Apoptotic Activity of MeCP2 Is Enhanced by C-Terminal Truncating Mutations

Abstract

Methyl-CpG binding protein 2 (MeCP2) is a widely abundant, multifunctional protein most highly expressed in post-mitotic neurons. Mutations causing Rett syndrome and related neurodevelopmental disorders have been identified along the entire MECP2 locus, but symptoms vary depending on mutation type and location. C-terminal mutations are prevalent, but little is known about the function of the MeCP2 C-terminus. We employ the genetic efficiency of Drosophila to provide evidence that expression of p.Arg294* (more commonly identified as R294X), a human MECP2 E2 mutant allele causing truncation of the C-terminal domains, promotes apoptosis of identified neurons in vivo. We confirm this novel finding in HEK293T cells and then use Drosophila to map the region critical for neuronal apoptosis to a small sequence at the end of the C-terminal domain. In vitro studies in mammalian systems previously indicated a role of the MeCP2 E2 isoform in apoptosis, which is facilitated by phosphorylation at serine 80 (S80) and decreased by interactions with the forkhead protein FoxG1. We confirm the roles of S80 phosphorylation and forkhead domain transcription factors in affecting MeCP2-induced apoptosis in Drosophila in vivo, thus indicating mechanistic conservation between flies and mammalian cells. Our findings are consistent with a model in which C- and N-terminal interactions are required for healthy function of MeCP2.

MECP2 and the biology of MECP2 duplication syndrome

“…This neurotoxicity is not observed when the MECP2‐E1 isoform is over‐expressed. Similar neurotoxicity has been described when human MECP2‐E2 is expressed in Drosophila (Williams et al., 2016). It may be noted that other studies have shown that in Drosophila , human MECP2 associates with chromatin, regulates transcription, and is phosphorylated at the same sites as in mammalian cells (Cukier et al., 2008).…”

“…Interestingly, loss‐of‐function mutations of FOXG1 cause a Rett‐like syndrome (previously known as congenital variant Rett syndrome), whereas duplication of the FOXG1 gene causes FOXG1 duplication syndrome or West syndrome, which like MDS, is characterized by epilepsy, motor abnormalities, and cognitive impairment (Hettige & Ernst, 2019; Hou et al., 2020; Wong et al., 2019). As observed in mammalian neurons, FOXG1 over‐expression protects against MECP2‐E2‐induced neurotoxicy in Drosophila (Williams et al., 2016). Interestingly, FOXG1 interacts with MECP‐E2 and FOXG1 expression is reduced in neurons primed to die.…”

“…A question of paramount importance with regard to therapies for MDS or MTS is whether the diseases are caused or accompanied by neurodegeneration as suggested by some studies (Zhou et al., 2006; Dastidar et al., 2012a; Williams et al., 2016; Montgomery et al., 2018, 2018). If MDS is indeed a neurodegenerative disorder, it is likely that regardless of the therapeutic approach employed, recovery of lost cognitive and motor function would be limited.…”

Rett and Rett-related disorders: Common mechanisms for shared symptoms?

“…91 However, phosphorylation of MeCP2 at Ser80 reduces interaction with FOXG1 and promotes apoptosis. 102 Unlike the E2 isoform, MeCP2-E1 is not bound by FOXG1 and does not promote apoptosis when overexpressed. In contrast to the regulation of MeCP2 phosphorylation, both depolarization and IGF-1 increase phosphorylation of FOXG1.…”

Methyl-CpG Binding Protein 2 in Alzheimer Dementia

“…In vivo , a human MeCP2-e2 isoform gain-of-function mutation promoted apoptosis in Drosophila motor neurons [59]. In addition, MeCP2 overexpression led to neuronal loss in the hippocampus, cortex, and cerebellum in a MeCP2 triplication syndrome mouse model [52].…”