Aspects moléculaires du déterminisme sexuel : régulation génique et pathologie

Anti-Müllerian hormone: A function beyond the Müllerian structures

The anti-Müllerian hormone (AMH) is a heterodimeric glycoprotein belonging to the TGFb superfamily implicated in human embryonic development. This hormone was first described as allowing regression of the epithelial embryonic Müllerian structures in males, which would otherwise differentiate into the uterus and fallopian tubes. It activates a signaling pathway mediated by two transmembrane receptors. Binding of AMH to its receptor induces morphological changes leading to the degeneration of Müllerian ducts. Recently, new data has shown the role played by this hormone on structures other than the genital tract. If testicular AMH expression decreases in humans over the course of a lifetime, synthesis may persist in other tissues in adulthood. The mechanisms underlying its production have been unveiled. The aim of this review is to describe the different pathways in which AMH has been identified and plays a pivotal role.

[Ovarian failure: New treatments in perspective?]

The premature loss of ovarian function may have physical and psychological consequences. A better understanding of its mechanism is therefore needed. Because they are affecting the oocyte quality, the decline of the ovarian reserve and high maternal age are implicated in many defects leading to chromosomal defects, modifications of gene expression or alterations of the mitochondrial pattern of the oocyte. However, cellular therapies such as ovarian follicle activation or isolation of ovarian stem cells are promising treatments of ovarian failure.

[The Sertoli cell]

The Sertoli cell is essential for the formation and functioning of the testis. This is the first cell to differentiate into the initially bipotential genital ridge and is the only somatic cell present in seminiferous tubules. Maturation involves the loss of proliferative capacity, formation of intercellular tight junctions and the appearance of some specific markers. We can consider schematically two distinct roles associated with different features: a process of sexual differentiation with testicular formation and a role in spermatogenesis allowing the germ cells progression into sperm through close contact in the seminiferous tubules. These events, separated in time, are in fact intimately linked.

Polymorphismes du chromosome Y et fertilité masculine

Molecular anomalies of the Y chromosome leading to male infertility are mainly microdeletions of the long arm of the Y chromosome. Three recurrently deleted portions of the long arm are the AZFa, AZFb and AZFc (AZF: Azoospermia Factor) regions. Complete deletions of the AZFc region are found in 10% of cases of severe male infertility. In addition to the AZF deletions, certain classes of Y chromosome (haplogroups) may also predispose to male infertility and could be transmitted to future male descents by various Assisted Reproductive Techniques (ART). Since the first discovery of microdeletions, the sequence of the Y chromosome has become available, revealing the mechanisms underlying deletion formation and also resulting in a coherent screening strategy. Recently, partial deletions of the AZF regions have been described. The significance of these deletions in the clinical context remains to be defined.