The sexual differentiation of germ cells into spermatozoa or oocytes is strictly regulated by their gonadal environment, testis or ovary, which is determined by the presence or absence of the Y chromosome, respectivel...The sexual differentiation of germ cells into spermatozoa or oocytes is strictly regulated by their gonadal environment, testis or ovary, which is determined by the presence or absence of the Y chromosome, respectively. Hence, in normal mammalian development, male germ cells differentiate in the presence of X and Y chromosomes, and female germ cells do so in the presence of two X chromosomes. However, gonadal sex reversal occurs in humans as well as in other mammalian species, and the resultant XX males and XY females can lead healthy lives, except for a complete or partial loss of fertility. Germ cells carrying an abnormal set of sex chromosomes are efficiently eliminated by multilayered surveillance mechanisms in the testis, and also, though more variably, in the ovary. Studying the molecular basis for sex-specific responses to a set of sex chromosomes during gametogenesis will promote our understanding of meiotic processes contributing to the evolution of sex determining mechanisms. This review discusses the fate of germ cells carrying various sex chromosomal compositions in mouse models, the limitation of which may be overcome by recent successes in the differentiation of functional germ cells from embryonic stem cells under experimental conditions.展开更多
Germ cells are the precursors of the sperm and oocytes and hence are critical for survival of the species. In mammals, they are specified during fetal life, migrate to the developing gonads and then undergo a critical...Germ cells are the precursors of the sperm and oocytes and hence are critical for survival of the species. In mammals, they are specified during fetal life, migrate to the developing gonads and then undergo a critical period during which they are instructed, by the soma, to adopt the appropriate sexual fate. In a fetal ovary, germ cells enter meiosis and commit to oogenesis, whereas in a fetal testis, they avoid entry into meiosis and instead undergo mitotic arrest and mature toward spermatogenesis. Here, we discuss what we know so far about the regulation of sex-specific differentiation of germ cells, considering extrinsic molecular cues produced by somatic cells, as well as critical intrinsic changes within the germ cells. This review focuses almost exclusively on our understanding of these events in the mouse model.展开更多
Germ cells make two major decisions when they move from an indeterminate state to their final stage of gamete production.One decision is sexual commitment for sperm or egg production,and the other is to maintain mitot...Germ cells make two major decisions when they move from an indeterminate state to their final stage of gamete production.One decision is sexual commitment for sperm or egg production,and the other is to maintain mitotic division or entry into meiosis.It is unclear whether the two decisions are made as a single event or separate events,because there has been no evidence for the presence of germ cell sex prior to meiosis.Here we report direct evidence in the fish rainbow trout that gonia have distinct sexuality.We show that dazl expression occurs in both male and female gonia but exhibits differential intracellular distribution.More strikingly,we show that boule is highly expressed in male gonia but absent in female gonia.Therefore,mitotic gonia possess sex,sperm/egg decision and mitosis/meiosis decision are two independent events,and sperm/egg decision precedes mitosis/meiosis decision in rainbow trout,making this organism a unique vertebrate model for mechanistic understanding of germ cell sex differentiation and relationship between the two decisions.展开更多
文摘The sexual differentiation of germ cells into spermatozoa or oocytes is strictly regulated by their gonadal environment, testis or ovary, which is determined by the presence or absence of the Y chromosome, respectively. Hence, in normal mammalian development, male germ cells differentiate in the presence of X and Y chromosomes, and female germ cells do so in the presence of two X chromosomes. However, gonadal sex reversal occurs in humans as well as in other mammalian species, and the resultant XX males and XY females can lead healthy lives, except for a complete or partial loss of fertility. Germ cells carrying an abnormal set of sex chromosomes are efficiently eliminated by multilayered surveillance mechanisms in the testis, and also, though more variably, in the ovary. Studying the molecular basis for sex-specific responses to a set of sex chromosomes during gametogenesis will promote our understanding of meiotic processes contributing to the evolution of sex determining mechanisms. This review discusses the fate of germ cells carrying various sex chromosomal compositions in mouse models, the limitation of which may be overcome by recent successes in the differentiation of functional germ cells from embryonic stem cells under experimental conditions.
文摘Germ cells are the precursors of the sperm and oocytes and hence are critical for survival of the species. In mammals, they are specified during fetal life, migrate to the developing gonads and then undergo a critical period during which they are instructed, by the soma, to adopt the appropriate sexual fate. In a fetal ovary, germ cells enter meiosis and commit to oogenesis, whereas in a fetal testis, they avoid entry into meiosis and instead undergo mitotic arrest and mature toward spermatogenesis. Here, we discuss what we know so far about the regulation of sex-specific differentiation of germ cells, considering extrinsic molecular cues produced by somatic cells, as well as critical intrinsic changes within the germ cells. This review focuses almost exclusively on our understanding of these events in the mouse model.
基金the Biomedical Research Council of Singapore(R-08-1-21-19-585&SBIC-SSCC C-002-2007).
文摘Germ cells make two major decisions when they move from an indeterminate state to their final stage of gamete production.One decision is sexual commitment for sperm or egg production,and the other is to maintain mitotic division or entry into meiosis.It is unclear whether the two decisions are made as a single event or separate events,because there has been no evidence for the presence of germ cell sex prior to meiosis.Here we report direct evidence in the fish rainbow trout that gonia have distinct sexuality.We show that dazl expression occurs in both male and female gonia but exhibits differential intracellular distribution.More strikingly,we show that boule is highly expressed in male gonia but absent in female gonia.Therefore,mitotic gonia possess sex,sperm/egg decision and mitosis/meiosis decision are two independent events,and sperm/egg decision precedes mitosis/meiosis decision in rainbow trout,making this organism a unique vertebrate model for mechanistic understanding of germ cell sex differentiation and relationship between the two decisions.
