This paper compares corneal development in the normal and in the Mov13 mutant mouse homozygote which does not synthesize type I collagen. During the period 12–14 days of development, there is no obvious difference between cellular organization in the normal and the mutant corneas or, indeed, elsewhere in the eye. In particular, there is normal colonization of the mutant cornea by the mesenchymal cells which will form the endothelium and the fibroblasts. In the early stages of stromal deposition (less than 14 days), when relatively little collagen is normally laid down, mutant and wild-type corneas differ only in that mutant collagen fibrils are less uniform than normal ones. Later development in the Mov13 mutant cannot usually be studied because almost all mutant embryos are dead by 14 days, but we now have two homozygous embryos from a single, 16-day litter. Their stromas obviously differed from those of their normal littermates: there was markedly less collagen in the mutant cornea and the collagen that was deposited lacked orthogonal organization. Fibril morphology also differed: the diameters of fibrils in the normal corneas peaked sharply at about 20 nm, whereas the diameters of mutant fibrils were spread over the range 5–15 nm, with only a small percentage overlapping the normal distribution. These results suggest that type I collagen is of negligible importance in controlling the cellular organization of the cornea, but has a dominant role in the formation of normal 20 nm fibrils and of normal stromal organization. They also show that, as collagen production is markedly lower in the mutant than in the wild-type cornea, the production of other collagens cannot compensate in any way for the lack of type I collagen.(ABSTRACT TRUNCATED AT 250 WORDS)

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