Researchers Dr. Phil Sharp and Dr. Adrian Krainer describe alternative splicing of genes.
Phil Sharp: Many genes in our body are expressed as RNA in different cell types, a skin cell, a bone cell, a brain cell. But in one cell type, the pattern of splicing of the sense pieces together is different than the pattern in another cell type and that's called alternative splicing. So it's alternative splicing because the splicing pattern in one cell is different than the splicing pattern in another cell and therefore the proteins in those two cells are different. And that can make a great deal of difference because one protein can function, splice in one pattern in one cell one way and then another spliced differently in another way. So, you know, if you're designing drugs or you're looking at functionality of mutations they can differ due to this alternative splicing between different cells.
Adrian Krainer: Alternative splicing means that the splicing machinery selects certain exons or parts of certain exons differently in a proportion of the molecules that it splices. So it's a way to take a gene and from its primary transcript, generate two or more mRNAs that can encode two or more proteins.
The splicing machinery has a choice. It sees this string of exons and it chooses what to join to what. It isn't always product A or product B, you could have some proportion of the molecules choose pathway A and the rest choose pathway B and that is the case with SMN2. If it were to completely skip exon 7, that maybe a lethal change in the absences of SMN1. In reality, it makes some full length protein.
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