Ps. Burgoyne et al., Evidence that the testis determination pathway interacts with a non-dosagecompensated, X-linked gene, INT J DEV B, 45(3), 2001, pp. 509-512
In a number of mammals, including mouse and man, it has been shown that at
equivalent gestational ages, males are developmentally more advanced than f
emales, even before the gonads form. In mice, although some strains of Y ch
romosome exert a minor accelerating effect in pre-implantation development,
it is a post-implantation effect of the difference in X chromosome constit
ution that is the major cause of the male/female developmental difference.
Thus XX females are retarded in their development by about 1.5 h relative t
o (XO)-O-M females or XY males; however, they are more advanced than (XO)-O
-P females by about 4 h. It has been suggested that this early developmenta
l difference between XX and XY embryos may "weight the dice" in favour of o
varian and testicular development, respectively, although expression of Sry
will normally overcome any such bias. Here we test this proposal by compar
ing the relative frequencies of female, hermaphrodite and male development
in (XO)-O-P, XX and (XO)-O-M mice that carry an incompletely penetrant Sry
transgene. The results show that testicular tissue develops more frequently
in XX,Sry transgenics than in either of the two types of XO transgenics. T
hus the incidence of testicular development is affected by X dosage rath er
than by the developmental hierarchy. Th is implies there is a non-dosage c
ompensated gene (or genes) on the X chromosome, which interacts with the te
stis-determining pathway. Since the pseudoautosomal region (PAR) is known t
o escape X-inactivation, penetrance of the Sry transgene was also assessed
in (XY)-Y-M*(X) mice that have two doses of the PAR but have a single dose
of all genes proximal to the distal X marker Amel. These mice showed simila
r levels of testicular development to (XO)-O-M mice with the transgene; thu
s the non-dosage compensated X gene maps outside the PAR.