CHANGES IN LEVELS OF MESSENGER-RNA ENCODING MYOSIN HEAVY-CHAIN IN PORCINE TRACHEALIS DURING ONTOGENY

We determined the steady-state level of mRNA for myosin heavy chain (M HC) from airway smooth muscle during maturation in domestic swine. Tis sues were excised, and airway smooth muscle was dissected from three n eonatal (NEO), three 2-wk-old swine (2ws), three 10-wk-old swine (10ws ), and three adult swine. Total RNA was isolated, fractionated, and tr ansferred to a nitrocellulose membrane (Northern blot). A single-stran ded oligonucleotide of 63-nt was synthesized corresponding to the 3' c oding region of the chicken gizzard MHC cDNA. This region appeared to be highly conserved (92% nucleotide sequence homology with the corresp onding portion of rabbit uterine smooth muscle MHC cDNA). Northern blo ts, which were loaded with equivalent quantities of total RNA, were pr obed with gammaP-32-labeled synthetic oligonucleotide, and, under stri ngent washing conditions, the 5' end-labeled DNA was hybridized to a s ingle band of the expected molecular weight. The mRNA for total myosin was quantified using autoradiograms of blots, and signal intensity wa s measured as integrated areas expressed as arbitrary densitometric un its X mm (AU). The content of mRNA for MHC was substantially greater i n NEO than in more mature animals; maximal area was 1.33 +/- 0.15 AU f or NEO, 0.33 +/- 0.05 AU for 2ws, 0.30 +/- 0.04 AU for 10ws, and 0.34 +/- 0.08 AU for adult swine (P < 0.05, NEO versus 2ws, 10ws, and adult ). Rehybridization of each blot with a 28S ribosomal RNA probe confirm ed comparable total RNA loadings for all tissue samples. Since this ol igomeric probe measured total smooth muscle MHC mRNA, these results im ply that the steady-state expression of MHC mRNA is greatest in NEO an d within 2 wk of birth.