bluuebunny/crossref_metadata_2025_split huggingface dataset:
The three dominant female-sterile mutations of the Drosophila ovo gene are point mutations that create new translation-initiator AUG codons
Authors: Mével-Ninio Maryvonne , Fouilloux Eric , Guénal Isabelle , Vincent Alain 
Published: April 2021

ABSTRACT
The Drosophila ovo gene, which encodes a putative transcription factor (Ovo) with TFIIIA-like zinc fingers, is required for female germline survival and proper oogenesis. Three dominant female-sterile ovoD mutations cause ovarian abnormalities that define an allelic series, with ovoD1 displaying the stronger phenotype and ovoD3 the weaker. We report here that all three ovoD mutations are point mutations that create new in-frame methionine codons in the 5′ part of ovo. There are two types of over-lapping ovo transcription units, ovoα and ovoβ. By using various ovo-lacZ reporter genes, we determined that the long Ovo isoforms starting at methionine M1, present in transcripts ovoα, are expressed at low levels only in mature oocytes. Short Ovo isoforms are translated from methionine M373, the first in-frame start codon present in tran-script ovoβ, and correspond to the activity defined by recessive loss of function ovo mutations. The new AUGs created in ovoD mutations all are located upstream of the M373 initiation site. Our results support the hypothesis that they can substitute for M373 as translation starts and initiate the synthesis of Ovo proteins that have extra amino acids at their N termini. We propose that premature expression of long Ovo protein isoforms occurs in ovoD mutants and interferes with wild-type Ovo function in con-trolling female germline differentiation.
Two distinct roles for Ras in a developmentally regulated cell migration
Authors: Lee Tzumin , Feig Larry , Montell Denise J. 
Published: April 2021

ABSTRACT
Receptor tyrosine kinases have been shown to promote cell movement in a variety of systems. The Ras protein, a well-documented downstream effector for receptor tyrosine kinases, may contribute to receptor tyrosine kinase-mediated motility. In the present study, we have examined the role of Ras in the migration of a small subset of follicle cells, known as the border cells, during Drosophila oogenesis. A dominant-negative Ras protein inhibited cell migration when expressed specifically in border cells during the period when these cells normally migrate. When expressed prior to migration, dominant-negative Ras promoted premature initiation of migration. Conversely, expression of constitutively active Ras prior to migration resulted in a significant delay in the initiation step. Fur-thermore, the defect in initiation of border cell migration found in slbo1, a mutation at the locus that encodes Drosophila C/EBP, was largely rescued by reducing Ras activity in border cells prior to migration. Taken together, these observations indicate that Ras activity plays two distinct roles in the border cells: (1) reduction in Ras activity promotes the initiation of that migration process and (2) Ras activity is required during border cell migration. We further examined the possible involvement of two downstream effectors of Ras in border cell migration. Raf activity was dispensable to border cell migration while reduced Ral activity inhibited initiation. We therefore suggest that Ras plays a critical role in the dynamic regulation of border cell migration via a Raf-inde-pendent pathway.
Lineage-specific morphogenesis in the developing pancreas: role of mesenchymal factors
Authors: Gittes George K. , Galante Philip E. , Hanahan Douglas , Rutter William J. , Debas Haile T. 
Published: April 2021

ABSTRACT
Pancreatic organogenesis has been a classic example of epitheliomesenchymal interactions. The nature of this interaction, and the way in which endocrine, acinar and ductal cell lineages are generated from the embryonic foregut has not been determined. It has generally been thought that mesenchyme is necessary for all aspects of pancreatic development. In addition islets have been thought to derive, at least in part, from ducts. We microdissected 11-day embryonic mouse pancreas and developed several culture systems for assays of differentiation: (i) on transparent filters; (ii) suspended in a collagen I gel; (iii) suspended in a basement membrane rich gel; (iv) under the renal capsule of an adult mouse. Epithelia were grown either with or without mesenchyme, and then assayed histologically and immunohistochemically. Epithelium with its mesenchyme (growth systems i-iv) always grew into fully differentiated pancreas (acinar, endocrine, and ductal elements). In the basement membrane-rich gel, epithelium without mesenchyme formed ductal structures. Under the renal capsule of the adult mouse the epithelium without mesenchyme exclusively formed clusters of mature islets. These latter results represent the first demonstration of pure islets grown from early pancreatic precursor cells. In addition, these islets seemed not to have originated from ducts.
We propose that the default path for growth of embryonic pancreatic epithelium is to form islets. In the presence of basement membrane constituents, however, the pancreatic anlage epithelium appears to be programmed to form ducts. Mesenchyme seems not to be required for all aspects of pancreatic development, but rather only for the formation of acinar structures. In addition, the islets seem to form from early embryonic epithelium (which only express non-acinar genes). This formation occurs without any specific embryonic signals, and without any clear duct or acinus formation.
The tangled-1 mutation alters cell division orientations throughout maize leaf development without altering leaf shape
Authors: Smith Laurie G. , Hake Sarah , Sylvester Anne W. 
Published: April 2021

ABSTRACT
It is often assumed that in plants, where the relative positions of cells are fixed by cell walls, division orientations are critical for the generation of organ shapes. However, an alternative perspective is that the generation of shape may be controlled at a regional level independently from the initial orientations of new cell walls. In support of this latter view, we describe here a recessive mutation of maize, tangled-1 (tan-1), that causes cells to divide in abnormal orientations throughout leaf development without altering overall leaf shape. In normal plants, leaf cells divide either transversely or longitudinally relative to the mother cell axis; transverse divisions are associated with leaf elongation and longitudinal divisions with leaf widening. In tan-1 mutant leaves, cells in all tissue layers at a wide range of developmental stages divide transversely at normal frequencies, but longitudinal divisions are largely substituted by a variety of aberrantly oriented divisions in which the new cell wall is crooked or curved. Mutant leaves grow more slowly than normal, but their overall shapes are normal at all stages of their growth. These observations demonstrate that the generation of maize leaf shape does not depend on the precise spatial control of cell division, and support the general view that mechanisms independent from the control of cell division orientations are involved in the generation of shape during plant development.
Maternal mRNA encoding the orphan steroid receptor SpCOUP-TF is localized in sea urchin eggs
Authors: Vlahou Antonia , Gonzalez-Rimbau Maria , Flytzanis Constantin N. 
Published: April 2021

ABSTRACT
The SpCOUP-TF gene is a highly conserved sea urchin homologue of the vertebrate COUP-TFs and the Drosophila seven up subfamily of transcription factors, which are members of the orphan steroid hormone receptors. Whole-mount in situ hybridization experiments, using three sea urchin species, detect the maternal SpCOUP-TF mRNA deposited unevenly in the oocytes, mature eggs and the blastomeres of the early embryo. The localization pattern indicates that, in all three sea urchin species, the maternal SpCOUP-TF mRNA is placed in the egg in a fixed position relative to the embryonic axes, i.e. lateral to the animal-vegetal and at 45° angle to the oralaboral (ventral-dorsal) axis. The embryonic expression of the SpCOUP-TF gene is spatially restricted in the oral ectoderm of the early embryo and, at later stages, in the cells of the ciliated band, the neurogenic cell lineage of the sea urchin embryo. The SpCOUP-TF mRNA, the first sea urchin maternal mRNA encoding a transcription factor that is specifically localized with respect to both embryonic axes in the egg, could be involved in early specification events in the sea urchin embryo.
TGF-β signals and a prepattern in Xenopus laevis endodermal development
Authors: Henry Gilbert L. , Brivanlou Iman H. , Kessler Daniel S. , Hemmati-Brivanlou Ali , Melton Douglas A. 
Published: April 2021

ABSTRACT
We have analyzed two gene products expressed in the early endoderm of Xenopus laevis: Xlhbox-8, a pancreas-specific transcription factor and intestinal fatty acid binding protein (IFABP), a marker of small intestinal epithelium. Expression of the pancreas marker relies on cell signaling mediated by both the TGFβ and FGF classes of secreted peptide growth factors, whereas, expression of the more posterior small intestinal marker does not. Endodermal explants devoid of mesoderm express both markers in a regionalized manner. Cortical rotation is required for the expression of the more anterior marker, Xlhbox-8, but not for the small intestinal marker, IFABP. These findings suggest that endodermal patterning is dependent, in part, on the same events and signals known to play important roles in mesodermal development. Furthermore, inhibition of TGFβ signaling in the endoderm leads to ectopic expression of both mesodermal and ectodermal markers, suggesting that TGFβ signaling may play a general role in the segregation of the three embryonic germ layers.
Ectopic expression of Hoxa-1 in the zebrafish alters the fate of the mandibular arch neural crest and phenocopies a retinoic acid-induced phenotype
Authors: Alexandre Daniel , Clarke Jonathan D. W. , Oxtoby Elli , Yan Yi-Lin , Jowett Trevor , Holder Nigel 
Published: April 2021

ABSTRACT
Considerable evidence has demonstrated that retinoic acid influences the formation of the primary body axis in vertebrates and that this may occur through the regulation of Hox gene expression. In this study, we show that the phenotype induced by exogenous retinoic acid in the zebrafish can also be generated by the overexpression of Hoxa-1 following injection of synthetic RNA into the fertilised egg. The isolation, sequence and expression pattern of the zebrafish Hoxa-1 gene is described. We show that exogenously applied retinoic acid causes the ectopic accumulation of Hoxa-1 message during gastrulation in the hypoblast in the head region. Overexpression of Hoxa-1 following injection of RNA causes abnormal growth of the anterior hindbrain, duplication of Mauthner neurons in rhombomere (r) 2 and fate changes of r2 mesenchymal and neurogenic neural crest. These results are discussed in terms of the role of Hoxa-1 in controlling anterior hindbrain patterning and the relationship between expression of Hoxa-1 and retinoic acid.
A muscle-specific variant of microtubule-associated protein 4 (MAP4) is required in myogenesis
Authors: Mangan Mary E. , Olmsted J. B. 
Published: April 2021

ABSTRACT
Microtubule-associated protein 4 (MAP4) transcripts vary in different mouse tissues, with striated muscle (skeletal and cardiac) expressing 8and 9-kb transcripts preferentially to the more widely distributed 5.5and 6.5-kb transcripts (West, R. W., Tenbarge, K. M. and Olmsted, J. B. (1991). J. Biol. Chem. 266, 21886-21896). Cloning of the sequence unique to the muscle transcripts demonstrated that these mRNAs vary from the more ubiquitous ones by a single 3.2-kb coding region insertion within the projection domain of MAP4. During differentiation of the myogenic cell line, C2C12, muscle-specific MAP4 transcripts appear within 24 hours of growth in differentiation medium, and a larger MAP4 isotype (350×103Mr) accumulates to high levels by 48 hours of differentiation. In situ hybridization analyses of transcript distribution in mouse embryos demonstrated that muscle-specific transcripts appear early in myogenesis. To block the expression of the muscle-specific MAP4, stable lines of C2C12 cells were generated bearing an antisense construct with the musclespecific MAP4 sequence. Myoblast growth was unaffected whereas myotube formation was severely perturbed. Fusion occurred in the absence of the muscle MAP4 isotype, but the multinucleate syncytia were short and apolar, microtubules were disorganized and normal anisotropic myofibrils were absent. The patterns of expression of the muscle-specific transcripts and the antisense experiments indicate that this unique structural form of MAP4 plays a critical role in the formation and maintenance of muscle.
Polyembryonic development: insect pattern formation in a cellularized environment
Authors: Grbic Miodrag , Nagy Lisa M. , Carroll Sean B. , Strand Michael 
Published: April 2021

ABSTRACT
The polyembryonic wasp Copidosoma floridanum produces up to 2000 individuals from a single egg. During the production of individual embryos the original anteroposterior axis of the egg is lost and axial patterning must subsequently be reestablished within each embryo. The mechanism by which this occurs is unknown. In most insects, egg polarity is established during oogenesis and early development takes place in a syncytium. In Drosophila melanogaster, the syncytium is considered essential for establishing the morphogenetic gradients that initiate segmental patterning. However, we found that development of C. floridanum occurs almost exclusively in a cellularized environment. To determine whether the D. melanogaster patterning cascade is conserved in the absence of a syncytium, we analyzed the expression of Even-skipped, Engrailed and Ultrabithorax/Abdominal-A during polyembryonic development. Here we show that in spite of the absence of a syncytium, the elements of the D. melanogaster segmentation hierarchy are conserved. The segment-polarity gene Engrailed and the homeotic genes Ultrabithorax/Abdominal-A are expressed in a conserved pattern relative to D. melanogaster. However, we detect an alteration in the expression of the Even-skipped antigen. Even-skipped is initially expressed in segmentally reiterated stripes and not in a pair-rule pattern as it is in D. melanogaster. We also observe that the expression of these regulatory proteins does not occur during the early proliferative phases of polyembryony. Our results indicate that a syncytium is not required for segmental patterning in this insect.
Regional specification of motoneurons along the anterior-posterior axis is independent of the notochord
Authors: Fukushima Mikiko , Nakamura Masaaki , Ohta Kunimasa , Okamura Ryouichi , Negi Akira , Tanaka Hideaki 
Published: April 2021

ABSTRACT
Cek8 and low affinity NGF receptor (LNGFR) are expressed at high levels on the chick spinal motoneurons of the brachial and lumbar segments from embryonic day (E) 5 to E7, but weakly on the motoneurons of the non-limbinnervating segments. We determined by means of heterotopic neural tube transplantation, that the expression of these molecules was already intrinsically determined at E2. We used these spatiotemporal specific molecules as markers of motoneuron subpopulations. To analyze how motoneurons acquire regional specification along the anterior-posterior (A-P) axis and in the transverse plane, we observed the expression of these molecules on ectopic motoneurons induced by implanting a supernumerary notochord or floor plate at E2. The ectopic motoneurons induced by the graft obtained from either the thoracic or lumbar segments had the same expression profile as the normal motoneurons at each A-P level. These findings suggest that regional specification of motoneurons, at least of Cek8 and LNGFR expression, is independent of the notochord and the floor plate and that the whole neural tube appears to be committed to differentiate into the motoneuron subtypes along the A-P axis at the operative stages.
Gliolectin is a novel carbohydrate-binding protein expressed by a subset of glia in the embryonic Drosophila nervous system
Authors: Tiemeyer Michael , Goodman Corey S. 
Published: April 2021

ABSTRACT
Interactions between embryonic neural cells generate the specific patterns of connectivity observed in nervous systems. Cell surface carbohydrates have been proposed to function in cellular recognition events guiding such interactions. Carbohydrate-binding proteins (lectins) that recognize specific oligosaccharide ligands in embryonic neural tissue provide a molecular mechanism for carbohydrate-mediated cell-cell interactions in neural development. Therefore, we have screened an embryonic Drosophila melanogaster cDNA library, expressed in COS1 cells, for carbohydrate-binding activity. COS1 cells expressing putative Drosophila lectins were identified and recovered based on their adhesion to immobilized preparations of neutral and zwitterionic glycolipids extracted from Drosophila embryos. We have identified an endogenous lectin expressed during Drosophila embryogenesis. The cloned lectin, designated ‘gliolectin’, possesses a novel protein sequence with a calculated molecular mass of 24,993. When expressed in Drosophila S2 cells, the lectin mediates heterophilic cellular aggregation. In embryos, gliolectin is expressed by a subset of glial cells found at the midline of the developing nervous system. Expression is highest during the formation of the Drosophila embryonic axonal commissures, a process requiring midline glial cell function. Immunoprecipitation with a monoclonal antibody against gliolectin yields a protein of Mr=46,600 from Drosophila embryonic membranes, suggesting that post-translational modification of gliolectin is extensive. Epitope-tagged chimeric proteins composed of the amino terminal one-half of gliolectin and the Fc region of human IgG bind a small subset of the total glycolipids extracted from Drosophila embryos, demonstrating that the lectin activity of gliolectin can discriminate between oligosaccharide structures. The presence of gliolectin in the developing Drosophila embryonic nervous system further supports a role for cell surface carbohydrates in cell-cell recognition and indicates that the molecular diversity of animal lectins is not yet completely defined.
The Drosophila genes crumbs and stardust are involved in the biogenesis of adherens junctions
Authors: Grawe Ferdi , Wodarz Andreas , Lee Bill , Knust Elisabeth , Skaer Helen 
Published: April 2021

ABSTRACT
Morphogenetic movements of epithelia during development underlie the normal elaboration of the final body plan. The tissue integrity critical for these movements is conferred by anchorage of the cytoskeleton to the membrane at sites of cell adhesion, mediated by adherens junctions, initially spot and later belt-like, zonular structures, which encircle the apical side of the cell. Loss-offunction mutations in the Drosophila genes crumbs and stardust lead to the loss of cell polarity in most ectodermally derived epithelia, followed in some, such as the epidermis, by extensive apoptosis. Here we show that both mutants fail to establish proper zonulae adherentes in the epidermis. Our results suggest that the two genes are involved in different aspects of this process. Further, they are compatible with the hypothesis that crumbs delimits the apical border, where the zonula adherens usually forms and where Crumbs protein is normally most abundant. In contrast, stardust seems to be required at an earlier stage for the assembly of the spot adherens junctions. In both mutants, the defects observed at the ultrastructural level are preceded by a misdistribution of Armadillo and DEcadherin, the homologues of β-catenin and E-cadherin, respectively, which are two constituents of the vertebrate adherens junctions. Strikingly, expansion of the apical membrane domain in epidermal cells by overexpression of crumbs also abolishes the formation of adherens junctions and results in the disruption of tissue integrity, but without loss of membrane polarity. This result supports the view that membrane polarity is independent of the formation of adherens junctions in epidermal cells.
Initiation patterns of flower and floral organ development in Arabidopsis thaliana
Authors: Bossinger Gerd , Smyth David R. 
Published: April 2021

ABSTRACT
Sector boundary analysis has been used to deduce the number and orientation of cells initiating flower and floral organ development in Arabidopsis thaliana. Sectors were produced in transgenic plants carrying the Ac transposon from maize inserted between the constitutive 35S promoter and the GUS reporter gene. Excision of the transposon results in a blue-staining sector. Plants were chosen in which an early arising sector passed from vegetative regions into the inflorescence and through a mature flower. The range of sector boundary positions seen in mature flowers indicated that flower primordia usually arise from a group of four cells on the inflorescence flank. The radial axes of the mature flower are apparently set by these cells, supporting the concept that they act as a structural template. Floral organs show two patterns of initiation, a leaf-like pattern with eight cells in a row (sepals and carpels), or a shoot-like pattern with four cells in a block (stamens). The petal initiation pattern involved too few cells to allow assignment. The numbers of initiating cells were close to those seen when organ growth commenced in each case, indicating that earlier specification of floral organ development does not occur. By examining sector boundaries in homeotic mutant flowers in which second whorl organs develop as sepal-like organs rather than petals, we have shown that their pattern of origin is position dependent rather than identity dependent.
The GAGA factor is required in the early Drosophila embryo not only for transcriptional regulation but also for nuclear division
Authors: Bhat Krishna Moorthi , Farkas Gabriella , Karch Francois , Gyurkovics Henrik , Gausz Janos , Schedl Paul 
Published: April 2021

ABSTRACT
The GAGA protein of Drosophila was first identified as a stimulatory factor in in vitro transcription assays using the engrailed and Ultrabithorax promoters. Subsequent studies have suggested that the GAGA factor promotes transcription by blocking the repressive effects of histones; moreover, it has been shown to function in chromatin remodeling, acting together with other factors in the formation of nuclease hypersensitive sites in vitro. The GAGA factor is encoded by the Trithorax-like locus and in the studies reported here we have used the maternal effect allele Trl13C to examine the functions of the protein during embryogenesis. We find that GAGA is required for the proper expression of a variety of developmental loci that contain GAGA binding sites in their upstream regulatory regions. The observed disruptions in gene expression are consistent with those expected for a factor involved in chromatin remodeling. In addition to facilitating gene expression, the GAGA factor appears to have a more global role in chromosome structure and function. This is suggested by the spectrum of nuclear cleavage cycle defects observed in Trl13C embryos. These defects include asynchrony in the cleavage cycles, failure in chromosome condensation, abnormal chromosome segregation and chromosome fragmentation. These defects are likely to be related to the association of the GAGA protein with heterochromatic satellite sequences which is observed throughout the cell cycle.