Specific deletion of FHA domain containing SLMAP isoform in mice impacts embryonic development without affecting Hippo signaling. AP Dias, T Rehmani, M Salih BS Tuana

Abstract

The tail-anchored membrane protein SLMAP3 has been proposed to negatively regulate Hippo signaling and impact cell proliferation. Proteomics have defined SLMAP in complex with STRIPAK a multiprotein interactome consisting of Germinal center kinases and PP2A phosphatase. Data also suggests that the N-terminal FHA domain of SLMAP3 can bind Hippo kinase (MST 1/2) while it‘s coiled-coil regions can integrate PP2A phosphatase to modulate the downstream phosphorylation of YAP/TAZ for cytoplasmic retention. Nuclear YAP/TAZ serve as coactivators of TEAD mediated transcription of genes involved in cell proliferation and organogenesis. The physiological importance of SLMAP3 and it‘s in vivo function in regulating Hippo and organ development remains to be determined. We report that mice with specific deletion of SLMAP3 isoform were embryonic lethal where most organs including muscle, brain, spinal cord, kidney, lungs, intestines, cartilage and bone exhibited severe developmental deficits. The SLMAP3 deficient embryos were ~30% smaller (p<0.05) with small organs compared to wild types. The analysis of Hippo components MST1/2 and YAP/TAZ indicated no changes in their phosphorylation status in embryos or tissue such as muscle and the neural tube due to the loss of SLMAP3. RNA-Seq of whole embryos showed no significant changes to downstream targets of Hippo signaling in SLMAP3-KO. In addition, SLMAP3 loss had no obvious effect on cell proliferation assessed with Ki-67/pH3 staining in embryogenesis. Mouse primary embryonic fibroblasts (MEFs) isolated from embryos deficient in SLMAP3 had no changes in YAP and MST1/2 phosphorylation or proliferation while RNA-seq analysis indicated no changes in TEAD regulated gene activity. Further, phospho-proteomics of MEF lysates revealed no changes in Hippo signaling in SLMAP3 loss, nor in pathways associated with cell proliferation or death. Similarly, knockout of SLMAP3 in myoblast displayed no changes in Hippo signaling or proliferation capacity. These data indicate that SLMAP3 is critically important for embryonic development through unique mechanisms and do not implicate the involvement of Hippo signaling. Supported by CIHR. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.