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 t o the COOH terminus of the 130-kDa myosin light chain kinase (MLCK). Teloki n 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 mR NA hybridization that telokin mRNA is restricted to the smooth muscle cell layers within adult smooth muscle tissues. In situ mRNA analysis of mouse e mbryos also revealed that telokin expression is restricted to smooth muscle tissues during embryonic development. Telokin mRNA expression was first de tected in mouse gut at embryonic day 11.5; no telokin expression was detect ed in embryonic cardiac or skeletal muscle. Expression of telokin was also found to be regulated during postnatal development of the male and female r eproductive tracts. In both uterus and vas deferens, telokin protein expres sion greatly increased between days 7 and 14 of postnatal development. The increase in telokin expression correlated with an increase in the expressio n of several other smooth muscle-restricted proteins, including smooth musc le myosin and alpha -actin.