Comparative studies on the expression patterns of three troponin T genes during mouse development

In vertebrates, three troponin T (TnT) genes, cardiac TnT (cTnT), skeletal muscle fast-twitch TnT (fTnT), and slow-twitch TnT (sTnT), have evolved for the regulation of striated muscle contraction. To understand the mechanism for muscle fiber-specific expression of the TnT genes, we compared their e xpression patterns during mouse development. Our data revealed that the TnT expression in the developing embryo was not as restricted as that in the a dult. In addition to a strong expression in the developing heart beginning at day 7.5 p.c (postcoitum), the cTnT transcript was detected at later stag es in some skeletal muscles, where beginning at day 11.75 p.c. the fTnT and sTnT genes were also expressed. Only sTnT but not fTnT was found transient ly in the developing heart. At day 13.5 p.c., expressions of all three gene s were detected in the developing tongue and this co-expression continued t o day 16.5 p.c. with the fTnT isoform being predominant. At this stage, ove rlapping and distinct expression patterns of both sTnT and fTnT genes were also evident in many developing skeletal muscles. These data suggest that d ifferent muscles during development undergo a complex change in TnT isoform s resulting in different contractile properties. Unexpectedly, the cTnT tra nscript was persistently found in the developing bladder, where presumably smooth muscle is present. In transgenic mice, expression of a LacZ gene dri ven by a rat cTnT promoter (-497 to +192 bp) was very similar to that of th e endogenous cTnT gene, suggesting that this promoter contained regulatory elements sufficient for the control of tissue-specific cTnT expression duri ng development. Anat Rec 263:72-84, 2001. (C) 2001 Wiley-Liss, Inc.