Alternative splicing in the brain of mice and rats generates transferrin transcripts lacking, as in humans, the signal peptide sequence

Transferrin (Tf), the iron-transport protein of vertebrate serum, is mainly synthesized in hepatocytes but is also found in other cell-types including oligodendrocytes. Our laboratory has characterized in a human oligodendrial cell line the presence of a new Tf transcript containing an alternative exon 1b replacing the classical exon 1 and conducting to the elimination of the signal peptide sequence. In this manuscript, we show by RT-PCR and 5'-RACE experiments that alternative transcripts also exist in mouse and rat and are found in brain mRNA preparations. Mouse alternative first exon is homologous to human exon 1b while rat Tf gene was found to use a new first exon named 1c. In all species, the alternative transcript does not contain the signal peptide sequence and possibly encode for a Tf protein devoid of signal peptide showing that this phenomenon is not restricted to human gene. We also present genomic sequence data from the previously unknown 5' genomic rat region, which allowed the alignment of the alternative exons 1 in the three species.