PRSS54

PRSS54 is a testis-expressed serine protease that functions in acrosome biogenesis and sperm head morphogenesis (PMID:35863763). During spermiogenesis it localizes to the acrosomal granule and subsequently extends along the inner acrosomal membrane, persisting in the acrosome region of mature sperm (PMID:35863763). Loss of PRSS54 in mice causes male subfertility with characteristic acrosome ultrastructural defects—unfused vacuoles, detached and eccentrically positioned acrosomal granules, and asymmetrical nuclear elongation—together with impaired sperm-zona penetration, phenotypes reversed by a Prss54 transgene (PMID:35863763). Mechanistically, PRSS54 physically associates with the acrosomal proteins ZPBP1, ZPBP2, ACRBP, and ZP3R and is required for their proper spatial distribution without altering their abundance, linking it to organization of the acrosomal compartment rather than to partner protein stability (PMID:35863763). PRSS54 also modulates the threshold for the acrosome reaction, as its loss renders sperm hypersensitive to acrosome reaction inducers (PMID:35863763). The protein is proteolytically processed from ~50 kDa in testis to ~42 kDa in mature sperm during sperm maturation (PMID:35863763), a maturation step that depends on the epididymal binding partner SPEM2 (PMID:38421455).

1. 2020 Medium

   An initial test of whether PRSS54 is individually required for male fertility found it dispensable, framing the open question of whether the gene has a subtle or redundant role detectable only with finer analysis.

   Evidence CRISPR/Cas9 knockout with fertility testing, histology, and sperm morphology in mice

   PMID:31403672

   Open questions at the time

   • Standard fertility readouts may miss subfertility or ultrastructural defects
   • No molecular or interaction data on PRSS54 function
2. 2022 High

   Detailed knockout and rescue analysis established that PRSS54 is functionally required for normal acrosome biogenesis and sperm head shaping, resolving its cellular role beyond the earlier dispensability claim.

   Evidence CRISPR/Cas9 knockout, Prss54 transgene rescue, TEM ultrastructure, and fertility/sperm-zona penetration assays in mice

   PMID:35863763

   Open questions at the time

   • Protease catalytic activity and physiological substrates not directly demonstrated
   • Apparent contradiction with the 2020 dispensability finding not mechanistically reconciled
3. 2022 Medium

   Localization across spermiogenesis defined where PRSS54 acts—the acrosomal granule and inner acrosomal membrane—connecting its subcellular position to the granule-positioning phenotype.

   Evidence Immunofluorescence and transmission electron microscopy in spermatids and mature sperm

   PMID:35863763

   Open questions at the time

   • Mechanism targeting PRSS54 to the acrosomal granule unknown
   • Dynamics of membrane extension not resolved
4. 2022 Medium

   Co-IP and knockout redistribution analysis identified the acrosomal protein partners of PRSS54 and showed it organizes their distribution, indicating a scaffolding/organizing role within the acrosome.

   Evidence Co-immunoprecipitation plus immunofluorescence/Western blot of ZPBP1, ZPBP2, ACRBP, ZP3R in Prss54-/- mice

   PMID:35863763

   Open questions at the time

   • Direct versus indirect nature of each interaction not dissected
   • Whether partners are proteolytic substrates of PRSS54 untested
5. 2022 Medium

   Acrosome reaction induction assays showed PRSS54 sets the threshold for the acrosome reaction, linking its structural role to a functional checkpoint in fertilization.

   Evidence Acrosome reaction induction assays in Prss54-/- versus control sperm

   PMID:35863763

   Open questions at the time

   • Molecular basis of threshold modulation unknown
   • Single functional assay, single lab
6. 2022 Medium

   Immunoblot comparison of testis versus sperm extracts revealed maturation-associated proteolytic processing of PRSS54, raising the question of what enzyme drives the cleavage.

   Evidence Western blot of testis (~50 kDa) versus mature sperm (~42 kDa) extracts

   PMID:35863763

   Open questions at the time

   • No direct cleavage assay; processing inferred from size shift
   • Cleavage site and responsible protease not defined here
7. 2024 Medium

   Identification of SPEM2 as a binding partner required for PRSS54 processing placed PRSS54 downstream of an epididymal maturation pathway.

   Evidence Co-immunoprecipitation and Western blot of PRSS54 in Spem2-/- epididymal sperm

   PMID:38421455

   Open questions at the time

   • Whether SPEM2 acts directly or recruits another protease unknown
   • Functional consequence of impaired processing for fertility not quantified here
8. 2024 Low

   Epigenetic drug experiments showed PRSS54 expression is silenced in somatic cells by DNA methylation and histone deacetylation, characterizing it as a cancer-testis-type gene.

   Evidence qRT-PCR in HCT116 and Caco-2 colon cancer lines after 5-aza-2'-deoxycytidine and trichostatin A treatment

   PMID:39208330

   Open questions at the time

   • Single method (qPCR), no protein-level confirmation
   • No functional role in somatic or cancer cells established

• The catalytic activity and physiological substrates of PRSS54 as a serine protease remain undefined, leaving open whether its acrosomal functions depend on proteolysis or on non-catalytic organization.
• No demonstrated enzymatic activity or substrate
• Catalytic-dead rescue not reported
• Direct cleavage site mapping absent