A GENE-EXPRESSION PROFILE OF HUMAN CORNEAL EPITHELIUM AND THE ISOLATION OF HUMAN KERATIN-12 CDNA

Purpose. To describe tile quantitative and qualitative aspects of gene expression in human corneal epithelium and to discover novel cornea-s pecific genes. Methods. A 3'-directed cDNA library was constructed wit h messenger RNA prepared from normal human corneal epithelial cells, a nd inserts in 1069 randomly chosen clones were sequenced. These sequen ces were compared with each other to determine the frequency of appear ance and were searched against GenBank for identification. The resulta nt expression profile, a list of gene species and their recurrences, r eflected the composition of mRNA in the cornea. Recurrently appearing sequences, representing abundant transcripts, were compared with seque nces in expression profiles obtained from seven other tissues and from those in dbEST to discover cornea-specific genes. Results. The expres sion profile of human corneal epithelium showed that the most abundant transcript in this tissue was that for apolipoprotein J. Altogether 6 2 genes were suggested to be vert active, including calcyclin, alpha-e nolase, keratin 3, connexin 43, and 12 novel genes. Thr expression of four of these 12 novel genes seemed to be limited to cornea because th ey were not found in seven other expression profiles nor in dbEST. Ful l-length cDNA corresponding to one of these (GS8025), isolated from a separately made cDNA Library, contained open reading frame highly homo logous to mouse keratin 12, which is known to be cornea specific. Conc lusions. An expression profile of corneal epithelium provides probes t o monitor physiological and pathologic conditions of this tissue in te rms of gene expression. Furthermore, by comparing this profile with th ose of other tissues, probes to isolate genes uniquely transcribed in corneal epithelium are determined, These genes are assumed to carry un ique functions for this tissue and are candidate genes for inherited d iseases that manifest only in cornea. As an example, human cornea-spec ific keratin was isolated, and partial cDNA sequences for three more c ornea-specific genes were presented.