A gene expression profile of human corneal epithelium and the isolation of human keratin 12 cDNA.

PURPOSE

To describe the quantitative and qualitative aspects of gene expression in human corneal epithelium and to discover novel cornea-specific genes.

METHODS

A 3'-directed cDNA library was constructed with messenger RNA prepared from normal human corneal epithelial cells, and inserts in 1069 randomly chosen clones were sequenced. These sequences were compared with each other to determine the frequency of appearance and were searched against GenBank for identification. The resultant expression profile, a list of gene species and their recurrences, reflected the composition of mRNA in the cornea. Recurrently appearing sequences, representing abundant transcripts, were compared with sequences in expression profiles obtained from seven other tissues and from those in dbEST to discover cornea-specific genes.

RESULTS

The expression profile of human corneal epithelium showed that the most abundant transcript in this tissue was that for apolipoprotein J. Altogether 62 genes were suggested to be very active, including calcyclin, alpha-enolase, keratin 3, connexin 43, and 12 novel genes. The expression of four of these 12 novel genes seemed to be limited to cornea because they were not found in seven other expression profiles nor in dbEST. Full-length cDNA corresponding to one of these (GS8025), isolated from a separately made cDNA library, contained open reading frame highly homologous to mouse keratin 12, which is known to be cornea specific.

CONCLUSIONS

An expression profile of corneal epithelium provides probes to monitor physiological and pathologic conditions of this tissue in terms of gene expression. Furthermore, by comparing this profile with those of other tissues, probes to isolate genes uniquely transcribed in corneal epithelium are determined. These genes are assumed to carry unique functions for this tissue and are candidate genes for inherited diseases that manifest only in cornea. As an example, human cornea-specific keratin was isolated, and partial cDNA sequences for three more cornea-specific genes were presented.