C. Berezowsky et J. Bag, DEVELOPMENTALLY REGULATED TROPONIN-C MESSENGER-RNAS OF CHICKEN SKELETAL-MUSCLE, Biochemistry and cell biology, 70(2), 1992, pp. 156-165
Fast and slow/cardiac troponin C (TnC) are the two different isoforms
of TnC. Expression of these isoforms is developmentally regulated in v
ertebrate skeletal muscle. Therefore, in our studies, the pattern of t
heir expression was analyzed by determining the steady-state levels of
both TnC mRNAs. It was also examined if mRNAs for both isoforms of Tn
C were efficiently translated during chicken skeletal muscle developme
nt. We have used different methods to determine the steady-state level
s of TnC mRNAs. First, probes specific for the fast and slow TnC mRNAs
were developed using a 390 base pair (bp) and a 255 bp long fragment,
of the full-length chicken fast and slow TnC cDNA clones, respectivel
y. Our analyses using RNA-blot technique showed that fast TnC mRNA was
the predominant isoform in embryonic chicken skeletal muscle. Followi
ng hatching, a significant amount of slow TnC mRNA began to accumulate
in the skeletal (pectoralis) muscle. At 43 weeks posthatching, the sl
ow TnC mRNA was nearly as abundant as the fast isoform. Furthermore, a
majority of both slow and fast TnC mRNAs was found to be translationa
lly active. A second method allowed a more reliable measure of the rel
ative abundance of slow and fast TnC mRNAs in chicken skeletal muscle.
We used a common highly conserved 18-nucleotide-long sequence towards
the 5'-end of these mRNAs to perform primer extension analysis of bot
h mRNAs in a single reaction. The result of these analyses confirmed t
he predominance of fast TnC mRNA in the embryonic skeletal muscle, whi
le significant accumulation of slow TnC mRNA was observed in chicken b
reast (pectoralis) muscle following hatching. In addition to primer ex
tension analysis, polymerase chain reaction was used to amplify the fa
st and slow TnC mRNAs from cardiac and skeletal muscle. Analysis of th
e amplified products demonstrated the presence of significant amounts
of slow TnC mRNA in the adult skeletal muscle.