGC migration from the gut into the genital ridges and would also allow signalling interactions between PGCs.
We show also that the first PGCs to emigrate from the hind gut, between 9 and 9.5 d.p.c., do so directly into the area where the genital ridges will form. This suggests that an adhesive interaction between these ‘pioneer germ cells’ and the target tissue may play a role in the localisation of PGCs into the genital ridges as they aggregate.
A functional test for maternally inherited cadherin in Xenopus shows its importance in cell adhesion at the blastula stage
Authors: Heasman Janet , Ginsberg Dorit , Geiger Benjamin , Goldstone Kim , Pratt Travis , Yoshida-Noro Chikako , Wylie Chris 
Published: April 2021

ABSTRACT
We report here on the consequences of reducing the expression of EP-cadherin at the earliest stages of Xenopus development. Injection of oligodeoxynucleotides antisense to maternal EP-cadherin mRNA into full-grown oocytes reduced the mRNA level in oocytes, and the protein level in blastulae. Adhesion between blastomeres was significantly reduced, as seen in whole embryos, and in assays of the ability of blastomeres to reaggregate in culture. This effect was especially conspicuous in the inner cells of the blastula and included the disruption of the blastocoel. The severity of the EP-cadherin mRNA depletion and of the disaggregation phenotype was dose dependent. This phenotype was rescued by the injection into EP-cadherin mRNA-depleted oocytes of the mRNA coding for a related cadherin, E-cadherin, that is normally expressed at the gastrula stage in the embryonic ectoderm.
A central role for epidermal segment border cells in the induction of muscle patterning in the Drosophila embryo
Authors: Volk Talila , VijayRaghavan K. 
Published: April 2021

ABSTRACT
The correct patterning of muscles in the Drosophila embryo depends on the migration of developing muscles over the ectoderm and on the attachment of these muscles to specific attachment sites. We investigate the mechanisms that are involved in this process and describe experiments that allow a genetic dissection of the role of the ectoderm in muscle migration and attachment.
We show that cells along the segmental border in the ectoderm are used by the developing muscles to reach their attachment sites. These segment border cells are recognized by dissociated myotubes in single suspensions in culture. Thus, developing muscles have properties that allow the specific recognition of the segment border cells and migrate to attach to these cells. The segment border cells are absent in the mutant wingless and naked. In these mutants, the muscles are severely disorganized. We show that this is not a mere consequence of disruption of the epidermis, since, in the mutant patched, where segmental patterning is affected, the segment border cells are present near their normal position; the muscles in this mutant are relatively organized. Similarly, in the mutant lines where ectopic segment border cells are present, the observed muscle derangement correlates well with the ectopic attachment sites that are present.
Finally, we have analyzed mutants at the stripe locus and have shown that lethal alleles disrupt muscle organization during embryogenesis. Enhancer-trap alleles of stripe that we have analyzed show reporter gene expression in the segment border cells.
Our results indicate a role for the segment border cells in guidance of migrating muscle fibers to their attachment sites.
Primordial germ cell migration in Drosophila melanogaster is controlled by somatic tissue
Authors: Jaglarz Mariusz K. , Howard Kenneth R. 
Published: April 2021

ABSTRACT
In Drosophila, as in many other organisms, primordial germ cells show invasive and migratory behavior moving from their site of origin to the somatic component of the gonad. At a characteristic time in development, the primordial germ cells pass across the primordium of the gut and migrate on its outer surface toward the mesoderm, where they eventually associate with the somatic tissues of the gonad. Here we demonstrate that the exit and migration are specific behaviors of the primordial germ cells and that they are controlled by the somatic tissue of the embryo rather than by a germ cell autonomous clock. Using mutations, we show that these controlling somatic events probably occur in the tissue of the gut primordium itself.
The mouse tissue plasminogen activator gene 5′ flanking region directs appropriate expression in development and a seizure-enhanced response in the CNS
Authors: Carroll Pamela M. , Tsirka Stella E. , Richards William G. , Frohman Michael A. , Strickland Sidney 
Published: April 2021

ABSTRACT
Tissue plasminogen activator (t-PA) is a secreted serine protease implicated in multiple aspects of development. In the adult rat brain, transcription of t-PA is an immediate-early response in the hippocampus following treatments that induce neuronal plasticity. To study the sequence elements that govern transcription of this gene, in situ analysis was used to define t-PA’s temporal and spatial expression pattern in midgestation embryos. Transgenic mice were then generated carrying t-PA 5′ flanking sequences linked to the E. coli lacZ gene. Constructs containing 4 kb of the flanking sequences (4.0TAMGAL) confer β-galactosidase activity mostly to the same tissues that exhibit high levels of t-PA mRNA by in situ analysis. In 4.0TAMGAL embryos from embryonic day 8.5 (E8.5) to 13.5 (E13.5), the majority of expression observed is localized to neural ectoderm-derived tissues. β-galactosidase activity is first detected in restricted neuromeres in the midbrain and diencephalon, at E8.5 and E9.5 respectively. At E10.5, transgene expression is observed in neural crest-derived cranial nerves and dorsal root ganglia, but not placode-derived cranial nerves. From E10.5 to E13.5, β-galactosidase activity is observed in postmitotic neurons of the midbrain, spinal cord, neural retina and the developing olfactory system. β-galactosidase activity is also detected in areas undergoing tissue remodeling such as the pinna of the ear, whisker follicles and the limbs. In adult mice, lacZ is expressed in the hippocampus and this expression was found to be enhanced upon seizure in the giant pyramidal neurons of CA3. These results reinforce the concept that t-PA plays a role in neurogenesis and morphogenesis, and identifies the promoter region that directs its transcriptional regulation both in development and in the CNS.
Distribution of, and a putative role for, the cell-surface neutral metallo-endopeptidases during mammalian craniofacial development
Authors: Spencer-Dene Bradley , Thorogood Peter , Nair Sean , Kenny A. John , Harris Malcolm , Henderson Brian 
Published: April 2021

ABSTRACT
Endopeptidase-24.11 (neutral endopeptidase, neprilysin, ‘enkephalinase’, EC 3.4.24.11) and endopeptidase-24.18 (endopeptidase-2, meprin, EC 3.4.24.18) are cell-surface zinc-dependent metallo-endopeptidases able to cleave a variety of bioactive peptides including growth factors. We report the first study of the cellular and tissue distribution of both enzymes and of the mRNA for NEP during embryonic development in the rat. Endopeptidase-24.11 protein was first detected at E10 in the lining of the gut and, at E12, the enzyme was present on the notochord, medial and lateral nasal processes, otocyst, mesonephros, heart and neuroepithelium. In contrast, at this time endopeptidase-24.18 was present only on the apical surface of the neuroepithelial cells. By E14 and E16, NEP was also detected in a wide range of craniofacial structures, notably the palatal mesenchyme, the choroid plexus, tongue and perichondrium. The distribution of endopeptidase-24.18 at these stages was restricted to the inner ear, the nasal conchae, and ependymal layer of the brain ventricles and the choroid plexus. Although endopeptidase-24.11 had been detectable in the craniofacial vasculature at E12 and E14, this was no longer apparent at E16. Significantly, the distribution of endopeptidase-24.11 mRNA closely matched the immunolocalization of the protein at all stages investigated.
In order to explore the functional role of these enzymes, inhibition studies were carried out using two selective inhibitors of endopeptidase-24.11, phosphoramidon and thiorphan. E9.5 and E10.5 embryos exposed to either inhibitor displayed a characteristic, asymmetric abnormality consisting of a spherical swelling, possibly associated with a haematoma, predominantly on the left side of the prosencephalon, and the severity of this defect appeared to be a dose-dependent phenomenon. This study suggests that these enzymes play previously unrecognized roles during mammalian embryonic development.
YIGSR domain of laminin binds surface receptors of mesenchyme and stimulates migration during gastrulation in sea urchins
Authors: Crawford Bryan D. , Burke Robert D. 
Published: April 2021

ABSTRACT
During gastrulation in sea urchins, cells at the tip of the archenteron extend filopodia that attach to the blastocoel wall and are thought to assist in the elongation of the archenteron. Upon completion of gastrulation, these cells migrate into the blastocoel. Time-lapse video records were made of preparations from which ectodermal cells have been removed, leaving the archenteron, mesenchyme cells and blastocoelar extracellular matrix (ECM) bounded by the basal lamina. In preparations of late gastrulae, cells at the tip of the archenteron extend filopodia that attach to the basal lamina and pull it inward, collapsing the preparation. This collapse does not occur in preparations made prior to the elongation phase and can be inhibited with cytochalasin B and azide, but not with colchicine. Migratory behavior increased in preparations treated with the laminin-derived peptide Tyr-Ile-Gly-Ser-Arg (YIGSR). Cells extend and retract filopodia, collapse the ECM and migrate out of the preparation. This behavior was not observed in preparations treated with whole laminin, fibronectin or Arg-Gly-Asp-Ser (RGDS) peptides. Cells in preparations treated with YIGSR extend significantly more processes than those incubated in RGDS, laminin, fibronectin or BSA. This effect is titratable between 10−3 and 10−6 M. Whole laminin has a significant inhibitory effect on the number of cell processes observed. Double labelling experiments with biotinylated laminin or biotinylated CDPGYIGSR and a mesenchyme-specific monoclonal antibody (Sp12) reveal that laminin and CDPGYIGSR label mesenchymal and non-mesenchymal cells. A CDPGYIGSR affinity column binds a 125I-labelled cell surface component, which elutes with YIGSR and has an Mr of about 80×103 on SDS-PAGE. We propose that cells at the tip of the archenteron attach to the basal lamina during archenteron elongation, and that domains of laminin containing YIGSR in the basal lamina of the target region stimulate migratory behavior in these cells.
Disruption of morphogenesis and transformation of the suspensor in abnormal suspensor mutants of Arabidopsis
Authors: Schwartz Brian W. , Yeung Edward C. , Meinke David W. 
Published: April 2021

ABSTRACT
The suspensor is the first differentiated structure produced during plant embryogenesis. In most angiosperms, the suspensor functions early in development to provide nutrients and growth regulators to the embryo proper. In Arabidopsis, the suspensor undergoes programmed cell death at the torpedo stage and is not present in mature seeds. We have identified at least 16 embryo-defective mutants of Arabidopsis that exhibit an enlarged suspensor phenotype at maturity. In this report, we focus on seven abnormal suspensor mutants, which define three genetic loci (sus1, sus2 and sus3). Recessive mutations at each of these loci disrupt morphogenesis in the embryo proper and consistently result in the formation of a large suspensor. Defects in the embryo proper appear by the globular stage of development; abnormalities in the suspensor are detected soon after at the heart stage. Storage protein and lipid bodies, which normally accumulate only in the embryo proper late in embryogenesis, are present in both the arrested embryo proper and enlarged suspensor. Therefore, cell differentiation in the embryo proper can proceed in the absence of normal morphogenesis, and the suspensor can be transformed into a structure with features normally restricted to the embryo proper. These observations are consistent with a model in which normal development of the embryo proper limits growth and differentiation of the suspensor. Altered development of the embryo proper in mutant seeds leads indirectly to proliferation of suspensor cells and expression of properties characteristic of the embryo proper. Ultimately, growth of the transformed suspensor is limited by the same genetic defect that disrupts development of the embryo proper. The availability of multiple alleles of sus1 and sus2, including T-DNA tagged alleles of each, will facilitate the cloning of these essential genes and molecular analysis of interactions between the embryo proper and suspensor early in development.
Discrete endogenous signals mediate neural competence and induction in P19 embryonal carcinoma stem cells
Authors: Pruitt Steven C. 
Published: April 2021

ABSTRACT
Endogenous signals capable of inducing neuroectodermal differentiation are expressed by differentiating P19 EC cells in vitro. The present study demonstrates that at least two discrete signals are required. One is expressed by isolated primitive streak mesoderm-like cell lines and has the capacity to induce the expression of Pax-3 but, alone, induces neural differentiation inefficiently. The second signal is not expressed by the primitive streak mesoderm-like cell line but is present in conditioned media from differentiating P19 EC cells following DMSO treatment. This signal does not induce either Pax-3 expression or morphological differentiation and does not commit stem cells to a neuroectodermal fate. Rather, it acts synergistically with the signal derived from the primitive streak mesoderm-like cells to increase the efficiency with which stem cells respond initially by Pax-3 expression and subsequently by differentiation towards neural lineages. The activity of this second signal can be replaced by forskolin and 3-isobutyl-1-methyl-xanthine suggesting that its effects are transduced by a cyclic nucleotide-dependent pathway.
Pollen-pistil interactions and developmental regulation of pollen tube growth in Arabidopsis
Authors: Kandasamy Muthugapatti K. , Nasrallah June B. , Nasrallah Mikhail E. 
Published: April 2021

ABSTRACT
A developmental analysis of pollination responses in Arabidopsis implicates pollen as well as stigma maturation factors in the acquisition of reproductive function. In the anther, competence of pollen to germinate and to produce pollen tubes in situ occurred late in development. In the pistil, competence to support pollen germination and tube growth extended over a broad developmental window, and abundant as well as efficient pollen tube development was observed on pistils at anthesis and for a period of 1-2 days prior to flower opening. In contrast, pollen tube growth on immature pistils was found to proceed at low efficiency, at reduced growth rates, and with lack of directionality. Based on the pattern of pollen tube growth at different stages of pistil maturation, temporally regulated signals emanating from specialized cells of the pistil are inferred to be operative in each of the four identified phases of pollen tube growth. In the stigma and the stylar transmitting tissue, these signals directed the path of intra-specific pollen tubes as well as pollen tubes from another cruciferous genera, Brassica. By contrast, in the ovary, signaling by the ovule was effective only on intra-specific pollen tubes and was thus identified as the basis of inter-specific incompatibility. Furthermore, the acquisition of reproductive function was found to involve, in addition to the induction of a variety of stimulatory signals, a heretofore unrecognized developmental restriction in the capacity of epidermal surfaces of the flower to support pollen tube growth.
dachshund encodes a nuclear protein required for normal eye and leg development in Drosophila
Authors: Mardon Graeme , Solomon Noah M. , Rubin Gerald M. 
Published: April 2021

ABSTRACT
Neural specification and differentiation in the Drosophila eye sweep across the unpatterned epithelial monolayer of the eye imaginal disc following a developmental wave termed the morphogenetic furrow. The furrow begins at the posterior margin of the eye imaginal disc and moves anteriorly as a linear front. Progression of the furrow requires the function of hedgehog, which encodes a secreted signaling protein. We characterize mutations in dachshund, a gene that encodes a novel nuclear protein required for normal cell-fate determination of imaginal disc cells. In the absence of dachshund function, cells at the posterior margin of the eye disc fail to follow a retinal differentiation pathway and appear to adopt a cuticle fate instead. These cells are therefore unable to respond to pattern propagation signals such as hedgehog and furrow initiation does not occur. In contrast, cells in more anterior portions of the eye disc are able to differentiate as retinal cells in the absence of dachshund activity and respond normally to patterning signals. These results suggest that posterior margin cells are distinct from other cells of the eye imaginal disc by early stages of development. dachshund is also necessary for proper differentiation of a subset of segments in the developing leg. Null mutations in dachshund result in flies with no eyes and shortened legs.
The Notch signalling pathway is required for Enhancer of split bHLH protein expression during neurogenesis in the Drosophila embryo
Authors: Jennings Barbara , Preiss Anette , Delidakis Christos , Bray Sarah 
Published: April 2021

ABSTRACT
The Enhancer of split locus is required during many cell-fate decisions in Drosophila, including the segregation of neural precursors in the embryo. We have generated monoclonal antibodies that recognise some of the basic helix-loop-helix proteins encoded by the Enhancer of split locus and have used them to examine expression of Enhancer of split proteins during neurogenesis. The proteins are expressed in a dynamic pattern in the ventral neurogenic region and are confined to those ectodermal cells that surround a neuroblast in the process of delaminating. There is no staining in the neuroblasts themselves. We have also examined the relationship between Enhancer of split protein accumulation and the Notch signalling pathway. Protein expression is abolished in a number of neurogenic mutant backgrounds, including Notch, but is increased as a result of expressing a constitutively active Notch product. We conclude that Notch signalling activity is directly responsible for the accumulation of basic helix-loop-helix proteins encoded by the Enhancer of split locus.