Lrig1 and Lrig3 cooperate to control Ret receptor signaling, sensory axonal growth and epidermal innervation

Lrig3-deficient mice exhibit strain-specific alterations in liver fat accumulation, intestinal morphology, and middle ear inflammation

The transmembrane protein leucine-rich repeats and immunoglobulin-like domains 3 (LRIG3) regulates fat metabolism and bone morphogenetic protein (BMP) signaling. Lrig3-deficient mice exhibit impaired development of the snout and the inner ear lateral canal, neural defects, and cardiac hypertrophy in adulthood. However, no thorough and unbiased analysis of the physiological functions of Lrig3 has previously been performed. To address this knowledge gap, we performed histopathological examination of 42 tissues and organs from 1-year-old female C57BL/6JBomTac and 129S1-U mice with different Lrig3 genotypes. Among the scored pathologies, three were significantly associated with Lrig3 genotype: spontaneous macrovesicular hepatocellular degeneration (hepatocellular steatosis) was less prevalent in Lrig3-deficient C57BL/6JBomTac mice, whereas dilated or flaccid ileum and otitis media were more common in Lrig3-deficient 129S1-U mice. To further investigate hepatic steatosis phenotypes, 8-week-old C57BL/6JBomTac mice of both sexes and different Lrig3 genotypes were subjected to consuming a high-fat diet (HFD) for 8 weeks. The HFD regimen led to relatively few cases of hepatocellular steatosis, with no significant differences among the genotypes; however, female Lrig3-deficient mice presented reduced microvesicular hepatocellular degeneration compared with their wild-type littermates. This study revealed that Lrig3 regulates liver fat accumulation, intestinal morphology, and middle ear inflammation in a mouse strain-dependent manner.

Lrig1 regulates cell fate specification of glutamatergic neurons via FGF-driven Jak2/Stat3 signaling in cortical progenitors

The cell-intrinsic mechanisms underlying the decision of a stem/progenitor cell to either proliferate or differentiate remain incompletely understood. Here, we identify the transmembrane protein Lrig1 as a physiological homeostatic regulator of FGF2-driven proliferation and self-renewal of neural progenitors at early-to-mid embryonic stages of cortical development. We show that Lrig1 is expressed in cortical progenitors (CPs), and its ablation caused expansion and increased proliferation of radial/apical progenitors and of neurogenic transit-amplifying Tbr2+ intermediate progenitors. Notably, our findings identify a previously unreported EGF-independent mechanism through which Lrig1 negatively regulates neural progenitor proliferation by modulating the FGF2-induced IL6/Jak2/Stat3 pathway, a molecular cascade that plays a pivotal role in the generation and maintenance of CPs. Consistently, Lrig1 knockout mice showed a significant increase in the density of pyramidal glutamatergic neurons placed in superficial layers 2 and 3 of the postnatal neocortex. Together, these results support a model in which Lrig1 regulates cortical neurogenesis by influencing the cycling activity of a set of progenitors that are temporally specified to produce upper layer glutamatergic neurons.

Etv4 regulates nociception by controlling peptidergic sensory neuron development and peripheral tissue innervation

The perception of noxious environmental stimuli by nociceptive sensory neurons is an essential mechanism for the prevention of tissue damage. Etv4 is a transcriptional factor expressed in most nociceptors in dorsal root ganglia (DRG) during the embryonic development. However, its physiological role remains unclear. Here, we show that Etv4 ablation results in defects in the development of the peripheral peptidergic projections in vivo, and in deficits in axonal elongation and growth cone morphology in cultured sensory neurons in response to NGF. From a mechanistic point of view, our findings reveal that NGF regulates Etv4-dependent gene expression of molecules involved in extracellular matrix (ECM) remodeling. Etv4-null mice were less sensitive to noxious heat stimuli and chemical pain, and this behavioral phenotype correlates with a significant reduction in the expression of the pain-transducing ion channel TRPV1 in mutant mice. Together, our data demonstrate that Etv4 is required for the correct innervation and function of peptidergic sensory neurons, regulating a transcriptional program that involves molecules associated with axonal growth and pain transduction.