Identification of sex determination cascade in stingless bees
Flávia Cristina de Paula Freitas, Flávia Cristina de Paula Freitas , Josephine Buchholz , Francis Morais Franco Nunes , Alexandre dos Santos Cristino , Zilá Luz Paulino Simões
Departamento de Genética, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brazil; Departamento de Genética, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brazil ; Department Institute of Biology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany ; Departamento de Genética e Evolução, Universidade Federal de São Carlos, São Carlos, Brazil ; Translational Research Institute, The University of Queensland, Brisbane, Australia ; Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brazil
Sex determination is one of the major developmental events in higher metazoans. In honeybees, the sex determination cascade is initiated by the allelic composition of complementary sex determiner (csd) gene: males develop from hemizygous or homozygous embryos, whereas females develop from heterozygous embryos. In females, different alleles of csd act to form female-specific variants of feminizer (fem) and doublesex (dsx). In males, male-specific variants of fem and dsx are formed by default and do not require csd participation. The transcription factor dsx is highly conserved in insects, nematodes and vertebrates and is a terminal signal of the sex determination cascade that regulates sexual differentiation. However, in stingless bees, the components of sex determination cascade are not fully known. Here, we searched for orthologs of the honeybee fem and dsx genes in Meliponini species. We identified splicing variants of fem and dsx in male and female in the stingless bees Frieseomelitta varia, Melipona quadrifasciata and Scaptotrigona postica using Sanger sequencing. fem transcripts found in F. varia present both complete SDP and Apis Csd domains, and an incomplete RRM domain, which is similar to the structure of csd gene of honey bees. However, the comparison to fem gene sequence of other bee species confirmed the identity of F. varia fem due to the lack of the hypervariable region, which characterizes csd gene. The architecture of dsx splicing variants in the stingless bees is very similar to the one observed in honeybee: the male dsx variant presents both DM and dsx dimer domains, female dsx variant shows complete DM domain but truncated dsx dimer domain. Our results showed that the terminal components of the sex determination cascade are highly conserved in the members of Apini and Meliponini tribes. Yet, further studies are needed to unravel the nature of the initial sex-determining signal in stingless bees.