The ATP-sensitive K+-channel (KATP) controls early left–right patterning in Xenopus and chick embryos

Abstract

Consistent left-right asymmetry requires specific ion currents. We characterize a novel laterality determinant in Xenopus laevis: the ATP-sensitive K+-channel (KATP). Expression of specific dominant-negative mutants of the Xenopus Kir6.1 pore subunit of the KATP channel induced randomization of asymmetric organ positioning. Spatio-temporally controlled loss-of-function experiments revealed that the KATP channel functions asymmetrically in LR patterning during very early cleavage stages, and also symmetrically during the early blastula stages, a period when heretofore largely unknown events transmit LR patterning cues. Blocking KATP channel activity randomizes the expression of the left-sided transcription of Nodal. Immunofluorescence analysis revealed that XKir6.1 is localized to basal membranes on the blastocoel roof and cell-cell junctions. A tight junction integrity assay showed that KATP channels are required for proper tight junction function in early Xenopus embryos. We also present evidence that this function may be conserved to the chick, as inhibition of KATP in the primitive streak of chick embryos randomizes the expression of the left-sided gene Sonic hedgehog. We propose a model by which KATP channels control LR patterning via regulation of tight junctions.

Far from solved: A perspective on what we know about early mechanisms of left–right asymmetry

“…This model is also not consistent with the timing of perturbations that are known to disrupt asymmetry far upstream of unilateral gene expression such as left-sided Nodal (Yost, 1991;Fukumoto et al, 2005a,b;Adams et al, 2006;Danilchik et al, 2006;Vandenberg and Levin, 2010). Early windows of activity indicated by the LR phenotypes of pharmacological blockades initiated at early vs. later time periods are supported by data showing that some gene-specific ion transporter constructs randomize LR asymmetry when injected at the 1 cell stage but lose the ability to do so by the four-cell stage (Aw et al, 2010).…”

Local and long-range endogenous resting potential gradients antagonistically regulate apoptosis and proliferation in the embryonic CNS

“…Such patterns of resting potential within living tissues (bioelectric signals) have been studied in the context of their roles in cell migration and wound healing (Cao et al, 2013, Jaffe, 1979, McCaig et al, 2005, Richard B. Borgens, 1989, Zhao et al, 2006 and have long been proposed to direct growth and form in vivo (Burr, 1932). Bioelectric signals are implicated in vertebrate appendage regeneration , Tseng et al, 2010, cancer initiation and metastasis (Binggeli and Weinstein, 1986b, Blackiston et al, 2011, Brackenbury, 2012, Chernet and Levin, 2013b, Lobikin et al, 2012b, left-right patterning (Aw et al, 2008, Aw et al, 2010, Levin et al, 2002, planarian head induction (Beane et al, 2011, Beane et al, 2013, Marsh and Beams, 1947, and eye and brain formation (Nuckels et al, 2009, Pai et al, 2015, Pai et al, 2012a, Pai et al, 2012b. Thus bioelectric signals have been shown to be important regulators of large-scale patterning and tissue and organ identity (Levin, 2009, Levin, 2013a, Levin and Stevenson, 2012, Tseng and Levin, 2013a.…”

Where have the organizers gone? – The growth control system as a foundation of physiology

“…[15] The growth control system is not only an aggregate of cells and molecules, but also an intricate web of morphogen gradient field [7,8,15] intertwined with bioelectric field[12] , [14] which exists due to asymmetric distribution of ion channels and ion pumps in cells and tissues. [13,16] Morphogen signaling and bioelectromagnetic field are mutually supportive in coordinating growth control [13,14,16]. Endogenous bioelectromagnetic fields are known to control protein kinase, inositol phospholipid signaling, calcium influx in wound healing, morphogenesis and cell migration.…”