The ultraviolet opsin is the first opsin expressed during retinal development of salmonid fishes.
OBJECTIVE
To determine the spatial and temporal progression of opsin appearance during retinal development of salmonid fishes (genus Oncorhynchus and Salmo).


METHODS
Reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization with riboprobes against the five classes of opsins present in salmonids (UV, blue, green, red, and rhodopsin) were used to establish the sequence of opsin appearance and the localization of opsins to specific morphologic photoreceptor types.


RESULTS
Both detection methods revealed that UV opsin mRNA was expressed first and was followed closely by red opsin mRNA. In situ hybridization results indicated the following opsin sequence: UV, red, rhodopsin, green, and blue. The UV opsin riboprobe labeled single cones, whereas the red and green riboprobes labeled opposite members of double cones. The blue riboprobe started labeling single center cones approximately 1 month after initial UV riboprobe labeling, confirming a switch in opsin expression of these cones from UV to blue. All probes first labeled a small patch of cells in the centrotemporal retina, and expression then expanded primarily toward the temporal and dorsal retina, with the exception of the blue opsin which expanded ventrally at first.


CONCLUSIONS
The sequence of cone opsin appearance in salmonid fishes is similar to that in mammals, in which a violet-blue (SWS1) opsin is expressed first followed by a red (M/LWS) opsin. This sequence is different from that in zebrafish, goldfish, and chick, in which red and green opsins are expressed first. As in mammals, rhodopsin expression in salmonid fishes arises after the first cone opsin. The findings show similarity in the sequence of opsin expression between a group of lower vertebrates, the salmonid fishes, and mammals.
Cheng
Christiana L
CL
Department of Biological Sciences, Simon Fraser University, 8888, University Drive, Burnaby, British Columbia, V5A 1S6, Canada.
Gan
Kathlyn J
KJ
Flamarique
Iñigo Novales
IN
D000818:Animals; D004625:Embryo, Nonmammalian / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D017403:In Situ Hybridization; D015347:RNA Probes; D012333:RNA, Messenger / Q000378:metabolism; D012160:Retina / Q000196:embryology*; D017949:Retinal Cone Photoreceptor Cells / Q000196:embryology / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017299:Rod Opsins / Q000235:genetics*; D012474:Salmon / Q000196:embryology*
D015347:RNA Probes; D012333:RNA, Messenger; D017299:Rod Opsins; C095855:long-wavelength opsin; C095853:short-wavelength opsin