ABERRANT ANOGENITAL DISTANCE IN XXSXR (SEX-REVERSED) PSEUDOMALE MICE

Anogenital distance (AGD), a sex differentiation marker in mice (Mus m usculus), is thought to be a secondary sexual trait exclusively regula ted by androgens during development. However, recent studies suggest t hat some so-called secondary sexual traits may be influenced by sex-ch romosomal genotype. To explore this question further we studied the AG D of the XXSxr 'sex-reversed' mouse, which has adequate androgens for masculinization. The AGDs of adult and prepubertal XY, XYSxr carrier, XXSxr 'sex-reversed' and XX mice were measured. We found that adult XX Sxr 'sex-reversed' mice (which we refer to as pseudomales) and XYSxr c arriers have shorter mean AGDs than their XY siblings. Prepubertal XXS xr animals also have shorter mean AGDs than their XY siblings when AGD is expressed as a proportion of body length. XX adult and prepubertal mice have significantly shorter AGDs than the other genotypes at simi lar stages of development. The differences in AGD between adult and pr epubertal XY and XXSxr sibs, and adult XY and XYSxr sibs, reported her e, do not appear to be due to androgen levels, since adult testicular and serum testosterone levels are higher in pseudomales and carriers t han in XY mice, and fetal pseudomale androgen levels also appear to be at least as high as those of normal males. Furthermore, the AGD diffe rences between genotypes are not correlated to differences in testis s ize. We conclude that the differences are likely to be due to a tissue specific effect of the genetic constitution of the individuals, as is the case with scrotal development in the marsupial Macropus eugenii ( the tammar wallaby).