LRP5L is a human transcribed locus represented in UniProtKB by a 252-amino-acid protein model composed of five LDL-receptor class B repeats; an alternative isoform changes residues 220-224 and lacks residues 225-252. In human lens epithelial cells and anterior lens capsules, plasmid-expression and siRNA experiments implicated LRP5L and the P36R variant in altered laminin gamma-1 and c-MAF expression associated with congenital membranous cataract. Endogenous protein production and the molecular basis of these effects remain unresolved. Current official NCBI Gene and HGNC records independently classify the locus as a pseudogene; UniProtKB retains a conflicting reviewed PE2 transcript-evidence protein model, which does not establish endogenous translation.
Loading supporting contentβ¦
Download this section (compressed HTML)Q: Does LRP5L produce a stable endogenous protein in the human lens or any other tissue, and which current transcript and isoform encode it if so?
Suggested experts: Sun L, Ge H, Liu P
Q: Does P36R still map to a translated LRP5L open reading frame under the current human locus model, and does it segregate independently of other candidate variants in the cataract family?
Suggested experts: Sun L, Song F, Liu H
Q: Are the reported laminin gamma-1 and c-MAF expression changes reproduced by endogenous locus-specific perturbation, and are they mediated by an LRP5L protein, an LRP5L RNA, or an indirect construct effect?
Suggested experts: Sun L, Wang C, Tang X
Experiment: Perform phased long-read RNA sequencing and ribosome profiling across the LRP5L locus in human lens tissue and HLE B-3 cells, followed by targeted parallel-reaction-monitoring mass spectrometry using peptides unique to the predicted isoform 1 and isoform 2 products. Include synthetic heavy-peptide standards, a confirmed low-abundance lens protein as a positive control, and genomic/transcript mapping filters that exclude homologous LRP-family reads.
Hypothesis: The LRP5L locus is transcribed but does not produce a stable endogenous 252-amino-acid protein, consistent with the current NCBI pseudogene model.
Type: transcriptomics, ribosome profiling, and targeted proteomics
Experiment: Use multiple non-overlapping CRISPRi guides and transcript-targeted antisense oligonucleotides to perturb endogenous LRP5L in HLE B-3 cells and a human lens-organoid model. Rescue with sequence-verified isoform 1, isoform 2, and P36R constructs expressed at near-endogenous levels, then quantify LAMC1 and c-MAF RNA/protein over time. Pair the rescue with translation-dead RNA constructs to distinguish protein-mediated from RNA-mediated effects and include matched empty-vector and unrelated-repeat-protein controls.
Hypothesis: The reported effects on laminin gamma-1 and c-MAF require a specific LRP5L transcript or translated isoform and are altered by P36R.
Type: endogenous perturbation and isoform-rescue assay
Experiment: Conditional on detecting endogenous translation, introduce a small epitope tag at the endogenous locus without altering the alternative C terminus and analyze localization by orthogonal microscopy and biochemical fractionation. Identify reproducible proximity-labeling or affinity-purification partners for each supported isoform, with untagged cells and LRP5/LRP6 analyzed separately as controls rather than assumed homologues.
Hypothesis: If an endogenous LRP5L polypeptide exists, its native localization and interaction partners differ from those of the full-length LRP5 and LRP6 receptors.
Type: endogenous tagging, localization, and interaction proteomics
What is not known β curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: Whether the human LRP5L locus produces a stable endogenous polypeptide is unknown, and the transcript(s), translation start site, and isoform(s) that could generate such a product have not been reconciled with the current pseudogene model.
OPEN BIOLOGYCURATION WHOLLY_DARK
What is known: Transcript-derived cDNA models historically supported the 252-amino-acid A4QPB2 sequence and its C-terminal alternative isoform, and UniProtKB retains a reviewed PE2 entry. In contrast, current NCBI Gene classifies LRP5L as a pseudogene and exposes only non-coding and non-coding-model transcript classes; HGNC independently assigns locus type pseudogene. UniProtKB lists MassIVE, PaxDb, PeptideAtlas, and ProteomicsDB 689/690 cross-references, but remains PE2. Those links establish database indexing, not locus-unique endogenous peptide detection, and no such confirmation is captured in the reviewed local evidence.
Significance: Protein existence is prerequisite to assigning any protein molecular function, localization, or biological process and to interpreting P36R as a protein-altering variant.
What would resolve it: Reconstruct the locus with phased long-read RNA sequencing, test translation by ribosome profiling, and seek locus-unique endogenous peptides with targeted mass spectrometry in human lens and other expressing tissues; then reconcile the RefSeq and UniProtKB records against those results.
Provenance (the field's own admissions):
Gap: The molecular mechanism connecting LRP5L perturbation or the P36R construct to laminin gamma-1 and c-MAF expression is unknown, including whether the reported effects are direct, require an endogenous translated product, or are specific to a particular transcript or isoform.
OPEN BIOLOGY MF_DARK
What is known: A single study reported P36R in a congenital membranous cataract family and reported that wild-type and P36R plasmids plus LRP5L siRNA altered laminin gamma-1 and c-MAF expression in HLE B-3 cells and human anterior lens capsules. The cached abstract establishes perturbation-dependent expression effects but not an intrinsic molecular activity, direct interaction, native localization, or endogenous protein production.
Significance: Resolving the mechanism is necessary to distinguish a protein-mediated lens phenotype from transcript-level regulation, construct-specific effects, or a linked variant and to determine whether any GO annotation is warranted.
What would resolve it: Reproduce the phenotype with locus-specific CRISPR perturbations in lens models, rescue with sequence-verified isoform 1, isoform 2, and P36R constructs matched to current genomic models, and test direct versus indirect control of laminin gamma-1 and c-MAF with time-resolved transcript and protein measurements.
Provenance (the field's own admissions):
Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)