The rod photoreceptor pattern is set at the optic vesicle stage and requires spatially restricted cVax expression.
How and when positional identities in the neural retina are established have been addressed primarily with respect to the topographic projections of retinal ganglion cells onto their targets in the brain. Although retinotectal map formation is a prominent manifestation of retinal patterning, it is not the only one. Photoreceptor subtypes are arranged in distinct, species-specific patterns. The mechanisms used to establish photoreceptor patterns have been relatively unexplored at the mechanistic level. We performed ablations of the eye anlage in chickens and found that removal of the anterior or dorsal optic vesicle caused loss of the area centralis, which is a rod-free central area of the retina, and severely disorganized other aspects of the rod pattern. These observations indicate that the anteroposterior and dorsoventral distribution of rods is determined by the optic vesicle stage. To investigate the molecular mechanisms involved, the rod distribution was analyzed after viral misexpression of several patterning genes that were previously shown to be important in positional specification of retinal ganglion cells. Ectopic expression of FoxG1, SOHo1,or GH6 transcription factors expressed in the anterior optic vesicle and/or optic cup, respectively, did not affect the rod pattern. This pattern therefore appears to be specified by an activity acting before, or in parallel with, these factors. In contrast, misexpression of the ventrally restricted transcription factor, cVax, severely disturbed the rod pattern.
Schulte
Dorothea
D
Department of Genetics and Howard Hughes Medical Institute, Harvard Medical School, Boston, Massachusetts 02115, USA. schulte@mpih-frankfurt.mpg.de
Peters
Maureen A
MA
Sen
Jonaki
J
Cepko
Constance L
CL
D000818:Animals; D030161:Avian Proteins / Q000378:metabolism* / Q000502:physiology; D019521:Body Patterning; D002642:Chick Embryo; D003714:Denervation / Q000379:methods; D051858:Forkhead Transcription Factors / Q000502:physiology; D015870:Gene Expression / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D018398:Homeodomain Proteins / Q000378:metabolism*; D017403:In Situ Hybridization / Q000379:methods; D009419:Nerve Tissue Proteins / Q000502:physiology; D036121:Receptor, EphA3 / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000196:embryology / Q000378:metabolism*
D030161:Avian Proteins; D051858:Forkhead Transcription Factors; D018398:Homeodomain Proteins; D009419:Nerve Tissue Proteins; C085723:SOHO-1 protein, Gallus gallus; C402296:Vax protein, chicken; D036121:Receptor, EphA3