The Mutation masculinizer (man) Defines a Sex-Determining Gene With Maternal and Zygotic Functions in Musca domestica L.

Abstract

In Musca domestica, the primary signal for sex determination is the dominant factor M, which is assumed to regulate a postulated female-determining gene F. Presence of M prevents expression of F so that male development ensues. In the absence of M, F can become active, which dictates the female pathway. The existence of F is inferred from FD, a dominant factor that is epistatic to M. We describe a new mutation masculinizer, which has all the properties expected for a null or strongly hypomorphic allele of F: (1) it maps to the same chromosomal location as FD, (2) homozygous man/man animals develop as males, (3) homozygous man/man clones generated in man/+ female larvae differentiate male structures, (4) man has a sex-determining maternal effect. About a third of the morphological males synthesize yolk proteins, which indicates that they are intersexual in internal structures. The maternal effect of man is complete in offspring that derive from homozygous man/man pole cells transplanted into female hosts. In this case, all man/+ progeny become fertile males that do not produce yolk proteins. A sex-determining maternal effect has previously been demonstrated for FD. Like F, maternal man + is needed for zygotic man + to become active, providing further evidence that man is a loss-of-function allele of F.

Divergent evolution of genetic sex determination mechanisms along environmental gradients

“…Temperature likely plays a causal role in maintaining these gradients by affecting the SD process [41][42][43][44] . Temperature effects on housefly SD have been reported in the form of biased sex ratios produced in wildtype crosses 42 as well as in females carrying the masculinizer (man) mutation, another variant of tra 21,37 . The man mutation represents a maternal-effect maledetermining gene, where man-carrying females can produce all-male progeny even if the progeny do not carry an Mfactor.…”

“…However, such models typically do not explicitly consider the underlying molecular mechanisms of sex determination. Although sex is determined by genes in species with GSD, environmental conditions can affect SD by modifying the expression levels of these genes 21,22 . Despite clear evidence that such environmental effects may perturb the action of GSD mechanisms (e.g., 4 ), their effect on the evolution of GSD systems is still unknown.…”

The Y-Chromosomal and Autosomal Male-Determining M Factors of Musca domestica Are Equivalent

“…Another mechanism of sex determination could result from an amorphic mutation in the F gene. The recessive mutation masculinizer (man) has the expected properties of such a mutation: it transforms genotypically female animals into males and maps to the position of F (SCHMIDT et al 1997). Homozygous man/man animals develop as males, whereas heterozygous man/+ zygotes enter the female pathway.…”

“…Variations in the amount of maternal products could also give rise to new mechanisms of sex determination. Zygotic F activity appears to require the presence of maternally synthesized Fproduct, so that male development ensues if maternal Factivity is inhibited (HILFIKER- KLEINER et al 1994;SCHMIDT et al 1997). This appears to be the case when M"'is introduced into the female germ line: genotypically female offspring deriving from these germ cells become males (HILFIKER-KLEINER et al 1994).…”

“…Similarly, the mutation man shows a maternal effect leading to male development of genotypically female offspring that derived from transplanted man/man pole cells. This suggested that in these eggs the amount of maternal Fproduct is reduced such that the zygotic F gene cannot become active, and these zygotes enter the male pathway (SCHMIDT et al 1997). Another example for sex determination by a maternal effect is given by the dominant mutation Amhenogenic (Ag).…”