bluuebunny/crossref_metadata_2025_split huggingface dataset:
5-HT causes an increase in cAMP that stimulates, rather than inhibits, oocyte maturation in marine nemertean worms
Authors: Stricker Stephen A. , Smythe Toni L. 
Published: April 2021

ABSTRACT
In the nemertean worms Cerebratulus lacteus and Micrura alaskensis, 5-HT (=5-hydroxytryptamine, or serotonin) causes prophase-arrested oocytes to mature and complete germinal vesicle breakdown (GVBD). To identify the intracellular pathway that mediates 5-HT stimulation, follicle-free oocytes of nemerteans were assessed for GVBD rates in the presence or absence of 5-HT after being treated with various modulators of cAMP, a well known transducer of 5-HT signaling and an important regulator of hormone-induced maturation in general. Unlike in many animals where high levels of intra-oocytic cAMP block maturation, treatment of follicle-free nemertean oocytes with agents that elevate cAMP (8-bromo-cAMP, forskolin or inhibitors of phosphodiesterases) triggered GVBD in the absence of added 5-HT. Similarly, 5-HT caused a substantial cAMP increase prior to GVBD in nemertean oocytes that had been pre-injected with a cAMP fluorosensor. Such a rise in cAMP seemed to involve G-protein-mediated signaling and protein kinase A (PKA) stimulation, based on the inhibition of 5-HT-induced GVBD by specific antagonists of these transduction steps. Although the downstream targets of activated PKA remain unknown, neither the synthesis of new proteins nor the activation of MAPKs (mitogen-activated protein kinases) appeared to be required for GVBD after 5-HT stimulation. Alternatively, pre-incubation in roscovitine, an inhibitor of maturation-promoting factor (MPF), prevented GVBD, indicating that maturing oocytes eventually need to elevate their MPF levels, as has been documented for other animals. Collectively, this study demonstrates for the first time that 5-HT can cause immature oocytes to undergo an increase in cAMP that stimulates, rather than inhibits, meiotic maturation. The possible relationship between such a form of oocyte maturation and that observed in other animals is discussed.
A requirement forNotchin the genesis of a subset of glial cells in theDrosophilaembryonic central nervous system which arise through asymmetric divisions
Authors: Udolph Gerald , Rath Priyadarshini , Chia William 
Published: April 2021

ABSTRACTIn the Drosophila central nervous system (CNS) glial cells are known to be generated from glioblasts, which produce exclusively glia or neuroglioblasts that bifurcate to produce both neuronal and glial sublineages. We show that the genesis of a subset of glial cells, the subperineurial glia (SPGs), involves a new mechanism and requires Notch. We demonstrate that the SPGs share direct sibling relationships with neurones and are the products of asymmetric divisions. This mechanism of specifying glial cell fates within the CNS is novel and provides further insight into regulatory interactions leading to glial cell fate determination. Furthermore, we show that Notch signalling positively regulates glial cells missing (gcm) expression in the context of SPG development.
Developmentally distinct MYB genes encode functionally equivalent proteins in Arabidopsis
Authors: Lee Myeong Min , Schiefelbein John 
Published: April 2021

ABSTRACT
The duplication and divergence of developmental control genes is thought to have driven morphological diversification during the evolution of multicellular organisms. To examine the molecular basis of this process, we analyzed the functional relationship between two paralogous MYB transcription factor genes, WEREWOLF (WER) and GLABROUS1 (GL1), in Arabidopsis. The WER and GL1 genes specify distinct cell types and exhibit non-overlapping expression patterns during Arabidopsis development. Nevertheless, reciprocal complementation experiments with a series of gene fusions showed that WER and GL1 encode functionally equivalent proteins, and their unique roles in plant development are entirely due to differences in their cis-regulatory sequences. Similar experiments with a distantly related MYB gene (MYB2) showed that its product cannot functionally substitute for WER or GL1. Furthermore, an analysis of the WER and GL1 proteins shows that conserved sequences correspond to specific functional domains. These results provide new insights into the evolution of the MYB gene family in Arabidopsis, and, more generally, they demonstrate that novel developmental gene function may arise solely by the modification of cis-regulatory sequences.
Induced repatterning of type XVIII collagen expression in ureter bud from kidney to lung type: association with sonic hedgehog and ectopic surfactant protein C
Authors: Lin Yanfeng , Zhang Shaobing , Rehn Marko , Itäranta Petri , Tuukkanen Juha , Heljäsvaara Ritva , Peltoketo Hellevi , Pihlajaniemi Taina , Vainio Seppo 
Published: April 2021

ABSTRACTEpithelial-mesenchymal tissue interactions regulate the formation of signaling centers that play a role in the coordination of organogenesis, but it is not clear how their activity leads to differences in organogenesis. We report that type XVIII collagen, which contains both a frizzled and an endostatin domain, is expressed throughout the respective epithelial bud at the initiation of lung and kidney organogenesis. It becomes localized to the epithelial tips in the lung during the early stages of epithelial branching, while its expression in the kidney is confined to the epithelial stalk region and is lost from the nearly formed ureter tips, thus displaying the reverse pattern to that in the lung. In recombinants, between ureter bud and lung mesenchyme, type XVIII collagen expression pattern in the ureter bud shifts from the kidney to the lung type, accompanied by a shift in sonic hedgehog expression in the epithelium. The lung mesenchyme is also sufficient to induce ectopic lung surfactant protein C expression in the ureter bud. Moreover, the shift in type XVIII collagen expression is associated with changes in ureter development, thus resembling aspects of early lung type epigenesis in the recombinants. Respecification of collagen is necessary for the repatterning process, as type XVIII collagen antibody blocking had no effect on ureter development in the intact kidney, whereas it reduced the number of epithelial tips in the lung and completely blocked ureter development with lung mesenchyme. Type XVIII collagen antibody blocking also led to a notable reduction in the expression of Wnt2, which is expressed in the lung mesenchyme but not in that of the kidney, suggesting a regulatory interaction between this collagen and Wnt2. Respecification also occurred in a chimeric organ containing the ureter bud and both kidney and lung mesenchymes, indicating that the epithelial tips can integrate the morphogenetic signals independently. A glial cell line-derived neurotrophic factor signal induces loss of type XVIII collagen from the ureter tips and renders the ureter bud competent for repatterning by lung mesenchyme-derived signals. Our data suggest that differential organ morphogenesis is regulated by an intra-organ patterning process that involves coordination between inductive signals and matrix molecules, such as type XVIII collagen.
Secreted FGFR3, but not FGFR1, inhibits lens fiber differentiation
Authors: Govindarajan Venkatesh , Overbeek Paul A. 
Published: April 2021

ABSTRACT
The vertebrate lens has a distinct polarity with cuboidal epithelial cells on the anterior side and differentiated fiber cells on the posterior side. It has been proposed that the anterior-posterior polarity of the lens is imposed by factors present in the ocular media surrounding the lens (aqueous and vitreous humor). The differentiation factors have been hypothesized to be members of the fibroblast growth factor (FGF) family. Though FGFs have been shown to be sufficient for induction of lens differentiation both in vivo and in vitro, they have not been demonstrated to be necessary for endogenous initiation of fiber cell differentiation. To test this possibility, we have generated transgenic mice with ocular expression of secreted self- dimerizing versions of FGFR1 (FR1) and FGFR3 (FR3). Expression of FR3, but not FR1, leads to an expansion of proliferating epithelial cells from the anterior to the posterior side of the lens due to a delay in the initiation of fiber cell differentiation. This delay is most apparent postnatally and correlates with appropriate changes in expression of marker genes including p57KIP2, Maf and Prox1. Phosphorylation of Erk1 and Erk2 was reduced in the lenses of FR3 mice compared with nontransgenic mice. Though differentiation was delayed in FR3 mice, the lens epithelial cells still retained their intrinsic ability to respond to FGF stimulation. Based on these results we propose that the initiation of lens fiber cell differentiation in mice requires FGF receptor signaling and that one of the lens differentiation signals in the vitreous humor is a ligand for FR3, and is therefore likely to be an FGF or FGF-like factor.
Drosophila OVO regulates ovarian tumor transcription by binding unusually near the transcription start site
Authors: Lü Jining , Oliver Brian 
Published: April 2021

ABSTRACT
Evolutionarily conserved ovo loci encode developmentally regulated, sequence-specific, DNA-binding, C2H2-zinc-finger proteins required in the germline and epidermal cells of flies and mice. The direct targets of OVO activity are not known. Genetic experiments suggest that ovo acts in the same regulatory network as ovarian tumor (otu), but the relative position of these genes in the pathway is controversial. Three OVO-binding sites exist in a compact regulatory region that controls germline expression of the otu gene. Interestingly, the strongest OVO-binding site is very near the otu transcription start, where basal transcriptional complexes must function. Loss-of-function, gain-of-function and promoter swapping constructs demonstrate that OVO binding near the transcription start site is required for OVO-dependent otu transcription in vivo. These data unambiguously identify otu as a direct OVO target gene and raise the tantalizing possibility that an OVO site, at the location normally occupied by basal components, functions as part of a specialized core promoter.
Low proliferative and high migratory activity in the area ofBrachyuryexpressing mesoderm progenitor cells in the gastrulating rabbit embryo
Authors: Viebahn Christoph , Stortz Christof , Mitchell Sally A. , Blum Martin 
Published: April 2021

General mechanisms initiating the gastrulation process in early animal development are still elusive, not least because embryonic morphology differs widely among species. The rabbit embryo is revived here as a model to study vertebrate gastrulation, because its relatively simple morphology at the appropriate stages makes interspecific differences and similarities particularly obvious between mammals and birds. Three approaches that centre on mesoderm specification as a key event at the start of gastrulation were chosen.(1) A cDNA fragment encoding 212 amino acids of the rabbit Brachyury gene was cloned by RT-PCR and used as a molecular marker for mesoderm progenitors. Whole-mount in situ hybridisation revealed single Brachyury-expressing cells in the epiblast at 6.2 days post conception, i.e. several hours before the first ingressing mesoderm cells can be detected histologically. With the anterior marginal crescent as a landmark, these mesoderm progenitors are shown to lie in a posterior quadrant of the embryonic disc, which we call the posterior gastrula extension (PGE), for reasons established during the following functional analysis.(2) Vital dye (DiI) labelling in vitro suggests that epiblast cells arrive in the PGE from anterior parts of the embryonic disc and then move within this area in a complex pattern of posterior, centripetal and anterior directions to form the primitive streak.(3) BrdU labelling shows that proliferation is reduced in the PGE, while the remaining anterior part of the embryonic disc contains several areas of increased proliferation. These results reveal similarities with the chick with respect to Brachyury expression and cellular migration. They differ, however, in that local differences in proliferation are not seen in the pre-streak avian embryo. Rather, rabbit epiblast cells start mesoderm differentiation in a way similar to Drosophila, where a transient downregulation of proliferation initiates mesoderm differentiation and, hence, gastrulation.
Tail regression inCiona intestinalis(Prochordate) involves a Caspase-dependent apoptosis event associated with ERK activation
Authors: Chambon Jean-Philippe , Soule Jonathan , Pomies Pascal , Fort Philippe , Sahuquet Alain , Alexandre Daniel , Mangeat Paul-Henri , Baghdiguian Stephen 
Published: April 2021

Two apoptotic events take place during embryonic development of Ciona intestinalis. The first concerns extra-embryonic cells and precedes hatching. The second controls tail regression at metamorphosis, occurs through a polarized wave originating from tail extremity, and is caspase dependent. This was shown by: (1) in vivo incorporation of a fluorescent marker of caspase activation in different cell types of the tail; (2) detection of an activated form of caspase 3-like protein by western blotting; and (3) failure of 30% of larvae to undergo metamorphosis after treatment of fertilized eggs with a pan-caspase inhibitor. In addition, Ciona embryos express a single ERK protein, specifically phosphorylated at metamorphosis. ERK activation was shown to be located in cells of the tail. Addition of MEK inhibitor in the culture medium prevented ERK activation and metamorphosis. In silico analysis of Ciona genome pointed to 15 caspases with high homology with humans, and a single ERK gene with high homology to both mammalian ERK1 and ERK2. It is concluded that the sequence of events leading to metamorphosis includes ERK phosphorylation followed by caspase-dependent apoptosis and tail regression.Movies available on-line
A novel positive transcriptional feedback loop in midbrain-hindbrain boundary development is revealed through analysis of the zebrafishpax2.1promoter in transgenic lines
Authors: Picker Alexander , Scholpp Steffen , Böhli Heike , Takeda Hiroyuki , Brand Michael 
Published: April 2021

The pax2.1 gene encodes a paired-box transcription factor that is one of the earliest genes to be specifically activated in development of the midbrain and midbrain-hindbrain boundary (MHB), and is required for the development and organizer activity of this territory. To understand how this spatially restricted transcriptional activity of pax2.1 is achieved, we have isolated and characterized the pax2.1-promoter using a lacZ and a GFP reporter gene in transient injection assays and transgenic lines. Stable transgenic expression of this reporter gene shows that a 5.3-kb fragment of the 5′ region contains most, but not all, elements required for driving pax2.1 expression. The expressing tissues include the MHB, hindbrain, spinal cord, ear and pronephros. Transgene activation in the pronephros and developing ear suggests that these pax2.1-expressing tissues are composed of independently regulated subdomains. In addition, ectopic but spatially restricted activation of the reporter genes in rhombomeres 3 and 5 and in the forebrain, which do not normally express endogenous pax2.1, demonstrates the importance of negative regulation of pax2.1.Comparison of transgene expression in wild-type and homozygous pax2.1 mutant no isthmus (noi) embryos reveals that the transgene contains control element(s) for a novel, positive transcriptional feedback loop in MHB development. Transcription of endogenous pax2.1 at the MHB is known to be initially Pax2.1 independent, during activation in late gastrulation. In contrast, transgene expression requires the endogenous Pax2.1 function. Transplantations, mRNA injections and morpholino knock-down experiments show that this feedback regulation of pax2.1 transcription occurs cell-autonomously, and that it requires eng2 and eng3 as known targets for Pax2.1 regulation. We suggest that this novel feedback loop may allow continuation of pax2.1 expression, and hence development of the MHB organizer, to become independent of the patterning machinery of the gastrula embryo.
A crucial role of β1 integrins for keratinocyte migration in vitro and during cutaneous wound repair
Authors: Grose Richard , Hutter Caroline , Bloch Wilhelm , Thorey Irmgard , Watt Fiona M. , Fässler Reinhard , Brakebusch Cord , Werner Sabine 
Published: April 2021

Integrins are ubiquitous transmembrane receptors that play crucial roles in cell-cell and cell-matrix interactions. In this study, we have determined the effects of the loss of β1 integrins in keratinocytes in vitro and during cutaneous wound repair. Flow cytometry of cultured β1-deficient keratinocytes confirmed the absence of β1 integrins and showed downregulation of α6β4 but not of αv integrins. β1-null keratinocytes were characterised by poor adhesion to various substrates, by a reduced proliferation rate and by a strongly impaired migratory capacity. In vivo, the loss of β1 integrins in keratinocytes caused a severe defect in wound healing. β1-null keratinocytes showed impaired migration and were more densely packed in the hyperproliferative epithelium. Surprisingly, their proliferation rate was not reduced in early wounds and even increased in late wounds. The failure in re-epithelialisation resulted in a prolonged inflammatory response, leading to dramatic alterations in the expression of important wound-regulated genes. Ultimately, β1-deficient epidermis did cover the wound bed, but the epithelial architecture was abnormal. These findings demonstrate a crucial role of β1 integrins in keratinocyte migration and wound re-epithelialisation.
Movies available on-line
The inhibition of cell aggregation by a pure serum protein
Authors: Curtis A. S. G. , Greaves M. F. 
Published: April 2021

ABSTRACT
The aggregation of isolated cells into coherent multicellular bodies is widely thought to be due mainly if not entirely to the adhesiveness of the cells for one another, according to Moscona (1961a, b), Curtis (1962) and Steinberg (1962a) amongst others. In consequence the aggregation of cells from dispersed (disaggregated) tissues has been widely used as a test for the degree of adhesiveness shown by the cells, and conditions affecting aggregation have been interpreted as affecting cell adhesion. Using this type of test Moscona (1961a, b) found that embryonic chick cells would not aggregate at temperatures below 14° C. It was also discovered that aggregation was inhibited at 37° C. by puromycin and actinomycin D (Moscona & Moscona, 1963), by glucosamine-HCl (Garber, 1963), and by chloramphenicol (Nakanishi et al., 1963). Moscona concluded from the failure of aggregation at low temperatures that the metabolic synthesis of an adhesive substance was being prevented under such conditions and this interpretation was reinforced by the evidence of chemical inhibition of aggregation. Moscona (1962) suggested that the adhesive substance was responsible for producing cell to cell adhesion. In all these experiments cells were aggregated in media containing serum, usually horse serum.
Studies on some aspects of the rôle of sulfhydryl groups in morphogenesis
Authors: Mulherkar Leela , Rao K. Vasudeva , Joshi Sanjivani S. 
Published: April 2021

ABSTRACT
The importance of sulfhydryl compounds in the process of morphogenesis was pointed out by Brachet (1950). Using specific inhibitors of -SH such as chloroacetophenone, it has been shown that embryos develop a number of malformations when the activity of -SH groups is interfered with (Beatty, 1951; Deuchar, 1957; Lakshmi, 1962a). It has been observed that the abnormalities are mainly in the nervous system and these findings are in agreement with the distribution of -SH groups in embryos of amphibia (Brachet, 1950) and chick (Rulon, 1935). These studies have vindicated the importance of -SH containing proteins stressed by Brachet. In the present report are described some studies using chloroacetophenone (CAP) as an -SH inhibitor and cysteine to reverse its action.
Ultrastructure of the blastopore cells in the newt
Authors: Perry Margaret M. , Waddington C. H. 
Published: April 2021

ABSTRACTLongitudinal and transverse sections of the flask-shaped blastopore cells in the early gastrula of Triturus alpestris have been examined in the electron microscope. The cytoplasm may be divided into three main regions; a distal, superficial, granular zone; a vesicular and, more proximally, a pigment zone in the necks; and the main body of the cell with nucleus, yolk platelets and lipid droplets. A thin, continuous dense layer of extracellular material covers the cells at the free surface. Numerous microtubules oriented parallel to the main axes are found grouped in the necks. Other prominent organelles are vesicles, which from their structure have been divided into three categories, the alpha, beta and gamma vesicles. Longitudinal flanges extending along the necks are complexly interwound with those of adjacent cells and bind the cells firmly together in this region. Neither the extracellular layer, nor the superficial granular layer, is considered to exert a contractile force which would cause the cells to become elongated; rather the change in shape is brought about by active elongation within the internal cytoplasm, in which the microtubular system plays an important part. The material in the cell tips probably results from the passive accumulations of substances which originally covered a larger surface area. The alpha vesicles are common to all cells in the embryo, whereas the beta and gamma vesicles are characteristic of the blastopore cells. The function of these organelles is at present unknown, although there are some structural similarities between the beta vesicles and lysosomal particles described in other organisms.
Whisker growth after removal of the dermal papilla and lengths of follicle in the hooded rat
Authors: Oliver R. F. 
Published: April 2021

ABSTRACT
The arrangement and mode of growth of the major vibrissae on the upper lip of the hooded rat has been studied. There was an antero-posterior gradation in rates of growth and club lengths produced in each of the vertical rows. The longest vibrissae were produced at the fastest rate in the larger follicles in the posterior vertical rows. There was a similar antero-posterior gradation in the times for a phase of growth throughout each of the vertical rows. There are no overall waves of growth on the upper lip; phases of growth are entered into by the vertical rows individually. The suggestion is made that the above behaviour may be related to the mode of development of the vibrissae in the embryo. A method has been described for the removal of the dermal papilla in situ and the removal of dermal papillae and various lengths of whisker root (‘root ends’) have been performed to determine the effects of these operations on whisker growth. After removal of dermal papillae, all 18 follicles produced generations of whiskers; 15 of these follicles produced vibrissae of normal or nearly normal length. After removal of root ends, whiskers of shorter than normal length were produced from 28 out of 37 follicles. Conclusive evidence was obtained that generations of vibrissae can be produced after complete removal of the dermal papilla. The degree of regeneration, as expressed by the length of post-operative whiskers produced, was apparently dependent on the amount of proximal follicle root removed.