The objectives of this article as I saw them were, (1) to show how fetal gonads acquire
the ability to function as endocrine organs, and (2), to show the mechanisms by which the
endocrine secretions modulate male development. The researchers went through an
extremely extensive explanation of the formation of the sexual phenotypes by detailing
the development of germ cells. They explained how women's and men's gonads appear
identical until Leydig cells, which synthesize testosterone, appear in the connective
tissue. This is when differentiation begins.
The mechanism that this differentiation occurs is as follows. There are two duct systems
which are basically sex specific. In men, Wolffian ducts are dominant and Mullerian
ducts are regressive. Whereas in women it is just the opposite. Jost believed that the
fetal testis secret a hormone which causes such a differentiation. In order to confirm
this belief, he removed the gonads from embryos, prior to the onset of phenotypic
differentiation. All resulted in female phenotypes. The male phenotype is induced and
will not manifest if the proper secretions are not made from the testis.
Although the article fails to mention how, "Jost deduced that two secretions from the
fetal testis are essential for male development - Mullerian-inhibiting substance and
androgen." The mechanism in which spermatogenic tubules form Mullerian-inhibiting
substance is still unclear to scientists. Problems with improper levels of this hormone
result in genetic and phenotypic reproductive disorders.
The other hormone secreted by the testis is testosterone. It has two functions; it
promotes maturation of the spermatogenic tubules (and is therefore indirectly effecting
the levels of Mullerian-inhibiting substance), and it has its well known essential role
in the development of the male genital tract.
Throughout this article there were several areas where it seemed to me, issues were
unresolved, however seemed to me that we have the technology to resolve them. For
instance "The Character of the acceptor sites within the nucleus (that is, whether
protein or DNA) and their number are not resolved." Couldn't one do a radioactive trace
or a non-vital stain of some sort to distinguish the protein from the DNA.
The development of one's sex is therefore far more than just a genetic decision, it is
(once again) a complex cascade of hormones acting on receptors. These receptors go on
to activate effector molecules which activate target molecules. If at any point this
system is disrupted in any way, one either has the underdevelopment or incorrect
development of the phenotypical gonadal characteristics.
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