Ectopic hair cell-like cell induction by Math1 mainly involves direct transdifferentiation in neonatal mammalian cochlea

• LER cells possessed high ability to proliferate post-explanted.
• LER cells cannot differentiate into hair cells without Math1 expression.
• LER cells induced to hair cell-like cells by Math1 mainly via direct transdifferentiation.
• Newly formed hair cells cannot divide.

Math1, also known as Atoh1, is a basic helix-loop-helix transcription factor that plays a key role in hair cells (HCs) development. Previous studies have reported that Math1 gene transfer could induce the production of ectopic hair cell-like cells both in vitro and in vivo. Here, we focused on the mechanism of ectopic hair cell-like cellular differentiation from cells in the lateral epithelial ridge (LER) of cochlea with a human adenovirus serotype 5 (Ad5) vector encoding both Math1 and the reporter gene EGFP. Within the Ad5-EGFP-Math1 infection, hair-cell like cells could be detected in the LER. 5′-Bromo-2′ deoxyuridine (BrdU) incorporation test results at different time points suggested that LER cells possessed high potential to proliferation, but they could not transdifferentiate into hair cells spontaneously. Almost all of Math1 induced hair cell-like cells were BrdU negative when BrdU incorporation occurred after Math1 expression. In conclusion, Math1 induced hair cell-like cells from LER cells mainly underwent direct trans-differentiation instead of mitosis of LER cells or newly hair cell-like cells.