EXPRESSION OF PHOSPHOLAMBAN MESSENGER-RNA DURING EARLY AVIAN MUSCLE MORPHOGENESIS IS DISTINCT FROM THAT OF ALPHA-ACTIN

We have studied the expression of phospholamban during the early devel opment of chick embryos by in situ hybridization and have compared it to that of alpha-cardiac and alpha-skeletal actin. In adult cross-stri ated muscles there is only one phospholamban gene and it is expressed exclusively in the heart and slow muscles. In the heart phospholamban transcripts were first detected at stage 14 in the region of presumpti ve ventricle and at stage 20 in the atrium. In the myotomal portion of the somites phospholamban mRNA was first detected at stage 20, which lagged behind the appearance of the alpha-actins. In the limb rudiment s all three mRNAs were barely detectable through stage 24, but increas ed by stage 28+. However, quantitative analysis of signal intensity at stage 28+ indicated that less phospholamban mRNA is present in the li mb bud than in the myotome since for phospholamban the ratio of the si gnal density in the myotome to that in the limb rudiments was about tw ice the value of the ratio determined for the alpha-actins. Northern b lot analysis of embryonic day 11 chick fast pectoralis muscle showed t hat phospholamban mRNA was not detected in vivo while alpha-cardiac ac tin mRNA was. Moreover, no phospholamban mRNA was detected in primary cultures derived from pectoralis muscle of the same age. In concert wi th previous observations that phospholamban is not detectable at stage 30-32 in wing or thigh muscle, these results suggest that phospholamb an mRNA is expressed independently of the alpha-actins in the limb bud s during early myogenesis. (C) 1993 Wiley-Liss, Inc.