Immunohistochemical expression of G protein α-subunit isoforms in rat and monkey Merkel cell-neurite complexes

Abstract

The true function of Merkel cells (MCs) is still enigmatic, though the localization of various kinds of neurotransmitter-like substances in MCs has been revealed by immunohistochemistry. Most of the neurotransmitters act on target cells via seven-transmembrane receptors coupled to heterotrimeric G proteins. The heterotrimeric G proteins include various subfamilies that contribute to different signal transduction pathways. Therefore investigation of specific types of G proteins in MCs and related axon terminals (MC-axon terminals) should contribute to the elucidation of the function of MCs. In this study, we investigated the expression patterns of alpha-subunit isoforms of G proteins in MC-neurite complexes of the rat and monkey by enzymatic and fluorescence immunohistochemistry. MC-axon terminals of the rat and monkey showed positive immunoreactions of Galphao and Galphai1. Those of the monkey also showed a weak immunoreaction of Galphas. On the other hand, MCs of both animals showed positive immunoreactions of Galphao, Galphai1, Galphaq, and Galphaz. In addition, MCs of the monkey showed weak immunoreactions of Galphas. Galphao- and Galphai1-like immunoreactions in the MC-axon terminals suggest that MCs suppressively regulate receptive functions of type I mechanosensory nerve terminals. On the other hand, the localization of Galpha-subunits in MCs suggests that these cells are regulated with hormones, neurotransmitter-like substances, or growth factors.

Immunohistochemical expressions of mGluR5, P2Y2 receptor, PLC-?1, and IP3R-I and -II in Merkel cells in rat sinus hair follicles

“…hf Hair follicle, rs ring sinus terminals are likely to possess different kinds of G proteins (Tachibana et al 2001). The MCs of the monkey and rat showed positive immunoreactions of Gao, Gaq, and Gaz, whereas Merkel axon terminals showed immunoreactions of Gao and Gai (Tachibana et al 2001). It is known that Gq protein couples to group I mGluRs, including mGluR5 and mGluR1 (Pin and Duvoisin 1995) as well as to P2Y group ATP receptors (Ralevic and Burnstock 1998).…”

“…It can be seen that MCs are positive for both anti-IP3R-I and -II antibodies but not for anti-IP3R-III antibody. hf Hair follicle, rs ring sinus terminals are likely to possess different kinds of G proteins (Tachibana et al 2001). The MCs of the monkey and rat showed positive immunoreactions of Gao, Gaq, and Gaz, whereas Merkel axon terminals showed immunoreactions of Gao and Gai (Tachibana et al 2001).…”

“…We have recently studied the expression of a-subunit isoforms of heterotrimeric G proteins in Merkel endings to try to obtain some clues for identification of significant receptors in these structures (Tachibana et al 2001). We found that Merkel axon terminals of the rat and monkey probably possess Go and Gi proteins, whereas MCs themselves possess Go, Gq, and Gz proteins (Tachibana et al 2001).…”

Evidence for distinct populations of human Merkel cells

“…dendritic or round cells. In addition, MCs can be found with and without association to nerve Wbers (Fantini and Johansson 1995;Narisawa and Kohda 1995;Tachibana et al 2001;Uchigasaki et al 2004). The various putative functions ascribed to MCs might also be allocated to distinct populations.…”

What's new in histochemistry and cell biology?

“…In order to shed more light on the MC function, the expression patterns of alpha-subunit isoforms of G proteins in MC-neurite complexes of the rat and monkey was studied by enzymatic and fluorescence immunohistochemistry (Tachibana et al 2001). The detection of Gαo-and Gαi1-like immunoreactions in the MC-axon terminals suggested that MCs suppressively regulate receptive functions of type I mechanosensory nerve terminals.…”