Zebrafish reveal new roles for Fam83f in hatching and DNA damage-mediated autophagic responses
The FAM83 (Family with sequence similarity 83) family is highly conserved in vertebrates, yet little is known of the functions of these proteins beyond a correlation with oncogenesis. Of the family, FAM83F is of particular interest because it is the only membrane targeted FAM83 protein. FAM83F has been shown to activate the canonical Wnt signalling pathway and bind to and stabilize p53 when overexpressed, two pathways often dysregulated in disease.  Insights into gene function can often be gained by studying the roles they play during development, and here we report the generation of fam83f knock-out (fam83f-/-) zebrafish, which we have used to elucidate the role of Fam83f in vivo. We show that endogenous fam83f is most strongly expressed in the proteolytic enzyme containing hatching gland of developing zebrafish embryos, and that fam83f-/- embryos hatch earlier than WT counterparts, despite developing at a comparable temporal rate. We demonstrate that fam83f-/- embryos are more sensitive to ionizing radiation than WT embryos, a finding that contrasts with the previously reported role of FAM83F as a stabilizer of p53. Transcriptomic analysis shows that loss of fam83f causes downregulation of phosphatidylinositol-3-phosphate (PI(3)P) binding proteins and impairment of cellular degradation pathways, particularly autophagy, which is a crucial component of the DNA damage response. Finally, we show that Fam83f protein is itself targeted to the lysosome when expressed in cultured cells, and that this localization is dependent upon a C' terminal signal sequence.  The zebrafish lines we have generated here suggest for the first time that Fam83f plays an important role in autophagic/lysosomal processes, resulting in dysregulated hatching and increased sensitivity to genotoxic stress in vivo. Overall design: fam83fa-/- zebrafish are more sensitive to ionizing radiation (IR) than WT counterparts. We conducted bulk RNA-seq on WT vs two different fam83fa-/- (K1 and K2) zebrafish lines by subjecting 24 hpf embryos from each genotype to IR then extracting total RNA at 2 and 10 hours following treament (t1 and t2).  Three biological replicates of a minimum of 10 embryos per replicate were sequenced by bulk RNA-seq to to identify any differences in the DNA damage response between WT and fam83fa-/- mutants. Treatments: AD = Actinomycin D in DMSO vehicle IR = ionizing radiation (20 Grays gamma radiation) unDMSO = untreated AD control (vehicle only i.e. DMSO) un = untreated IR control