LON-8 is a small (162 aa) secreted protein produced by hypodermal cells (hyp4 and hyp7) in C. elegans. It contains an N-terminal signal peptide and a nematode-specific BPTI-like domain (IPR057449). Loss-of-function mutations cause a Long (Lon) body size phenotype due to increased cell size (not cell number or ploidy), as well as grossly abnormal male ray morphology resembling Ram mutants. lon-8 functions independently of the Sma/Mab (TGF-beta/BMP) pathway and genetically interacts with cuticle collagen modifying enzymes dpy-11 and dpy-18. The protein is conserved across Rhabditid nematodes.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005576 extracellular region | IEA GO_REF:0000044 | ACCEPT | Summary: LON-8 contains an N-terminal signal peptide and is secreted from hypodermal cells. When the signal peptide is present in a reporter construct, GFP is secreted and diffuses, confirming extracellular localization. This IEA annotation based on UniProt subcellular location is correct. Reason: LON-8 is established as a secreted protein. The signal peptide is required for function (hu187 allele lacking it is non-functional). Extracellular region is an appropriate general localization. Supporting Evidence: PMID:17374156 ...Y59A8B.20 is therefore likely to be a secreted protein...Clear localization to this cell is only visible when the signal sequence is deleted, implying that in the presence of this sequence Y59A8B.20 is secreted and diffuses... file:worm/lon-8/lon-8-deep-research-falcon.md the gene was shown to encode a **small secreted precursor protein** (signal peptide-bearing) expressed in the hypodermis. |
| GO:0060102 cuticular extracellular matrix | ISM PMID:17374156 Regulation of Caenorhabditis elegans body size and male tail... | ACCEPT | Summary: LON-8 is secreted from hypodermal cells and genetically interacts with cuticle collagen modifying enzymes dpy-11 and dpy-18. While direct localization to the cuticle has not been shown (the protein diffuses when secreted), the functional connection to cuticle collagen processing and the body morphology phenotype support cuticular ECM as the likely site of action. Reason: The ISM annotation is reasonable given that LON-8 is secreted from the hypodermis (which synthesizes the cuticle), genetically interacts with cuticle collagen modifying enzymes, and its loss-of-function phenotype (Lon body, abnormal ray morphology) is consistent with cuticle defects. Falcon deep research adds that a 2025 endogenous LON-8::mNG knock-in (Ragle et al.) directly localizes LON-8 to cuticle structures including the male tail fan, providing experimental support beyond the original diffuse-reporter data. Supporting Evidence: PMID:17374156 ...both dpy-11(RNAi) and dpy-18(RNAi) completely suppress the lon-8 body size phenotype...strongly suggesting that the function of these three genes are intimately linked... file:worm/lon-8/lon-8-deep-research-falcon.md report systematic endogenous tagging of aECM components including **LON-8::mNG**, describing LON-8 as a secreted protein implicated in cuticle morphology. They further report localization to cuticle structures including the **male tail fan**, and note atypical FRAP recovery for LON-8::mNG in the L4 vulva relative to most knock-ins. |
| GO:0003674 molecular_function | ND GO_REF:0000015 | ACCEPT | Summary: No specific molecular function has been experimentally determined for LON-8. The ND (No biological Data) annotation is appropriate. The protein contains a BPTI-like nematode-specific domain (IPR057449), but no biochemical activity has been demonstrated. Reason: No molecular function assay has been performed on LON-8. While the BPTI-like domain suggests possible protease inhibitor or protease modulating activity, this has not been tested. Note that the related C. elegans Kunitz-domain protein BLI-5 was shown to activate rather than inhibit serine proteases, so domain-based function prediction is unreliable for this protein family in nematodes. Supporting Evidence: file:worm/lon-8/lon-8-deep-research-bioreason-sft.md BioReason predicts extracellular matrix structural constituent (GO:0005201) based on the BPTI-like domain, but this is undemonstrated and the nematode Kunitz domain family shows unexpected biochemical activities. |
| GO:0035264 multicellular organism growth | IMP PMID:17374156 Regulation of Caenorhabditis elegans body size and male tail... | ACCEPT | Summary: lon-8 loss-of-function causes increased body length (Lon phenotype), demonstrating that LON-8 normally acts to limit body growth. The qualifier acts_upstream_of_or_within_negative_effect accurately captures that LON-8 negatively regulates growth, without asserting a specific mechanism. The increased body size results from increased cell size, not cell number or ploidy. Reason: Two deletion alleles (hu187, hu188) and RNAi all cause a Lon phenotype. lon-8 mutants grow faster during larval development and early adulthood. The negative effect qualifier is appropriate because LON-8 normally restrains growth. Falcon deep research independently summarizes lon-8 as a regulator of larval elongation/body size, consistent with this annotation, and notes the effect is largely independent of DBL-1/Sma/Mab transcriptional control while genetically interacting with collagen modifiers dpy-11 and dpy-18. Supporting Evidence: PMID:17374156 ...Both alleles gave a clear Lon phenotype...throughout larval development, they outgrew their wild-type counterparts at a rate comparable to that of lon-1(e185) animals... file:worm/lon-8/lon-8-deep-research-falcon.md lon-8/Y59A8B.20 encodes a small secreted hypodermal protein that functions in the extracellular cuticle/aECM to regulate larval elongation/body size and male ray morphology, acting largely independently of DBL-1/Sma/Mab transcriptional control but genetically interacting with collagen-modifying enzymes dpy-11 and dpy-18. |
| GO:0045138 nematode male tail tip morphogenesis | IMP PMID:17374156 Regulation of Caenorhabditis elegans body size and male tail... | ACCEPT | Summary: lon-8 mutant males display grossly abnormal ray morphology, with thickened, clumped rays resembling Ram mutants. This demonstrates that LON-8 is required for normal male tail morphogenesis. The positive effect qualifier indicates LON-8 promotes normal ray development. Despite abnormal morphology, males can still mate. Reason: Both hu187 and hu188 alleles show extensive male ray morphological defects. lon-8 is expressed in the ventral tail hypodermal cells that surround the developing rays. The phenotype resembles Ram mutants which affect cuticle apposition around rays. Falcon deep research corroborates a male tail role: an apical extracellular matrix review (Cohen & Sundaram 2020) lists LON-8 among proteins important for building male rays, and the 2025 endogenous knock-in localizes LON-8 to the male tail fan. Supporting Evidence: PMID:17374156 ...All rays appear morphologically abnormal, but rays 5 and 6 are most severely affected...lon-8(hu187) and lon-8(hu188) males can mate, suggesting that ray sensory function is intact even though ray morphology is grossly abnormal... file:worm/lon-8/lon-8-deep-research-falcon.md Review on *C. elegans* apical extracellular matrices lists **LON-8** among proteins important for building **male rays**, describing it as a **short, secreted peptide/protein** in the ray/cuticle context |
| GO:0040015 negative regulation of multicellular organism growth | IMP PMID:17374156 Regulation of Caenorhabditis elegans body size and male tail... | NEW | Summary: lon-8 loss-of-function causes a Lon phenotype with increased body length during larval development and early adulthood, indicating LON-8 normally negatively regulates multicellular organism growth. This is a more specific annotation than GO:0035264 with negative effect qualifier, and directly reflects the observed biology. Reason: The existing annotation uses GO:0035264 (multicellular organism growth) with acts_upstream_of_or_within_negative_effect qualifier. GO:0040015 (negative regulation of multicellular organism growth) more precisely captures the role of LON-8 as a negative regulator and is supported by the same mutant phenotype data. Supporting Evidence: PMID:17374156 ...Both alleles gave a clear Lon phenotype...throughout larval development, they outgrew their wild-type counterparts at a rate comparable to that of lon-1(e185) animals... file:worm/lon-8/lon-8-deep-research-falcon.md The strongest interpretation supported by experimental genetics is that LON-8 is a **secreted hypodermal factor acting on the cuticle/aECM**, influencing body length and specialized cuticular structures (male rays). |
Loading supporting content…
Download this section (compressed HTML)Q: Does LON-8 have serine protease inhibitor activity, or does it activate proteases like the related Kunitz-domain protein BLI-5?
Suggested experts: Soete G, Korswagen HC
Q: Is LON-8 physically associated with cuticle collagens or collagen modifying enzymes, or does it act indirectly?
Suggested experts: Soete G, Korswagen HC
Q: What is the relationship between lon-8 and the Ram pathway genes that produce similar male tail phenotypes?
Suggested experts: Soete G, Korswagen HC
Experiment: Express and purify recombinant LON-8 and test for inhibition or activation of serine proteases in vitro, as was done for BLI-5. Include cuticle-relevant proteases such as BLI-4.
Hypothesis: LON-8 has serine protease inhibitor or modulator activity via its BPTI-like domain.
Experiment: Perform co-immunoprecipitation or yeast two-hybrid experiments between LON-8 and DPY-11/DPY-18 to determine whether the genetic interaction reflects a physical interaction.
Hypothesis: LON-8 physically interacts with cuticle collagen processing enzymes DPY-11 and DPY-18.
Experiment: Generate a functional LON-8 fusion protein with a small epitope tag (rather than GFP which diffuses) and perform immunoelectron microscopy to determine precise subcellular localization within the cuticle layers.
Hypothesis: LON-8 localizes specifically to the cuticle rather than diffusing broadly in the extracellular space.
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)