bluuebunny/crossref_metadata_2025 huggingface dataset:
The regulation and function of the helix-loop-helix gene, asense, in Drosophila neural precursors
Authors: Jarman Andrew P. , Brand Michael , Jan Lily Y. , Jan Yuh Nung
Published: April 2021

asense is a member of the achaete-scute complex (AS-C) of helix-loop-helix genes involved in Drosophila neurogenesis. Unlike the other AS-C members, which are expressed in subsets of the ectodermal areas (proneural clusters) that give rise to neural precursors, asense is one of a number of genes that are specifically expressed in the neural precursors themselves (the neural precursor genes). We have identified a mutant asense phenotype that may reflect this later expression pattern. As a step in understanding the determination of neural precursors from the proneural clusters, we have investigated the potential role of the AS-C products as direct transcriptional activators of neural precursor genes by analysing the regulation of asense. Using genomic rescues and asense-lacZ fusion genes, the neural precursor regulatory element has been identified. We show that this element contains binding sites for AS-C/daughterless heterodimers. Deletion of these sites reduces the expression from the fusion gene, but significant expression is still achieved, pointing to the existence of other regulators of asense in addition to the AS-C. asense differs from the other AS-C members in its expression pattern, regulation, mutant phenotype and some DNA-binding properties.
Control of flower development in Arabidopsis thaliana by APETALA1 and interacting genes
Authors: Bowman John L. , Alvarez John , Weigel Detlef , Meyerowitz Elliot M. , Smyth David R.
Published: April 2021

Mutations in the APETALA1 gene disturb two phases of flower development, flower meristem specification and floral organ specification. These effects become manifest as a partial conversion of flowers into inflorescence shoots and a disruption of sepal and petal development. We describe the changes in an allelic series of nine apetala1 mutants and show that the two functions of APETALA1 are separable. We have also studied the interaction between APETALA1 and other floral genes by examining the phenotypes of multiply mutant plants and by in situ hybridization using probes for several floral control genes. The results suggest that the products of APETALA1 and another gene, LEAFY, are required to ensure that primordia arising on the flanks of the inflorescence apex adopt a floral fate, as opposed to becoming an inflorescence shoot. APETALA1 and LEAFY have distinct as well as overlapping functions and they appear to reinforce each other’s action. CAU - LIFLOWER is a newly discovered gene which positively regulates both APETALA1 and LEAFY expression. All functions of CAULIFLOWER are redundant with those of APETALA1. APETALA2 also has an early function in reinforcing the action of APETALA1 and LEAFY, especially if the activity of either is compromised by mutation. After the identity of a flower primordium is specified, APETALA1 interacts with APETALA2 in controlling the development of the outer two whorls of floral organs.
The expression of a zebrafish gene homologous to Drosophila snail suggests a conserved function in invertebrate and vertebrate gastrulation
Authors: Hammerschmidt Matthias , Nüsslein-Volhard Christiane
Published: April 2021

Snail, a zinc finger protein, is required for the formation of the ventral furrow and the mesoderm during gastrulation of the Drosophila embryo. snail homologues have been cloned from Xenopus and mouse. We have isolated a zebrafish homologue of snail, designated sna-1. Like its Drosophila counterpart, Sna-1 protein is nuclear. Maternal and zygotic sna-1 transcripts are ubiquitously distributed in zebrafish embryos of cleavage and blastula stages. In gastrulating embryos, sna-1 is expressed in involuting cells of the germ ring, but not in those at the dorsal midline, the presumptive notochordal region. After involution, the expression is maintained in the paraxial mesoderm and becomes prominent in the muscle pioneer precursors, followed by expression at the posterior somite boundaries. Later, sna-1 is expressed in neural crest and mesodermal derivatives of the head region. Sna-1 expression is induced in animal cap cells by activin A. The early sna-1 expression pattern in gastrulating zebrafish no tail (ntl) mutant embryos is normal except a reduction in the level of sna-1 transcription, suggesting that Ntl protein is not the key activator of sna-1 transcription in vivo, but might be involved in the enhancement or maintenance of sna-1 transcription. Data obtained in studies with ectopic ntl expression support this model.
Variable and multiple expression of Protease Nexin-1 during mouse organogenesis and nervous system development
Authors: Mansuy Isabelle M. , van der Putten Herman , Schmid Peter , Meins Marita , Botteri Florence M. , Monard Denis
Published: April 2021

Protease Nexin-1 (PN-1) also known as Glia-Derived Nexin (GDN) inhibits the activity of several serine proteases including thrombin, tissue (tPA)and urokinase (uPA)-type plasminogen activators. These and other serine proteases seem to play roles in development and tissue homeostasis. To gain insight into where and when PN-1 might counteract serine protease activities in vivo, we examined its mRNA and protein expression in the mouse embryo, postnatal developing nervous system and adult tissues. These analyses revealed distinct temporal and spatial PN-1 expression patterns in developing cartilage, lung, skin, urogenital tract, and central and peripheral nervous system. In the embryonic spinal cord, PN-1 expression occurs in cells lining the neural canal that are different from the cells previously shown to express tPA. In the developing postnatal brain, PN-1 expression appears transiently in many neuronal cell populations. These findings suggest a role for PN-1 in the maturation of the central nervous system, a phase that is accompanied by the appearance of different forms of PN-1. In adults, few distinct neuronal cell populations like pyramidal cells of the layer V in the neocortex retained detectable levels of PN-1 expression. Also, mRNA and protein levels did not correspond in adult spleen and muscle tissues. The widespread and complex regulation of PN-1 expression during embryonic development and, in particular, in the early postnatal nervous system as well as in adult tissues suggests multiple roles for this serine protease inhibitor in organogenesis and tissue homeostasis.
Differential expression of neurotrophin receptors during renal development
Authors: Durbeej Madeleine , Söderström Stine , Ebendal Ted , Birchmeier Carmen , Ekblom Peter
Published: April 2021

Early kidney differentiation is driven by local cell-cell interactions. The metanephrogenic mesenchyme stimulates the epithelial ureter bud to grow and branch, whereas the ureter bud stimulates the mesenchyme to convert into a new epithelium. These interactions may be dependent on local growth factors and their receptors. We studied the expression of receptors for nerve growth factors during kidney development. Expression of the lowand high-affinity receptors was cell-type specific. The low-affinity NGF receptor was found in the uninduced mesenchyme at early developmental stages, but in the glomerular podocytes at later developmental stages. In contrast, the high-affinity trkB receptor was found in the cortical mesenchyme cells that will differentiate into stroma. The trkC receptor was found only weakly expressed and in a few parts of the collecting ducts. The role of these receptors and c-ros, a receptor-type kinase expressed on the tip of the ureter bud, was studied by modified antisense oligonucleotides. However, we found that both sense, antisense and nonsense phosphorothioate oligonucleotides inhibited mouse and rat embryonic kidney development in vitro. The oligonucleotides appeared to be toxic for rodent embryonic kidneys in the experimental conditions that we used. Moreover, oligonucleotides did not penetrate well into the epithelial sheets in the organ cultures. We conclude that studies with phosphorothioate antisense oligonucleotides in organ cultures of embryonic kidneys should be interpreted with caution. Our current data do not allow us to not assign a function for the lowor highaffinity NGF receptors or c-ros in kidney development.
A dual requirement for neurogenic genes in Drosophila myogenesis
Authors: Bate Michael , Rushton Emma , Frasch Manfred
Published: April 2021

In wild-type embryos of Drosophila melanogaster, the formation of differentiated larval muscles is preceded by the segregation of small numbers of progenitor or founder cells in the embryonic mesoderm. The founder cells, characterised by the expression of genes encoding putative transcription factors such as S59 or vestigial, fuse with neighbouring myoblasts to form syncytial precursors of individual muscles. Founder cell segregation is deranged in embryos mutant for any of the neurogenic genes: enlarged clusters of cells expressing S59 or vestigial are detected at the sites where small numbers of founder cells segregate in the wild type. In addition, muscle differentiation is deranged in such embryos in a way that appears to be closely linked to the extent of epidermal disruption caused by the neurogenic phenotype: myoblast fusion is limited to regions of the mesoderm beneath the residual epidermis left by the hyperplasia of the nervous system, and late expression of S59 and vestigial is lost from mesoderm not lying within the margins of the residual epidermis. Thus neurogenic gene functions appear to be required both for the normal segregation of founder cells and for muscle differentiation. It is not clear whether either of these requirements reflects an essential function for any or all of the neurogenic genes within the mesoderm itself.
Cell polarity in early C. elegans development
Authors: Goldstein Bob , Hird Steven N. , White John G.
Published: April 2021

The polarization of the embryonic axes is a key event in embryogenesis, being one of the earliest manifestations of the shape and form of the organism. The acquisition of polarity by individual blastomeres is one of the earliest indicators of commitment to a particular pathway of differentiation. These phenomena have been studied in the development of C. elegans both at the cellular and organismal level. This review summarizes what is known about how polarity is established in the blastomeres of this organism, how the division axes of polarized cells are determined, and how the embryonic axes are set up.
Investigations into the control of cell form and polarity: the use of morphological mutants in fission yeast
Authors: Snell Valery , Nurse Paul
Published: April 2021

The fission yeast has been extensively used for investi-gating the cell cycle and is now being used to initiate studies into the control of cell form. There are a number of factors contributing to the generation of polarity in this organism, which are closely linked with the control of the cell cycle, including the redistributions of cytoskeletal components throughout the cycle and their correlation with patterns of end growth seen at different cell cycle stages. The controlled positioning of elements such as the nucleus and septum with respect to other cellular structures in order to produce viable daughter cells is clearly an important part of the fission yeast life cycle. This review will describe work already published concerning the control of cell form in this organism, including the isolation of various mutants displaying abnormal polarity, and will introduce work currently in progress to identify new elements involved in this control.
Digital malformations in the mouse foetus caused by X-radiation during pregnancy
Authors: Nogami Hiroshi
Published: April 2021

Six groups of mice of the ddN-strain were exposed to a single, whole body X-radiation of 200 r. on the different days between the 8th and the 13th day of pregnancy. Others were exposed to 150 r. or 300 r. on the 12th day of pregnancy. Mice of the CF1strain were also exposed to 200 r. on the 12th day of pregnancy. Embryonic and foetal digits were examined both externally and microscopically 2, 6, 12, 18, 24, 48 and 72 hr. after X-radiation. After that they were examined at 1-day intervals until the 19th day of foetal age. Their ossified skeleton was studied by the Dawson method and their cartilaginous one was studied by Noback’s modification of van Wijhe’s method. The critical stage for digital malformations in the ddN-mouse was presumed to be in the beginning of the 12th day of embryonic stage. Digital rays with precartilage concentrations of the mesenchyme became obvious at this period. The incidence of digital malformations was proportional to the X-ray dose employed. Most malformations were of the reduction type, i.e. partial or complete ectrodactylism. The number of digits missing was proportional to the X-ray dose. The 2nd and the 3rd digits were most susceptible, while the 4th digit was most resistant. It was noticed that each malformation manifested itself also in various transitional forms. Differences between the ddN- and the CF1-strain in their tendency to manifest digital abnormalities were observed. Localized foci of cellular necrosis were already evident in the primordia of the digital bud 2 hr. after X-radiation and the pyknotic nuclei were almost eliminated after 24 hr. The prospective pattern of malformations could already be detected externally before the cleft between the digits became marked.
Oögenesis in the guinea-pig
Authors: Ioannou J. M.
Published: April 2021

Estimations were made of the numbers of germ cells in the guinea-pig ovary from embryonic stages to maturity. A volumetric method was used to estimate the numbers of oögonia and Oöcytes in animals aged 26 to 55 days p.c., while counts were made of the numbers of germ cells present between 60 days p.c. and 12 months p.p. Neither the mitotic activity of oögonia nor the successive stages of meiotic prophase are closely synchronized. The process of oögenesis ceases at about 50 days p.c. Large numbers of Oöcytes are found in the leptotene stage at 35 days, in zygotene at about 40 days, and in pachytene at 50 days p.c. Thereafter the proportion of Oöcytes in the diplotene phase increases, so that by a few days after birth all the Oöcytes are in this stage. By 1 month p.p., however, two types of Oöcyte in diplotene are found in large numbers. The first is comparable to the corresponding stage in rat, man and the chick, while the second displays a very contracted nucleus. The latter type rapidly gains predominance, and by 12 months p.p. 94 per cent, of the germ cells belong to it. The number of germ cells per ovary increases from about 27,000 at 30 days p.c. to reach a peak of almost 105,000 by 41 days p.c.; subsequently it declines to some 13,000 by 12 months p.p. This decline is caused by a steady process of atresia which affects germ cells from the earliest stages of development.
Transplantation of embryonic cartilage and bone on to the chorioallantois of the chick
Authors: Stephenson N. G. , Tomkins J. K. N.
Published: April 2021

Transplantation of embryonic limb cartilage and bone to the chick chorioallantois has been carried out, using donors from the various tetrapod classes. The results may be correlated with the degree of phyletic relationship between the donor and host. Avian cartilage and bone continued to grow even when the donor was of a species and genus distinct from those of the chick host. On the other hand, when the donor belonged to another tetrapod class, only one of these embryonic tissues, namely cartilage, grew. There is a differential response of the tissues of a particular donor to a xenoplastic environment. Embryonic cartilage from amphibian, reptilian and mammalian donors will continue to grow xenoplastically when transplanted to the chick chorioallantois, whereas bone from such donors will not grow. The age factor is important in all xenoplastic results. Young donor cartilage grows well, but with increasing age there is a gradual reduction in its ability to do so. Embryonic cartilage from cold-blooded donors shows a high degree of temperature tolerance. Amphibian cartilage continues to grow xenoplastically at the chick incubation temperature (38° C.), whereas a temperature of 25° C. is known to be lethal to tadpoles of the particular donor species. Embryonic reptilian cartilage survives temperatures ranging from at least 4°C. to 38° C. The differential response of embryonic tissues to the transplantation environment is evident in development at stages much earlier than those at which immunological mechanisms are known to operate. It appears to be based on the metabolic requirements of particular tissues. The less specialized the nutritional requirements of a tissue are, the better its chances of obtaining from a xenoplastic environment the appropriate metabolites which are essential not only for its survival, but also for its continuing growth and differentiation.
Vertebral malformation in the mouse foetus caused by X-radiation of the mother during pregnancy
Authors: Murakami Ujihiro , Kameyama Yoshiro
Published: April 2021

Mice of the ddN and CF1 strains were exposed to a single dose of 200 r. X-radiation between the 8th and 13th day of pregnancy, and the foetal skeletons were examined on the 19th day of pregnancy. The phenomenon of a head-to-tail gradient shift in vertebral malformations as the stage of pregnancy at radiation advanced was less marked in the result in the ddN strain, but in the CF1 strain it was of similar proportions to that obtained by hypoxia. However, after X-radiation, malformations in the cervical and thoracic vertebrae presented two peaks of susceptibility. The first peak in malformation frequency may result from an effect of X-radiation upon the early somite stage or it may be an indirect effect. The second peak may originate from a direct effect upon the primordium, i.e. upon the sclerotome itself. The incidence of cervical malformations was higher in the group treated on the 8th or 9th day, and in the group treated on the 11th day of pregnancy. The malformations presented such characteristics as enlarged rami of the posterior arch of the 1st cervical vertebra or, in the latter group, fusion of the cervical vertebrae. There were also differences in the frequency of involvement of the vertebrae in these two strains which may be due to differences in the rate of differentiation of the vertebral primordium. Other differences were seen in the incidence of cervical ribs, of absence of the 13th rib, and of lumbar ribs. Such regional differentiation seems to be influenced by the genetic constitution.
The rôle of the germinal vesicle in oöcyte maturation in anurans as revealed by the removal and transplantation of nuclei
Authors: Nikitina T. A. , Dettlaff L. A. , Stroeva O. G.
Published: April 2021

A study of nucleo-cytoplasmic interactions in pre-embryonic development, at maturation stages in particular, is of great interest. During this period ooplasmic segregation takes place, specific properties of the cortex arise, and the cytoplasm obtains information from the oöcyte nucleus which promotes the development of the embryo during all the changes related to fertilization, cleavage and blastulation (Wilson, 1925; Raven, 1961; Brachet, 1957, 1960; Briggs & King, 1959; Neyfakh, 1962).
Cytosolic interaction between deltex and Notch ankyrin repeats implicates deltex in the Notch signaling pathway
Authors: Diederich Robert J. , Matsuno Kenji , Hing Huey , Artavanis-Tsakonas Spyros
Published: April 2021

Genetic data from Drosophila have suggested a functional relationship between the novel cytoplasmic protein encoded by the deltex locus and the transmembrane receptor encoded by Notch. We have demonstrated a direct interaction between these proteins from expression studies conducted in cultured cells, in yeast, and in the imaginal wing disc. deltex binds specifically to the Notch ankyrin repeats, a region that is crucial for Notch signaling and that constitutes the most conserved domain among Notch family members. In addition, we present a new Notch allele, Nsu42c, that is associated with a missense mutation within the fifth ankyrin repeat. In addition to representing a new class of viable Notch allele, this mutation behaves similarly to mutations of deltex and further implicates the ankyrin repeats in Notch function.
Epithelium formation in the Drosophila midgut depends on the interaction of endoderm and mesoderm
Authors: Tepass Ulrich , Hartenstein Volker
Published: April 2021

The reorganization of mesenchymal cells into an epithelial sheet is a widely used morphogenetic process in metazoans. An example of such a process is the formation of the Drosophila larval midgut epithelium that develops through a mesenchymal-epithelial transition from endodermal midgut precursors. We have studied this process in wild type and a number of mutants that show defects in midgut epithelium formation. Our results indicate that the visceral mesoderm serves as a basal substratum to which endodermal cells have to establish direct contact in order to form an epithelium. Furthermore, we have analyzed the midgut phenotype of embryos mutant for the gene shotgun, and the results suggest that shotgun directs adhesion between midgut epithelial cells, which is independent from the adhesion between endoderm and visceral mesoderm.
The gene serpent has homeotic properties and specifies endoderm versus ectoderm within the Drosophila gut
Authors: Reuter Rolf
Published: April 2021

The gut of Drosophila consists of ectodermally derived foregut and hindgut and endodermally derived midgut. Here I show that the gene serpent plays a key role in the development of the endoderm. serpent embryos lack the entire midgut and do not show endodermal differentiation. They gastrulate normally and form proper amnioproctodeal and anterior midgut invaginations. However, the prospective anterior midgut cells acquire properties that are usually found in ectodermal foregut cells. In the posterior region of the embryo, the prospective posterior midgut forms an additional hindgut which is contiguous with the normal hindgut and which appears to be a serial duplication, not a mere enlargement of the hindgut. The fate shifts in both the anterior and the posterior part of the srp embryo can be described in terms of homeotic transformations of anterior midgut to foregut and of posterior midgut to hindgut. serpent appears to act as a homeotic gene downstream of the terminal gap gene huckebein and to promote morphogenesis and differentiation of anterior and posterior midgut.
Localization of vasa protein to the Drosophila pole plasm is independent of its RNA-binding and helicase activities
Authors: Liang Lu , Diehl-Jones William , Lasko Paul
Published: April 2021

The Drosophila gene vasa encodes a DEAD-box protein, which is localized during early oogenesis to the perinuclear region of the nurse cells and later to the pole plasm at the posterior end of the oocyte. Posterior localization of vasa protein depends upon the functions of four genes: capu, spir, osk and stau. We have found that localization of vasa to the perinuclear nuage is abolished in most vas alleles, but is unaffected by mutations in four genes required upstream for its pole plasm localization. Thus localization of vasa to the nuage particles is independent of the pole plasm assembly pathway. Furthermore, electron-dense nuage particles are less abundant in the cytoplasm of nurse cells from vas mutants that fail to exhibit perinuclear localization, suggesting that the formation of the nuage depends upon vas function. Eight of nine vas point mutations cause codon substitutions in a region conserved among DEADbox genes. The proteins from two mutant alleles that retain the capacity to localize to the posterior pole of the oocyte, vasO14 and vasO11, are both severely reduced in RNAbinding and -unwinding activity as compared to the wildtype protein on a variety of RNA substrates including in vitro synthesized pole plasm RNAs. Initial recruitment of vasa to the pole plasm must consequently depend upon protein-protein interactions but, once localized, vasa must bind to RNA to mediate germ cell formation.
Cortical granule biogenesis is active throughout oogenesis in sea urchins
Authors: Laidlaw Michael , Wessel Gary M.
Published: April 2021

Cortical granules are secretory vesicles formed in the eggs of most animals and are essential for the prevention of polyspermy in these organisms. We have studied the biogenesis of cortical granules in sea urchin oocytes by identifying cDNA clones that encode proteins targeted selectively to the cortical granules. These cDNA clones were identified by an immunoscreen of a cDNA library using antibodies to proteins of the fertilization envelope. Four different mRNAs were identified, ranging from 4 kb to 13 kb in length, that encoded proteins targeted specifically to cortical granules. Accumulation of these mRNAs began very early in oogenesis, in oocytes approximately 10-15 μm in diameter, and continued throughout oogenesis. The mRNAs reached peak abundance (on a per cell basis) in germinal vesicle stage oocytes, and the accumulation of each mRNA was linear with respect to oocyte growth. During breakdown of the germinal vesicle these mRNAs were degraded so that in eggs the mRNA signals were at background levels. Antibodies generated to recombinant proteins made from each of these cDNA clones showed that in the oocyte each cognate protein appeared early in oogenesis. These proteins accumulated only in cortical granules: no accumulation was seen in the cytoplasm, in Golgi, or in other vesicles, and no heterogeneity of the contents was seen within the population of cortical granules. Using these antibodies we show that cortical granules accumulated linearly throughout oogenesis. Prior to germinal vesicle breakdown, cortical granules accumulated throughout the cytoplasm of oocytes and increased in number as the oocytes enlarged; the rate of synthesis appeared equal at each stage. At oocyte maturation the cortical granules moved to the cell periphery coincident with the complete degradation of mRNAs encoding these proteins. These results show that the genes encoding cortical granule proteins are coordinately activated throughout oogenesis and that the pathway of protein biosynthesis and targeting to these regulated secretory granules is functional throughout oogenesis in this animal.
Patterns of localization and cytoskeletal association of two vegetally localized RNAs, Vg1 and Xcat-2
Authors: Forristall Caryl , Pondel Marc , Chen Lihua , King Mary Lou
Published: April 2021

In Xenopus, localization of a rare class of mRNAs during oogenesis is believed to initiate pattern formation in the early embryo. We have determined the pattern of RNA localization for one of these RNAs, Xcat-2, which encodes a putative RNA-binding protein related to Drosophila nanos (Mosquera, L., Forristall, C., Zhou, Y. and King, M. L. (1993) Development 117, 377-386). Xcat-2 is exclusively localized to the mitochondrial cloud in stage I oocytes, moves with this body into the vegetal cortex during stage II and, later, partitions into islands consistent with it being a component of the germ plasm. As previously shown, Vg1 is not localized to the vegetal cortex until stage IV and distributes to all vegetal blastomeres during development. We found a direct correlation between the localized condition of these RNAs and their recovery in a detergent-insoluble fraction. We present evidence suggesting that differential RNA binding to a cytoskeletal component(s) in the vegetal cortex determines the pattern of inheritance for that RNA in the embryo.
DWnt-4, a novel Drosophila Wnt gene acts downstream of homeotic complex genes in the visceral mesoderm
Authors: Graba Yacine , Gieseler Kathrin , Aragnol Denise , Laurenti Patrick , Mariol Marie-Christine , Berenger Hélene , Sagnier Thierry , Pradel Jacques
Published: April 2021

Wnt genes encode putative cell signalling proteins which play crucial roles during development. From a library of DNA fragments associated, in vivo, with Ultrabithorax proteins, we isolated a novel Drosophila Wnt gene, DWnt-4. Neither a paralog nor an ortholog of the gene exist in the current repertoire of full-length Wnt sequences. DWnt-4 maps close (30 kb) to wingless, suggesting that the two Wnt genes derive from a duplication that occurred early in evolution, since they are significantly diverged in sequence and structure. Developmental expression of DWnt-4 partially overlaps that of wingless. The gene is transcribed following a segment polaritylike pattern in the posteriormost cells of each parasegment of the ectoderm, and at two locations that correspond to parasegments 4 and 8 of the visceral mesoderm. The control of DWnt-4 expression in the visceral mesoderm involves a network of regulatory molecules that includes Ultrabithorax and other proteins from the homeotic complex (HOM-C), as well as the TGF-β decapentaplegic gene product.
Control of Drosophila head segment identity by the bZIP homeotic gene cnc
Authors: Mohler Jym , Mahaffey James W. , Deutsch Elizabeth , Vani Kodela
Published: April 2021

Mutational analysis of cap’n’collar (cnc), a bZIP transcription factor closely related to the mammalian erythroid factor NF-E2 (p45), indicates that it acts as a segmentspecific selector gene controlling the identity of two cephalic segments. In the mandibular segment, cnc has a classical homeotic effect: mandibular structures are missing in cnc mutant larvae and replaced with duplicate maxillary structures. We propose that cnc functions in combination with the homeotic gene Deformed to specify mandibular development. Labral structures are also missing in cnc mutant larvae, where a distinct labral primordia is not properly maintained in the developing foregut, as observed by the failure to maintain and elaborate patterns of labral-specific segment polarity gene expression. Instead, the labral primordium fuses with the esophageal primordium to contribute to formation of the esophagus. The role of cnc in labral development is reciprocal to the role of homeotic gene forkhead, which has an identical function in the maintenance of the esophageal primordium. This role of homeotic selector genes for the segment-specific maintenance of segment polarity gene expression is a unique feature of segmentation in the preoral head region of Drosophila.
Expression of the labial group Hox gene HrHox-1 and its alteration induced by retinoic acid in development of the ascidian Halocynthia roretzi
Authors: Katsuyama You , Wada Shuichi , Yasugi Sadao , Saiga Hidetoshi
Published: April 2021

Ascidian embryogenesis shares several developmental features with vertebrates. Thus, it is presumed that some molecular mechanisms that are critical for vertebrate development may also act in the early development of ascidians. Here, we investigated expression of the ascidian labial group Hox gene HrHox-1 in the development of Halo-cynthia roretzi. HrHox-1 showed a spatially restricted expression pattern along the anterior-posterior axis, which is remarkably similar to that of the vertebrate gene, Hoxb-1. The expression of HrHox-1, however, was exclusively in tissues of ectoderm origin unlike its vertebrate counterpart. Exposure of the embryos to 10−6 M all-trans retinoic acid induced a larval phenotype with elimination of the anteriormost structures, the papillae. In this phenotype, the level of HrHox-1 expression was enhanced and ectopic expression was observed at the anterior terminal epidermis where the papillae are otherwise formed. These observations suggest that there are some conserved mechanisms in the spatial regulation of expression of labial group genes in embryogenesis of ascidians and vertebrates.
Ectopic cyclin E expression induces premature entry into S phase and disrupts pattern formation in the Drosophila eye imaginal disc
Authors: Richardson Helena , O’Keefe Louise V. , Marty Thomas
Published: April 2021

During animal development, cell proliferation is controlled in many cases by regulation of the G1 to S phase transition. Studies of mammalian tissue culture cells have shown that the G1-specific cyclin, cyclin E, can be rate limiting for progression from G1 to S phase. During Drosophila development, down-regulation of cyclin E is required for G1 arrest in terminally differentiating embryonic epidermal cells. Whether cyclin E expression limits progression into S phase in proliferating, as opposed to differentiating, cells during development has not been investigated. Here we show that Drosophila cyclin E (DmcycE) protein is absent in G1 phase cells but appears at the onset of S phase in proliferating cells of the larval optic lobe and eye imaginal disc. We have examined cells in the eye imaginal epithelium, where a clearly defined developmentally regulated G1 to S phase transition occurs. Ectopic expression of DmcycE induces premature entry of most of these G1 cells into S phase. Thus in these cells, control of DmcycE expression is required for regulated entry into S phase. Significantly, a band of eye imaginal disc cells in G1 phase was not induced to enter S phase by ectopic expression of DmcycE. This provides evidence for additional regulatory mechanisms that operate during G1 phase to limit cell proliferation during development. These results demonstrate that the role of cyclin E in regulating progression into S phase in mammalian tissue culture cells applies to some, but not all, cells during Drosophila development. Ectopic expression of DmcycE in the eye imaginal disc disrupts normal pattern formation, highlighting the importance of coordinating cell proliferation with developmental processes for correct patterning in the developing eye. These studies establish DmcycE as a target of regulatory mechanisms that coordinate cell proliferation with other developmental events.
A Drosophila protein related to the human zinc finger transcription factor PRDII/MBPI/HIV-EP1 is required for dpp signaling
Authors: Staehling-Hampton Karen , Laughon Allen S. , Hoffmann F. Michael
Published: April 2021

Little is known about the signal transduction pathways by which cells respond to mammalian TGF-βs or to decapentaplegic (dpp), a Drosophila TGF-β-related factor. Here we describe the genetic and molecular characterization of Drosophila schnurri (shn), a putative transcription factor implicated in dpp signaling. The shn protein has eight zinc fingers and is related to a human transcription factor, PRDII/MBPI/HIV-EP1, that binds to nuclear factor-κB-binding sites and activates transcription from the HIV long terminal repeat (LTR). shn mRNA is expressed in a dynamic pattern in the embryo that includes most of the known target tissues of dpp, including the dorsal blastoderm, the mesodermal germlayer and parasegments 4 and 7 of the midgut. Mutations in shn affect several developmental processes regulated by dpp including induction of visceral mesoderm cell fate, dorsal/ventral patterning of the lateral ectoderm and wing vein formation. Absence of shn function blocks the expanded expression of the homeodomain protein bagpipe in the embryonic mesoderm caused by ectopic dpp expression, illustrating a requirement for shn function downstream of dpp action. We conclude that shn function is critical for cells to respond properly to dpp and propose that shn protein is the first identified downstream component of the signal transduction pathway used by dpp and its receptors.
Progressive maturation of chromatin structure regulates HSP70.1 gene expression in the preimplantation mouse embryo
Authors: Thompson Eric M. , Legouy Edith , Elisabeth Christians , Renard Jean-Paul
Published: April 2021

In the widely studied model organisms, Drosophila and Xenopus, early embryogenesis involves an extended series of nuclear divisions prior to activation of the zygotic genome. The mammalian embryo differs in that the early cleavage phase is already characterized by regulated cell cycles with specific zygotic gene expression. In the mouse, where major activation of the zygotic genome occurs at the 2-cell stage, the HSP70.1 gene is among the earliest genes to be expressed. We investigated the developmentally regulated expression of this gene during the preimplantation period, using a luciferase transgene, with or without flanking scaffold attachment regions (SARs). Cleavage stage-specific modifications in expression profiles were examined in terms of histone H4 acetylation status, topoisomerase II activity, and the localisation of HMG-I/Y, a nuclear protein with known affinity for the AT-tracts of SARs. We demonstrate that HSP70.1-associated transcription factors are not limiting, and that instead, there is a progressive maturation of chromatin structure that is directly involved in HSP70.1 regulation during early mouse development.
The active migration of Drosophila primordial germ cells
Authors: Jaglarz Mariusz K. , Howard Kenneth R.
Published: April 2021

We describe our analysis of primordial germ cell migration in Drosophila wild-type and mutant embryos using high resolution microscopy and primary culture in vitro. During migratory events the germ cells form transient interactions with each other and surrounding somatic cells. Both in vivo and in vitro they extend pseudopodia and the accompanying changes in the cytoskeleton suggest that actin polymerization drives these movements.

These cellular events occur from the end of the blastoderm stage and are regulated by environmental cues. We show that the vital transepithelial migration allowing exit from the gut primordium and passage into the interior of the embryo is facilitated by changes in the structure of this epithelium.

Migrating germ cells extend processes in different directions. This phenomenon also occurs in primary culture where the cells move in an unoriented fashion at substratum concentration-dependent rates. In vivo this migration is oriented leading germ cells to the gonadal mesoderm. We suggest that this guidance involves stabilization of states of an intrinsic cellular oscillator resulting in cell polarization and oriented movement.
Blastomere derivation and domains of gene expression in the Spemann Organizer of Xenopus laevis
Authors: Vodicka Marie A. , Gerhart John C.
Published: April 2021

Spemann’s Organizer, located in the dorsal marginal zone of the amphibian gastrula, induces and differentiates dorsal axial structures characteristic of this and other vertebrates. To trace the cellular origins of the Xenopus Organizer, we labelled dorsal blastomeres of three of the four tiers (A, B and C) of the 32-cell embryo with green, red and blue fluorescent lineage tracers. A strong vegetalward displacement of labelled clones occurs between the late blastula and early gastrula stages but clones mix only slightly at their borders. The typical early gastrula Organizer is composed of approximately 10% A1 progeny in its animalmost region, 70% B1 progeny in the central region, and 20% C1 progeny in vegetal and deep regions. Variability in the composition of the early gastrula Organizer results from variability in the position of early cleavage planes and in pregastrulation movements. As the Organizer involutes during gastrulation, forming dorsal axial mesoderm, clonal boundaries are greatly dispersed by cell intermixing. Within a clone, deep cells are displaced and intermixed more than superficial cells. Variability in the distribution of progeny in the dorsal axial mesoderm of the late gastrula results mostly from variable intermixing of cells during gastrulation. Experiments to perturb later developmental events by molecular or embryonic manipulations at an early stage must take this variability into account along with the majority distributions of the fate map. Within the early gastrula Organizer, the genes Xbra, goosecoid, noggin and xNR3 are expressed differently in the animal-vegetal and superficial-deep dimensions. In situ hybridization and lineage labelling define distinct regions of the dorsal marginal zone. By the end of gastrulation, dorsal axial mesoderm cells derived from the Organizer have altered their expression of the genes Xbra, goosecoid, noggin and xNR3. At a given stage, a cell’s position in the embryo rather than its lineage may be more important in determining which genes it will express.
Pattern formation in Drosophila head development: the role of the orthodenticle homeobox gene
Authors: Royet Julien , Finkelstein Robert
Published: April 2021

Significant progress has been made towards understanding how pattern formation occurs in the imaginal discs that give rise to the limbs of Drosophila melanogaster. Here, we examine the process of regional specification that occurs in the eye-antennal discs, which form the head of the adult fruitfly. We demonstrate genetically that there is a graded requirement for the activity of the orthodenticle homeobox gene in forming specific structures of the developing head. Consistent with this result, we show that OTD protein is expressed in a graded fashion across the disc primordia of these structures and that different threshold levels of OTD are required for the formation of specific subdomains of the head. Finally, we provide evidence suggesting that otd acts through the segment polarity gene engrailed to specify medial head development.
The mab-21 gene of Caenorhabditis elegans encodes a novel protein required for choice of alternate cell fates
Authors: Chow King L. , Hall David H. , Emmons Scott W.
Published: April 2021

The gene mab-21, which encodes a novel protein of 386 amino acids, is required for the choice of alternate cell fates by several cells in the C. elegans male tail. Three cells descended from the ray 6 precursor cell adopt fates of anterior homologs, and a fourth, lineally unrelated hypodermal cell is transformed into a neuroblast. The affected cells lie together in the lateral tail epidermis, suggesting that mab-21 acts as part of a short-range pattern-formation mechanism. Each of the changes in cell fate brought about by mab-21 mutants can be interpreted as a posterior-toanterior homeotic transformation. mab-21 mutant males and hermaphrodites have additional pleiotropic phenotypes affecting movement, body shape and fecundity, indicating that mab-21 has functions outside the tail region of males. We show that the three known alleles of mab-21 are hypomorphs of a new gene. Mosaic analysis revealed that mab-21 acts cell autonomously to specify the properties of the sensory ray, but non-autonomously in the hypodermal versus neuroblast cell fate choice. Presence of cell signalling in the choice of the neuroblast fate was confirmed by cell ablation experiments. Mutations in mab-21 were shown previously to be genetic modifiers of the effects of HOMC/Hox gene mutations on ray identity specification. The results presented here support the conclusion that mab-21 acts as part of a mechanism required for correct cell fate choice, possibly involving the function of HOM-C/Hox genes in several body regions.
Target-independent diversification and target-specific projection of chemically defined retinal ganglion cell subsets
Authors: Yamagata Masahito , Sanes Joshua R.
Published: April 2021

In diverse vertebrate species, defined subsets of retinal ganglion cells (RGCs, the neurons that project from retina to brain) are distinguishable on the basis of their dendritic morphology, physiological properties, neurotransmitter content and synaptic targets. Little is known about when this diversity arises, whether diversification requires targetderived signals, and how subtype-specific projection patterns are established. Here, we have used markers for two chemically defined RGC subsets in chick retina to address these issues. Antibodies to substance P (SP) and the nicotinic acetylcholine receptor (AChR) β2 subunit label two small (<10%), mutually exclusive groups of RGCs in mature retina. SP and AChRs accumulate in distinct RGCs before retinotectal synapses have formed. Moreover, both populations of RGCs form in retinae that develop following tectal ablation or transplantation to the coelomic cavity. Thus, RGC subsets acquire distinct neurotransmitter phenotypes in the absence of extraretinal cues.

In the mature optic tectum, SPand AChR-positive RGC axonal arbors are confined to distinct retinorecipient (synaptic) laminae. In the developing tectum, Spand AChR-positive axons are initially intermingled in a superficial fiber layer, but then enter and arborize in appropriate laminae soon after those laminae form. Importantly, SPpositive axons, which synapse in a superficial lamina, never extend into the deeper, AChR-positive lamina. Tectal interneurons rich in SP receptors are concentrated in the lamina to which SP-positive RGC axons project, and a set of cholinergic (choline acetyltransferase-positive) tectal projection neurons elaborate dendrites in the lamina to which AChR-positive RGC axons project. These populations of tectal neurons, which are likely targets of the RGC subsets, form in tecta that develop following enucleation. Thus, RGCs and their targets can diversify in each others absence. Accordingly, we propose that the lamina-selective connectivity we observe reflects the presence of complementary cues on RGC subsets and their laminar targets.
Ligands of steroid/thyroid receptors induce cone photoreceptors in vertebrate retina
Authors: Kelley Matthew W. , Turner Jennifer K. , Reh Thomas A.
Published: April 2021

The mechanisms by which multipotent progenitor cells are directed to alternative cell identities during the histogenesis of the vertebrate central nervous system are likely to involve several different types of signaling systems. Recent evidence indicates that 9-cis retinoic acid, which acts through members of the steroid/thyroid superfamily of receptors, directs progenitor cells to the rod photoreceptor cell fate. We now report that another effector of this family of receptors, thyroid hormone, induces an increase in the number of cone photoreceptors that develop in embryonic rat retinal cultures, and that combinations of 9-cis retinoic acid and triiodothyronine cause isolated progenitor cells to differentiate as either rods or cones, depending on the relative concentrations of the ligands. These results implicate thyroid hormone in CNS cell fate determination, and suggest that different photoreceptor phenotypes may be modulated through the formation of thyroid/retinoid receptor heterodimers.
The Drosophila homeotic target gene centrosomin (cnn) encodes a novel centrosomal protein with leucine zippers and maps to a genomic region required for midgut morphogenesis
Authors: Heuer Josef G. , Li Kaijun , Kaufman Thomas C.
Published: April 2021

The products of the homeotic genes in Drosophila are transcription factors that are necessary to impose regional identity along the anterior-posterior axis of the developing embryo. However, the target genes under homeotic regulation that control this developmental process are largely unknown. We have utilized an immunopurification method to clone target genes of the Antennapedia protein (ANTP). We present here the characterization of centrosomin (cnn), one of the target genes isolated using this approach. The spatial and temporal expression of the cnn gene in the developing visceral mesoderm (VM) of the midgut and the central nervous system (CNS) of wild-type and homeotic mutant embryos is consistent with the idea that cnn is a homeotic target. In the VM, Antp and abdominal-A (abd-A) negatively regulate cnn, while Ultrabithorax (Ubx) shows positive regulation. In the CNS, cnn is regulated positively by Antp and negatively by Ubx and abd-A. Characterization of a cDNA encoding CNN predicts a novel structural protein with three leucine zipper motifs and several coiledcoil domains exhibiting limited homology to the rod portion of myosin. Immunocytochemical results demonstrate that the cnn encoded protein is localized to the centrosome and the accumulation pattern is coupled to the nuclear and centrosome duplication cycles of cleavage. In addition, evidence suggests that the expression of the cnn gene in the VM correlates with the morphogenetic function of Ubx in that tissue, i.e., the formation of the second midgut constriction. The centrosomal localization of CNN and the involvement of microtubules in midgut morphogenesis suggest that this protein may participate in mitotic spindle assembly and the mechanics of morphogenesis through an interaction with microtubules, either directly or indirectly.