Merth, K. | bioRxiv Science

bioRxiv2026

Human-specific multicopy gene FRMPD2 promotes synapse formation via recruitment of neuroligin 1

FRMPD2 is a human-specific multi-copy gene with higher mRNA expression in brain tissue, but its role in synapse formation and neurodevelopment remains unknown. We find that FRMPD2 is a neuron-specific protein with a high expression level in human brains compared to rodent brains. FRMPD2 overexpression in rat neurons stimulates synaptogenesis, leading to increased synaptic activities. Importantly, our results show that FRMPD2 via its PDZ domains recruits and enhances neuroligin-1 protein levels at the postsynaptic sites, and via its FERM domain interacts with the F-actin network in the spine. Increased expression of FRMPD2 also promotes spine formation and maturation, a foundational process for synapse formation. In developing embryonic mouse brains expressing higher FRMPD2 protein levels, we observed delayed neuronal migration, presumably promoting a protracted timeline for cortical lamination as a feature in human brain development. Behaviorally, mice with FRMPD2 overexpression in the brain demonstrate enhanced spatial memory retention. These findings indicate an important function for FRMPD2 in neuronal connectivity, brain development, and cognitive function.

neuroscience↗

bioRxiv2025

Reactivation of the X-linked Nexmif Gene Corrects Mosaic NEXMIF Deficiency in Heterozygous Female Mice

We have previously demonstrated that heterozygous (HET) female mice lacking one copy of the X-linked gene Nexmif display autistic-like phenotypes, memory impairments, and deficits in synapse and neuron morphology. Due to random X Chromosome Inactivation (XCI), the HET mouse brain contains two populations of neurons: NEXMIF-expressing cells (wildtype, WT) and NEXMIF-lacking cells (knockout, KO). Interestingly, because KO cells contain a normal WT copy of Nexmif on the inactivated X chromosome (Xi), we wondered whether the silenced Xi-Nexmif could be reactivated to restore NEXMIF expression in neurons as a strategy to correct this mosaic deficiency in HET mice. To this end, we first tested pharmacological inhibition of XCI maintenance and found that intracortical administration of the DNA methylation inhibitor 5-aza-2-deoxycytidine combined with resveratrol (Aza+Resveratrol) increased NEXMIF expression in HET mice. Using a gene-specific approach, we developed a NEXMIF-targeted CRISPR activation (CRISPRa) system and found that it selectively increases NEXMIF transcription in human female cells and in vivo in WT female mice with minimal off-target effects. Importantly, CRISPRa restored NEXMIF expression in the KO neurons of HET primary cultures, effectively correcting XCI-driven mosaicism. These findings demonstrate that pharmacological- and especially CRISPRa-mediated reactivation of the Xi may serve as a strategy for the reversal of neuronal and behavioral impairments in Nexmif HET conditions.

molecular biology↗