The bioelectric control of metastatic processes during morphogenesis in Xenopus laevis.
Abstract: Understanding the mechanisms by which cellular communication and
large-scale pattern formation is coordinated in the developing embryo is of high priority
to developmental biology, regenerative medicine, and oncology. Proper patterning of body
axes during morphogenesis is important to the overall physiology of the organism, and
involves bioelectric processes in addition to chemical ... read moresignaling and genetic networks. We
first examined the effects of mutations in the cytoskeletal protein tubulin in the very
early steps of left-right patterning of frog embryos - a process known to involve
bioelectric signaling downstream of cytoskeletal transport. Our functional data demonstrate
a remarkable molecular conservation of mechanisms controlling laterality among widely
divergent phyla, and reveal the first few cleavages as the stage at which symmetry breaking
is initiated in the frog embryo. We then addressed bioelectric signaling in later
development, looking at the consequences of changing resting potential in vivo, by
specifically targeting chloride flux. Depolarization of the sparse, yet widely distributed
cell population expressing the glycine-gated chloride (GlyCl) channel non-cell-autonomously
induces the neoplastic-like conversion of melanocytes, characterized overproliferation,
inappropriate migration, and a change in overall melanocyte morphology. These drastic
changes in cell behavior occur via a serotonin-transporter-dependent increase of
extracellular serotonin. In addition to the metastatic phenotype induced in melanocytes, we
demonstrate disruptions to blood vessel and muscle patterning, the latter also occurring in
a serotonin-transporter-dependent manner. Taking advantage of a hypersensitive GlyCl mutant
we demonstrate that the depolarization of very few instructor cells (cells capable of
producing a metastatic phenotype in melanocytes) is sufficient to induce embryo-wide
hyperpigmentation. Using the same hypersensitive mutant under the control of
tissue-specific promoters, we show that instructor cells resident in muscle are more
effective in triggering the metastatic conversion of ectodermal melanocytes than those of
the nervous system. Surprisingly, the depolarization of muscle cells results in the
appearance of cells expressing muscle markers in neural regions, revealing new details on
the bioelectric reprogramming of cell behavior. Finally, we show that the neoplastic
conversion of melanocytes is mediated by cAMP, CREB, and the transcription factors Sox10
and Slug as well as the MSH-secreting melanotrope cells of the pituitary and formulate a
comprehensive computational model explaining the quantitative penetrance data for this
all-or-none phenotype within each treated population. These data reveal the upstream and
downstream mechanisms by which Vmem can function as an important biophysical regulator of
cell behavior, with implications for evolutionary biology, cancer therapeutics, and
Thesis (Ph.D.)--Tufts University, 2015.
Submitted to the Dept. of Biology.
Advisor: Michael Levin.
Committee: Susan Ernst, Kelly McLaughlin, Barry Trimmer, and Tobias Schatton.
Keywords: Molecular biology, Cellular biology, and Developmental biology.read less