Putative Functions of Novel Antennae Chemosensory Gene Repertoire of Male Tsetse Fly, Glossina morsitans morsitans

Abstract

Tsetse fly is a primary vector of Human African Trypanosomiasis and Animal African Trypanosomiasis. Tsetse fly exploits chemical cues from the environment to distinguish a non- from suitable hosts. Genes in tsetse fly antennae code for proteins and receptors that directly or indirectly mediate chemoreception. While chemoreception-associated genes have been annotated, antennal genes in the Glossina. m. morsitans genome with important functions have not been characterized. Antennaespecific raw reads from adult flies exposed to four treatments, namely, fed, unfedexposed to ε-nonalactone attractant, unfed-exposed to δ-nonalactone repellant and unfed-exposed to paraffin diluent (control) were mapped onto G. m. morsitans geneset. Reads that did not map were isolated and de novo assembled into transcripts. Protein-coding gene regions associated with these transcripts were predicted, annotated and curated as partial/complete genes. Annotated putative orthologs/homologs for these genes in Drosophila melanogaster (Dm), Musca domestica (Md) or Anopheles gambiae (Ag) genomes were identified. Finally, differential expression of the novel or existing genes in relation to odor exposures relative to no-odor control (unfed flies) were assessed and expression of existing genes quantified through qPCR. Results showed that 45.21% of the sequenced reads did not map to the gene set. These reads assembled into 72,428 unique transcripts that yielded 592 genes among which 202 were novel and 390 were improvements of existing genes in the G. m. morsitans genome. Among the novel genes, 94 had orthologs in Dm, Md or Ag and 88 had homologs in UniProt databases. These orthologs were putatively associated with non-canonical olfactory roles, thus providing insight into their specific roles in antennal physiological processes. A novel gene (GMOY014237.R1396) and 15 existing genes were differentially expressed in response to the attractant or repellent. Differential expression through qPCR analysis unveiled three antennal transcripts, i.e., the coat protein epsilon, cyclin-dependent kinase and odorant receptor 45, all three up-regulated in response to the attractant. Novel genes sequences were adopted by VectorBase, updating the existing G. m. morsitans annotations. This study identified 108 potentially tsetse fly-specific antennal genes. The novel antennal genes could be used as baseline data in studies of other tsetse fly species, and with an orientation towards attraction and or repellency in their control.