HB-EGF promotes horizontal basal cell proliferation and olfactory sensory neuron regeneration in the zebrafish olfactory epithelium

Abstract

Maintenance and regeneration of the zebrafish olfactory epithelium (OE) are supported by distinct progenitor cell populations that occupy discrete stem cell niches and respond to different tissue conditions. Globose basal cells (GBCs) reside at the inner and peripheral margins of the sensory OE and are constitutively active to replace sporadically dying olfactory sensory neurons (OSNs). In contrast, horizontal basal cells (HBCs) are more uniformly distributed across the tissue, including basal layers of the sensory region, and are selectively activated by acute injury conditions that affect the morphological integrity of the OE. Here we show that expression of the heparin-binding epidermal growth factor-like growth factor (HB-EGF) is strongly and transiently upregulated in response to OE injury and signals through the EGF receptor (EGFR), which is expressed by HBCs. Exogenous stimulation of the OE with recombinant HB-EGF promotes HBC expansion and OSN neurogenesis within the sensory OE, resembling the tissue response to injury. In contrast, pharmacological inhibition of HB-EGF shedding, HB-EGF availability, and EGFR signaling strongly attenuate or delay injury-induced HBC activity and OSN restoration without affecting maintenance neurogenesis by GBCs. Thus, HB-EGF/EGFR signaling appears to be a critical component of a complex signaling network that controls HBC activity and, consequently, repair neurogenesis in the zebrafish OE.