bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fibroblast growth factor is a direct neural inducer, which combined with noggin generates anterior-posterior neural pattern
Authors: Lamb Teresa M. , Harland Richard M. 
Published: April 2021

ABSTRACT
Neural tissue in developing Xenopus embryos is induced by signals from the dorsal mesoderm. Induction of anterior neural tissue could be mediated by noggin, a secreted polypeptide found in dorsal mesoderm. We show that bFGF, a known mesoderm inducer of blastula staged ectoderm, induces neural tissue from gastrula stage ectoderm. The type of neural tissue induced by bFGF from stage 10.25 ectoderm is posterior, as marked by Hox B9 expression. When bFGF and noggin are combined on early gastrula stage ectoderm, a more complete neural pattern is generated and no mesodermal tissue is detected. Explants treated with noggin and bFGF elongate and display distinct anterior and posterior ends marked by otx2 and Hox B9 expression, respectively. Furthermore, treatment of early gastrula ectoderm with noggin and bFGF results in the induction of En-2, a marker of the midbrain-hindbrain junction and Krox 20, a marker of the third and fifth rhombomeres of the hindbrain. Neither of these genes is induced by noggin alone or bFGF alone at this stage, suggesting a synergy in anterior-posterior neural patterning. The response of later gastrula (stage 11-12) ectoderm to bFGF changes so that Krox 20 and En-2 are induced by bFGF alone, while induction of more posterior tissue marked by Hox B9 is eliminated. The dose of bFGF affects the amount of neural tissue induced, but has little effect on the anteriorposterior character, rather the age of the ectoderm treated is the determinant of the response. Thus, an FGF signal may account for posterior neural induction, and anteriorposterior neural patterning could be partly explained by the actions of noggin and FGF, together with the changing response of the ectoderm to these factors.
Targeted ablation of glia disrupts axon tract formation in the Drosophila CNS
Authors: Hidalgo Alicia , Urban Joachim , Brand Andrea H. 
Published: April 2021

ABSTRACT
Glial cells are thought to play a role in growth cone guidance, both in insects and in vertebrates. In the developing central nervous system of the Drosophila embryo, the interface glia form a scaffold prior to the extension of the first pioneer growth cones. Growing axons appear to contact the glial scaffold as the axon tracts are established. We have used a novel technique for targeted cell ablation to kill the interface glia and thus to test their role in the establishment of the embryonic axon tracts. We show that ablation of the interface glia early in development leads to a complete loss of the longitudinal axon tracts. Ablation of the glia later in embryonic development results in defects comprising weakening and loss of axon fascicles within the connectives. We conclude that the interface glia are required first for growth cone guidance in the formation of the longitudinal axon tracts in the Drosophila embryo and then either to direct the follower growth cones, or to maintain the longitudinal axon tracts.
Identification and behavior of epithelial stem cells in the Drosophila ovary
Authors: Margolis Jonathan , Spradling Allan 
Published: April 2021

ABSTRACT
Throughout their lives, adult Drosophila females continuously produce oocytes, each surrounded by an epithelial monolayer of follicle cells. To characterize the somatic stem cells that give rise to ovarian follicle cells, we marked dividing cells using FLP-catalyzed mitotic recombination and analyzed the resulting clones. Each ovariole in young females contains, on average, two somatic stem cells located near the border of germarium regions 2a and 2b. The somatic stem cells do not coordinate their divisions either with each other or with the germline stem cells. As females age, initially mosaic ovarioles become monoclonal, indicating that functional somatic stem cells have a finite life span. Analysis of agametic flies revealed that somatic cells continue to divide in the absence of a germline. Under these conditions, the somatic stem cells develop near the tip of the ovariole (the normal site of the germline stem cells), and a subpopulation of somatic cells that normally separates the germline and somatic stem cells is missing.
Control of Drosophila tracheal branching by the novel homeodomain gene unplugged, a regulatory target for genes of the bithorax complex
Authors: Chiang Chin , Young Keith E. , Beachy Philip A. 
Published: April 2021

ABSTRACT
We have identified a novel Drosophila homeodomain gene, unplugged (unp), whose function is required for formation of the tracheal branches that penetrate the CNS. In unp mutant embryos the segmentally repeated ganglionic branches stall and fail to penetrate the CNS and the segment-specific cerebral branch and associated cerebral anastomosis fail to form. Expression of unp in the founder cells for the cerebral branch within the first tracheal metamere is repressed in posterior segments by Ubx and other bithorax complex genes. This pattern of expression and homeotic gene regulation is reproduced by an unusual 2.7 kb cis-regulatory sequence located downstream of the unp transcription unit. Since the unp protein is localized to the nucleus of tracheal precursor cells as they migrate and extend, unp protein appears to play a regulatory role in neural branching of the tracheae, and the segment-specific aspects of these neural branching patterns appear to be generated by homeotic regulation of unp expression.
Hormonal induction of Dopa decarboxylase in the epidermis of Drosophila is mediated by the Broad-Complex
Authors: Hodgetts Ross B. , Clark William C. , O’Keefe Sandra L. , Schouls Michelle , Crossgrove Kirsten , Guild Gregory M. , Kalm Laurence von 
Published: April 2021

ABSTRACT
The 2B5 early puff locus corresponds to the Broad-Complex (BR-C) and encodes a family of transcription factors whose members are induced by the molting hormone ecdysone. Mutations in the br subcomplementation group substantially reduce the levels of Dopa decarboxylase (DDC) in the epidermis of mature third instar larvae but not in mature second instar organisms. Enzyme levels are normal in the central nervous system of the two mutants examined. The specificity of these effects suggests that a product of the BRC locus mediates the rapid appearance of DDC in mature third instar larvae experiencing an elevated titer of ecdysone. The likely identity of this protein has been confirmed by pursuing the observation that the br28 allele is caused by the insertion of a P element into the Z2 DNAbinding domain. Both the transcript and a protein carrying this domain are present in the epidermis and a BR-C recombinant protein carrying the Z2 finger binds to the first intron of the Ddc gene. Five binding sites have been identified within the intron by DNAase I footprinting and a core consensus sequence has been derived which shares some identity with the consensus binding site of the Z2 protein to the Sgs-4 regulatory region. Our demonstration that Ddc is a target of BR-C in the epidermis is the first direct evidence of a role for this early gene in a tissue other than the salivary glands. The data reinforce the idea that BR-C, which clearly mediates a salivary gland-specific response to ecdysone, may play a widespread role in the hormone’s activation of gene cascades in other target tissues.
Specific modulation of ectodermal cell fates in Xenopus embryos by glycogen synthase kinase
Authors: Itoh Keiji , Tang Terry L. , Neel Benjamin G. , Sokol Sergei Y. 
Published: April 2021

ABSTRACT
Shaggy is a downstream component of the wingless and Notch signaling pathways which operate during Drosophila development. To address the role of glycogen synthase kinase 3β (GSK3β), a mammalian homologue of Shaggy, in vertebrate embryogenesis, it was overexpressed in Xenopus embryos. Microinjection of rat GSK3β mRNA into animal ventral blastomeres of 8-cell-stage embryos triggered development of ectopic cement glands with an adjacent anterior neural tissue as evidenced by in situ hybridization with Xotx2, a fore/midbrain marker, and NCAM, a pan-neural marker. In contrast, animal dorsal injection of the same dose of GSK3β mRNA caused eye deficiencies, whereas vegetal injections had no pronounced effects on normal development. Using several mutated forms of rat GSK3β, we demonstrate that the observed phenotypes are dose-dependent and tightly correlate with GSK3β enzymatic activity. Lineage tracing experiments showed that the effects of GSK3β are cell autonomous and that ectopic cement glands and eye deficiencies arose directly from cells containing GSK3β mRNA. Molecular marker analysis of ectodermal explants overexpressing GSK3β has revealed activation of Xotx2 and of cement gland marker XAG-1, but expression of NCAM and XIF-3 was not detected. Phenotypic effects of mRNA encoding a Xenopus homologue of GSK3β were identical to those of rat GSK3β mRNA. We hypothesize that GSK3β mediates the initial steps of neural tissue specification and modulates anteroposterior ectodermal patterning via activation of Otx2 transcription. Our observations implicate GSK3β in signaling pathways operating during neural tissue development and during specification of anterior ectodermal cell fates.
Six3, a murine homologue of the sine oculis gene, demarcates the most anterior border of the developing neural plate and is expressed during eye development
Authors: Oliver Guillermo , Mailhos Alvaro , Wehr Roland , Copeland Neal G. , Jenkins Nancy A. , Gruss Peter 
Published: April 2021

ABSTRACT
The Drosophila sine oculis homeobox-containing gene is known to play an essential role in controlling the initial events of pattern formation in the eye disc and is also required for the development of other parts of the fly visual system including the optic lobes. In this paper, we report the isolation of a sequence-related gene referred to as Six3. Based on its amino acid sequence, this gene can be included in the new Six/sine oculis subclass of homeobox genes. Early on, Six3 expression is restricted to the anterior neural plate including areas that later will give rise to ectodermal and neural derivatives. Later, once the longitudinal axis of the brain bends, Six3 mRNA is also found in structures derived from the anterior neural plate: ectoderm of nasal cavity, olfactory placode and Rathke’s pouch, and also the ventral forebrain including the region of the optic recess, hypothalamus and optic vesicles. Based on this expression pattern, we conclude that Six3 is one of the most anterior homeobox gene reported to date. The high sequence similarity of Six3 with the Drosophila sine oculis, and its expression during eye development, suggests that this gene is the likely murine homologue. This finding supports the idea that mammals and insects share control genes such as eyeless/Pax6 (Halder, G., Callaerts, P. and Gehring, W. J. (1995) Science 267, 1788-1792), and also possibly other members of the regulatory cascade required for eye morphogenesis. In Small eye (Pax6) mouse mutants Six3 expression is not affected. Finally, based on the chromosomal localization and the expression pattern of the mouse Six3 gene, the human Six3 cognate could be a good candidate to be at least one of the genes affected in patients with holoprosencephaly type 2 due to an interstitial deletion of 2p21-p22. This region shares a homology with the distal region of mouse chromosome 17 where Six3 has been mapped.
Regulative response of the cranial neural tube after neural fold ablation: spatiotemporal nature of neural crest regeneration and up-regulation of Slug
Authors: Sechrist John , Nieto M. Angela , Zamanian Roham T. , Bronner-Fraser Marianne 
Published: April 2021

ABSTRACT
After unilateral ablation of the avian cranial neural folds, the remaining neuroepithelial cells are able to replace the missing neural crest population (Scherson et al., 1993). Here, we characterize the cellular and molecular nature of this regulative response by defining: (1) the time and location of neural crest cell production by the neuroepithelium; (2) rostrocaudal axial differences in the regulative response; and (3) the onset of expression of Slug, a transcription factor present in premigratory and migrating neural crest cells. Using DiI and HNK-1 antibody labeling techniques, we find that neural crest regeneration occurs only after apposition of the remaining neuroepithelium with the epidermis, suggesting that the developmental mechanism underlying regeneration of the neural crest may recapitulate initial generation of the neural crest. The regulative response occurs maximally at the 3-5 somite stage, and slowly declines thereafter. Surprisingly, there are profound regional differences in the regenerative ability. Whereas a robust regulation occurs in the caudal midbrain/hindbrain, the caudal forebrain/rostral midbrain regenerates neural crest to a much lesser extent. After neural fold removal in the hindbrain, regenerated neural crest cells migrate in a segmental pattern analogous to that seen in unablated embryos; a decrease in regulative response appears to occur with increasing depth of the ablation. Up-regulation of Slug appears to be an early response after ablation, with Slug transcripts detectable proximal to the ablated region 5-8 hours after surgery and prior to emergence of neural crest cells. Both bilateral and unilateral ablations yield substantial numbers of neural crest cells, though the former recover less rapidly and have greater deficits in neural crest-derived structures than the latter. These experiments demonstrate that the regulative ability of the cranial neuroepithelium to form neural crest depends on the time, location and extent of neural fold ablation.
Overexpression of a membrane protein, neuropilin, in chimeric mice causes anomalies in the cardiovascular system, nervous system and limbs
Authors: Kitsukawa Takashi , Shimono Akihiko , Kawakami Atsushi , Kondoh Hisato , Fujisawa Hajime 
Published: April 2021

ABSTRACT
Neuropilin is a type 1 membrane protein, which is highly conserved among Xenopus frog, chicken and mouse. The extracellular part of the neuropilin protein is composed of three unique domains, each of which is thought to be involved in molecular and/or cellular interactions. In mice, neuropilin is expressed in the cardiovascular system, nervous system and limbs at particular developmental stages. To clarify the roles of neuropilin in morphogenesis in vivo, we generated mouse embryonic stem (ES) cell clones that constitutively expressed exogenous neuropilin, then produced chimeras using these ES cell clones. The chimeras overexpressed neuropilin and were embryonic lethal. The chimeric embryos exhibited several morphological abnormalities; excess capillaries and blood vessels, dilation of blood vessels, malformed hearts, ectopic sprouting and defasciculation of nerve fibers, and extra digits. All of these abnormalities occurred in the organs in which neuropilin is expressed in normal development. The variety of abnormalities occurring in these chimeric embryos suggested diverse functions of neuropilin in embryonic morphogesesis, which may be ascribed to multiple interaction domains identified in the molecule. Correct spatiotemporal expression of neuropilin seems to be essential for normal development of the cardiovascular system, nervous system and limbs.
Dual functions of wingless in the Drosophila leg imaginal disc
Authors: Wilder Elizabeth L. , Perrimon Norbert 
Published: April 2021

ABSTRACT
The Drosophila gene wingless is a member of the Wnt gene family, a group of genes that are involved in embryonic development and the regulation of cell proliferation. wingless encodes a secreted glycoprotein that plays a role in embryogenesis as well as in the development of adult structures. In the primordia of the adult limbs, the imaginal discs, wingless is expressed in an anterior ventral sector and is required for specification of ventral fate. Ectopic expression of low levels of Wingless in the leg discs leads to partial ventralization and outgrowths of the proximodistal axis. Wingless has thus been proposed to specify ventral fate in a concentration dependent manner (i.e., as a morphogen) and to organize the proximodistal axis. We have extended the analysis of Wingless function in the leg primordium through targeted ectopic expression. We find that Wingless has two functions in the leg disc. In the specification of ventral fate, our data indicate that Wingless does not function as a morphogen but instead appears to collaborate with other factors. In addition to its role in ventral fate specification, Wingless inhibits the commitment of dorsal cells toward a determined state and influences the regulation of proliferation. We propose a model in which Wingless achieves separate functions via spatially regulated mechanisms and discuss the significance of these functions during axial patterning and organization.
A regulatory role for the ABI3 gene in the establishment of embryo maturation in Arabidopsis thaliana
Authors: Nambara Eiji , Keith Kallie , McCourt Peter , Naito Satoshi 
Published: April 2021

ABSTRACT
The ABI3 gene product of Arabidopsis is essential for correct completion of seed maturation. A severe mutant allele at this locus results in seed that remain green, fail to establish desiccation tolerance, and that germinate at a developmental stage when wild-type seed will not. Moreover, the formation of leaf primordia and xylem differentiation, both characteristic of germinating wildtype seedlings, can be observed in embryos harvested 12 days after flowering. Thus, mature abi3 embryos reach a developmental state that more closely resembles the character of a developing seedling rather than that of a dormant embryo. Previous studies of this gene have resulted in the suggestion that ABI3 is a transducer of abscisic acid induced seed dormancy. Our results demonstrate that the ABI3 gene product can be most accurately described as one of the major regulators of the transition between embryo maturation and early seedling development, rather than simply a transducer of the abscisic acid signal.
Myogenic cell migration from somites is induced by tissue contact with medial region of the presumptive limb mesoderm in chick embryos
Authors: Hayashi Kensuke , Ozawa Eijiro 
Published: April 2021

ABSTRACT
It is known that myogenic cells in limb buds are derived from somites. In order to examine the potential of the limb primordium (presumptive limb somatopleure) to induce myogenic cell migration, we transplanted chick presumptive limb somatopleure to the flank region of an embryo, a region that does not normally contribute myogenic cells to the limb. Somitic cell migration was examined using a vital labeling technique. When the presumptive limb somatopleure was transplanted and was in contact with the host flank somite, somitic-cell migration toward the graft was observed. The labeled somitic cells within the graft were identified as myogenic cells in two ways: first, we found that N-cadherin-expressing cells appeared in the graft. Second, after 3 further days of incubation, the somitic cells formed dorsal and ventral masses and expressed sarcomeric myosin heavy chain within the graft. Cell migration occurred only when the somite was in contact with the medial region of the presumptive limb somatopleure. When the somite was not in contact with the limb somatopleure, or when the somite was in contact with the lateral region of the limb somatopleure, migration did not occur. These observations indicate that the potential to induce myogenic cell migration is restricted to the medial region of the presumptive limb somatopleure and that tissue contact is required.
Genesis and prevention of spinal neural tube defects in the curly tail mutant mouse: involvement of retinoic acid and its nuclear receptors RAR-β and RAR-γ
Authors: Chen Wei-Hwa , Morriss-Kay Gillian M. , Copp Andrew J. 
Published: April 2021

ABSTRACT
A role for all-trans-retinoic acid in spinal neurulation is suggested by: (1) the reciprocal domains of expression of the retinoic acid receptors RAR-β and RAR-γ in the region of the closed neural tube and open posterior neuropore, respectively, and (2) the preventive effect of maternally administered retinoic acid (5 mg/kg) on spinal neural tube defects in curly tail (ct/ct) mice. Using in situ hybridisation and computerised image analysis we show here that in ct/ct embryos, RAR-β transcripts are deficient in the hindgut endoderm, a tissue whose proliferation rate is abnormal in the ct mutant, and RAR-γ transcripts are deficient in the tail bud and posterior neuropore region. The degree of deficiency of RAR-γ transcripts is correlated with the severity of delay of posterior neuropore closure. As early as 2 hours following RA treatment at 10 days 8 hours post coitum, i.e. well before any morphogenetic effects are detectable, RAR-β expression is specifically upregulated in the hindgut endoderm, and the abnormal expression pattern of RAR-γ is also altered. These results suggest that the spinal neural tube defects which characterise the curly tail phenotype may be due to interaction between the ct gene product and one or more aspects of the retinoic acid signalling pathway.
Germ cell nuclei of male fetal mice can support development of chimeras to midgestation following serial transplantation
Authors: Kato Yoko , Tsunoda Yukio 
Published: April 2021

ABSTRACT
Chimeric embryos between fertilized eggs from F1 (C57BL×CBA) and 15.5-16.5 days post coitum (dpc) male fetal germ cells (FGCs) from CD-1 strain (glucose phosphate isomerase, Gpi-1a/a) mice were produced by nuclear transfer. Briefly, a single FGC was fused with enu-cleated oocytes and activated, and the reconstituted oocytes were cultured to the 2-cell stage. The nucleus from the reconstituted 2-cell embryos was then transferred into an enucleated blastomere of the same stage embryos derived from F1 mice to produce chimeric embryos. The reconsti-tuted 2-cell embryos, which synchronously divided to the 4-cell stage after treatment with nocodazole, were further cultured in vitro. Compacted morula and blastocysts were transferred to the uteri of pseudopregnant female mice. Some recipients were allowed to develop to term and the others were killed at mid gestation to analyze the contri-bution of donor FGC-derived cells. Survival to term was low with no chimeric animals. Glucose phosphate isomerase (GPI) analysis at midgestation revealed that some conceptuses had chimerism in the fetuses, trophoblast and yolk sac at day 10.5 of pregnancy. The contribution of donor cells was 37-47%, 19-65% and 12-63%, respectively. It was concluded that the nucleus from 15.5-16.5 dpc male fetal germ cells had the potency to develop into fetus, trophoblast and yolk sac after serial nuclear transfer with oocytes and fertilized embryos. The reason for the low viability of chimeric embryos is discussed.