bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mouse embryos lacking RXRα are resistant to retinoic-acid-induced limb defects
Authors: Sucov Henry M. , Izpisúa-Belmonte Juan-Carlos , Gañan Yolanda , Evans Ronald M. 
Published: April 2021

ABSTRACT
Embryonic exposure to the vitamin A metabolite retinoic acid (RA) causes malformations in numerous developing tissues, including the limbs, which serves as a model system of retinoic acid action. RA treatment of wild-type mouse embryos results in digit truncations and long bone reductions. These effects are mediated by products of the retinoic acid and retinoid X receptor genes (RARs and RXRs), members of the nuclear receptor family of liganddependent transcription factors. Mouse embryos homozygous for a mutation in the RXRα gene appear normal in limb development, although such embryos are phenotypically affected in other tissues. We now describe resistance to limb malformations normally induced by teratogenic RA exposure in the RXRα−/− background. RA treatments that cause limb defects in 100% of wild-type embryos fail to elicit malformations in RXRα homozygotes, implicating RXRα as a component in the teratogenic process in the limbs. Heterozygous embryos are intermediate in sensitivity to RA, suggesting the importance of RXRα gene dosage in limb teratogenesis. Expression of the RA-inducible gene RARβ2 was equivalent between wild-type and homozygous embryos after RA treatment. RA treatment also did not distinguish between wild-type and RXRα−/− embryos in the spatial expression of sonic hedgehog (Shh) and hoxd-12, two other genes implicated in limb development. However, the quantitative level of hoxd-12 expression was elevated in RXRα−/− embryos. These observations indicate that transcriptional processes which are inappropriately regulated in the mouse limb by exogenous RA require RXRα for their execution, and that specific teratogenic processes, as well as specific normal developmental processes under vitamin A control, occur through individual members of the RXR and RAR families.
Lineage restriction of the myogenic conversion factor myf-5 in the brain
Authors: Tajbakhsh Shahragim , Buckingham Margaret E. 
Published: April 2021

ABSTRACT
myf-5 is one of four transcription factors belonging to the MyoD family that play key roles in skeletal muscle determination and differentiation. We have shown earlier by gene targeting nlacZ into the murine myf-5 locus that myf-5 expression in the developing mouse embryo is closely associated with the restriction of precursor muscle cells to the myogenic lineage. We now identify unexpected expression of this myogenic factor in subdomains of the brain. myf-5 expression begins to be detected at embryonic day 8 (E8) in the mesencephalon and coincides with the appearance of the first differentiated neurons; expression in the secondary prosencephalon initiates at E10 and is confined to the ventral domain of prosomere p4, later becoming restricted to the posterior hypothalamus. This expression is observed throughout embryogenesis. No other member of the MyoD family is detected in these regions, consistent with the lack of myogenic conversion. Furthermore, embryonic stem cells expressing the myf-5/nlacZ allele yield both skeletal muscle and neuronal cells when differentiated in vitro. These observations raise questions about the role of myf-5 in neurogenesis as well as myogenesis, and introduce a new lineage marker for the developing brain.
Motoneuron fate specification revealed by patterned LIM homeobox gene expression in embryonic zebrafish
Authors: Appel Bruce , Korzh Vladimir , Glasgow Eric , Thor Stefan , Edlund Thomas , Dawid Igor B. , Eisen Judith S. 
Published: April 2021

ABSTRACT
In zebrafish, individual primary motoneurons can be uniquely identified by their characteristic cell body positions and axonal projection patterns. The fate of individual primary motoneurons remains plastic until just prior to axogenesis when they become committed to particular identities. We find that distinct primary motoneurons express particular combinations of LIM homeobox genes. Expression precedes axogenesis as well as commitment, suggesting that LIM homeobox genes may contribute to the specification of motoneuronal fates. By transplanting them to new spinal cord positions, we demonstrate that primary motoneurons can initiate a new program of LIM homeobox gene expression, as well as the morphological features appropriate for the new position. We conclude that the patterned distribution of different primary motoneuronal types within the zebrafish spinal cord follows the patterned expression of LIM homeobox genes, and that this reflects a highly resolved system of positional information controlling gene transcription.
Ommatidial polarity in the Drosophila eye is determined by the direction of furrow progression and local interactions
Authors: Strutt David I. , Mlodzik Marek 
Published: April 2021

ABSTRACT
The adult eye of Drosophila is a highly ordered structure. It is composed of about 800 ommatidia, each displaying precise polarity. The ommatidia are arranged about an axis of mirror image symmetry, the equator, which lies along the dorsoventral midline of the eye. We use hedgehog pathway mutants to induce ectopic morphogenetic furrows and use these as a tool to investigate the establishment of ommatidial polarity. Our results show that ommatidial clusters are self- organising units whose polarity in one axis is determined by the direction of furrow progression, and which can independently define the position of an equator without reference to the global coordinates of the eye disc.
Two distinct pathways for the localization of RNAs at the vegetal cortex in Xenopus oocytes
Authors: Kloc Malgorzata , Etkin Laurence D. 
Published: April 2021

ABSTRACT
We found that there are two major pathways by which RNAs are localized at the vegetal cortex during oogenesis of Xenopus laevis. One of these, through which Xlsirts, Xcat2 and Xwnt11 are localized, involves transport during stages 1 and 2 of oogenesis via a region of the mitochondr-ial cloud that we call the message transport organizer or METRO. This pathway involved three steps, transport of RNA from the GV to the mitochondrial cloud, sorting of the RNAs to specific regions of the METRO, and translo-cation to and anchoring at the vegetal cortex. These three RNAs exhibit a distinct pattern of spatial localization within the METRO when they approach the vegetal cortex. The other pathway is used by Vg1. We detected Vg1 throughout the oocyte cytoplasm during stages 1 and 2. During stage 3 it was translocated to the vegetal cortex and associated with the cortex overlapping the region at which the Xlsirt, Xcat2, and Xwnt11 RNAs are anchored. Our results also showed that anchoring of these RNAs was dependent in part on actin microfilaments, but was inde-pendent of microtubules. These results demonstrate a novel mechanism of translocation and RNA sorting used by RNAs several of which may be involved in the establish-ment of the embryonic body axis.
The somatic sex determines the requirement for ovarian tumor gene activity in the proliferation of the Drosophila germline
Authors: Nagoshi Rod N. , Patton J. Scott , Bae Eunkyung , Geyer Pamela K. 
Published: April 2021

ABSTRACT
Gametogenesis in Drosophila requires sex-specific interactions between the soma and germline to control germ cell viability, proliferation, and differentiation. To determine what genetic components are involved in this interaction, we examined whether changes in the sexual identity of the soma affected the function of the ovarian tumor (otu) and ovo genes. These genes are required cell autonomously in the female germline for germ cell proliferation and differentiation. Mutations in otu and ovo cause a range of ovarian defects, including agametic ovaries and tumorous egg cysts, but do not affect spermatogenesis. We demonstrate that XY germ cells do not require otu when developing in testes, but become dependent on otu function for proliferation when placed in an ovary. This soma-induced requirement can be satisfied by the induced expression of the 98×103Mr OTU product, one of two isoforms produced by differential RNA splicing. These results indicate that the female somatic gonad can induce XY germ cells to become ‘female-like’ because they require an oogenesis-specific gene. In contrast, the requirement for ovo is dependent on a cell autonomous signal derived from the X:A ratio. We propose that differential regulation of the otu and ovo genes provides a mechanism for the female germline to incorporate both somatic and cell autonomous inputs required for oogenesis.
XlPOU 2, a noggin-inducible gene, has direct neuralizing activity
Authors: Witta Samir E. , Agarwal Veena R. , Sato Sheryl M. 
Published: April 2021

ABSTRACT
XlPOU 2, a member of the class III POU domain family, is expressed initially in Spemann’s organizer, and later, in discrete regions of the developing nervous system in Xenopus laevis. XlPOU 2 may act downstream from initial neural induction events, since it is activated by the neural inducer, noggin. To determine if XlPOU 2 participates in the early events of neurogenesis, synthetic mRNA was microinjected into specific blastomeres of the 32-cell stage embryo. Misexpression of XlPOU 2 in the epidermis causes a direct switch in cell fate from an epidermal to a neuronal phenotype. In the absence of mesoderm induction, XlPOU 2 has the ability to induce a neuronal phenotype in uncommitted ectoderm. These data demonstrate the potential of XlPOU 2 to act as a master regulator of neurogenesis.
Soluble and cell-bound forms of steel factor activity play distinct roles in melanocyte precursor dispersal and survival on the lateral neural crest migration pathway
Authors: Wehrle-Haller Bernhard , Weston James A. 
Published: April 2021

ABSTRACT
Trunk neural crest cells segregate from the neuroepithelium and enter a ‘migration staging area’ lateral to the embryonic neural tube. After some crest cells in the migration staging area have begun to migrate on a medial pathway, a subpopulation of crest-derived cells remaining in the migration staging area expresses mRNAs for the receptor tyrosine kinase, c-kit, and tyrosinase-related protein-2, both of which are characteristic of melanocyte precursors. These putative melanocyte precursors are subsequently observed on the lateral crest migration pathway between the dermatome and overlying epithelium, and then dispersed in nascent dermal mesenchyme.
Melanocyte precursors transiently require the c-kit ligand, Steel factor for survival. Although Steel factor mRNA is transiently expressed in the dorsal dermatome before the onset of trunk neural crest cell dispersal on the lateral pathway, it is no longer produced by dermatomal cells when melanocyte precursors have dispersed in the dermal mesenchyme. To assess the role of Steel factor in migration of melanocyte precursors on the lateral pathway, we analyzed melanocyte precursor dispersal and fate on the lateral pathway of two different Sl mutants, Sl, a null allele, and Sld, which lacks cell surface-associated Steel factor but produces a soluble form. No melanocyte precursors were detected in the dermatome of embryos homozygous for the Sl allele or in W mutants that lack functional c-kit. In contrast, in embryos homozygous for the Sld allele, melanocyte precursors appeared on the lateral pathway, but subsequently disappear from the dermis. These results suggest that soluble Steel factor is required for melanocyte precursor dispersal on the lateral pathway, or for their initial survival in the migration staging area. In contrast, membrane-bound Steel factor appears to promote melanocyte precursor survival in the dermis.
Regulation of Spemann organizer formation by the intracellular kinase Xgsk-3
Authors: Pierce Sarah B. , Kimelman David 
Published: April 2021

ABSTRACT
Dorsal axis formation in the Xenopus embryo can be induced by the ectopic expression of several Wnt family members. In Drosophila, the protein encoded by the Wnt family gene, wingless, signals through a pathway that antagonizes the effects of the serine/threonine kinase zeste-white 3/shaggy. We describe the isolation and characterization of a Xenopus homolog of zeste-white 3/shaggy, Xgsk-3. A kinase-dead mutant of Xgsk-3, Xgsk-3K→R, has a dominant negative effect and mimics the ability of Wnt to induce a secondary axis by induction of an ectopic Spemann organizer. Xgsk-3K→R, like Wnt, induces dorsal axis formation when expressed in the deep vegetal cells, which do not contribute to the axis. These results indicate that the dorsal fate is actively repressed by Xgsk-3, which must be inactivated for dorsal axis formation to occur. Furthermore, our work suggests that the effects of Xgsk-3K→R are mediated by an additional intercellular signal.
Proteinase expression in early mouse embryos is regulated by leukaemia inhibitory factor and epidermal growth factor
Authors: Harvey M. B. , Leco K. J. , Arcellana-Panlilio M. Y. , Zhang X. , Edwards D. R. , Schultz G. A. 
Published: April 2021

ABSTRACT
Several proteinases from different multigene families have been implicated in the uterine invasion required for estab-lishment of pregnancy in some mammals. In this study, the expression of matrix metalloproteinase gelatinase B (MMP-9), urokinase-type plasminogen activator (uPA) and their inhibitors was investigated during early mouse embryo development. Transcripts for tissue inhibitors of metalloproteinases (TIMP-1,-2,-3) and uPA receptor were detected throughout pre- and peri-implantation develop-ment whilst MMP-9 and uPA mRNAs were first detected in peri-implantation blastocysts associated with the invasive phase of implantation. Through use of in situ hybridization, it was shown that MMP-9 transcripts were strongly expressed in the network of trophoblast giant cells at the periphery of implanting 7.5 day embryos and TIMP-3 transcripts were strongly expressed in the decidua imme-diately adjacent to the implanting embryo. uPA transcripts were preferentially expressed in the ectoplacental cone and its derivatives. Because these proteinases are regulated by growth factors and cytokines in other tissues, the effect of leukaemia inhibitory factor (LIF) and epidermal growth factor (EGF) on their activity was investigated. Both LIF and EGF, like the proteinases, have been implicated in peri-implantation development. Blastocysts collected on day 4 of pregnancy were cultured 2 days in TCM 199 + 10% fetal bovine serum to allow outgrowth followed by 24 hour culture in defined media containing either LIF or EGF. Conditioned media were assayed for uPA activity by a chromogenic assay and MMP activity by gelatin zymog-raphy. Both LIF and EGF stimulated uPA and MMP-9 activity in blastocyst outgrowths after 3 days of culture (day 7). Proteinase activity was assayed again at the 5th to 6th day of culture (day 9 to 10). EGF was found to have no effect whereas LIF decreased production of both pro-teinases. These results demonstrate that proteinase activity in early embryos can be regulated by growth factors and cytokines during the implantation process and, in particu-lar, they demonstrate the possible involvement of LIF in establishment of the correct temporal programme of pro-teinase expression.
Branching morphogenesis of embryonic mouse lung epithelium in mesenchyme-free culture
Authors: Nogawa Hiroyuki , Ito Takaaki 
Published: April 2021

ABSTRACT
Embryonic mouse lung epithelium was separated from its mesenchyme and cultured under mesenchyme-free conditions. When covered with Matrigel, the cultured epithelium underwent branching morphogenesis in medium containing acidic fibroblast growth factor (aFGF), in which the epithelial cells constructed a simple columnar cell layer forming a lumen, as seen in normal development. The epithelial growth and branching morphogenesis induced by aFGF was completely inhibited by an antibody against aFGF. Heparin caused extra epithelial growth in cooperation with aFGF, but its use resulted in luminal expansion instead of enhanced branching. Basic FGF induced abnormal morphogenesis of the epithelium, though the lumen formed was lined by a simple columnar cell layer. Epidermal growth factor could not maintain epithelial cell growth, and the epithelium became a smaller and smoother ball than that at the start of cultivation. When covered with a collagen gel instead of Matrigel, the epithelium remained in its initial form, neither newly branching nor becoming a smooth ball, in the presence of aFGF. These results show that the epithelium of lung rudiments was able to branch under mesenchyme-free culture conditions in which a basement membrane matrix and aFGF were substitutes for the mesenchyme.
Regulation of regional differences in the differentiation of cerebral cortical neurons by EGF family-matrix interactions
Authors: Ferri Raymond T. , Levitt Pat 
Published: April 2021

ABSTRACT
Both lineage-based and epigenetic regulation have been postulated as mechanisms to control the formation of discrete areas in the cerebral cortex, but specific genes or signaling pathways that may be involved have yet to be defined. In this paper, we examine whether progenitors, isolated from the cerebral wall prior to neurogenesis, can respond to exogenous cues by adopting a region-specific phenotype. The expression of the limbic system-associated membrane protein (LAMP), a neuron-specific marker of limbic cortical areas, was monitored in cultured neurons arising from precursors harvested from presumptive perirhinal (limbic) and sensorimotor (nonlimbic) zones at embryonic day 12 in the rat. Neuronal phenotype in all cultures was identified by expression of microtubule-associated protein-2 (MAP2). On a substrate of poly-lysine, over 80% of the precursors from the limbic area that differentiate into neurons express a LAMP+ phenotype. Approximately 20% of the neurons generated from precursors of the sensorimotor region become LAMP+. However, modification of the microenvironment had a significant effect on the differentiation of the sensorimotor precursors. When the nonlimbic precursors are grown on Matrigel, there is a 2-fold increase in the number of MAP2+/LAMP+ double-labeled neurons. Dissection of the Matrigel components reveals that in combination with growth factor-deficient Matrigel or collagen type IV, epidermal growth factor and transforming growth factor-α increase LAMP expression in the sensorimotor population. Delaying the addition of growth factor until after most cell division had ceased failed to increase the number of LAMP+ neurons. Another growth factor in Matrigel, platelet-derived growth factor, does not produce the same effect. Our results indicate that local signals can regulate the differentiation of cortical progenitors, providing a potential mechanism for establishing an early commitment to specific regional phenotypes in the developing cerebral wall that relate to future functional domains in the cortex.
Conditional root expansion mutants of Arabidopsis
Authors: Hauser Marie-Theres , Morikami Atsushi , Benfey Philip N. 
Published: April 2021

ABSTRACT
Regulation of cell expansion is essential to the formation of plant organs. We have characterized 21 mutations, representing six loci, that cause abnormal cell expansion in the root of Arabidopsis thaliana. The phenotype of these mutants is conditional upon the rate of root growth. Calculation of cell volumes indicated that the mutations resulted in defects in either the orientation or the extent of expansion or in both. Analysis of cortical microtubules in the mutants suggested that a shift in the orientation of cell expansion may not be dependent on a change in the orientation of the microtubules. Double mutant combinations resulted in loss of the conditional phenotype suggesting that the genes may act in a similar pathway or encode partially redundant functions.
Patterning of the mesoderm in Xenopus: dose-dependent and synergistic effects of Brachyury and Pintallavis
Authors: O’Reilly M.-A. J. , Smith J. C. , Cunliffe V. 
Published: April 2021

ABSTRACT
Widespread expression of the DNA-binding protein Brachyury in Xenopus animal caps causes ectopic mesoderm formation. In this paper, we first show that two types of mesoderm are induced by different concentrations of Brachyury. Animal pole explants from embryos injected with low doses of Xbra RNA differentiate into vesicles containing mesothelial smooth muscle and mesenchyme. At higher concentrations somitic muscle is formed. The transition from smooth muscle formation to that of somitic muscle occurs over a two-fold increase in Brachyury concentration.
Brachyury is required for differentiation of notochord in mouse and fish embryos, but even the highest concentrations of Brachyury do not induce this tissue in Xenopus animal caps. Co-expression of Brachyury with the secreted glycoprotein noggin does cause notochord formation, but it is difficult to understand the molecular basis of this phenomenon without knowing more about the noggin signal transduction pathway. To overcome this difficulty, we have now tested mesoderm-specific transcription factors for the ability to synergize with Brachyury. We find that coexpression of Pintallavis, but not goosecoid, with Brachyury causes formation of dorsal mesoderm, including notochord. Furthermore, the effect of Pintallavis, like that of Brachyury, is dose-dependent: a two-fold increase in Pintallavis RNA causes a transition from ventral mesoderm formation to that of muscle, and a further two-fold increase induces notochord and neural tissue. These results suggest that Pintallavis cooperates with Brachyury to pattern the mesoderm in Xenopus.
Role of MAP kinase in mesoderm induction and axial patterning during Xenopus development
Authors: LaBonne Carole , Burke Brenda , Whitman Malcolm 
Published: April 2021

ABSTRACT
We have examined the role of MAP kinase during mesoderm induction and axial patterning in Xenopus embryos. MAP Kinase Phosphatase (MKP-1) was used to inactivate endogenous MAP kinase and was found to prevent the induction of early and late mesodermal markers by both FGF and activin. In whole embryos, MKP-1 was found to disrupt posterior axial patterning, generating a phenotype similar to that obtained with a dominant inhibitory FGF receptor. Overexpression of either constitutively active MAP kinase or constitutively active MAP kinase (MEK) was sufficient to induce Xbra expression, while only constitutively active MEK was able to significantly induce expression of muscle actin. When MAP kinase phosphorylation was used as a sensitive marker of FGF receptor activity in vivo, this activity was found to persist at a low and relatively uniform level throughout blastula stage embryos. The finding that a low level of MAP kinase phosphorylation exists in unstimulated animal caps and is absent in caps overexpressing a dominant inhibitory FGF receptor provides a basis for our previous observation that overexpression of this receptor inhibits activin induction. These results indicate that FGFdependent MAP kinase activity plays a critical role in establishing the responsiveness of embryonic tissues to mesoderm inducers.