The zebrafish homologs of SET/I2PP2A oncoprotein: expression patterns and insights into their physiological roles during development

The oncoprotein SET/I2PP2A participates in various cellular mechanisms such as transcription, cell cycle regulation and cell migration. SET is also an inhibitor of the serine/threonine phosphatase PP2A, which is involved in the regulation of cell homeostasis. In zebrafish there are two paralogous set genes that encode Seta (269 aa) and Setb (275 aa) proteins which share 94% identity. We show here that seta and set b are similarly expressed in the eye, the otic vesicle, the brain and the lateral line system, as indicated by in situ hybridization labeling. Whole mount immunofluorescence analysis revealed the expression of Seta/b proteins in the eye retina, the olfactory pit and the lateral line neuromasts. Loss-of-function studies using antisense morpholino oligonucleotides targeting both seta and setb genes (MOab), resulted in increased apoptosis, reduced cell proliferation and morphological defects. The morphant phenotypes were partially rescued when MOab morpholino was co-injected with human SET mRNA. Knock down of setb with a transcription-blocking morpholino (MOb) resulted in phenotypic defects comparable to those induced by setb gRNA/Cas9 injections. In vivo labelling of hair cells showed a significantly decreased number of neuromasts in MOab-, MOb- and gRNA/Cas9- injected embryos. Microarray analysis of MOab morphant transcriptome revealed differential expression in gene networks controlling transcription in the sensory organs, including the eye retina, the ear and the lateral line. Collectively, our results suggest that seta and setb are required during embryogenesis and play roles in the zebrafish sensory system development.