SPATA20

SPATA20 (SSP411) is a thioredoxin-domain-containing protein expressed in a stage-dependent manner restricted to round and elongated spermatids during spermiogenesis (PMID:15223837, PMID:39091129). It is required for sperm head shaping and head-tail conjunction: loss of function in mice produces male sterility with smaller testes, reduced sperm counts and motility, and aberrant manchette structure, and SPATA20 physically interacts with the manchette-associated proteasome component PSMC3, linking it to the ubiquitin-proteasome system during spermatid morphogenesis (PMID:29247744). In humans, a nonsense mutation (p.Arg207*) destabilizes the protein and causes acephalic spermatozoa syndrome, accompanied by reduced expression of the head-tail coupling factor SPATA6 (PMID:36415156). SPATA20 stability is itself controlled by the UBL7-VCP-proteasome axis, which protects it from excessive proteasomal degradation within the head-tail coupling apparatus pathway (PMID:40268954). Beyond the male germ line, SPATA20 depletion in cancer cells elevates HIF-1α protein and transcriptional activity without altering HIF-1α degradation—consistent with inhibition of de novo HIF-1α synthesis—and promotes migration and invasion in a HIF-1α-dependent manner (PMID:38455399).

1. 2004 Medium

   Established the molecular identity, domain architecture, and expression pattern of the protein, defining it as a thioredoxin-family member confined to spermatids.

   Evidence cDNA cloning, in situ hybridization, IHC, Western blot, and 3D structural modeling in rat testes

   PMID:15223837

   Open questions at the time

   • No functional assay of the predicted thioredoxin activity
   • No in vivo loss-of-function phenotype
2. 2017 High

   Demonstrated SPATA20 is essential for spermiogenesis by linking its loss to defective head shaping and manchette structure, and connected it mechanistically to the proteasome via PSMC3 binding.

   Evidence PiggyBac transposon mouse knockout with morphological phenotyping plus proteome microarray and GST pull-down

   PMID:29247744

   Open questions at the time

   • PSMC3 interaction not validated reciprocally in vivo
   • Functional consequence of the SPATA20-PSMC3 interaction for proteasome activity not defined
3. 2022 Medium

   Translated the germ-cell role to human disease, showing a loss-of-function SPATA20 variant causes acephalic spermatozoa syndrome and reduces the head-tail coupling factor SPATA6.

   Evidence Whole-exome/Sanger sequencing and Western blot in a patient with clinical phenotyping

   PMID:36415156

   Open questions at the time

   • Single patient/lab
   • Mechanistic link between SPATA20 loss and reduced SPATA6 not established
   • ICSI rescue failure unexplained mechanistically
4. 2024 Medium

   Placed SPATA20 within a defined proteostatic pathway by showing its stability depends on UBL7-mediated protection from proteasomal degradation in the head-tail coupling apparatus.

   Evidence Two-step immunoprecipitation and mass spectrometry in a UBL7 knockout mouse model

   PMID:40268954

   Open questions at the time

   • Direct UBL7-SPATA20 binding interface not mapped
   • Single lab
5. 2024 Medium

   Revealed an unexpected somatic role, implicating SPATA20 as a suppressor of HIF-1α synthesis and of cancer cell migration/invasion.

   Evidence siRNA knockdown, transcriptional reporter, migration/invasion assays, and HIF-1α inhibitor rescue in cancer cells

   PMID:38455399

   Open questions at the time

   • Proposed AKT/cap-dependent translation mechanism not confirmed by reconstitution or mutagenesis
   • Single lab

• Whether SPATA20's thioredoxin domain has catalytic redox activity and how this connects to its roles in spermatid morphogenesis and HIF-1α regulation remains unresolved.
• No demonstrated enzymatic thioredoxin activity
• No structural model of SPATA20 complexes
• Mechanism unifying germ-cell and cancer roles unknown