Drosophila beanbag ( beba ) encodes an insect receptor tyrosine kinase associated with reproductive niche organisation

Abstract

Receptor tyrosine kinases (RTKs) are cell surface proteins that govern many critical cell fate decisions and their dysregulation is a major cause of diseases such as cancer. Much of what we know about how these proteins work in cells and tissues comes from model organisms such as the fruit fly Drosophila. Here, we identify and provide an initial characterisation of a previously unstudied Drosophila receptor tyrosine kinase encoded by CG3277, which we name beanbag (beba). Ectopic beba expression was associated with increased phosphor-Akt and diphospho-ERK signals and produced gain-of-function phenotypes resembling those caused by other Drosophila RTKs. Using a MiMIC-derived T2A-GAL4 allele, we show that Drosophila beba is expressed in digestive, nervous and reproductive systems, in locations suggestive of potential roles in endoreplication and/or stem cell niche support. Animals transheterozygous for beba loss-of-function alleles were viable, developed at a normal rate, and showed no detectable change in enterocyte DNA content under standard conditions. However, beba loss-of-function females had fewer ovarioles, consistent with a role in the ovarian terminal filament, and males had increased testis hub nuclei number and hub volume, suggesting beba may regulate somatic niche architecture in the Drosophila gonad. Phylogenetic analysis places Beba within a Ret/Tor-related RTK radiation and supports the existence of a distinct Beba family in insects. Together, these data support the classification of Beba as a lineage-restricted Drosophila RTK and implicate it in reproductive niche organisation.