Generation and Characterization of an Nxf7 Knockout Mouse to Study NXF5 Deficiency in a Patient with Intellectual Disability

Abstract

Members of the Nuclear eXport Factor (NXF) family are involved in the export of mRNA from the nucleus to the cytoplasm, or hypothesized to play a role in transport of cytoplasmic mRNA. We previously reported on the loss of NXF5 in a male patient with a syndromic form of intellectual disability. To study the functional role of NXF5 we identified the mouse counterpart. Based on synteny, mouse Nxf2 is the ortholog of human NXF5. However, we provide several lines of evidence that mouse Nxf7 is the actual functional equivalent of NXF5. Both Nxf7 and NXF5 are predominantly expressed in the brain, show cytoplasmic localization, and present as granules in neuronal dendrites suggesting a role in cytoplasmic mRNA metabolism in neurons. Nxf7 was primarily detected in the pyramidal cells of the hippocampus and in layer V of the cortex. Similar to human NXF2, mouse Nxf2 is highly expressed in testis and shows a nuclear localization. Interestingly, these findings point to a different evolutionary path for both NXF genes in human and mouse. We thus generated and validated Nxf7 knockout mice, which were fertile and did not present any gross anatomical or morphological abnormalities. Expression profiling in the hippocampus and the cortex did not reveal significant changes between wild-type and Nxf7 knockout mice. However, impaired spatial memory was observed in these KO mice when evaluated in the Morris water maze test. In conclusion, our findings provide strong evidence that mouse Nxf7 is the functional counterpart of human NXF5, which might play a critical role in mRNA metabolism in the brain.

Nxf7 deficiency impairs social exploration and spatio-cognitive abilities as well as hippocampal synaptic plasticity in mice

“…We have previously shown that spatial learning in the Morris water maze was significantly impaired in Nxf7 KO mice (Vanmarsenille et al, 2013 ). Further analysis indicated that this lower performance in the mutant group was not caused by differences in path length (Figure 3A , F 1,409 = 2.72, P > 0.1), nor in swimming speed ( F 1,409 = 1.19, P > 0.1, data not shown), but apparently due to lower accuracy in their search for the hidden platform.…”

“…In the present study, we modeled the functional consequences of NXF5 deficiency (Jun et al, 2001 ; Frints et al, 2003 ; Grillo et al, 2010 ), using mice deficient for Nxf7 , the likely murine homolog of human NXF5 (Vanmarsenille et al, 2013 ). We examined the effect of genetic deletion of the nuclear export factor Nfx7 on a variety of behavioral tests and related the observed phenotype to changes in hippocampal synaptic transmission.…”

“…Nxf7 -deficient mice (KO) were generated via targeted deletion of Nxf7 exon 3 as described in Vanmarsenille et al ( 2013 ). Briefly, homologous recombination of exon 3 in 129Sv embryonic stem cells (ES) cells, and subsequent crosses of chimeric offspring with C57Bl/6 mouse produced male knock-in animals.…”

“…Deletion of exon 3 was then achieved by mating a knock-in male with PGK-Cre-expressing females. For genotyping, PCR analysis of tail biopsies was performed as described before Vanmarsenille et al ( 2013 ). Standard breeding procedures included crossing heterozygous (HTZ) Nxf7 females with C57Bl/6 wildtype (WT) males, which resulted in male NXF7 KO offspring.…”

“…To investigate the importance of NXF5 in brain functioning more directly, we created a mouse model for this disorder. Based on detailed morphological, histological, and molecular analysis, we recently argued that Nxf7 is the functional analog of NXF5 , and that Nxf7 knockout (KO) mice may therefore represent the most valid model for human NXF5 deficiency (Vanmarsenille et al, 2013 ).…”