Analysis of human BBS protein homologues in insects support alternative non-ciliary functions

Abstract

Cilia and flagella were one of the characteristic traits of the last eukaryotic common ancestor and as such, are highly conserved among eukaryotes. Their proteomic makeup is consequently remarkably similar throughout all eukaryotic lineages. Recently, one subgroup of ciliary transport proteins in mammalian cells, the Bardet-Biedl Syndrome (BBS) proteins, was shown to have the ability to traverse the nuclear envelope, and to engage in protein-protein-interactions that modulate gene expression, signalling cascades, and cell homeostasis. Insects have been critically understudied in cilia biology because of their highly specialised cilia being localised on only a small subset of cell types. In this study, we present evidence that the BBSome, a hetero-octameric ciliary transport complex of BBS proteins, is largely conserved in multiple insect lineages. Using the honeybee Apis mellifera as a study system to explore BBS-associated gene expression, our analyses suggest that not all BBSome-associated genes are expressed equally, indicating possible non-ciliary functions. We also demonstrate that the expression of individual BBS proteins varies significantly between the tissues of queens and males in A. mellifera, especially in neuronal tissue. This result raises the question of what role BBS proteins play in these tissues and whether they are involved in gene regulation in insects. The potential gene regulatory function of BBS proteins should be explored in other eukaryotes due to their high degree of conservation.