Extensive alternate exon usage at the 5′ end of the sheep tropoelastin gene

Several overlapping cDNA clones were isolated from a λgt10 cDNA library constructed using polyA + RNA from neonatal sheep lung. DNA sequence analysis of these cDNA recombinants revealed the complete derived amino acid sequence of sheep tropoelastin. A comparison of DNA sequences from individual sheep tropoelastin cDNA also confirmed the presence of several tropoelastin mRNA isoforms in neonatal lung tissue. Coding domains corresponding to exons 13, 14 and 33 were present in several of the sheep tropoelastin cDNA fragments but absent in others. The relative amount of alternate usage of these exons was quantitated by polymerase chain amplification. In confirmation of previous studies in other mammalian species, extensive alternate usage of exon 33 was observed in total RNA isolated from aorta, nuchal ligament and pulmonary artery from neonatal sheep. In striking contrast to all previous studies, however, exons 13 and 14 were shown to be subject to almost the same level of alternate usage as exon 33 in all three neonatal sheep tissues examined.