Mlig-SKP1 Gene Is Required for Spermatogenesis in the Flatworm Macrostomum lignano

In a free-living flatworm, Macrostomum lignano, an S-phase kinase-associated protein 1 (SKP1) homologous gene was identified as enriched in proliferating cells, suggesting that it can function in the regulation of stem cells or germline cells since these are the only two types of proliferating cells in flatworms. SKP1 is a conserved protein that plays a role in ubiquitination processes as a part of the Skp1-Cullin 1-F-box (SCF) ubiquitin ligase complex. However, the exact role of Mlig-SKP1 in M. lignano was not established. Here, we demonstrate that Mlig-SKP1 is neither involved in stem cell regulation during homeostasis, nor in regeneration, but is required for spermatogenesis. Mlig-SKP1(RNAi) animals have increased testes size and decreased fertility as a result of the aberrant maturation of sperm cells. Our findings reinforce the role of ubiquitination pathways in germ cell regulation and demonstrate the conserved role of SKP1 in spermatogenesis.