An alternatively spliced, non-signaling insulin receptor modulates insulin sensitivity via insulin peptide sequestration in C. elegans

Abstract

In the nematode C. elegans, insulin signaling regulates development and aging in response to the secretion of numerous insulin peptides. Here, we describe a novel, non-signaling isoform of the nematode insulin receptor (IR), DAF-2B, that modulates insulin signaling by sequestration of insulin peptides. DAF-2B arises via alternative splicing and retains the extracellular ligand binding domain but lacks the intracellular signaling domain. A daf-2b splicing reporter revealed active regulation of this transcript through development, particularly in the dauer larva, a diapause stage associated with longevity. CRISPR knock-in of mScarlet into the daf-2b genomic locus confirmed that DAF-2B is expressed in vivo and is likely secreted. Genetic studies indicate that DAF-2B influences dauer entry, dauer recovery and adult lifespan by altering insulin sensitivity according to the prevailing insulin milieu. Thus, in C. elegans alternative splicing at the daf-2 locus generates a truncated IR that fine-tunes insulin signaling in response to the environment.

Splicing alterations in healthy aging and disease

“…Similarly, worms and insects also express multiple IR transcript isoforms, likely generated through a combination of AS and the usage of alternative intronic polyadenylation sites. These short truncated IR isoforms lacks the intracellular tyrosine kinase domain and can act as decoy receptors and soak up substrate (Martinez et al, 2020; Vastermark et al, 2013). In worms, overexpression of these short IR isoforms extends lifespan; however, in this organism, IR isoforms are most physiologically relevant in the entry and exit of the dormant dauer state (Martinez et al, 2020).…”

“…These short truncated IR isoforms lacks the intracellular tyrosine kinase domain and can act as decoy receptors and soak up substrate (Martinez et al, 2020; Vastermark et al, 2013). In worms, overexpression of these short IR isoforms extends lifespan; however, in this organism, IR isoforms are most physiologically relevant in the entry and exit of the dormant dauer state (Martinez et al, 2020). Continued research will reveal whether these isoforms are important in the context of physiological aging.…”

Natural variation in theirldgene family affects starvation resistance inC. elegans

“…Function of the irld family has been largely unexplored. Sequence homology suggests that IRLD proteins contain extracellular L domains, like insulin receptors, but lack a tyrosine kinase domain, suggesting they regulate insulin/IGF signaling by binding insulin-like peptides as decoy receptors (DLAKIC 2002), analogous to the recently reported function of the daf-2b truncated isoform of daf-2/InsR (MARTINEZ et al 2020). However, the irld genes also have homology to the EGF receptor, and family members hpa-1 and hpa-2 affect healthspan by acting through EGF signaling (IWASA et al 2010).…”

DAF-2/insulin IGF-1 receptor regulates motility during ageing by integrating opposite signaling from muscle and neuronal tissues

“…Three shorter isoforms have been reported (Ohno et al 2014). DAF-2B, which retains the extracellular ligand-binding domain but lacks the intracellular signaling domain, modulates insulin signaling by sequestering insulin peptides, but its expression is restricted to the developmental larval stages and is no longer observed in the adult stage (Martinez et al 2020). The DAF-2D and E isoforms lack part of the β-chain and IRS1 interaction domain and their function remains to be defined.…”