Trim46 contributes to the midbrain development via Sonic Hedgehog signaling pathway in zebrafish embryos

TRIM46 is a RING finger E3 ligase which belongs to TRIM (tripartite motif-containing) protein family. TRIM46 is required for neuronal polarity and axon specification by driving the formation of parallel microtubule arrays, whereas its embryological functions remain to be determined yet. Expression patterns and biological functions of trim46a, a zebrafish homologue of TRIM46, were studied in zebrafish embryo. First, maternal transcripts of trim46a were present at 1 cell stage whereas zygotic messages were abundant in the eyes, MHB (Midbrain-Hindbrain Boundary) and hindbrain at 24 hpf (hours post fertilization). Second, transcriptional regulatory region of trim46a contains cis-acting elements binding a transcriptional factor Foxa2. Transcription of foxa2 is positively regulated by Sonic Hedgehog (SHH), and treatment of cyclopamine, an SHH inhibitor, represses transcription of foxa2 in 4 hpf through 24 hpf embryos. Third, the transcriptional repression of foxa2 inhibited transcription of trim46a to cause developmental defects in the midbrain and MHB. Finally, spatiotemporal expression patterns of a midbrain marker otx2b in the developmental defects confirmed inhibition of SHH by cyclopamine caused underdevelopment of the midbrain and MHB at 24 hpf. We propose a signaling network where trim46a contributes to development of the midbrain and MHB via Foxa2, a downstream element of SHH signaling in zebrafish embryogenesis.