bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Drosophila homeobox gene optix is capable of inducing ectopic eyes by an eyeless-independent mechanism
Authors: Seimiya Makiko , Gehring Walter J. 
Published: April 2021

ABSTRACT
optix is a new member of the Six/so gene family from Drosophila that contains both a six domain and a homeodomain. Because of its high amino acid sequence similarity with the mouse Six3 gene, optix is considered to be the orthologous gene from Drosophila rather than sine oculis, as previously believed. optix expression was detected in the eye, wing and haltere imaginal discs. Ectopic expression of optix leads to the formation of ectopic eyes suggesting that optix has important functions in eye development. Although optix and sine oculis belong to the same gene family (Six/so) and share a high degree of amino acid sequence identity, there are a number of factors which suggest that their developmental roles are different: (1) the expression patterns of optix and sine oculis are clearly distinct; (2) sine oculis acts downstream of eyeless, whereas optix is expressed independently of eyeless; (3) sine oculis functions synergistically with eyes absent in eye development whereas optix does not; (4) ectopic expression of optix alone, but not of sine oculis can induce ectopic eyes in the antennal disc. These results suggest that optix is involved in eye morphogenesis by an eyeless-independent mechanism.
Functional analysis of the Drosophila Diaphanous FH protein in early embryonic development
Authors: Afshar Katayoun , Stuart Bridget , Wasserman Steven A. 
Published: April 2021

ABSTRACT
The Drosophila Formin Homology (FH) protein Diaphanous has an essential role during cytokinesis. To gain insight into the function of Diaphanous during cytokinesis and explore its role in other processes, we generated embryos deficient for Diaphanous and analyzed three cell-cycle-regulated actin-mediated events during embryogenesis: formation of the metaphase furrow, cellularization and formation of the pole cells. In dia embryos, all three processes are defective. Actin filaments do not organize properly to the metaphase and cellularization furrows and the actin ring is absent from the base of the presumptive pole cells. Furthermore, plasma membrane invaginations that initiate formation of the metaphase furrow and pole cells are missing. Immunolocalization studies of wild-type embryos reveal that Diaphanous localizes to the site where the metaphase furrow is anticipated to form, to the growing tip of cellularization furrows, and to contractile rings. In addition, the dia mutant phenotype reveals a role for Diaphanous in recruitment of myosin II, anillin and Peanut to the cortical region between actin caps. Our findings thus indicate that Diaphanous has a role in actin cytoskeleton organization and is essential for many, if not all, actin-mediated events involving membrane invagination. Based on known biochemical functions of FH proteins, we propose that Diaphanous serves as a mediator between signaling molecules and actin organizers at specific phases of the cell cycle.
Laser-induced gene expression in specific cells of transgenic zebrafish
Authors: Halloran Mary C. , Sato-Maeda Mika , Warren James T. , Su Fengyun , Lele Zsolt , Krone Patrick H. , Kuwada John Y. , Shoji Wataru 
Published: April 2021

ABSTRACT
Over the past few years, a number of studies have described the generation of transgenic lines of zebrafish in which expression of reporters was driven by a variety of promoters. These lines opened up the real possibility that transgenics could be used to complement the genetic analysis of zebrafish development. Transgenic lines in which the expression of genes can be regulated both in space and time would be especially useful. Therefore, we have cloned the zebrafish promoter for the inducible hsp70 gene and made stable transgenic lines of zebrafish that express the reporter green fluorescent protein gene under the control of a hsp70 promoter. At normal temperatures, green fluorescent protein is not detectable in transgenic embryos with the exception of the lens, but is robustly expressed throughout the embryo following an increase in ambient temperature. Furthermore, we have taken advantage of the accessibility and optical clarity of the embryos to express green fluorescent protein in individual cells by focussing a sublethal laser microbeam onto them. The targeted cells appear to develop normally: cells migrate normally, neurons project axons that follow normal pathways, and progenitor cells divide and give rise to normal progeny cells. By generating other transgenic lines in which the hsp70 promoter regulates genes of interest, it should be possible to examine the in vivo activity of the gene products by laser-inducing specific cells to express them in zebrafish embryos. As a first test, we laser-induced single muscle cells to make zebrafish Sema3A1, a semaphorin that is repulsive for specific growth cones, in a hsp70-sema3A1 transgenic line of zebrafish and found that extension by the motor axons was retarded by the induced muscle.
Recruitment of components of Polycomb Group chromatin complexes in Drosophila
Authors: Poux Sylvain , McCabe Donna , Pirrotta Vincenzo 
Published: April 2021

ABSTRACT
Polycomb Group complexes assemble at polycomb response elements (PREs) in vivo and silence genes in the surrounding chromatin. To study the recruitment of silencing complexes, we have targeted various Polycomb Group (PcG) proteins by fusing them to the LexA DNA binding domain. When LexA-PC, -PSC, -PH or -SU(Z)2 are targeted to a reporter gene, they recruit functional PcG-silencing complexes that recapitulate the silencing behavior of a PRE: silencing is sensitive to the state of activity of the target chromatin. When the target is transcriptionally active, silencing is not established but when the target is not active at syncytial blastoderm, it becomes silenced. The repressed state persists through embryonic development but cannot be maintained in larval imaginal discs even when the LexA-PcG fusion is constitutively expressed, suggesting a discontinuity in the mechanism of repression. These proteins also interact with other PC-containing complexes in embryonic nuclear extracts. In contrast LexA-PHO is neither able to silence nor to interact with PC-containing complexes. Analysis of pho mutant embryos and of PRE constructs whose PHO-binding sites are mutated suggests that, while PHO is important for silencing in imaginal discs, it is not necessary for embryonic PcG silencing.
Heparan sulfate proteoglycans are critical for the organization of the extracellular distribution of Wingless
Authors: Baeg Gyeong-Hun , Lin Xinhua , Khare Narmada , Baumgartner Stefan , Perrimon Norbert 
Published: April 2021

ABSTRACT
Recent studies in Drosophila have shown that heparan sulfate proteoglycans (HSPGs) are required for Wingless (Wg/Wnt) signaling. In addition, genetic and phenotypic analyses have implicated the glypican gene dally in this process. Here, we report the identification of another Drosophila glypican gene, dally-like (dly) and show that it is also involved in Wg signaling. Inhibition of dly gene activity implicates a function for DLY in Wg reception and we show that overexpression of DLY leads to an accumulation of extracellular Wg. We propose that DLY plays a role in the extracellular distribution of Wg. Consistent with this model, a dramatic decrease of extracellular Wg was detected in clones of cells that are deficient in proper glycosaminoglycan biosynthesis. We conclude that HSPGs play an important role in organizing the extracellular distribution of Wg.
The dermomyotome dorsomedial lip drives growth and morphogenesis of both the primary myotome and dermomyotome epithelium
Authors: Ordahl Charles P. , Berdougo Eli , Venters Sara J. , Denetclaw Wilfred F. 
Published: April 2021

ABSTRACT
The cellular and molecular mechanisms that govern early muscle patterning in vertebrate development are unknown. The earliest skeletal muscle to organize, the primary myotome of the epaxial domain, is a thin sheet of muscle tissue that expands in each somite segment in a lateral-to-medial direction in concert with the overlying dermomyotome epithelium. Several mutually contradictory models have been proposed to explain how myotome precursor cells, which are known to reside within the dermomyotome, translocate to the subjacent myotome layer to form this first segmented muscle tissue of the body. Using experimental embryology to discriminate among these models, we show here that ablation of the dorsomedial lip (DML) of the dermomyotome epithelium blocks further primary myotome growth while ablation of other dermomyotome regions does not. Myotome growth and morphogenesis can be restored in a DML-ablated somite of a host embryo by transplantation of a second DML from a donor embryo. Chick-quail marking experiments show that new myotome cells in such recombinant somites are derived from the donor DML and that cells from other regions of the somite are neither present nor required. In addition to the myotome, the transplanted DML also gives rise to the dermomyotome epithelium overlying the new myotome growth region and from which the mesenchymal dermatome will later emerge. These results demonstrate that the DML is a cellular growth engine that is both necessary and sufficient to drive the growth and morphogenesis of the primary myotome and simultaneously drive that of the dermomyotome, an epithelium containing muscle, dermis and possibly other potentialities.
REF-1, a protein with two bHLH domains, alters the pattern of cell fusion inC. elegansby regulating Hox protein activity
Authors: Alper Scott , Kenyon Cynthia 
Published: April 2021

ABSTRACTHox genes control the choice of cell fates along the anteroposterior (AP) body axis of many organisms. In C. elegans, two Hox genes, lin-39 and mab-5, control the cell fusion decision of the 12 ventrally located Pn.p cells. Specific Pn.p cells fuse with an epidermal syncytium, hyp7, in a sexually dimorphic pattern. In hermaphrodites, Pn.p cells in the mid-body region remain unfused whereas in males, Pn.p cells adopt an alternating pattern of syncytial and unfused fates. The complexity of these fusion patterns arises because the activities of these two Hox proteins are regulated in a sex-specific manner. MAB-5 activity is inhibited in hermaphrodite Pn.p cells and thus MAB-5 normally only affects the male Pn.p fusion pattern. Here we identify a gene, ref-1, that regulates the hermaphrodite Pn.p cell fusion pattern largely by regulating MAB-5 activity in these cells. Mutation of ref-1 also affects the fate of other epidermal cells in distinct AP body regions. ref-1 encodes a protein with two basic helix-loop-helix domains distantly related to those of the hairy/Enhancer of split family. ref-1, and another hairy homolog, lin-22, regulate similar cell fate decisions in different body regions along the C. elegans AP body axis.
A BAC transgenic analysis of the Mrf4/Myf5 locus reveals interdigitated elements that control activation and maintenance of gene expression during muscle development
Authors: Carvajal Jaime J. , Cox David , Summerbell Dennis , Rigby Peter W. J. 
Published: April 2021

ABSTRACT
The muscle-specific transcription factors Myf5 and Mrf4 are two of the four myogenic regulatory factors involved in the transcriptional cascade responsible for skeletal myogenesis in the vertebrate embryo. Myf5 is the first of these four genes to be expressed in the mouse. We have previously described discrete enhancers that drive Myf5 expression in epaxial and hypaxial somites, branchial arches and central nervous system, and argued that additional elements are required for proper expression (Summerbell, D., Ashby, P. R., Coutelle, O., Cox, D., Yee, S. P. and Rigby, P. W. J. (2000) Development 127, 3745–3757). We have now investigated the transcriptional regulation of both Myf5 and Mrf4 using bacterial artificial chromosome transgenesis. We show that a clone containing Myf5 and 140 kb of upstream sequences is sufficient to recapitulate the known expression patterns of both genes. Our results confirm and reinforce the conclusion of our earlier studies, that Myf5 expression is regulated differently in each of a considerable number of populations of muscle progenitors, and they begin to illuminate the evolutionary origins of this complex regulation. We further show that separate elements are involved in the activation and maintenance of expression in the various precursor populations, reflecting the diversity of the signals that control myogenesis. Mrf4 expression requires at least four elements, one of which may be shared with Myf5, providing a possible explanation for the linkage of these genes throughout vertebrate phylogeny. Further complexity is revealed by the demonstration that elements which control Mrf4 and Myf5 are embedded in an unrelated neighbouring gene.
Non-imprinted Igf2r expression decreases growth and rescues the Tme mutation in mice
Authors: Wutz A. , Theussl H. C. , Dausman J. , Jaenisch R. , Barlow D. P. , Wagner E. F. 
Published: April 2021

ABSTRACT
In the mouse the insulin-like growth factor receptor type 2 gene (Igf2r) is imprinted and maternally expressed. Igf2r encodes a trans-membrane receptor that transports mannose-6-phosphate tagged proteins and insulin-like growth factor 2 to lysosomes. During development the receptor reduces the amount of insulin-like growth factors and thereby decreases embryonic growth. The dosage of the gene is tightly regulated by genomic imprinting, leaving only the maternal copy of the gene active. Although the function of Igf2r in development is well established, the function of imprinting the gene remains elusive. Gene targeting experiments in mouse have demonstrated that the majority of genes are not sensitive to gene dosage, and mice heterozygous for mutations generally lack phenotypic alterations. To investigate whether reduction of Igf2r gene dosage by genomic imprinting has functional consequences for development we generated a non-imprinted allele (R2Δ). We restored biallelic expression to Igf2r by deleting a critical element for repression of the paternal allele (region 2) in mouse embryonic stem cells. Maternal inheritance of the R2Δ allele has no phenotype; however, paternal inheritance results in bialleleic expression of Igf2r, which causes a 20% reduction in weight late in embryonic development that persists into adulthood. Paternal inheritance of the R2Δ allele rescues the lethality of a maternally inherited Igf2r null allele and a maternally inherited Tme (T-associated maternal effect) mutation. These data show that the biological function of imprinting Igf2r is to increase birth weight and they also establish Igf2r as the Tme gene.
Studies on pattern regulation in hydra
Authors: Webster Gerald 
Published: April 2021

ABSTRACT
The dynamic behaviour of the factors (level of inhibition and threshold for inhibition) controlling hypostome formation in hydra has been investigated during regulation using transplantation techniques. The formation of a new hypostome following removal of the original hypostome is accompanied by restoration of the level of inhibition to that of the intact hydra. The maximum time for them to occur is about 9 h. It may be less— about 5 h which is the time taken for a new hypostome to form from the subhypostomal region, as shown in a previous paper. During the formation of a hypostome from the distal peduncle the threshold for inhibition rises in the presumptive hypostomal region. The results suggest that the factors controlling the time for hypostome formation and threshold for inhibition are closely linked. It has not been possible to demonstrate changes in threshold properties in regions other than the presumptive hypostomal region until some time after the new hypostome has formed. The time-threshold properties of a region are determined by its position on the linear axis in relation to the hypostome. The significance of the results in relation to polarized regulation in hydra and other hydroids is discussed, and the concepts developed are used to explain some cases of reversal of polarity following grafting. A model for proportionate regulation in a two-compartment system is presented, based on the concepts of control developed for hydra.
Action of actinomycin and puromycin upon frog oocyte maturation
Authors: Dettlaff T. A. 
Published: April 2021

ABSTRACT
In amphibians, as well as in other vertebrates, occytes start to mature under the action of hypophyseal gonadotropic hormones. (In this paper the term ‘maturation’ implies the transformation into ripe eggs of oocytes that have finished growing.) In the course of maturation the oocytes themselves and the follicle cells surrounding them undergo changes; the changes of these two cell types are not causally connected, their coincidence in time is easily broken in unfavourable conditions (Wright, 1945; Tchou-Su & Wang Yu-lan, 1958). As shown earlier (Dettlaff, Nikitina & Stroeva, 1964), hypophyseal gonadotropic hormones affect amphibian oocytes through the oocyte nucleus, the germinal vesicle. As a result of their action the nuclear sap of the germinal vesicle acquires the ability to induce cytoplasmic maturation (the property revealed by Delage on the oocytes of Asterias glacialis, 1899, 1901, and by Wilson on those of Cerebratulus lacteus, 1903). It is also well known that the presence of gonadotropin is required for oocyte maturation and ovulation only in the first part of maturation period (hormone-dependent maturation period). Shortly before disruption of the germinal vesicle membrane, the maturation processes acquire inertia and do not need further action of hypophyseal hormones (hormone-independent maturation period). It is of importance here that the main changes during maturation (dissolution of the germinal vesicle membrane, changes in the cytoplasmic properties) occur during the hormone-independent period.
An autoradiographic study of RNA synthesis during primary embryonic induction
Authors: Brahma S. K. 
Published: April 2021

ABSTRACT
Although much work has been done on the inducing factors involved in primary embryonic induction, we are far from understanding the mechanism of the phenomenon. Information concerning the changes in the synthetic patterns in the reacting tissue, which may be related to the induction, must be accumulated before we will be able to formulate a hypothesis on the mechanism of embryonic induction at a subcellular level. The work reported in this paper represents an effort to obtain preliminary information concerning the possible changes in RNA synthesis correlated with primary embryonic induction using the autoradiographic technique.
A light- and electron-microscopic study of primordial germ cells in the early mouse embryo
Authors: Spiegelman Martha , Bennett Dorothea 
Published: April 2021

ABSTRACTThe primordial germ cells (PGC’s) of the early mouse embryo have been identified in semi-thin and ultra-thin plastic sections on the combined bases of location and a distinctive set of morphological features. These cells originate extra-gonadally and their path of migration during the stages investigated agrees with results of previous histological and experimental studies. At 8–9 days of development, PGC’s are observed among the endoderm cells of the mid- and hindgut and the yolk stalk; at 10–11 days, PGC’s are seen in the dorsal mesentery, the dorsal coelomic lining, and in the rudimentary genital ridge; by 13 days, the gonad is abundantly populated with germ cells. During the migratory period the PGC’s appear as small (10–12 pm diameter), oval, basophilic cells which have a large nucleo-cytoplasmic ratio. These cells possess numerous free ribosomes and polysomes, a filamentous ground cytoplasm, and few profiles of endoplasmic reticulum. Mitochondria display small oval and thread-like profiles. A Golgi complex is not prominent in the PGC’s. The densely granular and fibrillar nucleus is often oval in outline but sometimes shows irregular contours. A large nucleolus is present. Although located among groups of cells that exhibit extensive cell junctions, the PGC’s have not been found to share such junctions with neighboring cells. Furthermore, the PGC’s possess small cytoplasmic processes that contain numerous microfilaments. These observations are interpreted as morphological correlates to the migratory activity of these cells.In the early PGC’s located in the gut, regions of the endoplasmic reticulum where membranes are closely apposed, perhaps fused, often present the appearance of annulate cisternae. In addition, compact aggregates of granulofibrillar material are found in the cytoplasm of these same cells. Neither of these structures is detected in the mesenteric PGC’s, the gonadal germ cells, or any other cell of the embryo at the stages studied. It is suggested that these two cytoplasmic elements may be related to further differentiation of the germ cells.The germ cells of the developing gonad are large, oval cells which possess a nucleus of very round contour. Both the nucleus and the cytoplasm retain a densely granular appearance. The expanded cytoplasm contains a large Golgi complex but still few profiles of endoplasmic reticulum. Free ribosomes and polysomes are abundant. The germ cells share extensive gap junctions with one another and with adjacent stromal cells.
Origin of the ectoplacental cone and secondary giant cells in mouse blastocysts reconstituted from isolated trophoblast and inner cell mass
Authors: Gardner R. L. , Papaioannou V. E. , Barton S. C. 
Published: April 2021

ABSTRACTInner cell mass (ICM) and trophoblast tissue were isolated from -day post-coitum mouse blastocysts that were homozygous for different electrophoretic variants of the enzyme glucose phosphate isomerase (GPI). Blastocysts were reconstituted from these tissues, transferred to pseudo-pregnant recipients and allowed to develop to the early somite stage. The embryo plus membranes and trophoblast were dissected and typed separately for GPI. Contamination of trophoblast with maternal decidual tissue was quantified. The trophoblast of the implanted embryos was almost exclusively of the trophoblastdonor GPI type. The embryos plus membranes were mainly of the ICM-donor type but most also showed a substantial proportion of trophoblast-donor type. It is argued that the ICM controls trophoblast proliferation by inhibiting giant cell transformation of adjacent trophoblast cells rather than through making a significant cellular contribution.
Interactions de l’œil et du lobe optique au cours de la croissance post-embryonnaire des Insectes odonates
Authors: Mouze Michel 
Published: April 2021

ABSTRACTDifferent types of experiments have been performed in order to disturb or to destroy the relations between the eye and the optic lobe and then to study these isolated organs. The results show that growth and differentiation of the eye is independent of the optic lobe. How-ever, the structure of ommatidia whose post-retinal fibres have been sectioned is markedly modified. The growth of the optic lobe is closely related to the presence of the eye and more precisely to the connexion with the post-retinal fibres. The volume of the optic lobe, especially the more external optic ganglia, is reduced after its relations with the eye are disturbed. More-over numerous abnormalities in its structure evince a disordered organization of new nerve fibres, which are attracted by the newly constituted zone of the lamina and exert a mitogenic action on the outer growing zone of the optic lobe. These fibres seem to exert a regulatory effect upon the differentiation and final position of the new ganglion cells.