Six6 and Six7 coordinately regulate expression of middle-wavelength opsins in zebrafish
Yohey Ogawa, Tomoya Shiraki, Yoshimasa Asano, Akira Muto, Koichi Kawakami, Yutaka Suzuki, Daisuke Kojima and Yoshitaka Fukada
PNAS (2019) 116 (10) 4651-4660 DOI:10.1073/pnas.1812884116
Color discrimination in the vertebrate retina is mediated by a combination of cone cell types expressing UV- (SWS1), blue- (SWS2), green- (RH2), and red- (LWS) sensitive photoreceptive molecules (opsins). Although the tetrachromatic cone system is retained in most non-mammalian vertebrate lineages, the transcriptional mechanism underlying gene expression of cone opsins remains elusive.
In this study, we found that the retinal transcription factors, sine oculis homeobox 6 (Six6) and Six7, synergistically and positively regulate gene expression of zebrafish SWS2 and RH2 opsins. Larvae deficient for both of these transcription factors showed heavily impaired visually driven foraging behavior and were unable to compete for food when reared in a group with normal siblings. The results suggest that six6 and six7 play a pivotal role in blue- and green-light sensitivity and daylight vision.
This research was done by a team composed of Prof. Yoshitaka Fukada, Dr. Daisuke Kojima, and Dr. Yohey Ogawa at the University of Tokyo, and the Laboratory of Molecular and Developmental Biology at the National Institute of Genetics (Prof. Koichi Kawakami, Dr. Akira Muto, and Dr. Tomoya Shiraki).
This work was supported by Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (KAKENHI) Grants (JP16J01681, JP16K20983, JP15K07144, JP18H04988, JP24227001, and JP17H06096).
Figure: (Left) Zebrafish deficient for both of the Six7 and Six6 (TKO) lost gene expression of zebrafish SWS2 (blue) and RH2 (green) opsins, indicating that the TKO showed lower middle-wavelength sensitivity. (Right) The TKO showed heavily impaired visually driven foraging behavior and were unable to compete for food when reared in a group with normal siblings (WT).