Abstract
Purpose: :
We examined the generation of rod and cone photoreceptors from retinal progenitors in the developing outer nuclear layer (ONL) of the pig retina.
Methods: :
Retinas were removed from pigs at various development ages, and retinal development was followed by H&E staining of retinal sections. Retinal progenitors and rod and cone photoreceptors progenitors were followed by immunostaining of retina sections.
Results: :
We identify a population of cone progenitors which are specified and in place in the outer two rows of the developing swine retina before mid-gestation. These cells are marked by Islet1 and recoverin, and they appear before NRL+ rods are specified from PAX6+ retinal progenitor cells. Further, we demonstrate that L/M opsin cones are generated from this population before S opsin cones.
Conclusions: :
These results provide the first evidence of a distinct population of cone progenitors, which are specified before mid-gestation. These cone progenitors do not differentiate and express opsins for 35 days, and they are distinct from the later-appearing rod progenitors. As they differentiate, the cone progenitors give rise sequentially to L/M opsin cones and the S opsin cones. The positioning of the cone progenitors in the outer retina leads to complete segregation of cones and rods in the adult with cones comprising the outer two rows of the ONL and rods all confined to the interior rows. Taken together, the results suggest differences in pathways leading to rod and cone specification in the mouse and pig.
Keywords: photoreceptors • differentiation • development