Age-related cone abnormalities in zebrafish with genetic lesions in sonic hedgehog.
OBJECTIVE
Sonic hedgehog (Shh) signaling is essential for photoreceptor differentiation and retinal cell survival in embryonic zebrafish. The study was conducted to determine whether adult heterozygous carriers of mutant alleles for the shh gene display retinal abnormalities.


METHODS
Retinal cryosections from young, middle-aged, and senescent wild-type and sonic-you(+/-) (syu(+/-)) zebrafish were probed with retinal cell type-specific markers. Contralateral retinal flatmounts from these fish, and from adult albino zebrafish subjected to light-induced photoreceptor damage followed by regeneration, were hybridized with blue cone opsin cRNA for quantitative analysis of the blue cone pattern. Retinal expression of shh mRNA was measured by quantitative RT-PCR.


RESULTS
Regions of cone loss and abnormal cone morphology were observed in the oldest syu(+/-) zebrafish, although no other retinal cell type was affected. This phenotype was age-related and genotype-specific. Cone distribution in the oldest syu(+/-) zebrafish was predominantly random, as assessed by measuring the short-range pattern, whereas that of wild-type fish and the younger syu(+/-) zebrafish was statistically regular. A measure of long-range pattern revealed atypical cone aggregation in the oldest syu(+/-) zebrafish. The light-treated albino zebrafish displayed random cone patterns immediately after light toxicity, but showed cone aggregation on regeneration. Retinas from the syu(+/-) fish showed reduced expression of shh mRNA compared with those of wild-type siblings.


CONCLUSIONS
The syu(+/-) zebrafish presents a model for the study of hereditary age-related cone abnormalities. The syu(+/-) retinas most likely experience progressive cone photoreceptor loss, accompanied by cone regeneration. Shh signaling may be required to maintain cone viability throughout life.
Stenkamp
Deborah L
DL
Department of Biological Sciences, University of Idaho, Moscow, Idaho 83844-3051, USA. dstenkam@uidaho.edu
Satterfield
Rosanna
R
Muhunthan
Kalyani
K
Sherpa
Tshering
T
Vihtelic
Thomas S
TS
Cameron
David A
DA
D000375:Aging / Q000502:physiology*; D000483:Alleles; D000818:Animals; D016923:Cell Death; D049109:Cell Proliferation; D019084:Fluorescent Antibody Technique, Indirect; D015870:Gene Expression / Q000502:physiology; D053823:Hedgehog Proteins / Q000235:genetics*; D017403:In Situ Hybridization; D020287:In Situ Nick-End Labeling; D008027:Light; D008856:Microscopy, Fluorescence; D009154:Mutation; D012333:RNA, Messenger / Q000378:metabolism; D011833:Radiation Injuries, Experimental / Q000209:etiology / Q000235:genetics* / Q000473:pathology; D012160:Retina / Q000528:radiation effects; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism / Q000473:pathology*; D012162:Retinal Degeneration / Q000209:etiology / Q000235:genetics* / Q000473:pathology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017299:Rod Opsins / Q000378:metabolism; D015027:Zebrafish / Q000235:genetics*; D029961:Zebrafish Proteins / Q000235:genetics*
D053823:Hedgehog Proteins; D012333:RNA, Messenger; D017299:Rod Opsins; D029961:Zebrafish Proteins; C095853:short-wavelength opsin