Lineage specific evolutionary events on SFTPB gene: Alu recombination-mediated deletion (ARMD), exonization, and alternative splicing events.

SFTPB gene encoding pulmonary surfactant protein has been investigated to have transcript variants related with transposable elements (TEs). To investigate the alternative splicing event on SFTPB gene, various primate samples (tissue RNA and genomic DNA) were used. Two different transcript variants (T1-2 and T2-2) were newly identified by RT-PCR analysis. T1-1,-2 and T2-1,-2 are TE-related and original transcripts, respectively. T1-1 transcript was investigated to be a lung and human specific alternative transcript. T2-1 transcript shows dominant expression pattern in lung tissues. T1-related TEs (LTR7B and AluSx) were investigated by genomic PCR and sequencing procedure of different primate genomic DNAs. Sequencing analysis indicated that they had been integrated into our common ancestor genome before the divergence of simian and prosimian and Alu recombination-mediated deletion (ARMD) event had been occurred on our common ancestor genome after the divergence of New World monkeys and Old World monkeys in SFTPB gene 3' UTR region. Taken together, integration event of LTR7B and AluSx on SFTPB gene seem to cause lineage specific events via general exonization event (New World monkeys and prosimian), ARMD event (Old World monkeys and hominoids), and alternative splicing (human) during the primate evolution.