Maternal provision of transformer-2 is required for female development and embryo viability in the wasp Nasonia vitripennis

Abstract

In insect sex determination a primary signal starts the genetic sex determination cascade that, in most insect orders, is subsequently transduced down the cascade by a transformer (tra) ortholog. Only a female-specifically spliced tra mRNA yields a functional TRA-protein that forms a complex with TRA2, encoded by a transformer-2 (tra2) ortholog, to act as a sex specific splicing regulator of the downstream transcription factors doublesex (dsx) and fruitless (fru). Here, we identify the tra2 ortholog of the haplodiploid parasitoid wasp N. vitripennis (Nv-tra2) and confirm its function in N. vitripennis sex determination. Knock down of Nv-tra2 by parental RNA interference (pRNAi) results in complete sex reversal of diploid offspring from female to male, indicating the requirement of Nv-tra2 for female sex determination. As Nv-tra2 pRNAi leads to frequent lethality in early developmental stages, maternal provision of Nv-tra2 transcripts is apparently also required for another, non-sex determining function during embryogenesis. In addition, lethality following Nv-tra2 pRNAi appears more pronounced in diploid than in haploid offspring. This diploid lethal effect was also observed following Nv-tra pRNAi, which served as a positive control in our experiments. As diploid embryos from fertilized eggs have a paternal chromosome set in addition to the maternal one, this suggests that either the presence of this paternal chromosome set or the dosage effect resulting from the diploid state is incompatible with the induced male development in N. vitripennis caused by either Nv-tra2 or Nv-tra pRNAi. The role of Nv-tra2 in activating the female sex determination pathway yields more insight into the sex determination mechanism of Nasonia.

Maternal provision of non‐sex‐specific transformer messenger RNA in sex determination of the wasp Asobara tabida

“…mellifera (Nissen et al ., ) and N . vitripennis (Geuverink et al ., ). A potential complex with the female‐specific TRA protein, as demonstrated in Drosophila melanogaster (Amrein et al ., ), can however only be formed at a later stage in development, when At‐tra F is actively transcribed in the zygote.…”

“…Ap. mellifera (Nissen et al, 2012) and N. vitripennis (Geuverink et al, 2017) do possess alternative splice variants of tra2, but these are present in both sexes and across all life stages.…”

Evidence for involvement of atransformerparalogue in sex determination of the waspLeptopilina clavipes

“…We performed protein–protein interaction assays in N. vitripennis to test the hypothetical TRA/TRA2 binding complex in Hymenoptera. Both tra and tra2 in N. vitripennis are required for the splicing of tra pre‐mRNA as well as dsx pre‐mRNA (Verhulst, Beukeboom, et al ., ; Geuverink et al ., ). In this study we demonstrated an interaction between TRA and TRA2 in N. vitripennis .…”

The transformer2 gene of the pumpkin fruit fly, Bactrocera tau (Walker), functions in sex determination, male fertility and testis development

“…On the contrary, Btau‐tra2 was multi‐transcribed into three transcript variants instead of only one transcript as occurs with the tra2 genes of other tephritids and M. domestica (Salvemini et al, ; Sarno et al, ; Schetelig & Handler, ; Liu et al, ). To date, tra2 genes that are transcribed into multi‐transcripts have been found in other insect groups; for example, three transcripts were found to be produced in T. castaneum (Shukla & Palli, ), four in D. melanogaster , Aedes aegypti (Amrein et al, ; Liu et al, ) and N. vitripennis (Geuverink et al, ), six in Ap. mellifera and Bo.…”

“…In some insects, tra2 genes function both in determining sex and also in embryonic development such as in Ap. mellifera (Nissen et al, 2012), T. castaneum (Shukla & Palli, 2013) and Nasonia vitripennis (Geuverink et al, 2017).…”