Summary Cerebral cavernous malformations (CCMs) are vascular disorders that affect up to 0.5% of the total population. About 20% of CCMs are inherited because of familial mutations in CCM genes, including CCM1 / KRIT1 , CCM2 / MGC4607 , and CCM3 / PDCD10 , whereas the etiology of a majority of simplex CCM-affected individuals remains unclear. Here, we report somatic mutations of MAP3K3 , PIK3CA , MAP2K7 , and CCM genes in CCM lesions. In particular, somatic hotspot mutations of PIK3CA are found in 11 of 38 individuals with CCMs, and a MAP3K3 somatic mutation (c.1323C>G [p.Ile441Met]) is detected in 37.0% (34 of 92) of the simplex CCM-affected individuals. Strikingly, the MAP3K3 c.1323C>G mutation presents in 95.7% (22 of 23) of the popcorn-like lesions but only 2.5% (1 of 40) of the subacute-bleeding or multifocal lesions that are predominantly attributed to mutations in the CCM1/2/3 signaling complex. Leveraging mini-bulk sequencing, we demonstrate the enrichment of MAP3K3 c.1323C>G mutation in CCM endothelium. Mechanistically, beyond the activation of CCM1/2/3-inhibited ERK5 signaling, MEKK3 p.Ile441Met ( MAP3K3 encodes MEKK3) also activates ERK1/2, JNK, and p38 pathways because of mutation-induced MEKK3 kinase activity enhancement. Collectively, we identified several somatic activating mutations in CCM endothelium, and the MAP3K3 c.1323C>G mutation defines a primary CCM subtype with distinct characteristics in signaling activation and magnetic resonance imaging appearance.

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Highlights d CASK CaM kinase domain binds to Mint1 with a nanomolar affinity d An elongated Mint1 fragment wraps around the back side of CaMK d Ca 2+ /CaM does not affect CASK-CaMK binding to Mint1 d The CASK/Mint1 structure explains some CASK variants found in patients

During the first few cell division cycles in zebrafish, distinct Ca 2+ transients are localized to the early embryonic cleavage furrows, where they accompany (and are required for) furrow positioning, propagation, deepening and apposition. It has previously been shown that the endoplasmic reticulum (ER) acts as the primary store for generating these Ca 2+ transients via release through inositol 1,4,5-trisphosphate receptors (IP 3 Rs). We hypothesised that maintaining the elevated levels of intracellular Ca 2+ required for deepening and apposition of the cleavage furrows in these large eggs might result in the depletion of the available ER Ca 2+ store, thus the role of store-operated Ca 2+ entry (SOCE) was examined. Newly fertilized, dechorionated embryos were incubated with various SOCE inhibitors, starting just prior to the onset of the first cell division cycle. The effect of these inhibitors on mitosis, furrow positioning, propagation, deepening and apposition, and the generation of the cytokinetic Ca 2+ transients was determined. Treatment with 2-APB or SKF 96365 had no major effect on mitosis, furrow positioning or propagation, but inhibited furrow deepening resulting in regression of the cleavage furrow. Both of these inhibitors also blocked the furrowing Ca 2+ transient, with SKF 96365 having a more profound inhibitory effect than 2-APB. In zebrafish, SOCE does not appear to be required for mitosis or the early stages of cytokinesis during the early embryonic cell division cycles, but it does appear to be essential for maintaining the elevated levels of [Ca 2+ ] i for the extended periods that are required during furrow deepening and daughter cell apposition.

Several unconventional myosins contain a highly charged single α helix (SAH) immediately following the calmodulin (CaM) binding IQ motifs, functioning to extend lever arms of these myosins. How such SAH is connected to the IQ motifs and whether the conformation of the IQ motifs-SAH segments are regulated by Ca fluctuations are not known. Here, we demonstrate by solving its crystal structure that the predicted SAH of myosin VIIa (Myo7a) forms a stable SAH. The structure of Myo7a IQ5-SAH segment in complex with apo-CaM reveals that the SAH sequence can extend the length of the Myo7a lever arm. Although Ca-CaM remains bound to IQ5-SAH, the Ca-induced CaM binding mode change softens the conformation of the IQ5-SAH junction, revealing a Ca-induced lever arm flexibility change for Myo7a. We further demonstrate that the last IQ motif of several other myosins also binds to both apo- and Ca-CaM, suggesting a common Ca-induced conformational regulation mechanism.