Katia Komitopoulou

The transformer gene in Bactrocera oleae: the genetic switch that determines its sex fate.

Transformer (tra) is the second gene of a regulatory cascade based on RNA splicing that determines sex in Drosophila melanogaster. Splicing of tra transcripts is regulated by the master gene Sex lethal and tra itself regulates splicing of the transcriptional regulator doublesex (dsx). We present the isolation and characterization of Botra, the olive fruit fly Bactrocera oleae orthologue to the Drosophila gene transformer. As in Drosophila, Botra transcripts are spliced in a sex‐specific manner so that only females encode a functional polypeptide of 422 amino acids, whereas males encode presumably nonfunctional peptide(s). The identification of multiple TRA/TRA‐2 binding sites within the Botra male‐specific exons, suggests an autoregulation mechanism of tra, through TRA/TRA2 activities. The fundamental role of the TRA protein in sex determination of Bactrocera was investigated by RNA interference, where the introduction of Botra dsRNA into embryos resulted in complete transformation of XX flies into fertile males.

The genome of the Mediterranean fruitflyceratitis capitata: Localization of molecular markers by in situ hybridization to salivary gland polytene chromosomes

We hybridized cloned DNA segments to salivary gland polytene chromosomes of the medfly,Ceratitis capitata, and thus established molecular markers for 24 sites on 6 out of 10 autosomal arms. An additional marker identified a medfly repetitive element that hybridizes to approximately 100 autosomal sites as well as a granular network that is thought to represent theX chromosome. Some of the markers correspond to 9 characterized transcription units, while 17 remain anonymous; at least 3 of the latter are restriction fragment length polymorphism (RFLP) markers. The characterized transcription units document that chromosomal arm 5L ofC. capitata is homologous to theDrosophila melanogaster X chromosome, in agreement with previous inferences based on the extensive conservation of linkage groups in Diptera.

Cloning and characterization of a cDNA encoding a male-specific serum protein of the Mediterranean fruit fly, Ceratitis capitata, with sequence similarity to odourant–binding proteins

Male‐specific serum proteins (MSSPs) are low molecular weight proteins which accumulate in high amounts in the haemolymph of adult males of the medfly Ceratitis capitata. By screening an expression library with anti‐MSSP antibodies, we have isolated and determined the nucleotide sequence of a cDNA clone coding for one of the male‐specific polypeptides (MSSP‐α). The MSSP‐α mRNA encodes a polypeptide of 144 amino acids with a secretory signal sequence of sixteen amino acids. Southern analysis indicated that there are multiple copies of MSSP genes in the medfly genome. Northern analysis showed that the MSSP mRNAs are synthesized only in adult males. The accumulation pattern of these mRNAs during development suggests that the expression of the MSSP genes is developmentally regulated at both transcriptional and translational levels. The predicted peptide sequence of MSSP‐α shows significant similarity to a group of pheromone‐ and general odourant‐binding proteins of insects.

Organization, evolution and expression of a multigene family encoding putative members of the odourant binding protein family in the medfly Ceratitis capitata

A multigene family encoding male specific serum polypeptides (MSSPs) that show significant structural similarity to the family of insect odourant binding proteins, has been characterized in the medfly Ceratitis capitata. This family comprises seven members classified in three subgroups, MSSP‐α, MSSP‐β and MSSP‐γ. The genes of subgroups α and β are clustered in tandem in a 35‐kb genomic region, and present an exceptionally high degree of similarity not only in their coding but also in the surrounding regions, while the genes of the γ subgroup are drastically divergent. Although MSSPs are predominantly expressed in the male fat body, detailed expression studies suggest that individual members of this family are expressed in a distinct sex‐ and tissue‐specific manner.

Expression and function of the Drosophila melanogaster ADH in male Ceratitis capitata adults: a potential strategy for medfly genetic sexing based on gene-transfer technology

The aim of development of a Mediterranean fruit fly Ceratitis capitata genetic sexing strain derives from the large scale SIT programmes being carried out to control this pest. Toward this direction, we present here the male‐specific expression of the Drosophila melanogaster alcohol dehydrogenase (ADH) in medfly transgenic adults generated by Minos‐mediated germ line transformation. This expression pattern is obtained by using a promoter fragment of the male‐specific gene MSSP‐α2 of the medfly. We show that the heterologous enzyme is functional in the medfly oxidizing both ethanol and 2‐propanol. Although leading to an approximately twofold increase of total ADH activity in male compared to female transgenic adults, these expression levels are not enough for performing genetic sexing when high doses of environmental alcohol are applied. This could be achieved either by further enhancement of the transgene expression or by generating an Adh− line to host the Minos insertions.