A conserved germline-specific Dsn1 alternative splice isoform supports oocyte and embryo development.

Alternative mRNA splicing can generate distinct protein isoforms to allow for the differential control of cell processes across cell types. However, alternative splice isoforms that differentially modulate distinct cell division programs have remained elusive. Here, we demonstrate that mammalian germ cells express an alternate mRNA splice isoform for the kinetochore component, DSN1, a subunit of the MIS12 complex that links the centromeres to spindle microtubules during chromosome segregation. This germline DSN1 isoform bypasses the requirement for Aurora kinase phosphorylation for its centromere localization due to the absence of a key regulatory region allowing DSN1 to display persistent centromere localization. Expression of the germline DSN1 isoform in somatic cells results in constitutive kinetochore localization, chromosome segregation errors, and growth defects, providing an explanation for its tight cell type-specific expression. Reciprocally, precisely eliminating expression of the germline DSN1 splice isoform in mouse models disrupts oocyte maturation and early embryonic divisions coupled with a reduction in fertility. Together, this work identifies a germline-specific splice isoform for a chromosome segregation component and implicates its role in mammalian fertility.