Investigating the role of brinp1 in zebrafish development

The Membrane Attack Complex - PerForin (MACPF) superfamily is known to have a diverse array of roles in immunity, embryonic development and neural function. BRINPs (Bone Morphogenetic Protein – Retinoic Acid Inducible Neural specific Proteins) are a family of three MACPF domain-containing proteins that are highly expressed during rodent neural development. Each contains a MACPF domain, but the remainder of the molecule has no significant sequence similarity to any other structurally or functionally characterised protein. BRINP orthologues are highly conserved across vertebrates, suggesting they perform essential functions. In rodents, all three Brinps are ubiquitously expressed in the brain at early embryonic stages, with Brinp1 most highly expressed. In postnatal to adult stages Brinp1 expression is restricted to the hippocampus, olfactory bulb, cerebellum and cerebral cortex. Only low expression of Brinp2 and Brinp3 is observed at these stages. In this study, the zebrafish animal model was used to study the function of brinps in the developing brain, and to determine the effect of disrupting their function. A bioinformatic approach was applied to explore the evolutionary relationships between BRINP family members. The locus arrangement of BRINP genes is conserved in mammals and teleosts. Full-length zebrafish orthologues were identified and cloned, and two additional brinp3 paralogues were discovered. Brinp gene expression in zebrafish was reminiscent of the expression in rodents. Expression was unrestricted in the brain at early stages (24 hpf) and localised to specific brain structures in older embryos (48-72 hpf). Expression was also observed in the primordial fin buds. In addition to the broad and overlapping expression pattern of all brinps, brinp1 was exclusively detected in the lateral line primordium. Through morpholino oligonucleotide gene silencing, loss of function of the brinp1 gene was examined and determined to result in pleiotropic defects in the developing embryo. At 48 hpf, embryos exhibited a curved body axis, aberrant neuromast formation and defects in axonal projections in the head and tail. Finally, this study has led to the identification of a pathway in which brinp1 may function. It was possible to reverse the effect of the curved tail and loss of neuromasts by 72 hpf using a Tyrosine kinase B (TrkB) receptor agonist, providing preliminary evidence that brinp1 functions in the BDNF/ TrkB receptor pathway.