A calcineurin-mediated scaling mechanism that controls a K+-leak channel to regulate morphogen and growth factor transcription

Abstract

The increase in activity of the two-pore potassium-leak channel Kcnk5b maintains allometric juvenile growth of adult zebrafish appendages. However, it remains unknown how this channel maintains allometric growth and how its bioelectric activity is regulated to scale these anatomical structures. We show the activation of Kcnk5b is sufficient to activate several genes that are part of important development programs. We provide in vivo transplantation evidence that the activation of gene transcription is cell autonomous. We also show that Kcnk5b will induce the expression of different subsets of the tested developmental genes in different cultured mammalian cell lines, which may explain how one electrophysiological stimulus can coordinately regulate the allometric growth of diverse populations of cells in the fin that use different developmental signals. We also provide evidence that the post-translational modification of serine 345 in Kcnk5b by calcineurin regulates channel activity to scale the fin. Thus, we show how an endogenous bioelectric mechanism can be regulated to promote coordinated developmental signaling to generate and scale a vertebrate appendage.

longfin causes cis-ectopic expression of the kcnh2a ether-a-go-go K+ channel to autonomously prolong fin outgrowth

“…Alternatively, ectopic Kcnh2a may prolong or enhance the production of pro-growth signaling molecules during the slowing outgrowth phase of fin regeneration. In support, Wnts and FGFs are produced by a mesenchyme-derived 'organizing center' or 'niche' cells at the distal blastema (Stewart et al, 2019 preprint;Tornini et al, 2016;Wehner et al, 2014), and the Kcn5b (alf ) K + channel cell-autonomously promotes growth factor production (Yi et al, 2021). We observed kcnh2a expression throughout regenerating mesenchyme, highest near the amputation site but still detectable in medial and distal blastema.…”

“…Mutations in kcnk5b (a K + channel; Perathoner et al, 2014), kcc4a/ slc12a7A (a K + Cl − co-transporter; Lanni et al, 2019), or over/ ectopic expression of the K + channels kcnj13, kcnj1b, kcnj10a and kcnk9c (Silic et al, 2020), and now kcnh2a (this study) all cause fin overgrowth. Each model may disrupt a common 'ion signaling' pathway featuring the fin outgrowth-restraining Ca 2+ -dependent phosphatase calcineurin (Daane et al, 2018;Harris et al, 2020;Kujawski et al, 2014;Lanni et al, 2019;Yi et al, 2021). Here, we found fin overgrowth in regenerating lof t2 fins was not enhanced by the calcineurin inhibitor FK506, suggesting ectopic Kcnh2a also inhibits calcineurin signaling.…”

“…Furthermore, recent work indicates reduced calcineurin activity in lof t2 fins (Cao et al, 2021). Alternatively, ectopic Kcnh2a could short-circuit calcineurinpromoted ion signaling dynamics mediated by Kcnk5b inhibition (Daane et al, 2018;Yi et al, 2021). These possibilities could be distinguished by determining whether expressing constitutively active calcineurin in the intra-ray mesenchyme lineage suppresses lof t2 fin overgrowth.…”

“…As a decoder of the ubiquitous cytosolic Ca 2+ second messenger, calcineurin links ion signaling and protein effector phosphorylation (Crabtree, 1999). Calcineurin may act directly upstream of Kcnk5b (alf ) to temper outgrowth and restore fin proportions (Daane et al, 2018;Yi et al, 2021). In mammals, diverse stimuli activate calcineurin by elevating intracellular Ca 2+ , including antigen engagement of the T-cell receptor complex (Rao, 2009), depolarization of cardiomyocytes (Parra and Rothermel, 2017) and neuronal ion channel activity (Baumgärtel and Mansuy, 2012).…”

KCNK18 Biallelic Variants Associated with Intellectual Disability and Neurodevelopmental Disorders Alter TRESK Channel Activity

“…Intriguingly, dysarthria, restlessness, headache and seizures have been observed in our patients and it is tempting to speculate that these symptoms could be associated, at least in part, with Y163D- and S252L-induced disruption of calcineurin-dependent TRESK channel activation in the brain. Recently, it has been proposed that calcineurin regulation of two-pore potassium-leak channel activity ( Kcnk5b ) mediates activation of developmental gene transcription, which controls a broad number of developmental pathways [ 31 ]. Similarly to TRESK channels, inwardly rectifying K + channels (Kir) control the resting potential of neurons and K + homeostasis in the brain.…”