Telokin expression is restricted to smooth muscle tissues during mouse development.

Telokin is a 17-kDa protein with an amino acid sequence that is identical to the COOH terminus of the 130-kDa myosin light chain kinase (MLCK). Telokin mRNA is transcribed from a second promoter, located within an intron, in the 3' region of the MLCK gene. In the current study, we show by in situ mRNA hybridization that telokin mRNA is restricted to the smooth muscle cell layers within adult smooth muscle tissues. In situ mRNA analysis of mouse embryos also revealed that telokin expression is restricted to smooth muscle tissues during embryonic development. Telokin mRNA expression was first detected in mouse gut at embryonic day 11.5; no telokin expression was detected in embryonic cardiac or skeletal muscle. Expression of telokin was also found to be regulated during postnatal development of the male and female reproductive tracts. In both uterus and vas deferens, telokin protein expression greatly increased between days 7 and 14 of postnatal development. The increase in telokin expression correlated with an increase in the expression of several other smooth muscle-restricted proteins, including smooth muscle myosin and alpha-actin.