DNAJC18

DNAJC18 is a type III DnaJ/HSP40 family protein implicated in germ cell maturation and cardiac development (PMID:29082339, PMID:39195995). In rat testis it is expressed in a stage-restricted manner beginning at postnatal week 4, localizing to late pachytene spermatocytes and round and elongated spermatids, where GFP-tagged protein shows cytoplasmic distribution consistent with a role in spermatid maturation (PMID:29082339). Loss-of-function of Dnajc18 in mice produces developmental cardiac structural abnormalities, and human DNAJC18 loss-of-function variants associate with altered left ventricular systolic function, establishing a requirement for the gene in cardiac homeostasis (PMID:39195995). Beyond these expression and phenotypic findings, the molecular mechanism, binding partners (including any client proteins or HSP70 partner), and biochemical activity of DNAJC18 have not been characterized in the available corpus.

1. 2017 Medium

   Whether DNAJC18 has a tissue-restricted expression pattern pointing to a specialized function was unknown; establishing germ-cell-specific, stage-dependent expression placed it in spermatid maturation.

   Evidence Northern blot, in situ hybridization, immunohistochemistry, and confocal microscopy of GFP-tagged protein in rat testis

   PMID:29082339

   Open questions at the time

   • No loss-of-function or rescue experiment to test functional requirement in spermatogenesis
   • No binding partner or client protein identified
   • Cytoplasmic localization does not define molecular activity or pathway
2. 2022 Medium

   Whether DNAJC18 has a physiological role beyond the testis was unresolved; mouse knockout and human genetic data established a requirement in cardiac structural development and function.

   Evidence Electrocardiography, echocardiography, and microcomputed tomography in single-gene-null mouse lines plus UK Biobank loss-of-function variant analysis

   PMID:39195995

   Open questions at the time

   • No molecular mechanism linking DNAJC18 to cardiac phenotype
   • No chaperone substrate or HSP70 partner demonstrated
   • Relationship between testicular and cardiac functions unexplained

• The biochemical activity of DNAJC18 as a putative HSP40 co-chaperone, its HSP70 partner, and its client proteins remain undefined.
• No reconstitution of J-domain/HSP70 stimulation
• No interactome or substrate identification
• No structural model