Calpain3 expression during human cardiogenesis.

Transcripts of calpain3, the gene involved in limb girdle muscular dystrophy type 2A, appear in organs other than the skeletal muscle during human development, the first of which being the early embryonic heart. We examined more precisely the spatio-temporal transcription pattern of calpain3 during human cardiogenesis and the appearance of its protein in fetal tissues, and correlated it to titin expression. Different events of the heart's maturation can be recognized: (i) the presence of titin RNA or protein constitute very precocious developmental cardiac markers appearing before the fusion of the two lateral endocardial tubes; (ii) the disappearance of calpain3 RNA from the ventricular compartment later in the embryonic heart. Finally, although calpain3 transcripts are present in the heart, the corresponding protein is not detected elsewhere than in skeletal muscle.