Effector and regulator: Diverse functions of C. elegans C-type lectin-like domain proteins

Abstract

In C. elegans, 283 clec genes encode a highly diverse family of C-type lectin-like domain (CTLD) proteins. Since vertebrate CTLD proteins have characterized functions in defense responses against pathogens and since expression of C. elegans clec genes is pathogen-dependent, it is generally assumed that clec genes function in C. elegans immune k. However, little is known about the relative contribution and exact function of CLEC proteins in C. elegans immunity. Here, we focused on the C. elegans clec gene clec-4, whose expression is highly upregulated by pathogen infection, and its paralogs clec-41 and clec-42. We found that, while mutation of clec-4 resulted in enhanced resistance to the Gram-positive pathogen Bacillus thuringiensis MYBt18247 (Bt247), inactivation of clec-41 and clec-42 by RNAi enhanced susceptibility to Bt247. Further analyses revealed that enhanced resistance of clec-4 mutants to Bt247 was due to an increase in feeding cessation on the pathogen and consequently a decrease in pathogen load. Moreover, clec-4 mutants exhibited feeding deficits also on non-pathogenic bacteria that were in part reflected in the clec-4 gene expression profile, which overlapped with gene sets affected by starvation or mutation in nutrient sensing pathways. However, loss of CLEC-4 function only mildly affected life-history traits such as fertility, indicating that clec-4 mutants are not subjected to dietary restriction. While CLEC-4 function appears to be associated with the regulation of feeding behavior, we show that CLEC-41 and CLEC-42 proteins likely function as bona fide immune effector proteins that have bacterial binding and antimicrobial capacities. Together, our results exemplify functional diversification within clec gene paralogs.

Identification and Functional Analysis of Cytokine-Like Protein CLEC-47 in Caenorhabditis elegans

“…Because clec-47 expression in C. elegans is associated with bacterial infection, we evaluated whether the purified MBP–CLEC-47–His protein demonstrated direct antimicrobial activity. Recombinant MBP–CLEC-47–His was utilized in the MIC assay, which was performed using the broth dilution method ( 11 , 31 ). However, recombinant CLEC-47 demonstrated no antimicrobial activity against E. faecium (Gram positive), S. aureus (Gram positive), K. pneumoniae (Gram negative), A. baumannii (Gram negative), P. aeruginosa (Gram negative), or K. aerogenes (Gram negative) up to the highest concentration tested (16 μg/ml) ( Fig.…”

“…The antimicrobial activity of recombinant protein in vitro was determined using the broth dilution method ( 11 , 31 ). Bacteria were cultured overnight and diluted to 5 × 10 5 CFU/ml.…”

“…C-type lectin domain-containing (CLEC) proteins and CUB_2 domain-containing proteins are the major putative effector families identified by transcriptional profiling ( 5 – 10 ). However, to date, there are only limited reports on the functions of the vast majority of C. elegans immune effectors, with the exception of some antimicrobial peptides and lytic proteins ( 11 ).…”

C. elegans: out on an evolutionary limb

“…It has been suggested that some of the nematode's expanded repertoire of 283 C-type lectin-like domain (CTLD) proteins might be involved in microbial detection (Pees et al 2016;, especially as at least two of them can direct bind bacteria (Miltsch et al 2014). Generally, however, although several CTLD proteins do play a role in resistance to infection, this appears not to involve direct pathogen recognition (Pees et al 2017(Pees et al , 2021Yunger et al 2017).…”

Protein Diversity and Immune Specificity of Hemocyanin From Shrimp Litopenaeus vannamei

“…Down syndrome cell adhesion molecule (Dscam) of Drosophila have the potential to express more than 18,000 isoforms of the immunoglobulin (Ig)-superfamily receptor ( 40 ). Similarly, the C-type lectin-like domain (CTLD) of C. elegans and fibrinogen-related proteins (FREPs) in the Pacific oyster Crassostrea gigas have diversity at nucleotide and protein levels ( 41 , 42 ). Hemocyanin (HMC) is a large copper-containing respiratory protein found in the hemolymph of mollusks and arthropods.…”