We report the cloning and characterization of rat α10, a previously unidentified member of the nicotinic acetylcholine receptor (nAChR) subunit gene family. The protein encoded by the α10 nAChR subunit gene is most similar to the rat α9 nAChR, and both α9 and α10 subunit genes are transcribed in adult rat mechanosensory hair cells. Injection of Xenopus laevis oocytes with α10 cRNA alone or in pairwise combinations with either α2-α6 or β2-β4 subunit cRNAs yielded no detectable ACh-gated currents. However, coinjection of α9 and α10 cRNAs resulted in the appearance of an unusual nAChR subtype. Compared with homomeric α9 channels, the α9α10 nAChR subtype displays faster and more extensive agonist-mediated desensitization, a distinct current–voltage relationship, and a biphasic response to changes in extracellular Ca ²⁺ ions. The pharmacological profiles of homomeric α9 and heteromeric α9α10 nAChRs are essentially indistinguishable and closely resemble those reported for endogenous cholinergic eceptors found in vertebrate hair cells. Our data suggest that efferent modulation of hair cell function occurs, at least in part, through heteromeric nAChRs assembled from both α9 and α10 subunits.

Microglial phagocytosis is required for neurogenic niche maintenance and response to injury; the TAM kinases Mer and Axl are expressed by microglia in the adult CNS, and mediate the clearance of apoptotic cells from the niche. Microglial phagocytosis is required for neurogenic niche maintenance and response to central nervous system (CNS) injury. Here Greg Lemke and colleagues show that the TAM receptor kinases Mer and Axl are expressed by microglia and in the adult CNS, and mediate the clearance of apoptotic cells from the neurogenic niche. This work demonstrates that TAM receptors act as controllers of microglial physiology, and are potential targets for therapeutic intervention in CNS disease. Microglia are damage sensors for the central nervous system (CNS), and the phagocytes responsible for routine non-inflammatory clearance of dead brain cells1. Here we show that the TAM receptor tyrosine kinases Mer and Axl2 regulate these microglial functions. We find that adult mice deficient in microglial Mer and Axl exhibit a marked accumulation of apoptotic cells specifically in neurogenic regions of the CNS, and that microglial phagocytosis of the apoptotic cells generated during adult neurogenesis3,4 is normally driven by both TAM receptor ligands Gas6 and protein S5. Using live two-photon imaging, we demonstrate that the microglial response to brain damage is also TAM-regulated, as TAM-deficient microglia display reduced process motility and delayed convergence to sites of injury. Finally, we show that microglial expression of Axl is prominently upregulated in the inflammatory environment that develops in a mouse model of Parkinson’s disease6. Together, these results establish TAM receptors as both controllers of microglial physiology and potential targets for therapeutic intervention in CNS disease.

Local macrophage clean-up: Infection, especially by helminths or bacteria, can cause tissue damage (see the Perspective by Bouchery and Harris). Minutti et al. studied mouse models of helminth infection and fibrosis. They expressed surfactant protein A (a member of the complement component C1q family) in the lung, which enhanced interleukin-4 (IL-4)-mediated proliferation and activation of alveolar macrophages. This activation accelerated helminth clearance and reduced lung injury. In the peritoneum, C1q boosted macrophage activation for liver repair after bacterial infection. By a different approach, Bosurgi et al. discovered that after wounding caused by migrating helminths in the lung or during inflammation in the gut of mice, IL-4 and IL-13 act only in the presence of apoptotic cells to promote tissue repair by local macrophages. Science , this issue p. 1076 , p. 1072 ; see also p. 1014