Hypomorphic and hypermorphic mouse models of <i>Fsip2</i> indicate its dosage-dependent roles in sperm tail and acrosome formation

ABSTRACT Loss-of-function mutations in multiple morphological abnormalities of the sperm flagella (MMAF)-associated genes lead to decreased motility and impaired male fertility. As an MMAF gene, function fibrous sheath-interacting protein 2 (FSIP2) remains largely unknown. In this work, we identified a homozygous truncating mutation FSIP2 infertile patient. Accordingly, constructed knock-in (KI) mouse model with mutation. parallel, established Fsip2 overexpression (OE) model. Remarkably, KI mice presented typical phenotype, whereas OE showed no gross anomaly except for tails increased length. Single-cell RNA sequencing testes uncovered altered expression related flagellum, acrosomal vesicle spermatid development. We confirmed at acrosome physical interaction gene Acrv1, marker. Proteomic analysis revealed changes proteins sited sheath, mitochondrial sheath vesicle. also pinpointed crucial motifs that are evolutionarily conserved species internal fertilization. Thus, work reveals dosage-dependent roles tail formation.