The Calcineurin Variant CnAβ1 Controls Mouse Embryonic Stem Cell Differentiation by Directing mTORC2 Membrane Localization and Activation

Abstract

Abstract:Embryonic stem cells (ESC) have the potential to generate all the cell lineages that will form the body. However, the molecular mechanisms underlying ESC differentiation and especially the role of alternative splicing in this process remain poorly understood. Here, we show that the alternative splicing regulator Mbnl1 promotes the generation of the atypical calcineurin Aβ variant CnAβ1 in mouse ESCs (mESC). CnAβ1 has a unique C-terminal domain that drives its localization mainly to Golgi apparatus by interacting with Cog8. CnAβ1 regulates the intracellular localization and activation of the mTORC2 complex. CnAβ1 knockdown results in delocalization of mTORC2 from the membrane to the cytoplasm, inactivation of the AKT/GSK3β/β-catenin signaling pathway and defective mesoderm specification. In summary, we unveil here the structural basis for the mechanism of action of CnAβ1 and its role in the differentiation of mESCs to the mesodermal lineage. Graphical Abstract Regulation of mesoderm specification by CnAβ1Gómez-Salinero et al. 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Regulation of mesoderm specification by CnAβ1Gómez-Salinero et al. knockdown results in delocalization of mTORC2 from the membrane to the cytoplasm, inactivation of the AKT/GSK3β/-catenin signaling pathway and defective mesoderm specification. In summary, we unveil here the structural basis for the mechanism of action of CnAβ1 and its role in the differentiation of mESCs to the mesodermal lineage. Page 2 of 36

Extensive alternative splicing transitions during postnatal skeletal muscle development are required for calcium handling functions

“…A splice variant, calcineurin Aβ1, has a C-terminal truncation so that the auto-inhibitory domain is missing. Overexpression of this splice variant improved cardiac function in mice (49,50). Calcineurin Aβ1 was not abundant in our RNA-seq analysis of skeletal muscle development, but it does give insight to functional consequences of an alternative isoform.…”

Calcineurin signaling in the heart: The importance of time and place

“…Remarkably, however, a cardiomyocyte-specific α MHC-Cn β 1 transgene does not provoke hypertrophy but exerts beneficial effects following myocardial infarction by promoting vascularization [34, 35]. How this is accomplished is not yet understood, however, interesting data is emerging that suggests CnAβ1 may be important for proper localization and signaling of mTORC2 complexes [34, 36]. …”

Inflammation‐induced mammalian target of rapamycin signaling is essential for retina regeneration

“…This kinase is a central component of the mTOR signaling pathway and forms multiprotein complexes, mTOR Complex 1 (mTORC1) and mTOR Complex 2 (mTORC2) (Meng, Frank, & Jewell, 2018). During mammalian development, mTOR activity is required for embryonic stem cell (ESC) self-renew and differentiation (Bulut-Karslioglu et al, 2016;Cherepkova, Sineva, & Pospelov, 2016;Gomez-Salinero et al, 2016). In the nervous system, mTOR is necessary for the maintenance, proliferation, and differentiation of neural stem cell and neural progenitor cell (Lee, Lim, Park, Park, & Koh, 2016;Li et al, 2017;Romine, Gao, Xu, So, & Chen, 2015;Yang et al, 2015).…”