Disparate tissue-specific expression of members of the tissue kallikrein multigene family of the rat.

To understand the regulatory diversity of the rat family of linked kallikrein genes, we have assayed the expression of family members in 20 major organs. Reverse transcription-polymerase chain reaction analysis using primers and hybridization probes specific for each of the 10 expressed kallikrein genes showed that no two family members share the same organ-specific pattern of expression. The only common site of expression for all 10 known active genes is the submandibular gland. The presence of the mRNA for at least one family member is detected in 19 of these 20 organs (liver excepted), from as few as three organs to as many as 18 for individual family members. For individual genes there can be more than a 10(5)-fold variation in mRNA levels among organs, from a limit of detection of slightly less than 1 mRNA molecule/10 cells to more than 10,000 mRNA molecules/cell. Despite high sequence conservation and close linkage, the members of this family are expressed in very different and complex patterns. A gradient of diversity of expression corresponds to the order of the genes within the kallikrein family locus.