Maternal Control of Haplodiploid Sex Determination in the Wasp Nasonia

Abstract

The Wasps and the Bees Sex development in bees and wasps depends on whether or not they develop from a haploid unfertilized egg (resulting in males) or diploid fertilized egg (resulting in females). Although these ploidy-level developmental processes are conserved among bees and wasps, the mechanisms that direct development down a male or female pathway differ significantly. By examining the sex-determining genes in the parasitoid wasp Nasonia , Verhulst et al. (p. 620 ) have shown that a maternal messenger RNA (mRNA) is necessary to initiate the female pathway. The mRNA operates in combination with conserved maternal and paternal genes to produce females, which explains why females are diploids. In unfertilized eggs, maternal provisioning of the gene transcript is too low to initiate the female pathway.

Insect sex determination: it all evolves around transformer

“…Interestingly, a comparison between dsx of hymenopterans A. mellifera and N. vitripennis revealed putative dsxRE/PRE binding sites that indeed have severely diverged from those of Diptera [23]. Similar dsxRE/PRE binding sites have been identified in the Nasonia fruitless gene [23] and in Nvtra [42 ]. Hence, the illustrious feminizing factor on the W chromosome in B. mori [46 ,47], may be an unconfirmed ortholog of tra that also functions as active feminizing factor.…”

“…In Nasonia female-specific tra is maternally provided to eggs. In embryos from fertilized eggs early zygotic expression of tra is higher than in embryos from unfertilized eggs, which initiates an auto regulatory loop of tra and results in female dsx splicing [42 ]. In embryos from unfertilized eggs no early zygotic expression of tra occurs and the auto regulatory loop does not establish, leading to male-specific tra and dsx splicing.…”

“…In the haplodiploid N. vitripennis it has been shown for the first time that sufficient levels of maternally provided tra mRNA in eggs are required for female development. Knockdown of tra in mothers leads to a diminished amount of maternally provided tra mRNA in eggs and results in diploid males [42 ]. In Drosophila, Sxl has been recruited upstream of tra and is female specifically regulated through its own auto regulatory loop.…”

“…In a fertilized egg, both a maternal and a paternal genome are present. The paternal set has an active, nonsilenced gene so that tra will be transcribed enabling the maternally provided tra mRNA to start auto regulation of tra, eventually leading to female development [42 ]. A mutant stain of N. vitripennis that produces gynandromorphs and females from haploid unfertilized eggs [66,67] may be explained by incomplete imprinting in the maternal germ line.…”

The genome of the fire ant Solenopsis invicta

“…Hymenopterans, including wasps, bees, and ants, have a haplo-diploid sex determination system whereby diploid eggs normally develop into females, and haploid eggs develop into males. In N. vitripennis, female development is initiated by maternally derived transformer/feminizer mRNA in the zygote (42). In contrast, sex is determined by the complementary sex determiner (csd) gene in A. mellifera (43,44): Eggs that are heterozygous at this locus develop into females, whereas hemizygous haploids and homozygous diploids develop into males.…”