Localization of cytosolic aldehyde dehydrogenase in the developing chick retina: in situ hybridization and immunohistochemical analyses.

Cytosolic aldehyde dehydrogenase (ALDH) mRNA is present at high levels in the undifferentiated chick retina. Tissue maturation is accompanied by a 20-25x decrease in transcript levels. To determine the spatial and temporal distribution pattern of the ALDH transcript and its encoded protein in the developing retina, in situ hybridization and immunohistochemical analyses were carried out using chick embryos at different stages of development. The ALDH transcript and protein were detected at the earliest stage tested, in the inner layer of the optic cup of stage 14 (day 2) embryos. Both the ALDH transcript and protein were found in the dorsal retina of chick embryos from stage 18 (day 3) to day 16 of incubation. Accumulation of the ALDH protein in the neurites of ganglion cells could readily be detected at early developmental stages. Staining of this ganglion fiber layer was strong in the dorsal retina and could be followed up to and into the optic nerve. By day 11, ALDH mRNA was located primarily in the ciliary margin and in the inner nuclear layer of the dorsal retina. In addition to these areas, the ALDH protein was also found in the inner plexiform and optic nerve fiber layers. These results suggest that environmental or transcriptional factors involved in the regulation of the ALDH gene are restricted to the dorsal retina at early developmental stages and that there is a requirement for the compartmentalization of the ALDH transcript/protein in the undifferentiated chick retina.