Ppp2r2a Knockout Mice Reveal That Protein Phosphatase 2A Regulatory Subunit, PP2A-B55α, Is an Essential Regulator of Neuronal and Epidermal Embryonic Development

Abstract

The serine/threonine protein phosphatase 2A (PP2A) is a master regulator of the complex cellular signaling that occurs during all stages of mammalian development. PP2A is composed of a catalytic, a structural, and regulatory subunit, for which there are multiple isoforms. The association of specific regulatory subunits determines substrate specificity and localization of phosphatase activity, however, the precise role of each regulatory subunit in development is not known. Here we report the generation of the first knockout mouse for the Ppp2r2a gene, encoding the PP2A-B55α regulatory subunit, using CRISPR/Cas9. Heterozygous animals developed and grew as normal, however, homozygous knockout mice were not viable. Analysis of embryos at different developmental stages found a normal Mendelian ratio of Ppp2r2a −/− embryos at embryonic day (E) 10.5 (25%), but reduced Ppp2r2a −/− embryos at E14.5 (18%), and further reduced at E18.5 (10%). No live Ppp2r2a −/− pups were observed at birth. Ppp2r2a −/− embryos were significantly smaller than wild-type or heterozygous littermates and displayed a variety of neural defects such as exencephaly, spina bifida, and cranial vault collapse, as well as syndactyly and severe epidermal defects; all processes driven by growth and differentiation of the ectoderm. Ppp2r2a −/− embryos had incomplete epidermal barrier acquisition, associated with thin, poorly differentiated stratified epithelium with weak attachment to the underlying dermis. The basal keratinocytes in Ppp2r2a −/− embryos were highly disorganized, with reduced immunolabeling of integrins and basement membrane proteins, suggesting impaired focal adhesion and hemidesmosome assembly. The spinous and granular layers were thinner in the Ppp2r2a −/− embryos, with aberrant expression of adherens and tight junction associated proteins. The overlying stratum corneum was either absent or incomplete. Thus PP2A-B55α is an essential regulator of epidermal stratification, and is essential for ectodermal development during embryogenesis.

The broad phenotypic spectrum of PPP2R1A-related neurodevelopmental disorders correlates with the degree of biochemical dysfunction

“…Although incompletely understood, PP2A phosphatases play important roles in mammalian brain development and function, 8 , 31 , 32 e.g., in regulating signaling 33 – 35 and preventing degeneration in neurons. 36 , 37 In 2015, PP2A dysfunction was reported as a new cause of syndromic intellectual disability and (neuro)developmental delay, involving de novo loss-of-function pathogenic variants in PPP2R1A and PPP2R5D , 4 and likely also in PPP2R5C and PPP2R5B , although the latter has not yet been functionally confirmed.…”

Engineering digitizer circuits for chemical and genetic screens in human cells

“…As the ERK pathway is upstream of AP-1 activation, this could explain their identification as positive regulators. PPP2R2A was also recognized by both reporters and encodes a regulatory subunit of protein phosphatase 2A, which has been shown to target various proteins in the PKC-induced AP-1 pathway, such as ERK-related proteins and c-Jun 33 . WDR48 was detected only by our reporter and encodes a regulator of deubiquinating complexes, for which knockdown experiments have led to an accumulation of PHLPP1, which dephosphorylates and inactivates PKC, indicating its connection to our pathway 34 , 35 .…”

Protein phosphatase 2A – structure, function and role in neurodevelopmental disorders

“…The PP2A-Bα and PP2A-Bδ isoforms PP2A-Bα (encoded by PPP2R2A) and PP2A-Bδ (encoded by PPP2R2D) are expressed in many tissues, including the brain. PPP2R2A is an essential gene, as homozygous KO mice die during embryonic development (Panicker et al, 2020). Specifically, PP2A-Bα is a critical regulator of epidermal stratification and ectoderm development (Panicker et al, 2020).…”

“…PPP2R2A is an essential gene, as homozygous KO mice die during embryonic development (Panicker et al, 2020). Specifically, PP2A-Bα is a critical regulator of epidermal stratification and ectoderm development (Panicker et al, 2020). Moreover, dysregulation of PP2A-Bα expression has been implicated in the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease (AD) (Sontag et al, 2004a,b) and Parkinson's disease (PD) (Park et al, 2016).…”