Question

Eukaryotic mRNAs can undergo alternative splicing. This is often used as a way to generate unique products in different cells of a multicellular organism. Let's assume that for a particular mRNA, exon 2 has normal 5' and 3' splice junctions, meaning that this exon will normally be recognized by the spliceosome for inclusion into the mature mRNA. Give me an explanation for how a different type of cell could block the inclusion of exon 2, so that it would not appear in the mature mRNA. 

Answer 1

Alternative splicing: ALternative usage of exons to generate multiple mature transcripts.
It increases the repertoire of transcriptome and proteome without affecting the genome i.e. A single gene can produce multiple mature transcripts and proteins.

Let us assume that a given primary transcript contains 5 exons.
The general splicing machinery includes all the exons in the mature transcript.

Alternative splicing can join the 3'-splice junction of exon-1 with the 5'-splice site of exon-3 thereby joining exon-1 with exon-3. This leads to the skipping of exon-2 in the mature transcript.
See the image.

Exon 1 Exon 2 Exon 3 Exon 4 Exon 5 Retention of all exons Exclusion of exon-2 Alternate splicing Exclusion of exon-2 and 4 Intron

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