Germinal and somatic cell interrelationships in gonadal sex differentiation

The influence of somatic cells affecting the differentiation and development of germ cells in gonadal differentiation is discussed.It has been confirmed that both the male and the female germ cells can be induced to enter meiosis under the influence of the rete ovarii.The interaction between germinal and somatic cells is also investigated using an « artificial » chimaeric gonad which contains somatic and germinal cells of opposite sexes.The results indicate that XY germ cells can survive in the XX somatic environment and are induced to enter meiosis precociously while XX germ cells fail to survive in an XY somatic environment.One of the major differences between the sexual differentiation of the ovary and testis is the time at which meiosis in the germ cells commences : in the female meiosis occurs during fetal life while in males it does not start until around the time of puberty (see Baker and 0, 1976 ;Zuckerman and Baker, 1977).In mammals, it is difficult to assess whether meiosis is actively induced in the ovary, prevented in the pre-pubertal testis, or whether both mechanisms operate.The purpose of the present communication is to discuss the result of a series of recent experiments which at least in part resolve this uncertainty. Meiotic inductor substance (MIS).It is well known that ovaries removed from early embryos cannot be maintained in organ culture : the germ cells fail to enter meiosis and subsequently degenerate (mouse : Wolff, 1952 ; hamster : Challoner, 1975 ; sheep : Mauleon, 1973).By contrast, meiosis can proceed normally in vitro if the ovaries are recovered after a critical stage of gonadal development (Martinovitch, 1938 ;Borghese and Venini, 1956 ;Baker and Neal, 1973 ;Challoner, 1975).These results clearly indicate that a specific substance has to be produced for a short period of time (less than 24 h in the ( 1 )