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N-Myc and L-Myc are essential for hair cell formation but not maintenance
Journal article   Peer reviewed

N-Myc and L-Myc are essential for hair cell formation but not maintenance

Benjamin J Kopecky, Rhonda DeCook and Bernd Fritzsch
Brain research, Vol.1484, pp.1-14
11/12/2012
DOI: 10.1016/j.brainres.2012.09.027
PMCID: PMC3482343
PMID: 23022312
url
https://www.ncbi.nlm.nih.gov/pmc/articles/3482343View
Open Access

Abstract

Sensorineural hearing loss results from damage to the hair cells of the organ of Corti and is irreversible in mammals. While hair cell regeneration may prove to be the ideal therapy after hearing loss, prevention of initial hair cell loss could provide even more benefit at a lower cost. Previous studies have shown that the deletion of Atoh1 results in embryonic loss of hair cells while the absence of Barhl1, Gfi1, and Pou4f3 leads to the progressive loss of hair cells in newborn mice. We recently reported that in the early embryonic absence of N-Myc (using Pax2-Cre), hair cells in the organ of Corti develop and remain until at least seven days after birth, with subsequent progressive loss. Thus, N-Myc plays a role in hair cell viability; however, it is unclear if this is due to its early expression in hair cell precursors and throughout the growing otocyst as it functions through proliferation or its late expression exclusively in differentiated hair cells. Furthermore, the related family member L-Myc is mostly co-expressed in the ear, including in differentiated hair cells, but its function has not been studied and could be partially redundant to N-Myc. To test for a long-term function of the Mycs in differentiated hair cells, we generated nine unique genotypes knocking out N-Myc and/or L-Myc after initial formation of hair cells using the well-characterized Atoh1-Cre. We tested functionality of the auditory and vestibular systems at both P21 and four months of age and under the administration of the ototoxic drug cisplatin. We conclude that neither N-Myc nor L-Myc is likely to play important roles in long-term hair cell maintenance. Therefore, it is likely that the late-onset loss of hair cells resulting from early deletion of the Mycs leads to an unsustainable developmental defect. ► Proto-oncogenes N-Myc and L-Myc are strongly expressed in organ of Corti hair cells. ► Late deletion of the Mycs after hair cell differentiation shows no loss of hair cells. ► Cisplatin application does not disproportionately affect mutant hair cells. ► Loss of hair cells in Pax2-Cre N-Myc mice is likely due to defect in proliferation. ► N-Myc and L-Myc are unlikely to play a role in therapeutic prevention of hearing loss.
 Prevention N-Myc Regeneration L-Myc Hearing Hair Cell

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