Generation and Characterization of Mice with Myh9 Deficiency

Abstract

Mutant alleles of MYH9 encoding a class II non-muscle myosin heavy chain-A (NMMHC-IIA) have been linked to hereditary megathrombocytopenia with or without additional clinical features that include sensorineural deafness, cataracts, and nephritis. To assess its biological role in the affected targets, particularly the inner ear, we have generated and characterized mice with Myh9 deficiency. These mice were generated using the XA136 ES cell line (BayGenomics, http://baygenomics.ucsf.edu/) carrying gene trap insertion in Myh9, within the intron flanking exons 4 and 5. Mice heterozygous for the Myh9 null allele, Myh9 +/- were expanded on C57BL/6J background. Intercross of the Myh9 +/- mice did not yield Myh9 -/- pups, indicating embryonic lethality, subsequently determined to occur at or before E7.5, thus precluding a post-natal analysis of the effects of complete Myh9 deficiency. The heterozygous mice were normal for their hearing, parameters of platelet integrity and renal function despite their Myh9 haplo-insufficiency. In addition, the age-dependent auditory threshold of the Myh9 +/- mice and their wild type littermates, spanning from 3 to 12 months of age, were similar indicating that Myh9 haplo-insufficiency does not contribute towards accelerated age-related hearing loss (AHL). The embryonic lethality associated with the complete Myh9 deficiency establishes a critical role for this non-muscle myosin in fetal development. The results of these studies do not support the Myh9 haploinsufficiency as a pathogenic factor in the etiology of auditory dysfunction.

Background Strain and the Differential Susceptibility of Podocyte-Specific Deletion of Myh9 on Murine Models of Experimental Glomerulosclerosis and HIV Nephropathy

“…None of the mice were homozygous KO animals, as this classical null allele of Myh9 results in early embryonic lethality when homozygous. The absence of an effect on Tg26 nephropathy from heterozygous loss of Myh9 in this previous study is consistent with the reports that mice with one copy of this null allele had either a very subtle phenotype of sensorineural hearing loss or no phenotype at all, leading to the conclusion that the Myh9 locus is not haploinsufficient [41], [42]. A similar conclusion on the lack of haploinsufficiency in humans can be inferred from the spectrum of mutations found among those with autosomal dominant MYH9 -related disease: there are scores of distinct missense mutations but no nonsense mutations (except in the last exon, in which nonsense mediated decay has little influence) [1].…”

Temporary reduction of distortion product otoacoustic emissions (DPOAEs) immediately following auditory brainstem response (ABR)

“…The ABR thresholds were determined using procedures described previously (Mhatre et al, 2007). Briefly, responses were recorded from silver wire electrodes inserted through the skin at the vertex (active electrode), ipsilateral mastoid (negative) and contralateral mastoid (ground).…”

APOL1 Variants Increase Risk for FSGS and HIVAN but Not IgA Nephropathy

“…21 Themice were maintained by backcrossing to B6 at Columbia University. For the HIV-1 transgenic mouse line, we backcrossed the well-characterized TgN (pNL43d14)26Lom 26 mice 27 to B6 mice for at least seven generations to generate heterozygous HIV-1 transgenic strain on the B6 genetic background (TgB6).…”

“…Homozygous inactivation of Myh9 results in embryoniclethalityatembryonicday6.5,but Myh9 haploinsufficient mice (Myh9 ϩ/Ϫ ), despite significantly reduced MYH9 protein level, are born normally and do not develop gross organ dysfunction. 20,21 Therefore, we examined Myh9 haploinsufficient mice Figure 1. Haplotype analysis localized the most significant signal within the APOL1 locus.…”