The mouse keratin 6 isoforms are differentially expressed in the hair follicle, footpad, tongue and activated epidermis

Keratin 6 (K6) is expressed constitutively in a variety of internal stratif ied epithelia as well as in palmoplantar epidermis and in specialized cells of the hair follicle, K6 expression can also be induced by hyperproliferat ive conditions as in wound healing or by conditions that perturb normal ker atinocyte function. The functional significance of the expression of K6 on keratinocyte biology under these disparate conditions is not known. Here we report on the characterization of two isoforms of mouse K6 that are encode d by separate genes. The two genes (denoted K6a and K6b) are linked, have t he same orientation and are actively transcribed. Sequence analysis reveale d, that although they encode almost identical products, they have distinctl y different regulatory regions, suggesting that the two K6 genes would be d ifferentially expressed. In an attempt to define the expression characteris tics of the K6 isoforms, we produced transgenic mice with each gene after m odifying the C-terminal sequences to enable detection of the transgenic pro teins with specific antibodies. The constitutive expression of the K6a tran sgene paralleled that of the endogenous genes in all K6 expressing tissues, except in the tongue. The K6b transgene was also expressed in these tissue s but, in contrast to K6a, was only expressed in suprabasal cells. Both K6 transgenes were also induced in the interfollicular epidermis in response t o phorbol esters, with K6a induced in all layers of the treated epidermis, while K6b was expressed only in suprabasal cells. These studies suggest tha t the K6 isoforms have overlapping yet distinct expression profiles.