STRC Research

STRC STRCP1 Activation Rescue

6 min read

STRC STRCP1 Activation Rescue

Hypothesis #27. Activate the endogenous STRCP1 paralog instead of editing STRC or delivering exogenous protein. STRCP1 is 100% identical to STRC at the variant locus (see STRC PE Phase 3_5 STRCP1-Aware Redesign), which has been treated purely as a problem. But if STRCP1 translates into protein, it is a native backup copy of STRC already present in every patient’s genome — including Misha’s. Flip the framing: instead of fighting the paralog, recruit it.

The reframe

Weeks of STRC work treated STRCP1 as an off-target risk that killed Prime Editing for STRC (hypothesis #7, C-tier) and demoted STRC ASO Exon Skipping (hypothesis #8, C-tier). The reasoning: STRCP1 is 100% identical at critical regions, so PE pegRNAs and ASOs hit both STRC and STRCP1 → paralog-level collateral damage.

This reasoning assumes STRCP1 is non-functional. That assumption was never tested at the protein level. The assumption rests on:

  • GENCODE biotype label transcribed_unprocessed_pseudogene
  • No published STRCP1 protein in UniProt
  • No STRCP1 disease associations

But STRC STRCP1 GTEx Expression Check found STRCP1 transcribed in all 54 GTEx tissues (TPM 0.01-2.6, peaking in cerebellum). The “silent paralog” escape path for PE/ASO was falsified by this transcription evidence. The corollary — if STRCP1 transcribes actively, does it translate? — was never pursued because the PE/ASO story was already C-tier-closed.

Why this works if STRCP1 translates

  • 100% sequence identity at critical regions means STRCP1 protein should be biochemically indistinguishable from STRC
  • Paternal 98 kb deletion and maternal c.4976A>C E1659A are both in STRC — STRCP1 would carry neither
  • Upregulating STRCP1 substitutes functional STRC without any gene therapy, any edit, any exogenous protein, any delivery problem beyond dCas9 or promoter-targeting AAV
  • Works on ANY STRC-null patient, not just Misha

Why nobody has done this

  1. Label bias. “Pseudogene” = academic write-off. Nobody runs ribosome-profiling or mass-spec on pseudogenes by default.
  2. Expression scale. STRCP1 TPM is 4-20× lower than STRC in high-STRC tissues. Even if it translates, base-level protein output might be too low — which is precisely why the hypothesis is activation, not just un-silencing. Boost transcription 4-10× via CRISPRa and STRCP1-output could reach STRC-rescue levels.
  3. No disease-association hook. DFNB16 gene therapy programs (Regeneron AAV.104, Iranfar 2026 dual-AAV, Holt lab) are all built around STRC delivery. Nobody asks “is there a paralog we could activate instead.”

The three-gate validation

Gate 1 — translation evidence (wet-lab, Holt lab)

Does STRCP1 produce protein? Options:

  • Ribosome profiling on OHC lysates (Holt lab has OHC models from STRC mouse work — may already have ribosome-profiling data)
  • Targeted mass-spec for STRCP1-unique tryptic peptides (requires STRCP1 protein sequence diverged enough from STRC; 100% identity at aa 1669-1680 target locus doesn’t preclude divergence elsewhere — full-protein alignment needed)
  • Pseudogene ORF analysis — check STRCP1 transcript for intact reading frame, absence of premature stop codons or frameshifts

Pass: at least one peptide unique to STRCP1 detected in OHC proteome, OR clean ribosome-profiling footprint over STRCP1 ORF, OR intact ORF with no premature stops.

Fail: STRCP1 has accumulated inactivating mutations that prevent translation. Hypothesis dies, no further work.

Gate 2 — activation tool design (computational + wet-lab)

If Gate 1 passes: design STRCP1 activation strategy.

  • CRISPRa (dCas9-VP64 / dCas9-VPR) at STRCP1 promoter. Needs STRCP1 promoter coordinates (chr15:~43,700,xxx based on STRC STRCP1 GTEx Expression Check) and sgRNAs specific to STRCP1 promoter, not STRC promoter. The 100 kb downstream position means promoters probably differ — leverageable for specificity.
  • Targeted demethylation (dCas9-TET1) — reverses pseudogene silencing if methylation is the primary suppression mechanism
  • Steric-block ASO on STRCP1 upstream repressor sites

Computational: sgRNA design targeting STRCP1-unique promoter region (BLAST against STRC genomic locus to confirm ≥3 mismatch discrimination in seed).

Wet-lab: HEK293 / OHC-like cell lines with CRISPRa test; measure STRCP1 mRNA and protein output.

Gate 3 — functional rescue (wet-lab, mouse model)

Cross STRC-null mouse with STRCP1-orthologous activator expressed only in OHCs. Do hair bundles form? Does ABR normalize? This is the ultimate test. 12-18 months, but cheaper than building a new AAV trial because it uses existing mouse lines.

Actually mouse biology complication: mouse STRC paralogous pseudogenes may not mirror human STRCP1 locus architecture. Human-only gate 3 via cochlear organoids or humanized mouse (xenograft or knock-in of human STRCP1 locus) — $50k-200k.

Scoring (preliminary)

  • Mechanism 2/5: speculative that STRCP1 translates; full hypothesis collapses if Gate 1 fails; but if it passes, mechanism becomes 4 (identical protein, same biology)
  • Delivery 2/5: CRISPRa AAV delivery is developed for other targets; Anc80L65 + dCas9-VP64 fits single AAV. STRCP1-specific sgRNA targeting feasibility unknown without promoter mapping
  • Misha-fit 4/5: works on paternal null same as #3 Mini-STRC, bypasses maternal E1659A by making STRCP1 protein which has no such mutation

min(2, 2, 4) = 2 → C-tier initially, with promotion path via Gate 1: if STRCP1 translates, jumps to A-tier (mech 4, deliv 3, misha 4 → min 3, A) because the only remaining blocker is activation tool design, which is not conceptually novel (CRISPRa has been in clinical trials since 2022).

Relationship to killed PE / C-tier ASO

The key insight reframes Prime Editing for STRC (#7) and STRC ASO Exon Skipping (#8) C-tier closes: the STRCP1-identity problem that killed those approaches becomes an asset here. Same paralog, opposite valence. If this hypothesis graduates to A or S, it doesn’t resurrect PE/ASO (they still have the collateral damage issue), but it occupies the same strategic slot: “endogenous correction without permanent exogenous protein.”

Immediate action

Single email to Holt lab: “Do you have ribosome-profiling data on STRC OHC samples? If yes, can you query STRCP1 ORF for ribosome occupancy? This would address whether the paralog translates, which is the blocker gate for a new hypothesis we’re pursuing.”

No compute work until Gate 1 returns a signal.

Connections

Graph View

Backlinks