Evidence for involvement of a transformer paralogue in sex determination of the wasp Leptopilina clavipes.

E Geuverink,F Chen,L W Beukeboom,M H K Linskens,M Van Leussen,K Kraaijeveld,J Pijpe,L Van De Zande

doi:10.1111/imb.12522

Abstract

Transformer (tra) is the central gear in many insect sex determination pathways and transduces a wide range of primary signals. Mediated by transformer-2 (tra2) it directs sexual development into the female or male mode. Duplications of tra have been detected in numerous Hymenoptera, but a function in sex determination has been confirmed only in Apis mellifera. We identified a tra2 orthologue (Lc-tra2), a tra orthologue (Lc-tra) and a tra paralogue (Lc-traB) in the genome of Leptopilina clavipes (Hymenoptera: Cynipidae). We compared the sequence and structural conservation of these genes between sexual (arrhenotokous) and asexual all-female producing (thelytokous) individuals. Lc-tra is sex-specifically spliced in adults consistent with its orthologous function. The male-specific regions of Lc-tra are conserved in both reproductive modes. The paralogue Lc-traB lacks the genomic region coding for male-specific exons and can only be translated into a full-length TRA-like peptide sequence. Furthermore, unlike LC-TRA, the LC-TRAB interstrain sequence variation is not differentiated into a sexual and an asexual haplotype. The LC-TRAB protein interacts with LC-TRA as well as LC-TRA2. This suggests that Lc-traB functions as a conserved element in sex determination of sexual and asexual individuals.

Highlights

Sex determination is a ubiquitous developmental process in eukaryotes
The transducing level of sex determination is conserved in L. clavipes
Two homologues of tra were detected in L. clavipes and both displayed strong amino acid sequence conservation compared to hymenopteran TRA orthologues

Summary

Introduction

Sex determination is a ubiquitous developmental process in eukaryotes. It entails the differentiation of two sexual functions and leads to the development of female and male morphologies and behaviours. Tra displays high sequence divergence amongst insects, possibly as a result of accommodating many different upstream primary signals in the cascade (Verhulst et al, 2010b). It contains a number of distinctive domains of which the most conserved is the Ceratitis-Apis-Musca (CAM) domain, which is believed to implement the autoregulatory splicing loop of tra (Hediger et al, 2010). Despite the rapid evolution of sex determination cascades, most insect species have a functionally conserved tra orthologue as the transducer of the primary signal. A model for the sex determination system of L. clavipes will be presented and compared to known mechanisms within the Hymenoptera

Results

Discussion

Experimental procedures