Ablation of RIC8A Function in Mouse Neurons Leads to a Severe Neuromuscular Phenotype and Postnatal Death

Abstract

Resistance to inhibitors of cholinesterase 8 (RIC8) is a guanine nucleotide exchange factor required for the intracellular regulation of G protein signalling. RIC8 activates different Gα subunits via non-canonical pathway, thereby amplifying and prolonging the G protein mediated signal. In order to circumvent the embryonic lethality associated with the absence of RIC8A and to study its role in the nervous system, we constructed Ric8a conditional knockout mice using Cre/loxP technology. Introduction of a synapsin I promoter driven Cre transgenic mouse strain (SynCre) into the floxed Ric8a (Ric8a F/F) background ablated RIC8A function in most differentiated neuron populations. Mutant SynCre +/- Ric8 lacZ/F mice were born at expected Mendelian ratio, but they died in early postnatal age (P4-P6). The mutants exhibited major developmental defects, like growth retardation and muscular weakness, impaired coordination and balance, muscular spasms and abnormal heart beat. Histological analysis revealed that the deficiency of RIC8A in neurons caused skeletal muscle atrophy and heart muscle hypoplasia, in addition, the sinoatrial node was misplaced and its size reduced. However, we did not observe gross morphological changes in brains of SynCre +/- Ric8a lacZ/F mutants. Our results demonstrate that in mice the activity of RIC8A in neurons is essential for survival and its deficiency causes a severe neuromuscular phenotype.

Targeted deletion of RIC8A in mouse neural precursor cells interferes with the development of the brain, eyes, and muscles

“…Moreover, similarly to the neuron‐specific ablation of RIC8A, the majority of P0 Nes;Ric8a CKO mice had myocardial hypoplasia and thinner myocardium. The myocardial defects were probably due to disturbed innervation as suggested earlier (Ruisu et al, ). In addition, the neural crest cells provide all parasympathetic innervation of the heart that controls the normal myocardial function (Kirby et al, ).…”

“…Moreover, a recent study in Drosophila showed that association of neuronal calcium sensor 1 with Ric8a co‐regulates the number of synapses and the probability of neurotransmitter release per synapse (Mansilla et al, ). In our previous study, we also found that RIC8A deficiency in differentiated neurons affects the neuromuscular signaling and the mutants exhibit highly similar phenotype and muscle fiber atrophy as the Nes;Ric8a CKO mice (Ruisu et al, ). These results strongly suggest that RIC8A may have a role in regulating muscle innervation.…”

“…In addition to defects in brain, eyes, and muscles, also a failure in heart, kidney, and thymus have been reported in the FCMD, WWS, or MEB patients (Devisme et al, ). Our previous data have shown that the removal of RIC8A from differentiated neurons in mice caused the development of markedly smaller hearts and impaired cardiac function (Ruisu et al, ). Hence, we analyzed the possible heart defects in Nes;Ric8a CKO mice and our findings can be summarized as follows: the majority of Nes;Ric8a CKO mice hearts had left coronary artery dilation.…”

B Lymphocyte–Specific Loss of Ric-8A Results in a Gα Protein Deficit and Severe Humoral Immunodeficiency

“…Conditional gene targeting using a floxed ric8 allele and an hGFAP-cre that targets Ric-8A expression in neural progenitors and astroglia resulted in mice with a disorganized Bergmann glial scaffolding, defective granule cell migration, and disrupted Purkinje cell positioning (22). A synapsin I promoter driven Cre ablated Ric-8A function in most differentiated neuron populations and resulted in early post natal death due to a severe neuromuscular phenotype (23). However, whether the phenotypes that arose in these conditionally ric8 targeted mice resulted from Gα protein deficiency or due to a loss of Ric-8A function in non-canonical G-protein signaling was unexplored in these studies.…”

Activator of G protein signaling 3 forms a complex with resistance to inhibitors of cholinesterase-8A without promoting nucleotide exchange on Gαi3

“…Furthermore, AGS3S was found to be expressed endogenously in mammalian heart [7]. Intriguingly, a recent report on Ric-8A knockout mice showed that the loss of Ric-8A results in early postnatal death with abnormal heart beat, heart muscle hypoplasia as well as misplaced sinoatrial node [36]. Mice lacking AGS3 also exhibit altered cardiovascular function [37].…”