Distinct roles of Haspin in stem cell division and male gametogenesis

The atypical protein kinase Haspin phosphorylates Histone H3 at threonine-3 (H3T3ph) during mitosis. H3T3ph creates a docking site for the Chromosomal Passenger Complex at the inner centromere, enabling correction of erratic microtubule-chromosome contacts and preventing chromosome mis-segregation. Surprisingly, Haspin knockout in the mouse does not cause developmental defects, except for testicular anomalies. Therefore, the physiological role of this kinase and the mechanistic significance of H3T3ph are in question. We show here that mouse embryonic stem cells that lack or overexpress Haspin are prone to chromosome misalignment. However, the cell population as a whole maintains the ability to expand and differentiate into multiple lineages. Although not essential for pluripotency, Haspin affects the expression of several testis-specific genes. Furthermore, the H3T3ph mark is detected in under-condensed chromatin domains of haploid spermatids, in cis with lysine/arginine methylation marks. We propose that Haspin controls a compound phospho-methyl switch and regulates testis-specific transcription. RNA sequence analysis of Stem cells lacking or over-expressing Haspin. 3 biological replicates were used for each case