[An update on gonadal differentiation].

Abstract

The Y chromosome plays a determinant rôle in human maleness. Studies on individuals with sex chromosome abnormalities indicate that a testis determining factor (TDF) is located on the short arm of the Y chromosome. A candidate gene, recently cloned, encodes a protein with multiple "finger" domains of a type known to bind DNA and control transcription. The puzzling finding that on the short arm of the X chromosome is located and homolog gene escaping X inactivation raises problems on the functional relationship of the two genes. The whole of the molecular studies using Y-specific probes have shown that XX males result from the transposition of TDF from the short arm of the Y to that of X chromosome; at least some XY females result from the same transposition, that leaves the Y chromosome without its distal short arm, TDF included. In XO males, the TDF is translocated to an autosome; according to the deletion of the latter, different malformation patterns may be present in these patients. If the presence or the absence of a critical segment of the Y chromosome do explain many instances of sex several, an outstanding problem is still represented by XX hermaphrodites since no Y-specific sequences have been found in their genome. Thus although the Y-chromosome testis- determining factor seems to play a pivotal rôle in sex determination, testicular tissue can be formed in the absence of it.