Cone differentiation with no photopigment coexpression.
OBJECTIVE
To decide whether the transitory coexpression of cone visual pigments described in the developing rat and gerbil retina is a universal feature of dichromatic mammalian species.


METHODS
The rabbit, a species widely used in eye research, was selected for the study and a search made for the presence of cones that bound more than one cone antibody during the first postnatal week. To plot the densities of individual cone types and to colocalize the two visual pigments, immunocytochemistry on retinal wholemounts and consecutive tangential sections, respectively, were used.


RESULTS
The sequence in which the visual pigments began to be expressed was the same as that observed in other mammals: first, rhodopsin; second, blue pigment; and last, green pigment. The striking increase in blue cone density numbers observed in the rat, however, did not occur in the rabbit. Instead, some days after the first blue cones appeared, the green cones also started to express their visual pigment, and this cone type soon outnumbered the blue cones. Within the limits of the immunocytochemical method, it was established that unlike the developing rat, the presence of double-labeled cones was not a character of the rabbit retina.


CONCLUSIONS
Visual pigment coexpression is an interesting phenomenon of retinal development, however, it is not the exclusive scenario of photoreceptor differentiation. Each species must be carefully studied before deciding whether its retinal cones synthesize both pigments during retinal development.
Szepessy
Z
Z
Department of Human Morphology and Developmental Biology, Semmelweis University, Budapest, Hungary.
Lukáts
A
A
Fekete
T
T
Barsi
A
A
Röhlich
P
P
Szél
A
A
D000818:Animals; D000831:Animals, Newborn; D002452:Cell Count; D002454:Cell Differentiation / Q000502:physiology*; D007124:Immunoenzyme Techniques; D011817:Rabbits; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology* / Q000378:metabolism; D012168:Retinal Pigments / Q000378:metabolism*
D012168:Retinal Pigments