A novel flatworm-specific gene family implicated in reproduction in Macrostomum lignano
Free-living flatworms, such as the planarian Schmidtea mediterranea, are extensively used as model organisms to study stem cells and regeneration. The majority of studies in planarians so far focused on broadly conserved genes. However, investigating what makes these animals different might be equally informative for understanding its biology. Here, we present a re-analysis of neoblast and germline transcriptional signatures in the flatworm M. lignano and combine it with the whole-animal electron microscopy atlas (nanotomy) as a reference platform for ultrastructural studies in M. lignano. We show that germline-enriched genes have a high fraction of flatworm-specific genes and identify Mlig-sperm1 gene as a member of a novel gene family conserved only in free-living flatworms and essential for producing healthy spermatozoa. This work demonstrates that investigation of flatworm-specific genes is crucial for understanding flatworm biology and establishes a basis for future research in this direction in M. lignano.