Molecular cloning and characterization of cDNA encoding mouse cytokeratin No. 19

We have isolated cDNA clones encoding the mouse cytokeratin No. 19 (Ck19) from an intestinal cDNA library using synthetic oligodeoxyribonucleotides as probes. We obtained four independent clones, which correspond to about 1.4-kb of ck19 cDNA. Nucleotide sequence analysis revealed that these cDNAs encode a protein of 44 541 Da composed of 403 amino acids (aa). The deduced aa sequence defines an α-helical central domain, and suggests that the protein lacks a C-terminal non-α-helical tail segment, characteristic of the human and bovine 40-kDa keratins (Ck19). The overall aa identity between mouse Ck19 and human and bovine Ck19 is very high, 82.7% and 82.4%, respectively. The coil-forming central domain of mouse Ck19 has 45-65% similarity to other type-I Ck polypeptides, while it displays only 20-30% similarity to type-II Ck polypeptides. Northern blot analysis showed that mouse ck19 mRNA is strongly expressed in adult intestine, stomach and uterus. Interestingly, it is expressed in a placental cell line and a retinoic acid-treated mouse teratocarcinoma cell line (F9), but not in a parietal yolk sac endoderm-like cell Une (PYS-2). This pattern of expression is very similar to that for the mouse gene encoding extra-embryonic endodermal cytoskeletal protein C (EndoC), suggesting they may be the same.