Transmembrane potential of GlyCl-expressing instructor cells induces a neoplastic-like conversion of melanocytes via a serotonergic pathway

Abstract

SUMMARYUnderstanding the mechanisms that coordinate stem cell behavior within the host is a high priority for developmental biology, regenerative medicine and oncology. Endogenous ion currents and voltage gradients function alongside biochemical cues during pattern formation and tumor suppression, but it is not known whether bioelectrical signals are involved in the control of stem cell progeny in vivo. We studied Xenopus laevis neural crest, an embryonic stem cell population that gives rise to many cell types, including melanocytes, and contributes to the morphogenesis of the face, heart and other complex structures. To investigate how depolarization of transmembrane potential of cells in the neural crest’s environment influences its function in vivo, we manipulated the activity of the native glycine receptor chloride channel (GlyCl). Molecular-genetic depolarization of a sparse, widely distributed set of GlyCl-expressing cells non-cell-autonomously induces a neoplastic-like phenotype in melanocytes: they overproliferate, acquire an arborized cell shape and migrate inappropriately, colonizing numerous tissues in a metalloprotease-dependent fashion. A similar effect was observed in human melanocytes in culture. Depolarization of GlyCl-expressing cells induces these drastic changes in melanocyte behavior via a serotonin-transporter-dependent increase of extracellular serotonin (5-HT). These data reveal GlyCl as a molecular marker of a sparse and heretofore unknown cell population with the ability to specifically instruct neural crest derivatives, suggest transmembrane potential as a tractable signaling modality by which somatic cells can control stem cell behavior at considerable distance, identify a new biophysical aspect of the environment that confers a neoplastic-like phenotype upon stem cell progeny, reveal a pre-neural role for serotonin and its transporter, and suggest a novel strategy for manipulating stem cell behavior.

Selective depolarization of transmembrane potential alters muscle patterning and muscle cell localization in Xenopus laevis embryos

“…We sought to investigate additional effects of selective depolarization of GlyR-expressing cells besides the previously-reported metastatic conversion of melanocytes (Blackiston et al, 2011). GlyR-expressing cells comprise a sparse, yet widely distributed cell population in the developing tadpole (Blackiston et al, 2011) and can be selectively targeted with the drug ivermectin (Ottesen and Campbell, 1994).…”

“…Previous work in Xenopus laevis embryos revealed the sensitivity of melanocytes (the pigmented cell derivatives of the embryonic stem cell population known as the neural crest) to the resting potential of specific other cells (Blackiston et al, 2011, Morokuma et al, 2008. Artificially depolarizing a widely-distributed cell population expressing the glycine-gated chloride channel (GlyR) in the developing frog embryo results in the neoplastic-like conversion of melanocytes in the absence of genetic damage or carcinogen exposure.…”

“…Artificially depolarizing a widely-distributed cell population expressing the glycine-gated chloride channel (GlyR) in the developing frog embryo results in the neoplastic-like conversion of melanocytes in the absence of genetic damage or carcinogen exposure. The melanocytes acquire properties associated with cancer: they over-proliferate, change their morphology toward a more dendritic shape, and become highly invasive, targeting heart, neural tube, blood vessels, and visceral organs; aberrant vasculogenesis is also observed (Blackiston et al, 2011, Lobikin et al, 2012. The GlyR-expressing cells were termed "instructor" cells, since they proved able to activate melanocyte metastatic conversion at a distance (non-cell-autonomously).…”

Xenopus: An ideal system for chemical genetics

“…Pigment cells are derived from pluripotent neural crest cells and can give rise to melanoma. So effects on pigment can relate to issues of neural crest induction, cell morphology, cell migration, cell biochemistry, as well as cancer biology (Blackiston et al, 2011;Tomlinson et al, 2009a,b;White et al, 2011).…”

“…Thus, they use a general ion channel inhibitor to show a phenotype and then narrow this down to a specific ion channel or pump . Recently they have also used ion channel drugs to identify new cell types (Blackiston et al, 2011).…”