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Robin Lovell-Badge

Publications and source records attributed to Robin Lovell-Badge.

7 recordsLinked to original sources
PubMed2003

dead end, a novel vertebrate germ plasm component, is required for zebrafish primordial germ cell migration and survival.

In most animals, primordial germ cell (PGC) specification and development depend on maternally provided cytoplasmic determinants that constitute the so-called germ plasm. Little is known about the role of germ plasm in vertebrate germ cell development, and its molecular mode of action remains elusive. While PGC specification in mammals occurs via different mechanisms, several germ plasm components required for early PGC development in lower organisms are expressed in mammalian germ cells after their migration to the gonad and are involved in gametogenesis. Here we show that the RNA of dead end, encoding a novel putative RNA binding protein, is a component of the germ plasm in zebrafish and is specifically expressed in PGCs throughout embryogenesis; Dead End protein is localized to perinuclear germ granules within PGCs. Knockdown of dead end blocks confinement of PGCs to the deep blastoderm shortly after their specification and results in failure of PGCs to exhibit motile behavior and to actively migrate thereafter. PGCs subsequently die, while somatic development is not effected. We have identified dead end orthologs in other vertebrates including Xenopus, mouse, and chick, where they are expressed in germ plasm and germ-line cells, suggesting a role in germ-line development in these organisms as well.

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PubMed2003

Multipotent cell lineages in early mouse development depend on SOX2 function.

Each cell lineage specified in the preimplantation mammalian embryo depends on intrinsic factors for its development, but there is also mutual interdependence between them. OCT4 is required for the ICM/epiblast lineage, and at transient high levels for extraembryonic endoderm, but also indirectly through its role in regulating Fgf4 expression, for the establishment and proliferation of extraembryonic ectoderm from polar trophectoderm. The transcription factor SOX2 has also been implicated in the regulation of Fgf4 expression. We have used gene targeting to inactivate Sox2, examining the phenotypic consequences in mutant embryos and in chimeras in which the epiblast is rescued with wild-type ES cells. We find a cell-autonomous requirement for the gene in both epiblast and extraembryonic ectoderm, the multipotent precursors of all embryonic and trophoblast cell types, respectively. However, an earlier role within the ICM may be masked by the persistence of maternal protein, whereas the lack of SOX2 only becomes critical in the chorion after 7.5 days postcoitum. Our data suggest that maternal components could be involved in establishing early cell fate decisions and that a combinatorial code, requiring SOX2 and OCT4, specifies the first three lineages present at implantation.

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PubMed2003

Expression of Sox3 throughout the developing central nervous system is dependent on the combined action of discrete, evolutionarily conserved regulatory elements.

SOX3 is one of the earliest neural markers in vertebrates and is thought to play a role in specifying neuronal fate. To investigate the regulation of Sox3 expression we identified cis-regulatory regions in the Sox3 promoter that direct tissue-specific heterologous marker gene expression in transgenic mice. Our results show that an 8.3 kb fragment, comprising 3 kb upstream and 3 kb downstream of the Sox3 transcriptional unit, is sufficient in a lacZ reporter construct to reproduce most aspects of Sox3 expression during CNS development from headfold to midgestation stages. The apparently uniform expression of Sox3 in the neural tube depends, however, on the combined action of distinct regulatory modules within this 8.3 kb region. Each of these gives expression in a subdomain of the complete expression pattern. These are restricted along both the rostral-caudal and dorso-ventral axes and can be quite specific, one element giving expression largely confined to V2 interneuron precursors. We also find that at least some of the regulatory sequences are able to drive expression of the transgene in the CNS Xenopus laevis embryos in a manner that reflects the endogenous Sox3 expression pattern. These results imply that the underlying mechanism regulating early CNS patterning is conserved, despite several substantial differences in neurogenesis between mammals and amphibians.

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PubMed2002

A model system for study of sex chromosome effects on sexually dimorphic neural and behavioral traits.

We tested the hypothesis that genes encoded on the sex chromosomes play a direct role in sexual differentiation of brain and behavior. We used mice in which the testis-determining gene (Sry) was moved from the Y chromosome to an autosome (by deletion of Sry from the Y and subsequent insertion of an Sry transgene onto an autosome), so that the determination of testis development occurred independently of the complement of X or Y chromosomes. We compared XX and XY mice with ovaries (females) and XX and XY mice with testes (males). These comparisons allowed us to assess the effect of sex chromosome complement (XX vs XY) independent of gonadal status (testes vs ovaries) on sexually dimorphic neural and behavioral phenotypes. The phenotypes included measures of male copulatory behavior, social exploration behavior, and sexually dimorphic neuroanatomical structures in the septum, hypothalamus, and lumbar spinal cord. Most of the sexually dimorphic phenotypes correlated with the presence of ovaries or testes and therefore reflect the hormonal output of the gonads. We found, however, that both male and female mice with XY sex chromosomes were more masculine than XX mice in the density of vasopressin-immunoreactive fibers in the lateral septum. Moreover, two male groups differing only in the form of their Sry gene showed differences in behavior. The results show that sex chromosome genes contribute directly to the development of a sex difference in the brain.

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PubMed2002

Dax1 expression is dependent on steroidogenic factor 1 in the developing gonad.

The nuclear hormone receptor DAX1 has been implicated in mammalian gonad development and sex determination. The expression of the gene in the gonad follows a dynamic pattern in time and place in the embryo and the adult. We have undertaken the first in vivo study of the regulation of Dax1 expression. Using a transgenic mouse approach we have identified a novel 500-bp region 4 kb upstream of the mouse Dax1 start codon that is essential for LacZ reporter gene expression in the embryonic gonad. Within this region, a highly conserved steroidogenic factor 1 (SF1) consensus-binding site is necessary to direct LacZ expression to the embryonic gonad implicating SF1 in the regulation of Dax1 in the developing gonad. Consistent with this, Dax1 is expressed at much reduced levels in gonads of embryos that are deficient in SF1. In addition, our results show that SF1 consensus-binding sites close to the start of Dax1 transcription are important in regulating levels of expression in the developing gonad. These studies have identified the critical in vivo regulatory region for expression of Dax1 in the early gonad and provide novel information on how a specific enhancer element acts in different cell types at different stages of development.

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PubMed2002

Sex-determining genes in mice: building pathways.

Sry is active in the mouse for a very brief period in somatic cells of the genital ridge to initiate Sertoli cell differentiation. SRY protein must act within the context of other gene products required for gonadal development and must itself act on one or more target genes that will ensure the further differentiation and maintenance of Sertoli cells. Over the last few years several genes have been found that have important roles in gonadal development and sex determination. These include genes encoding transcription factors such as Lhx9, Wt1, Sf1, Dax1, Gata4, Dmrt1 and Sox9, and some involved in cell cell signalling, including Amh, Wnt4 and Dhh. While more await discovery, it is now possible to start putting some of the known genes into pathways or networks. Sox9 probably occupies a critical role in mammals for both the initiation and maintenance of Sertoli cell differentiation. Data will be presented that are consistent with SRY acting directly on Sox9 to ensure its up-regulation. SF1 is also central to gonadal differentiation. Our results imply that it contributes to transcriptional activation of several relevant genes, not just those required for male development, including Sox9 and Amh, but also those that can have an antagonistic effect on Sertoli cell differentiation, such as Dax1. Progress in establishing other regulatory interactions will also be discussed.

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