BRCA1 is proposed to be a tumor suppressor gene. To explore the biological function of BRCA1, a partial deletion (amino acids 300-361) of mouse Brca1 exon 11 was introduced into the genome of embryonic stem (ES) cells by homologous recombination. Mice carrying one mutated allele of Brca1 appear normal and are fertile up to 10 months of age without any sign of illness. However, no viable progeny homozygous for the Brca1 mutant allele were obtained. Detailed analysis of large numbers of embryos at different stages of development indicated that the homozygous mutant concepti are severely retarded in growth as early as embryonic day 4.5 (E4.5) and are resorbed completely by E8.5. Although the homozygotes at E5.5-E6.5 are able to synthesize DNA and display distinguishable embryonic and extraembryonic structures, they fail to differentiate and form egg cylinders. Consequently, they were unable to form primitive streaks and undergo gastrulation. Consistent with these in vivo results, blastocysts homozygous for mutated Brca1 alleles are at a considerable disadvantage when grown in vitro. These observations suggest that Brca1 has an important role in the early development of mouse embryos.

Lumican regulates collagenous matrix assembly as a keratan sulfate proteoglycan in the cornea and is also present in the connective tissues of other organs and embryonic corneal stroma as a glycoprotein. In normal unwounded cornea, lumican is expressed by stromal keratocytes. Our data show that injured mouse corneal epithelium ectopically and transiently expresses lumican during the early phase of wound healing, suggesting a potential lumican functionality unrelated to regulation of collagen fibrillogenesis,e.g. modulation of epithelial cell adhesion or migration. An anti-lumican antibody was found to retard corneal epithelial wound healing in cultured mouse eyes. Healing of a corneal epithelial injury in Lum ^−/− mice was significantly delayed compared with Lum ^+/− mice. These observations indicate that lumican expressed in injured epithelium may modulate cell behavior such as adhesion or migration, thus contributing to corneal epithelial wound healing.

Keratocan (Kera) is a cornea-specific keratan sulfate proteoglycan (KSPG) in the adult vertebrate eye. It belongs to the small leucine-rich proteoglycan (SLRP) gene family and is one of the major components of extracellular KSPG in the vertebrate corneal stroma. The Kera gene is expressed in ocular surface tissues including cornea and eyelids during morphogenesis. Corneal KSPGs play a pivotal role in matrix assembly, which is accountable for corneal transparency. In humans, mutations of the KERA gene are associated with cornea plana (CNA2) that manifests decreases in vision acuity due to the flattened forward convex curvature of cornea. To investigate the biological role of the Kera gene and to establish an animal model for corneal plana, we generated Kera knockout mice via gene targeting. Northern and Western blotting and immunohistochemical analysis showed that no Kera mRNA or keratocan protein was detected in the Kera^–/– cornea. The expression levels of other SLRP members including lumican, decorin, and fibromodulin were not altered in the Kera^–/– cornea as compared with that of the wild-type littermates. Mice lacking keratocan have normal corneal transparency at the age of 12 months. However, they have a thinner corneal stroma and a narrower cornea-iris angle of the anterior segment in comparison to the wild-type littermates. As demonstrated by transmission electron microscopy, Kera^–/– mice have larger stromal fibril diameters and less organized packing of collagen fibrils in stroma than those of wild type. Taken together, our results showed that ablation of the Kera gene resulted in subtle structural alterations of collagenous matrix and did not perturb the expression of other SLRPs in cornea. Keratocan thus plays a unique role in maintaining the appropriate corneal shape to ensure normal vision.