Rescue of the genetically engineered Cul4b mutant mouse as a potential model for human X-linked mental retardation

Abstract

Mutation in CUL4B, which encodes a scaffold protein of the E3 ubiquitin ligase complex, has been found in patients with X-linked mental retardation (XLMR). However, early deletion of Cul4b in mice causes prenatal lethality, which has frustrated attempts to characterize the phenotypes in vivo. In this report, we successfully rescued Cul4b mutant mice by crossing female mice in which exons 4-5 of Cul4b were flanked by loxP sequences with Sox2-Cre male mice. In Cul4b-deficient (Cul4b(Δ)/Y) mice, no CUL4B protein was detected in any of the major organs, including the brain. In the hippocampus, the levels of CUL4A, CUL4B substrates (TOP1, β-catenin, cyclin E and WDR5) and neuronal markers (MAP2, tau-1, GAP-43, PSD95 and syn-1) were not sensitive to Cul4b deletion, whereas the number of parvalbumin (PV)-positive GABAergic interneurons was decreased in Cul4b(Δ)/Y mice, especially in the dentate gyrus (DG). Some dendritic features, including the complexity, diameter and spine density in the CA1 and DG hippocampal neurons, were also affected by Cul4b deletion. Together, the decrease in the number of PV-positive neurons and altered dendritic properties in Cul4b(Δ)/Y mice imply a reduction in inhibitory regulation and dendritic integration in the hippocampal neural circuit, which lead to increased epileptic susceptibility and spatial learning deficits. Our results identify Cul4b(Δ)/Y mice as a potential model for the non-syndromic model of XLMR that replicates the CUL4B-associated MR and is valuable for the development of a therapeutic strategy for treating MR.

Impaired Dendritic Development and Memory inSorbs2Knock-Out Mice

“…Previous studies demonstrate that adeno-associated virus (AAV) with serotype 2/9 can cross the blood-brain barrier to infect neurons (Foust et al, 2009), and EGFP with membrane-targeting signal (EGFPf) (Hancock et al, 1991) can promote spine labeling (Cai et al, 2013). Based on these findings, we developed a viral-based method to sparsely label neurons with EGFP.…”

“…P2A-iCre cassette was cloned into the modified vector to express GFP-P2A-iCre fusion protein. Concentrated viral particles expressing GFP or GFP-P2A-iCre were produced as previously described (Welch et al, 2007), and 0.5 l of each virus was transcranially injected into the DG of adult mice following the same procedures as reported previously (Barak et al, 2013).…”

Intellectual disability and autism spectrum disorders: Causal genes and molecular mechanisms

“…Lack of Cul4b in mice leads to embryonic lethality (Chen et al, 2012; Jiang et al, 2012). Some dendritic features, including the complexity, diameter, and spine density in the hippocampal neurons were affected by Cul4b deletion (Chen et al, 2012).…”

NRIP is a novel Z-disc protein to activate calmodulin signaling for skeletal muscle contraction and regeneration

“…This 19.2 kb mouse genomic DNA fragment was inserted into the NotISpeI site of pL253, in which the MC1-TK (thymidine kinase) gene served as a negative selection marker (Chen et al, 2012). The resulting construct was used as the backbone for subsequent insertion of a loxP sequence from pL452 into intron 2 and of a neo cassette with two flanking loxP sequences from pL452 into intron 1.…”

“…The G418-resistant ES cells were then transfected with the pBabepuro-Cre plasmid for Cre-recombinase-mediated loxP recombination to delete the NRIP exon 2. Homologous recombinant clones were identified by using Southern blot analysis, injected into blastocysts of C57BL/6JNarl mice and then implanted into pseudo-pregnant foster mothers (Chen et al, 2012). The chimeric males were recognized by coat color and were mated with C57BL/6JNarl females.…”