[GenBank: FJ535564], [GenBank: FJ535565], [GenBank: FJ535566], [GenBank: FJ535567] The vertebrate α-dystrobrevin gene has a complex gene structure, with multiple promoters, alternative 3' exons and alternatively spliced exons.
The number of possible isoforms can be much higher in genes with Multiple Alternative Splicing decision Sites (MASS), due to the combinatorial arrangement of multiple alternate exons (see an example of MASS gene in Figure 1B).
For example, the microphthalmia transcription factor (MITF) has well-documented function in differentiation in several distinct lineages, and has multiple alternative 5' non-coding exons driven by different promoters [ 38, 39].
Defective mRNA splicing can lead to multiple alternative transcripts including those with retained introns, cassette exons, alternate promoters/terminators, extended or truncated exons, and reduced exons.
The following classes of events are currently implemented: exon skipping, cassette exons, alternative transcript start and termination, retention of single or multiple introns, and alternative exon ends (Supplemental Figure S14).
This feature of multiple alternative splicing regions separated by constitutive exons is shared by more than a quarter of human genes (Fededa et al., 2005).
The introns flanking alternate exons in transcripts whose maturation involves multiple alternative splicing decisions were compared to those whose maturation involves a single decision.
With respect to splicing 8.3% of genes had multiple alternative transcripts, but alternative splicing by exon-skipping was very rare.
As several metazoan H2A.Zs contain a conserved intron directly following the start ATG and possess multiple alternative splice acceptors within their second exon, it will be of interest to determine whether generation of alternative splice H2A.Z variants is not unique to O. dioica.
