Selective Cre‐mediated gene deletion identifies connexin 43 as the main connexin channel supporting olfactory ensheathing cell networks

Abstract

Many functions of glial cells depend on the formation of selective glial networks mediated by gap junctions formed by members of the connexin family. Olfactory ensheathing cells (OECs) are specialized glia associated with olfactory sensory neuron axons. Like other glia, they form selective networks, however, the connexins that support OEC connectivity in vivo have not been identified. We used an in vivo mouse model to selectively delete candidate connexin genes with temporal control from OECs and address the physiological consequences. Using this model, we effectively abolished the expression of connexin 43 (Cx43) in OECs in both juvenile and adult mice. Cx43‐deleted OECs exhibited features consistent with the loss of gap junctions including reduced membrane conductance, largely reduced sensitivity to the gap junction blocker meclofenamic acid and loss of dye coupling. This indicates that Cx43, a typically astrocytic connexin, is the main connexin forming functional channels in OECs. Despite these changes in functional properties, the deletion of Cx43 deletion did not alter the density of OECs. The strategy used here may prove useful to delete other candidate genes to better understand the functional roles of OECs in vivo.

Panglial gap junctions between astrocytes and olfactory ensheathing cells mediate transmission of Ca2+ transients and neurovascular coupling

“…Indeed, OECs and astrocytes are electrically and dye‐coupled and C×43kiECFP reporter mice showed that juxtaglomerular astrocytes as well as OECs can express C×43. This observation was further substantiated by our and other immunostainings (Piantanida et al, ; Rela et al, ; Roux et al, ; Theofilas, Steinhauser, Theis, & Derouiche, ). Hence, astrocytes and OECs might form homotypic gap junctions by C×43, in contrast to panglial coupling between astrocytes and oligodendrocytes, in which heterotypic gap junctions are built between C×43 (astrocyte) and C×47 (oligodendrocyte) or between C×30 (astrocyte) and C×32 (oligodendrocyte) (Orthmann‐Murphy, Freidin, Fischer, Scherer, & Abrams, ).…”

“…Indeed, OECs and astrocytes are electrically and dye-coupled and C×43kiECFP reporter mice showed that juxtaglomerular astrocytes as well as OECs can express C×43. This observation was further substantiated by our and other immunostainings (Piantanida et al, 2019;FIGURE 7 Gap junctions mediate transmission of Ca 2+ signals between OECs and astrocytes. (a) Induction of Ca 2+ transients in astrocytes (black trace) via the photolysis of caged tACPD resulted in delayed Ca 2+ responses in OECs (grey trace) that were suppressed by CBX (150 μM).…”

Olfactory ensheathing cells from the nasal mucosa and olfactory bulb have distinct membrane properties

“…OECs within the OB and OM have distinct gene expression profiles (Guerout et al, ), but it is currently unclear whether these genetically and spatially separate populations mediate common physiological mechanisms that ensure normal homeostasis and continual neuronal turnover. Previous studies in acute slices of the OB from juvenile mice have described a variable contribution of certain types of membrane channels to shaping the electrical responses of OECs (Piantanida et al, ; Rela et al, , ). Following the loss of gap junctional coupling, these OECs display heterogeneous membrane currents, with variable contributions from hyperpolarization‐activated inward rectifier K + currents and depolarization‐activated outward rectifier K + currents.…”

“…The physiological functions of peripheral OECs remain poorly understood at a cellular and molecular level (Chen, Kachramanoglou, Li, Andrews, & Choi, 2014;Gomez et al, 2018), and so it is currently unclear why this subtype of OECs could more successfully encourage neuronal regeneration. Much of our current understanding of neuroglial interactions comes from structural, molecular, and functional studies of rodent OECs, from either the OM or OB (Guerout et al, 2010;Hayat, Wigley, & Robbins, 2003;Higashi et al, 2001;Piantanida et al, 2019;Rash et al, 2005;Rela, Bordey, & Greer, 2010;Rela, Piantanida, Bordey, & Greer, 2015;Rieger, Deitmer, & Lohr, 2007). Studies of excised human OM tissues have also helped identify common markers in vivo (Choi, Law, Raisman, & Li, 2008;Liu et al, 2010;Oprych, Cotfas, & Choi, 2017).…”

“…OECs within the OB and OM have distinct gene expression profiles (Guerout et al, 2010), but it is currently unclear whether these genetically and spatially separate populations mediate common physiological mechanisms that ensure normal homeostasis and continual neuronal turnover. Previous studies in acute slices of the OB from juvenile mice have described a variable contribution of certain types of membrane channels to shaping the electrical responses of OECs (Piantanida et al, 2019;Rela et al, 2010Rela et al, , 2015.…”