Decoding combinatorial morphogen-bioelectric inputs: compartment-specific mechanisms of positional code interpretation in congenitally gradient-deficient and intact embryos
June 29
Single morphogen gradients provide much of the positional information that directs embryonic morphogenesis, yet their dynamic ranges are inherently ambiguous: a given ligand concentration may correspond to several potential cell fates. This ambiguity can compromise tissue patterning, with downstream consequences for organ architecture and physiological function. A supplementary layer of bioelectric signaling (changes in transmembrane voltage propagated through gap junctions) has been proposed to disambiguate these cues, granting cells access to the full spectrum of positional information via purely non-chemical means. Although this combinatorial strategy reliably improves axial pattern fidelity, the cellular mechanisms underlying the interpretation of the joint morphogen-bioelectric code remain largely unexplored.
The present study set out to map the embryonic compartments engaged in decoding this code and to specify their respective contributions to sensory (gradient detection) and interpretive (fate-assignment) processes. Three matched cohorts of Xenopus embryos were examined while exposed to five experimental conditions: (i) synchronous Wnt8a gradients plus patterned hyperpolarization (full code), (ii) isolated Wnt8a gradients, (iii) isolated patterned hyperpolarization, (iv) full code accompanied by extracellular matrix stiffening (mechanical context), and (v) scrambled Wnt8a/bioelectric patterns. Cohorts comprised congenitally gradient-deficient embryos rescued with bioelectric training, wild-type embryos conditioned to the code, and naïve wild-type controls. Whole-mount light-sheet imaging of calcium flux, genetically encoded voltage indicators, and single-cell spatial transcriptomics were combined to generate activation maps.
A largely left-lateral anteroposterior domain encompassing the Spemann organizer, the paraxial mesoderm, and the anterior neural plate exhibited robust activation across all cohorts when presented with the full code and with isolated Wnt8a. Isolated hyperpolarization engaged the same organizer territory only in the gradient-deficient cohort, implying compensatory sensitization of voltage-gated sensors. Despite overlapping activation maps, several findings distinguished expert tissues from naïve controls. A discrete “Transcriptional Decoder Hub” located at the boundary of the anterior neural ridge—homologous to the vertebrate eye field—was selectively recruited by isolated hyperpolarization in gradient-deficient embryos; Bayes factor analyses indicated weak or negligible evidence of recruitment in the other two cohorts.
Integration of morphogen and bioelectric cues was localized to the Zone of Polarizing Activity in gradient-deficient embryos but shifted to the mechanosensory somitic frontier in conditioned wild-type embryos, reflecting their divergent expertise in interpreting versus generating the code. Moreover, strong engagement of the core planar cell polarity module was observed in conditioned wild-type embryos, and multivariate regression linked variability in Vangl2/Prickle localization to individual patterning precision.
Taken together, combinatorial morphogen-bioelectric signaling represents a novel axis for accessing core patterning programs, midway between classical morphogenetic gradients and mechanobiology. The present work delineates both shared and cohort-specific embryonic structures that decode this bimodal positional language, providing a foundation for future efforts to harness bioelectric modulation for regenerative pattern control.