Sexual dimorphism of mouse fetal brain lesions after X-irradiation prior to gonadal differentiation.

Fractionated X-irradiation of gestational days 11-13 in the mouse, with doses between 3 x 1.05 and 3 x 1.33 Gy resulted in rosette-like clusters of primitive ependym-resembling cells dispersed within the cortex walls. Quantification of these abnormalities showed a general prevalence in the female fetuses, especially due to the larger number of rosettes in the females than in the males. It was concluded that X-irradiation acts on sex-specific differentiation steps, which are fully developed at the beginning of the fetal period. As it was recently speculated that these are linked to an early divergence of gene expression between the sexes, we suggest that X-chromosome damage may be involved in the pathogenesis of the dimorphic lesion pattern. While, in principle, this will valid for any fetal tissue, it only becames evident in the forebrain because of the outstanding relationship between cell necrosis and rosette development in this specific organ.