Microtubule-associated protein 1A is a modifier of tubby hearing (moth1)

Abstract

Once a mutation in the gene tub was identified as the cause of obesity, retinal degeneration and hearing loss in tubby mice 1-2 , it became increasingly evident that the members of the tub gene family (tulps) influence maintenance and function of the neuronal cell lineage [3][4][5][6] . Suggested molecular functions of tubby-like proteins include roles in vesicular trafficking 4,7 , mediation of insulin signaling 8 and gene transcription 9,10 . The mechanisms through which tub functions in neurons, however, have yet to be elucidated. Here we report the positional cloning of an auditory quantitative trait locus (QTL), the modifier of tubby hearing 1 gene (moth1) 11 , whose wildtype alleles from strains AKR/J, CAST/Ei and 129P2/OlaHsd protect tubby mice from hearing loss. Through a transgenic rescue experiment, we verified that sequence polymorphisms in the neuronspecific microtubule-associated protein 1a gene (Mtap1a) observed in the susceptible strain C57BL/6J (B6) are crucial for the hearing-loss phenotype. We also show that these polymorphisms change the binding efficiency of MTAP1A to postsynaptic density molecule 95 (PSD95), a core component in the cytoarchitecture of synapses. This indicates that at least some of the observed polymorphisms are functionally important and that the hearing loss in C57BL/6J-tub/ tub (B6-tub/tub) mice may be caused by impaired protein interactions involving MTAP1A. We therefore propose that tub may be associated with synaptic function in neuronal cells.The gene tub was first identified, through positional cloning efforts, as a gene with unknown function. A spontaneous mutation at the splice donor site in the last intron, which causes a replacement of the carboxy-terminal 44 amino acids with 24 amino acids that are not observed in the normal protein, leads to obesity associated with hyperinsulinemia and neurosensory deficits 1-2 . The fact that the targeted tub null allele 12 has the same phenotype as the spontaneous mutant confirms that this splice-site mutation is also the molecular basis for the spontaneous loss-of-function mutation.The moth1 locus is a major QTL that affects hearing in tubby mice. We previously showed that a single moth1 allele from strains AKR/J, CAST/EiJ or 129P2/OlaHsd was sufficient to protect B6-tub/tub mice from hearing loss 11 . The high level of significance for linkage of suppression of hearing loss (lod=33.4) observed on chromosome 2 suggested that finemapping by recombinant progeny testing 13 could be applied to the moth1 locus. We collected a total of 1,780 meioses, of which 1,330 came from an F2 (B6-tub/tub × AKR) intercross and 450 from an F2 (B6-tub/tub × CAST.B6-tub/tub) intercross (Fig. 1a). All animals recombinant with respect to the critical region were progeny-tested to confirm the Correspondence should be addressed to P.M.N. (pmn@jax.org). presence of the protective moth1 allele in the recombinant region (Fig. 1b). The minimal moth1 region is 0.17 ± 0.1 cM and flanked by markers D2Dcr11 and D2Pjn298. We assembled a physical contig...

Genetic Analyses of the Mouse Deafness Mutations Varitint-Waddler (Va) and Jerker (Espnje)

“…For instance, the dominant allele of modifier-of-tubby-hearing 1 (moth1), segregating in AKR/J, rescues hearing loss in a significant fraction of tubby homozygotes (Ikeda et al 1999). Recently, nonsynonymous sequence polymorphisms in the microtubule-associated protein 1a gene (Mtap1a) were associated with moth1 supporting previous evidence that tubby plays a role at synapses (Ikeda et al 2002). The molecular mechanisms underlying genetic modification are currently not well understood, but further studies will undoubtedly show how modifiers exert their effects on the mutant allele.…”

Auditory brainstem responses in 10 inbred strains of mice

“…Moreover, the measurement of ABR threshold has proven essential in identifying modifier genes (Ikeda et al, 2002;Johnson and Zheng, 2002;Johnson et al, 2000Johnson et al, , 2001Noben-Trauth et al, 1997Zheng and Johnson, 2001). However, previous studies have shown that, while some hearing impairments were characterized by significant changes in all ABR parameters such as the threshold, amplitude, and latency, others were associated with the abnormalities in the amplitude and latency but not the threshold (Evans et al, 1983;Fujiyoshi et al, 1994;Kanzaki et al, 1985).…”

“…The successful use of ABR threshold for assessment of the hearing sensitivity of mice has lead to strain characterization , gene localization (Galambos and Hecox, 1978;Henry, 2004;Hirose and Liberman, 2003;Huang and Buchwald, 1978;Hunter and Willott, 1987;Ikeda et al, 2002;Ingham et al, 1998;Jimenez et al, 1999;Johnson et al, 2001), and gene identification (Ikeda et al, 2002;Johnson et al, 2000Johnson et al, , 2001Johnson et al, , 2003 since 1997. Moreover, the measurement of ABR threshold has proven essential in identifying modifier genes (Ikeda et al, 2002;Johnson and Zheng, 2002;Johnson et al, 2000Johnson et al, , 2001Noben-Trauth et al, 1997Zheng and Johnson, 2001).…”

Microtubule Organization and Microtubule-Associated Proteins (MAPs)

“…MAP1A interacts with actin and postsynaptic components like PSD93/PSD95, and anchors NMDA receptors to the cytoskeleton, supporting their transport along the dendrites (Brenman et al 1998;Pedrotti et al 1994b;Reese et al 2007;Takei et al 2015). Loss of the MAP1A-PSD95 interaction has been associated with hearing loss, due to defects in synaptic function (Ikeda et al 2002). MAP1A also ⁄ ä has a presynaptic function.…”