bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pituitary ontogeny of the Snell dwarf mouse reveals Pit-1-independent and Pit-1-dependent origins of the thyrotrope
Authors: Lin Sheng-Cai , Li Sen , Drolet Daniel W. , Rosenfeld Michael G. 
Published: April 2021

ABSTRACT
The anterior pituitary provides a model to study the molecular mechanisms responsible for emergence of distinct cell types within an organ. Dwarf mice (Snell) that express a mutant form of the tissue-specific POU-domain transcription factor Pit-1 fail to generate three cell types, including the thyrotrope (S. Li, E. B. Crenshaw, E. J. Rawson, D. S. Simmons, L. Swanson and M. G. Rosenfeld (1990), Nature 347, 528-533). Analyses of wild-type and Pit-1-defective mice, presented here, have revealed that thyrotropes unexpectedly arise from two independent cell populations. The first population is Pit-1-independent and appears on e12 in the rostral tip of the developing gland, but phenotypically disappears by the day of birth. The second is Pit-1-dependent and arises subsequently in the caudomedial portion of the developing gland (e15.5), following the initial expression of Pit-1 in this region. The failure of caudomedial thyrotrope cells to appear in the Snell dwarf, and the observation that Pit-1 can bind to and transactivate the TSHβ promoter, apparently enhanced by its phosphorylation, suggests that Pit-1 is directly required for the appearance of this distinct population that serves as the precursors of the mature thyrotrope cell type. These data suggest that different molecular mechanisms, based on the actions of distinct transcription factors, can serve to independently generate a specific cell phenotype during mammalian organogenesis.
Novel tenascin variants with a distinctive pattern of expression in the avian embryo
Authors: Tucker R. P. , Spring J. , Baumgartner S. , Martin D. , Hagios C. , Poss P. M. , Chiquet-Ehrismann R. 
Published: April 2021

ABSTRACT
Previous studies have shown that several forms of the glycoprotein tenascin are present in the embryonic extracellular matrix. These forms are the result of alternative splicing, which generates tenascin variants with different numbers of fibronectin type III repeats. We have used degenerate primers and PCR to isolate a novel tenascin exon from an avian genomic library. Genomic clones contained a sequence encoding a fibronectin type III repeat that corresponds to repeat ‘C’ from the variable domain of human tenascin. To demonstrate that tenascin containing repeat ‘C’ is actually synthesized by avian cells, a mono-specific antiserum was raised against a repeat ‘C’ fusion protein. This antiserum recognized a novel high-molecular-weight variant on immunoblots of tenascin isolated from chicken embryo fibroblast-conditioned medium, and stained tendons on frozen sections of chicken embryos. A cDNA probe specific for mRNA encoding repeat ‘C’ was used for in situ hybridization. This probe hybridized in a subset of the embryonic tissues labelled with a universal tenascin probe, including tendons, ligaments and mesenchyme at sites of epithelial-mesenchymal interactions. Finally, we provide evidence that additional fibronectin type III repeats, one corresponding to a recently discovered human repeat as well as one entirely novel sequence, also exists in chicken tenascin mRNA. These data indicate that tenascin is present in the embryonic matrix in a multitude of forms and that these forms have distinctive distributions that may reflect more than one function for tenascin in development.
Regulation of oligodendrocyte differentiation: a role for retinoic acid in the spinal cord
Authors: Noll Elizabeth , Miller Robert H. 
Published: April 2021

ABSTRACT
During development, oligodendrocyte precursors undergo sequential stages of differentiation characterized by expression of distinct cell surface properties and proliferative responses. Although both PDGF and bFGF are mitogenic for these cells, the factors that regulate the progression of oligodendrocyte precursors through their differentiative program remain unclear.
One factor present in the embryonic spinal cord that may regulate differentiation of oligodendrocyte precursors is retinoic acid. Here we show that retinoic acid inhibits the maturation of embryonic spinal cord oligodendrocyte precursors in vitro at an early, highly motile stage of differentiation, characterized by the expression of A2B5 immunoreactivity. Basic FGF acts both as a mitogen and an inhibitor of spinal cord oligodendrocyte precursor maturation, but at a significantly later stage of differentiation, characterized by the expression of O4 immunoreactivity. In the presence of RA both the mitogenic and differentiation inhibiting effects of bFGF are abolished, consistent with RA acting as an early regulator of oligodendrocyte differentiation. During embryonic development, oligodendrocyte precursors arise initially from a distinct group of cells at the ventral ventricular zone of the spinal cord. Myelination of the entire spinal cord is dependent on the migration of immature precursor cells to peripheral developing white matter. Since the embryonic spinal cord has the capacity to release relatively high levels of retinoids, we propose that RA inhibits oligodendrocyte differentiation during early embryonic development permitting their dispersal throughout the entire spinal cord.
bundle sheath defective, a mutation that disrupts cellular differentiation in maize leaves
Authors: Langdale Jane A. , Kidner Catherine A. 
Published: April 2021

SUMMARY
Post-primordial differentiation events in developing maize leaves produce two photosynthetic cell types (bundle sheath and mesophyll) that are morphologically and biochemically distinct. We have isolated a mutation that disrupts the differentiation of one of these cell types in light-grown leaves. bundle sheath defective 1-mutable 1 (bsd1-m1) is an unstable allele that was induced by transposon mutagenesis. In the bundle sheath cells of bsd1-m1 leaves, chloroplasts differentiate aberrantly and C4 photosynthetic enzymes are absent. The development of mesophyll cells is unaffected. In dark-grown bsd1-m1 seedlings, morphological differentiation of etioplasts is only disrupted in bundle sheath cells but photosynthetic enzyme accumulation patterns are altered in both cell types. These data suggest that, during normal development, the Bsd1 gene directs the morphological differentiation of chloroplasts in a lightindependent and bundle sheath cell-specific fashion. In contrast, Bsd1 gene action on photosynthetic gene expression patterns is cell-type independent in the dark (C3 state) but bundle sheath cell-specific in the light (C4 state). Current models hypothesize that C4 photosynthetic differentiation is achieved through a light-induced interaction between bundle sheath and mesophyll cells (J. A. Langdale and T. Nelson (1991) Trends in Genetics 7, 191–196). Based on the data shown in this paper, we propose that induction of the C4 state restricts Bsd1 gene action to bundle sheath cells.
Sex determination of the Drosophila germ line: tra and dsx control somatic inductive signals
Authors: Steinmann-Zwicky Monica 
Published: April 2021

SUMMARY
In Drosophila, the sex of germ cells is determined by cell-autonomous and inductive signals. XY germ cells autonomously enter spermatogenesis when developing in a female host. In contrast, XX germ cells non-autonomously become spermatogenic when developing in a male host. In first instar larvae with two X chromosomes, XX germ cells enter the female or the male pathway depending on the presence or absence of transformer (tra) activity in the surrounding soma. In somatic cells, the product of tra regulates the expression of the gene double sex (dsx) which can form a male-specific or a female-specific product. In dsx mutant larvae, XX and XY germ cells develop abnormally, with a seemingly intersexual phenotype. This indicates that female-specific somatic dsx products feminize XX germ cells, and male-specific somatic dsx products masculinize XX and XY germ cells. The results show that tra and dsx control early inductive signals that determine the sex of XX germ cells and that somatic signals also affect the development of XY germ cells.
XX germ cells that develop in pseudomales lacking the sex-determining function of Sxl are spermatogenic. If, however, female-specific tra functions are expressed in these animals, XX germ cells become oogenic. Furthermore, transplanted XX germ cells can become oogenic and form eggs in XY animals that express the female-specific function of tra. Therefore, TRA product present in somatic cells of XY animals or in animals lacking the sex-determining function of Sxl, is sufficient to support developing XX germ cells through oogenesis.
Interacting functions of snail, twist and huckebein during the early development of germ layers in Drosophila
Authors: Reuter Rolf , Leptin Maria 
Published: April 2021

ABSTRACT
Two zygotic genes, snail (sna) and twist (twi), are required for mesoderm development, which begins with the formation of the ventral furrow. Both twi and sna are expressed ventrally in the blastoderm, encode transcription factors and promote the invagination of the ventral furrow by activating or repressing appropriate target genes. However, sna and twi alone do not define the position of the ventral furrow, since they are also expressed in ventral cells that do not invaginate. We show that huckebein (hkb) sets the anterior and the posterior borders of the ventral furrow, but acts by different modes of regulation. In the posterior part of the blastoderm, hkb represses the expression of sna in the endodermal primordium (which we suggest to be adjacent to the mesodermal primordium). In the anterior part, hkb antagonizes the activation of target genes by twi and sna. Here, bicoid permits the co-expression of hkb, sna and twi, which are all required for the development of the anterior digestive tract. We suggest that mesodermal fate is determined where sna and twi but not hkb are expressed. Anteriorly hkb together with sna determines endodermal fate, and hkb together with sna and twi are required for foregut development.
Mef2 gene expression marks the cardiac and skeletal muscle lineages during mouse embryogenesis
Authors: Edmondson Diane G. , Lyons Gary E. , Martin James F. , Olson Eric N. 
Published: April 2021

ABSTRACT
Members of the MEF2 family of transcription factors bind a conserved A/T-rich sequence in the control regions of many skeletal and cardiac muscle genes. To begin to assess the roles of the different Mef2 genes in the control of muscle gene expression in vivo, we analyzed by in situ hybridization the expression patterns of the Mef2a, Mef2c and Mef2d genes during mouse embryogenesis. We first detected MEF2C expression at day 7.5 postcoitum (p.c.) in cells of the cardiac mesoderm that give rise to the primitive heart tube, making MEF2C one of the earliest markers for the cardiac muscle lineage yet described. By day 8.5, MEF2A, MEF2C and MEF2D mRNAs are all detected in the myocardium. By day 9.0, MEF2C is expressed in rostral myotomes, where its expression lags by about a day behind that of myf5 and several hours behind that of myogenin. MEF2A and MEF2D are expressed at a lower level than MEF2C in the myotome at day 9.5 and are detected in more embryonic tissues than MEF2C. Expression of each of the MEF2 transcripts is observed in muscle-forming regions within the limbs at day 11.5 p.c. and within muscle fibers throughout the embryo at later developmental stages. The expression of MEF2C in the somites and fetal muscle is distinct from that of MEF2A, MEF2D and the myogenic bHLH regulatory genes, suggesting that it may represent a distinct myogenic cell type. Neural crest cells also express high levels of MEF2 mRNAs between days 8.5 and 10.5 of gestation. After day 12.5 p.c., MEF2 transcripts are detected at high levels in specific regions of the brain and ultimately in a wide range of tissues. The distinct patterns of expression of the different Mef2 genes during mouse embryogenesis suggest that these genes respond to unique developmental cues and support the notion that their products play roles in the regulation of muscle-specific transcription during establishment of the cardiac and skeletal muscle lineages.
Extracellular cAMP can restore development in Dictyostelium cells lacking one, but not two subtypes of early cAMP receptors (cARs). Evidence for involvement of cAR1 in aggregative gene expression
Authors: Soede Ron D. M. , Insall Robert H. , Devreotes Peter N. , Schaap Pauline 
Published: April 2021

ABSTRACT
Extracellular cAMP induces expression of several classes of developmentally regulated genes in Dictyostelium. Four highly homologous surface cAMP receptors (cARs) were identified earlier, but involvement of specific cARs in gene regulation has not been clarified. Cells lacking the chemotactic receptor, cAR1, neither aggregate nor express developmentally regulated genes. Expression of aggregative genes is in wild-type cells induced by nanomolar cAMP pulses and repressed by persistent micromolar cAMP stimuli, which induce expression of prespore and prestalkenriched genes during the postaggregative stages of development. We show here that in cell lines carrying a cAR1 gene disruption, nanomolar pulses cannot induce aggregative gene expression. Remarkably, micromolar cAMP can induce expression of aggregative genes in car1− cells as well as expression of prespore and prestalk-enriched genes, and furthermore restores their ability to form normal slugs and fruiting bodies. These data indicate that cAR1 mediates aggregative but not postaggregative gene expression and morphogenesis, and suggest that after gene disruption, its function is partially taken over by a lower affinity receptor that is not subjected to desensitization. The absence of another early cAMP receptor, cAR3, does not affect development. However, in a car1−/car3− double mutant, cAMP stimulation cannot restore any developmental gene expression, indicating that cAR3 may have substituted for cAR1 in car1− cell lines.
βHeavy-spectrin has a restricted tissue and subcellular distribution during Drosophila embryogenesis
Authors: Thomas Claire M. , Kiehart Daniel P. 
Published: April 2021

ABSTRACT
The components of the membrane skeleton play an important role in maintaining membrane structure during the dynamic changes in cell shape that characterize development. βHeavy-spectrin is a unique β-spectrin from Drosophila melanogaster that is closer in size (Mr=430×103) to dystrophin than to other β-spectrin members of the spectrin/α-actinin/dystrophin gene super-family. Here we establish that both the subcellular localization of the βHeavyspectrin protein and the tissue distribution of βHeavyspectrin transcript accumulation change dramatically during embryonic development.
Maternally loaded protein is uniformly distributed around the plasma membrane of the egg. During cellularization it is associated with the invaginating furrow canals and in a region of the lateral membranes at the apices of the forming cells (apicolateral). During gastrulation the apicolateral staining remains and is joined by a new apical cap, or plate, of βHeavy-spectrin in areas where morphogenetic movements occur. These locations include the ventral and cephalic furrows and the posterior midgut invagination. Thus, dynamic rearrangement of the subcellular distribution of the protein is precisely coordinated with changes in cell shape.
Zygotic message and protein accumulate after the germ band is fully extended, in the musculature, epidermis, hindgut, and trachea of the developing embryo. βHeavyspectrin in the epidermis, hindgut, and trachea is apically localized, while the protein in the somatic and visceral musculature is not obviously polarized.
The distribution of βHeavy-spectrin suggests roles in establishing an apicolateral membrane domain that is known to be rich in intercellular junctions and in establishing a unique membrane domain associated with contractile processes.
FlyBase -The Drosophila genetic database
Authors: Ashburner Michael , Drysdale Rachel 
Published: April 2021

ABSTRACT
The first recorded scientific publication on Drosophila was 310 years ago (Mentzel, 1684). By 1980 about 35,000 papers on Drosophila had been published and at the time of writing this total had risen to over 60,000. By the year 2000, there will be over 80,000 Drosophila publications — and the on-going publication rate will be more than 4,000 a year. There is nothing unique in this rate of growth — it is typical for any “active” subject to double its output every fifteen years (see de Solla Price, 1986). Sooner or later, of course, the curve must plateau but, until it does, the individual scientist faces an obvious problem. Not all of the papers published will be of the standard of those in Development. Nevertheless, just sifting those that are worthy of reading from those that are not will be (indeed is) a daunting task. What is to be done? The answer is obvious, we must exploit the power of computers to point us to papers that we need to read. We must also exploit the power of computers to provide us with basic data about our organism. Luckily, there is every prospect that the power of engines to process and access these data will increase, and their relative cost decrease, with the growth in scientific information.
Lazarillo, a new GPI-linked surface lipocalin, is restricted to a subset of neurons in the grasshopper embryo
Authors: D. Ganfornina María , Sánchez Diego , Bastiani Michael J. 
Published: April 2021

ABSTRACT
Lazarillo, a protein recognized by the monoclonal antibody 10E6, is expressed by a subset of neurons in the developing nervous system of the grasshopper. It is a glycoprotein of 45×103Mr with internal disulfide bonds and linked to the extracellular side of the plasma membrane by a glycosylphosphatidylinositol moiety. Peptide sequences obtained from affinity purified adult protein were used to identify an embryonic cDNA clone, and in situ hybridizations confirmed that the distribution of the Lazarillo mRNA paralleled that of the monoclonal antibody labeling on embryos. Sequence analysis defines Lazarillo as a member of the lipocalin family, extracellular carriers of small hydrophobic ligands, and most related to the porphyrinand retinol-binding lipocalins. Lazarillo is the first example of a lipocalin anchored to the plasma membrane, highly glycosylated, and restricted to a subset of developing neurons.
Transforming growth factor α disrupts the normal program of cellular differentiation in the gastric mucosa of transgenic mice
Authors: Sharp Richard , Babyatsky Mark W. , Takagi Hitoshi , Tågerud Sven , Wang Timothy C. , Bockman Dale E. , Brand Stephen J. , Merlino Glenn 
Published: April 2021

ABSTRACT
Transforming growth factor alpha (TGFα) evokes diverse responses in transgenic mouse tissues in which it is over-expressed, including the gastric mucosa, which experiences aberrant growth and a coincident repression of hydrochloric acid production. Here we show that ectopically expressed TGFα induces an age-dependent cellular reorganization of the transgenic stomach, in which the surface mucous cell population in the gastric pit is greatly expanded at the expense of cells in the glandular base. Immunohistochemical analysis of BrdU incorporation into DNA demonstrated that although mature surface mucous cells were not proliferating, DNA synthesis was enhanced by approximately 67% in the glandular base and isthmus, where progenitor cells reside. RNA blot and in situ hybridization were employed to determine temporal and spatial expression patterns of specific markers representing a variety of exocrine and endocrine gastric cell types. Mature parietal and chief cells were specifically depleted from the glandular mucosa, as judged by a 6- to 7-fold decrease in the expression of genes encoding H+,K+-ATPase, which is required for acid secretion, and pepsinogen C, respectively. The reduction of these markers coincided in time with the activation of TGFα transgene expression in the neonatal stomach. The rate of cell death in the glandular region was not overtly different. Significantly, the loss of parietal and chief cells occurred without a concomitant loss of their respective cellular precursors. In contrast to exocrine cells, D and G endocrine cells were much less severely affected, based on analysis of somatostatin and gastrin expression. Analysis of these dynamic changes indicates that TGFα can induce selective alterations in terminal differentiation and proliferation in the gastric mucosa, and suggests that TGFα plays an important physiological role in the normal regulation of epithelial cell renewal.
Lamina–specific cues guide outgrowth and arborization of retinal axons in the optic tectum
Authors: Yamagata Masahito , Sanes Joshua R. 
Published: April 2021

ABSTRACT
In the chick, retinal axons enter the optic tectum through a superficial lamina, then branch into distinct deeper retinorecipient laminae, where they arborize and form synapses. To study factors that guide this laminar selectivity, we devised an organotypic culture system in which a transverse tectal section is overlaid with a retinal explant large enough to allow unimpeded access to all tectal laminae. Outgrowth, branching, and arborization patterns of retinal axons on tectal slices were lamina-selective, indicating the existence of localized cues that guide retinal axons. Further studies suggested that some of these cues are: (1) associated with cell membranes or extracellular matrix (because axons grew selectively on chemically fixed tectal sections); (2) intrinsic to the tectum (because axons grew selectively on tectal sections prepared from enucleated embryos); (3) distinct from topographic cues (because axons from nasal and temporal retina behaved similarly on anterior tectal slices); and (4) selective for retinal axons (because axons growing from other explants exhibited different laminar preferences).
Expression of floricaula in single cell layers of periclinal chimeras activates downstream homeotic genes in all layers of floral meristems
Authors: Hantke Sabine S. , Carpenter Rosemary , Coen Enrico S. 
Published: April 2021

ABSTRACT
We show that the flowering sectors on plants mutant for floricaula (flo), a meristem identity gene in Antirrhinum majus, are periclinal chimeras expressing flo in either the L1, L2 or L3 cell layer. Flower morphology is almost normal in L1 chimeras, but altered in L2 and L3 chimeras. Expression of flo in any one cell layer results in the expression of organ identity genes, deficiens (def) and plena (ple) in all three cell layers of the chimeras, showing that flo acts inductively to promote gene transcription. The activation of both def and ple is delayed, and the expression domain of def is reduced, accounting for some of the phenotypic properties of the chimeras. Furthermore, we show that flo exhibits some cell-autonomy with respect to autoregulation.