Alternative splicing (AS) is a widespread mechanism with an important role in increasing transcriptome and proteome diversity by generating multiple different products from the same gene. Evolutionary studies of AS have focused primarily on the conservation of alternatively spliced sequences or of the AS pattern of those sequences itself. Less is known about the evolution of the regulation of AS, but several studies, working from different perspectives, have recently made significant progress. Here, we categorize the different levels of AS evolution, (...) and summarize the studies on evolution of AS regulation, which point to a high level of evolutionary conservation of the regulation of AS events conserved between related species. This suggests that the quantitative regulation of AS is an intrinsic part of AS function. We discuss the potential role of changes in developmental regulation of AS as an additional layer in complex gene regulatory networks and in the emergence of genetic novelties. (shrink)

The creeping vole Microtus oregoni exhibits remarkably transformed sex chromosome biology, with complete chromosome drive/drag, X‐Y fusions, sex reversed X complements, biased X inactivation, and X chromosome degradation. Beginning with a selfish X chromosome, I propose a series of adaptations leading to this system, each compensating for deleterious consequences of the preceding adaptation: (1) YY embryonic inviability favored evolution of a selfish feminizing X chromosome; (2) the consequent Y chromosome transmission disadvantage favored X‐Y fusion (“XP”); (3) Xist‐based silencing of Y‐derived (...) XP genes favored a second X‐Y fusion (“XM”); (4) X chromosome dosage‐related costs in XPXM males favored the evolution of XM loss during spermatogenesis; (5) X chromosomal dosage‐related costs in XM0 females favored the evolution of XM drive during oogenesis; and (6) degradation of the non‐recombining XP favored the evolution of biased X chromosome inactivation. I discuss recurrent rodent sex chromosome transformation, and selfish genes as a constructive force in evolution. (shrink)