EXPRESSION OF HUMAN MYOMETRIAL G-ALPHA(S) MESSENGER-RIBONUCLEIC-ACID TRANSCRIPT DURING PREGNANCY AND LABOR - INVOLVEMENT OF ALTERNATIVE SPLICING PATHWAYS

We have shown previously that expression of 46 and 54 kDa human myomet rial G alpha(s) protein isoforms is increased during gestation and the n subsequently decreased during labour. These proteins appear to be co ded for by G alpha(s)-Small (with a serine residue at position 72) and G alpha(s)-Large (with a serine residue at position 87) mRNA splice v ariants respectively. In the study presented here we have used a G alp ha(s) cDNA template to generate [P-32]cytidine cRNA riboprobes for use in RNase protection assays, so as to measure total myometrial G alpha (s) mRNA levels in relation to the pattern of expression of G alpha(s) mRNA splice variants during pregnancy and labour. We report that tota l levels of human myometrial G alpha(s) mRNA remain similar in non-pre gnant and pregnant women but are substantially reduced during parturit ion. Our data also provide strong evidence that alternative splicing o f G alpha(s) precursor mRNA has a primary role in regulating expressio n of G alpha(s) protein isoforms during pregnancy and labour. The addi tional serine codon in G alpha(s) pregnancy involves a switch in alter native splicing pathways. We speculate that this switch may be due to a change in specificity of splicing factors that are modulated during pregnancy and labour.