The dynamics of
retinal embryogenesis have been well characterized previously in terms of cell proliferation, genesis and migration, whereas overall cell type differentiation within the
retinal layers has been less thoroughly explored. In the present study, phenotypical differentiation of all 7 major
retinal cell types was examined in the developing porcine retina using one cell-specific immunohistochemical marker per cell type. At the end of the first trimester at
E39 (39 days after gestation), neurofilament labeled
ganglion cells,
recoverin labeled photoreceptors,
vimentin labeled Müller cells and
synaptophysin labeled presynaptic vesicles were found.
Rhodopsin labeled rod photoreceptors were present at E60, whereas cone
transducin labeled cone photoreceptors were not seen until E99. Differentiation of inner nuclear cells coincided with the appearance of the
retinal layers at E70-E99 with the presence of
parvalbumin labeled amacrine cells,
calbindin labeled horizontal cells and PKC labeled rod bipolar cells. At postnatal day 4, all
retinal subtypes except for cone photoreceptors displayed a labeling pattern corresponding to the one found in the adult porcine retina. The immunohistochemical labeling pattern suggests that phenotypic differentiation of the 7 principal
retinal cell types in the porcine retina follows a central-to-peripheral spatio-temporal gradient similar to the one reported for cell proliferation and genesis. Differentiation of the non-laminated
retinal cell mass appears to be initiated at its outer and inner margins and progresses inwards, a process which ends in the formation of the characteristic plexiform and nuclear layers. The dynamics of
retinal cell type differentiation are of interest from a
biological standpoint and are also important for therapeutical strategies in
retinal degenerative disease.