MeCP2 Regulates the Synaptic Expression of a Dysbindin-BLOC-1 Network Component in Mouse Brain and Human Induced Pluripotent Stem Cell-Derived Neurons

Abstract

Clinical, epidemiological, and genetic evidence suggest overlapping pathogenic mechanisms between autism spectrum disorder (ASD) and schizophrenia. We tested this hypothesis by asking if mutations in the ASD gene MECP2 which cause Rett syndrome affect the expression of genes encoding the schizophrenia risk factor dysbindin, a subunit of the biogenesis of lysosome-related organelles complex-1 (BLOC-1), and associated interacting proteins. We measured mRNA and protein levels of key components of a dysbindin interaction network by, quantitative real time PCR and quantitative immunohistochemistry in hippocampal samples of wild-type and Mecp2 mutant mice. In addition, we confirmed results by performing immunohistochemistry of normal human hippocampus and quantitative qRT-PCR of human inducible pluripotent stem cells (iPSCs)-derived human neurons from Rett syndrome patients. We defined the distribution of the BLOC-1 subunit pallidin in human and mouse hippocampus and contrasted this distribution with that of symptomatic Mecp2 mutant mice. Neurons from mutant mice and Rett syndrome patients displayed selectively reduced levels of pallidin transcript. Pallidin immunoreactivity decreased in the hippocampus of symptomatic Mecp2 mutant mice, a feature most prominent at asymmetric synapses as determined by immunoelectron microcopy. Pallidin immunoreactivity decreased concomitantly with reduced BDNF content in the hippocampus of Mecp2 mice. Similarly, BDNF content was reduced in the hippocampus of BLOC-1 deficient mice suggesting that genetic defects in BLOC-1 are upstream of the BDNF phenotype in Mecp2 deficient mice. Our results demonstrate that the ASD-related gene Mecp2 regulates the expression of components belonging to the dysbindin interactome and these molecular differences may contribute to synaptic phenotypes that characterize Mecp2 deficiencies and ASD.

Mutations in the BLOC-1 Subunits Dysbindin and Muted Generate Divergent and Dosage-dependent Phenotypes

“…For example, the schizophrenia-associated dysbindin reduction is highly penetrant in the hippocampus of schizophrenia patients (32,38). In addi- 2) tion, the hippocampal formation of Bloc1s5 mu/mu and other BLOC-1 mutants prominently display BLOC-1 null phenotypes or phenotypes associated with regulators of BLOC-1 expression such as Mecp2 (17,33,34,36,39).…”

“…We used a Bloc1s6 pallidin antibody whose immunoreactivity is absent in Bloc1s6 pa/pa brains (29,39). VAMP2 immunoreactivity was used as a marker of presynaptic tissue and a control counterstain.…”

Pallidin protein in neurodevelopment and its relation to the pathogenesis of schizophrenia

“…The patients are characterized by experiencing distortions of reality and disturbances of thought and language, and tend to withdraw from social contact (1). Neurotransmitter disturbances are considered an important factor leading to the development of schizophrenia (2). The fact that the functions of multiple known susceptibility genes seem to relate them to the neurotransmitter system provides molecular evidence for the validity of the neurotransmitter hypothesis.…”

Stem Cells on the Brain: Modeling Neurodevelopmental and Neurodegenerative Diseases Using Human Induced Pluripotent Stem Cells

“…This epigenetic “memory” can impact the study of certain disease loci, which may remain silenced after reprogramming (Amenduni et al, 2011; Ananiev, Williams, Li, & Chang, 2011; Chamberlain et al, 2010; Cheung et al, 2011; Farra et al, 2012; K.-Y. Kim, Hysolli, & Park, 2011; Larimore et al, 2013; J. Liu et al, 2012c; Mekhoubad et al, 2012; Urbach, Bar-Nur, Daley, & Benvenisty, 2010).…”

“…When modeling X-linked disorders with female iPSCs, the specific X chromosome that is inactivated is crucial for the presentation of a mutation-dependent phenotype, as only the mutant gene is expressed when one X chromosome is inactivated, and only the wild-type gene is expressed when the other is inactivated, drastically impacting resulting neuronal characteristics (Amenduni et al, 2011; Ananiev et al, 2011; Cheung et al, 2011; Farra et al, 2012; K.-Y. Kim et al, 2011; Larimore et al, 2013; J. Liu et al, 2012c; Marchetto et al, 2010a; Mekhoubad et al, 2012).…”