Collagen IV mRNA expression during development of the mouse retina: an in situ hybridization study

During development of the nervous system, neuronal migration and axonal growth depend on specific interactions with molecules in the extracellular matrix. In a recent study of laminin expression, it was shown that laminin B1 mRNA was expressed by both nonneural cells and the retinal ganglion cells during development of the mouse retina. Because collagen IV is associated with laminin in basement membranes, this report examined whether collagen IV mRNA also is expressed by neurons and nonneural cells during retinal development.

Collagen IV was localized by immunocytochemistry, whereas the sites of collagen IV mRNA synthesis were identified by in situ hybridization.

Collagen IV immunostaining was detected at embryonic day 12 (E-12), the earliest stage examined. At E-12 and E-15, collagen was found in the lens, the embryonic (hyaloid) blood vessels, and the internal limiting membrane (ILM) of the retina. At E-17, immunostaining was reduced in the ILM, whereas the lens and hyaloid were strongly stained. Collagen was barely detected in the ILM in postnatal retinas. In the in situ hybridization experiments, at E-12, collagen IV mRNA was found in the lens and the hyaloid vessels. Only sparsely labeled cells were present in the retina. After E-17, the density of labeling in these structures decreased dramatically. Collagen IV mRNA was not found in the retina at any stage in development or in the adult. Northern blot analysis showed that a 6 Kb collagen IV transcript was present in the eye.

These findings establish that high levels of collagen IV are present at the ILM only during early development (E-12 to E-17), when most axonal growth occurs. Retinal collagen IV is possibly derived from nonretinal sources, such as the lens, or more likely from the hyaloid vessels.