Nuclear galectins: Functionally redundant components in processing of pre-mRNA

We describe a novel activity for nuclear galectins-1 and -3. Data presented indicate that these galectins are required factors in the splicing of pre-messenger RNA. Addition of saccharide ligands with high affinity for galectins inhibits pre-mRNA splicing in an in vitro assay using nuclear extracts isolated from HeLa cells. Depletion of the galectins from nuclear extracts by lactose-agarose affinity chromatography results in a splicing-deficient extract whereas depletion using a control saccharide affinity matrix does not affect splicing. The splicing activity of the galectin-depleted extract can be reconstituted by the addition of either recombinant galectin-1 or -3, suggesting that galectin splicing activity is functionally redundant. We further discuss this redundancy of galectin function in splicing, the nature of potential nuclear ligands for the galectins and several possible mechanisms of galectin action in the splicing pathway.