Zoological Studies

Vol. 61, 2022

(update: 2022.5.10)

Correlated Expression of the Opsin Retrogene LWS-R and its Host Gene in Two Poeciliid Fishes

Chia-Hao Chang1,*

1Department of Science Education, National Taipei University of Education, No.134, Sec.2, Heping E. Rd., Da’an District, Taipei City 10671, Taiwan. *Correspondence: E-mail: chiahao0928@gmail.com (Chang). Tel.: +886-4-23590121#32453.

Received 4 August 2021 / Accepted 22 February 2022
Communicated by John Wang

The important role of retrogenes in genome evolution and species differentiation is becoming increasingly accepted. One synapomorphy among cyprinodontoid fish is a retrotransposed version of a long-wavelength sensitive (LWS) opsin gene, LWS-R, within an intron of the gephyrin (GPHN) gene. These two genes display opposing orientations. It had been speculated that LWS-R hijacks the cis-regulatory elements of GPHN for transcription, but whether their expression is correlated had remained unclear. Here, in silico predictions identified putative promoters upstream of the translation start site of LWS-R, indicating that its transcription is driven by its own promoter rather than by the GPHN promoter. However, consistent expression ratios of LWS-R:GPHN in the eyeball and brain of fishes indicate that the respective gene transcriptions are correlated. Co-expression is potentially modulated by histone exchange during GPHN transcription. Two isoforms were detected in this study, i.e., intron-free and intron-retaining. Intron-free LWS-R was only expressed in the eyeball of fishes, whereas intron-retaining LWS-R occurred in both eyeball and brain. Expression of vision-associated LWS-R beyond the eyeball supports that it is co-expressed with more ubiquitous GPHN.

Key words: Retrotransposition, Opsin, Promoter, Gephyrin, Histone exchange, Intron retention.

Citation: Chang CH. 2022. Correlated expression of the opsin retrogene LWS-R and its host gene in two poeciliid fishes. Zool Stud 61:16. doi:10.6620/ZS.2022.61-16.

Supplementary materials: Fig. S1