Tissue specificity of a new splice form of the human lysyl hydroxylase 2 gene.

In this study we present the first report of alternative RNA splicing in a gene for lysyl hydroxylase (LH) in a normal population. This splicing event, which we have observed in the LH2 gene, appears to be tissue specific. The LH2 isoform was recently cloned and sequenced from a human kidney cDNA library and predicted to encode a 737 amino acid protein. In the present study, we have isolated a cDNA for LH2 from human skin fibroblasts that codes for a protein of 758 amino acids, of which 21 amino acids are encoded by a new exon. This 63-bp exon, designated exon 13A, is located between exons 13 and 14 of the originally-described LH2 gene. Amplification of cDNAs by PCR, using primers from exons 13 and 14, showed the presence of two distinct LH2 mRNA populations. A 209-bp transcript was expressed in mRNAs isolated from all tissues examined and was the only transcript expressed in skin, lung, aorta and dura, whereas in mRNAs from spleen, cartilage, liver, kidney, frontal lobe and placenta, an additional shorter 146-bp transcript was amplified. DNA sequence analysis showed that these two mRNAs resulted from the alternative splicing of exon 13A. The transcript containing exon 13A is expressed as the major LH2 form in all tissues except kidney and spleen. Analysis of genomic DNA from skin, placenta and spleen showed that both transcripts were generated from the same LH2 gene. Both upstream (intron 13) and downstream (intron 13A) sequences bordering exon 13A had normal consensus sequences for the acceptor (ag) and donor (gt) splice sites. Preliminary studies indicated that only single transcripts which included exon 13A were amplified from normal fetal skin at different stages of gestation. This suggests that although exon 13A is variably expressed in different tissues, this alternative splicing event is not developmentally regulated.