Primary sex determination: genetics and biochemistry

Area of Science:

• Mammalian Developmental Biology
• Reproductive Endocrinology
• Molecular Genetics

Background:

• The H-Y antigen is proposed as the primary inducer of mammalian sex differentiation, directing indifferent gonads towards testicular development.
• Phylogenetic conservatism supports the role of H-Y antigen in sex determination across species.
• Existing evidence links H-Y antigen status to specific sex development anomalies.

Purpose of the Study:

• To investigate the role of H-Y antigen in primary sex differentiation in mammals.
• To explore the mechanism of H-Y antigen action and its receptor interactions.
• To understand how H-Y antigen dysfunction leads to sex development disorders.

Main Methods:

• Serological testing to define H-Y antigen presence and absence.
• In vitro organogenesis assays using fetal calf gonads.
• Cell culture studies with H-Y antigen-producing cells (Daudi) and gonadal cells.
• Biochemical characterization of H-Y antigen molecules.

Main Results:

• XX males are H-Y positive and fertile; XY females are H-Y negative and lack testes.
• Soluble H-Y antigen induces testicular organogenesis in XX gonads in vitro.
• Gonadal cells possess specific receptors for H-Y antigen, leading to H-Y positivity.
• H-Y antigen is secreted as an 18,000 MW protein by Daudi cells, with potential additional forms from Sertoli cells.

Conclusions:

• H-Y antigen, through specific receptor binding in the primordial gonad, initiates testicular differentiation irrespective of karyotype.
• Defects in H-Y antigen synthesis, dissemination, or binding underlie primary sex differentiation anomalies.
• Further research is needed to clarify the precise nature and function of different H-Y antigen molecular forms.