The gene for mouse epidermal filaggrin precursor. Its partial characterization, expression, and sequence of a repeating filaggrin unit.

Filaggrin is an important keratin intermediate filament-associated protein of terminally differentiated mammalian epidermis. Its aberrant expression has been implicated in a number of keratinizing disorders. We have isolated and sequenced a cDNA clone to mouse filaggrin, of 1.479 kilobase pairs, which represents less than 10% of the full-length mRNA estimated by Northern blot analysis to be 17 kilobases long. The cDNA clone delineates a 744-base pair repeat. This encodes a protein of 248 amino acids or 26,330 Da, which is almost identical to the known properties of mouse filaggrin in size, amino acid composition, and charge. Total mouse genomic DNA and the filaggrin gene isolated from a cosmid library were found to contain a super-stoichiometric repeat of the same size. These data support the hypothesis (Haydock, P.V., and Dale, B.A. (1986) J. Biol. Chem. 261, 12520-12525) that filaggrin is initially synthesized as a polyprotein precursor containing many tandem copies. However, our data suggest that the repeating filaggrin units of the precursor are not separated by "large linker" peptides as suggested by these authors. In situ hybridization was used to show that the filaggrin precursor mRNA is located precisely over the granular layer of the epidermis, indicating that expression of this gene is regulated at the transcriptional level as for the differentiation-specific keratin 1 protein. These probes will now permit detailed studies on the regulation of expression of the filaggrin gene.