D E V E L O P M E N T S I N SEXUAL O R G A N O G E N E S I S
277
Neurohumoral Control of Sexual Physiology. Demeusy and Veillet (1958)
and Demeusy (1962) have shown that removal of the eye stalks in
the immature male of Carcinus moenas results in hypertrophy of the androgenic gland, and concomitantly, the expected sexual maturation. In males
of the isopod, P. dilatatus, removal of the median and lateral anterior
regions of the protocerebrum of immature and mature individuals results
in hypertrophy of the androgenic gland and selective stimulation of the
growth of sexual characteristics (Juchault et al., 1965).
III. Epigenetic Factors in Sexual Organogenesis in Vertebrates
It is in vertebrates that the mechanisms of sexual differentiation and
organogenesis have been most extensively investigated since the work of
Lillie (1916, 1917). The role of the genetic structure (heteroploidy) and
that of epigenetic factors have been the object of a considerable number of
studies. This discussion will be confined to work related to epigenetic
factors and their relationship to the genetic constitution of the organism.
A. Lower Vertebrates: Amphibians and Fishes
The analysis of the freemartin in cattle led to the conclusion that intersexuality in the female twin was brought about by a chemical type of
mediator, an embryonic hormone produced by the male fetus. This resulted
in attempts to perform an artificial parabiosis before the differentiation of
sex. These experiments were originally conducted by Burns (1925, 1961),
then in a slightly different form by Humphrey (1945, 1948), who grafted
the prospective gonadal area from one embryo to another. These experiments demonstrated effectively the sexualizing action of one embryo on its
twin in heterosexual combinations (see Ponse, 1949, 1950; Burns, 1961).
Recent studies have been carried out along the following lines.
1. Sex Reversal in Xenopus laevis by Testicular Grafts
The genetic constitution is ZZ (d
7|
):ZW (9 ) in the anuran amphibian,
Xenopus laevis (Gallien, 1955a, 1956; Chang and Witschi, 1955). Mikamo
and Witschi (1963, 1964) returned to the study of sex reversal in this
species. A differentiated testis is implanted in larvae before sexual differentiation. By chance, the graft may be in a genetic male or a genetic female.
In the first stage, the testis graft induces a marked inhibition of the gonads
of the host, whether it is a genetic male or female. If, in a second stage, the
testis graft is removed, the vestigial gonads of the host resume their development. The medullary area, which is androgenic, has the advantage in
development, even in genetic females. In the latter case, the gonads of the
host become testes. Thus a neomale is obtained. Genetic analysis of the
offspring of these animals has shown (Table I) that the genetic females
had been transformed to neomales (Mikamo and Witschi, 1963). Crosses
were made either with control females (ZW) or with neofemales (ZZ)
277
Neurohumoral Control of Sexual Physiology. Demeusy and Veillet (1958)
and Demeusy (1962) have shown that removal of the eye stalks in
the immature male of Carcinus moenas results in hypertrophy of the androgenic gland, and concomitantly, the expected sexual maturation. In males
of the isopod, P. dilatatus, removal of the median and lateral anterior
regions of the protocerebrum of immature and mature individuals results
in hypertrophy of the androgenic gland and selective stimulation of the
growth of sexual characteristics (Juchault et al., 1965).
III. Epigenetic Factors in Sexual Organogenesis in Vertebrates
It is in vertebrates that the mechanisms of sexual differentiation and
organogenesis have been most extensively investigated since the work of
Lillie (1916, 1917). The role of the genetic structure (heteroploidy) and
that of epigenetic factors have been the object of a considerable number of
studies. This discussion will be confined to work related to epigenetic
factors and their relationship to the genetic constitution of the organism.
A. Lower Vertebrates: Amphibians and Fishes
The analysis of the freemartin in cattle led to the conclusion that intersexuality in the female twin was brought about by a chemical type of
mediator, an embryonic hormone produced by the male fetus. This resulted
in attempts to perform an artificial parabiosis before the differentiation of
sex. These experiments were originally conducted by Burns (1925, 1961),
then in a slightly different form by Humphrey (1945, 1948), who grafted
the prospective gonadal area from one embryo to another. These experiments demonstrated effectively the sexualizing action of one embryo on its
twin in heterosexual combinations (see Ponse, 1949, 1950; Burns, 1961).
Recent studies have been carried out along the following lines.
1. Sex Reversal in Xenopus laevis by Testicular Grafts
The genetic constitution is ZZ (d
7|
):ZW (9 ) in the anuran amphibian,
Xenopus laevis (Gallien, 1955a, 1956; Chang and Witschi, 1955). Mikamo
and Witschi (1963, 1964) returned to the study of sex reversal in this
species. A differentiated testis is implanted in larvae before sexual differentiation. By chance, the graft may be in a genetic male or a genetic female.
In the first stage, the testis graft induces a marked inhibition of the gonads
of the host, whether it is a genetic male or female. If, in a second stage, the
testis graft is removed, the vestigial gonads of the host resume their development. The medullary area, which is androgenic, has the advantage in
development, even in genetic females. In the latter case, the gonads of the
host become testes. Thus a neomale is obtained. Genetic analysis of the
offspring of these animals has shown (Table I) that the genetic females
had been transformed to neomales (Mikamo and Witschi, 1963). Crosses
were made either with control females (ZW) or with neofemales (ZZ)