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Germ cells are essential for sexual dimorphism in the medaka gonad.

ABSTRACT: To further elucidate the roles of germ cells in the sex differentiation of gonads, we have used the medaka, a teleost fish, to generate mutants that lack germ cells from the onset of gonadogenesis by the morpholino-mediated knockdown of cxcr4. The resulting germ-cell-deficient medaka show female-to-male sex reversal of their secondary sex characteristics, accompanied by increased levels of androgen and reduced levels of estrogen. A failure to maintain granulosa cells or estrogen-producing cells also occurs at early stages of sex differentiation in the cxcr4 morphants, before the initiation of gonadal morphogenesis. In contrast, androgen-producing cells are unaffected in germ-cell-deficient medaka of either sex. In addition, a single tube-like gonad that expresses male-specific genes is formed in these mutants irrespective of the genetic sex. Significantly, each of these mutant phenotypes occurs in a somatic cell-autonomous manner, suggesting that gonadal somatic cells are predisposed toward male development in the absence of germ cells. This highlights the importance of germ cells in the sexual dimorphism of the gonads.

SUBMITTER: Kurokawa H

PROVIDER: S-EPMC2040408 | biostudies-literature | 2007 Oct

REPOSITORIES: biostudies-literature

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Germ cells are essential for sexual dimorphism in the medaka gonad.

Kurokawa Hiromi H Saito Daisuke D Nakamura Shuhei S Katoh-Fukui Yuko Y Ohta Kohei K Baba Takashi T Morohashi Ken-ichiro K Tanaka Minoru M

Proceedings of the National Academy of Sciences of the United States of America 20071016 43

To further elucidate the roles of germ cells in the sex differentiation of gonads, we have used the medaka, a teleost fish, to generate mutants that lack germ cells from the onset of gonadogenesis by the morpholino-mediated knockdown of cxcr4. The resulting germ-cell-deficient medaka show female-to-male sex reversal of their secondary sex characteristics, accompanied by increased levels of androgen and reduced levels of estrogen. A failure to maintain granulosa cells or estrogen-producing cells ...[more]

PMID: 17940041

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Project description:BackgroundPrimordial germ cells (PGCs) give rise to gametes that are responsible for the development of a new organism in the next generation. Two modes of germ line specification have been described: the inheritance of asymmetrically-localized maternally provided cytoplasmic determinants and the induction of the PGC fate by other cell types. PGCs specification in zebrafish appears to depend on inheritance of germ plasm in which several RNA molecules such as vasa and nanos reside. Whether the specification mode of PGCs found in zebrafish is general for other fish species was brought into question upon analysis of olvas expression--the vasa homologue in another teleost, medaka (Oryzias latipes). Here, in contrast to the findings in zebrafish, the PGCs are found in a predictable position relative to a somatic structure, the embryonic shield. This finding, coupled with the fact that vasa mRNA, which is localized to the germ plasm of zebrafish but does not label a similar structure in medaka opened the possibility of fundamentally different mechanisms governing PGC specification in these two fish species.ResultsIn this study we addressed the question concerning the mode of PGC specification in medaka using embryological experiments, analysis of RNA stability in the PGCs and electron microscopy observations. Dramatic alterations in the somatic environment, i.e. induction of a secondary axis or mesoderm formation alteration, did not affect the PGC number. Furthermore, the PGCs of medaka are capable of protecting specific RNA molecules from degradation and could therefore exhibit a specific mRNA expression pattern controlled by posttrancriptional mechanisms. Subsequent analysis of 4-cell stage medaka embryos using electron microscopy revealed germ plasm-like structures located at a region corresponding to that of zebrafish germ plasm.ConclusionTaken together, these results are consistent with the idea that in medaka the inheritance of maternally provided asymmetrically-localized cytoplasmic determinants directs cells to assume the germ line fate similar to zebrafish PGCs.

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Germ cells are essential for sexual dimorphism in the medaka gonad.

Publications

Germ cells are essential for sexual dimorphism in the medaka gonad.

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