An independent construct for conditional expression of atonal homolog-1

Dual Regulatory Functions of SUFU and Targetome of GLI2 in SHH Subgroup Medulloblastoma

SUFU alterations are common in human Sonic Hedgehog (SHH) subgroup medulloblastoma (MB). However, its tumorigenic mechanisms have remained elusive. Here, we report that loss of Sufu alone is unable to induce MB formation in mice, due to insufficient Gli2 activation. Simultaneous loss of Spop, an E3 ubiquitin ligase targeting Gli2, restores robust Gli2 activation and induces rapid MB formation in Sufu knockout background. We also demonstrated a tumor-promoting role of Sufu in Smo-activated MB (∼60% of human SHH MB) by maintaining robust Gli activity. Having established Gli2 activation as a key driver of SHH MB, we report a comprehensive analysis of its targetome. Furthermore, we identified Atoh1 as a target and molecular accomplice of Gli2 that activates core SHH MB signature genes in a synergistic manner. Overall, our work establishes the dual role of SUFU in SHH MB and provides mechanistic insights into transcriptional regulation underlying Gli2-mediated SHH MB tumorigenesis.

Emerging Gene Therapies for Genetic Hearing Loss

Gene therapy, or the treatment of human disease using genetic material, for inner ear dysfunction is coming of age. Recent progress in developing gene therapy treatments for genetic hearing loss has demonstrated tantalizing proof-of-principle in animal models. While successful translation of this progress into treatments for humans awaits, there is growing interest from patients, scientists, clinicians, and industry. Nonetheless, it is clear that a number of hurdles remain, and expectations for total restoration of auditory function should remain tempered until these challenges have been overcome. Here, we review progress, prospects, and challenges for gene therapy in the inner ear. We focus on technical aspects, including routes of gene delivery to the inner ear, choice of vectors, promoters, inner ear targets, therapeutic strategies, preliminary success stories, and points to consider for translating of these successes to the clinic.

In Vivo Interplay between p27Kip1, GATA3, ATOH1, and POU4F3 Converts Non-sensory Cells to Hair Cells in Adult Mice

Hearing loss is widespread and persistent because mature mammalian auditory hair cells (HCs) are nonregenerative. In mice, the ability to regenerate HCs from surrounding supporting cells (SCs) declines abruptly after postnatal maturation. We find that combining p27^Kip1 deletion with ectopic ATOH1 expression surmounts this age-related decline, leading to conversion of SCs to HCs in mature mouse cochleae and after noise damage. p27^Kip1 deletion, independent of canonical effects on Rb-family proteins, upregulated GATA3, a co-factor for ATOH1 that is lost from SCs with age. Co-activation of GATA3 or POU4F3 and ATOH1 promoted conversion of SCs to HCs in adult mice. Activation of POU4F3 alone also converted mature SCs to HCs in vivo. These data illuminate a genetic pathway that initiates auditory HC regeneration and suggest p27^Kip1, GATA3, and POU4F3 as additional therapeutic targets for ATOH1-mediated HC regeneration.

Destabilization of Atoh1 by E3 Ubiquitin Ligase Huwe1 and Casein Kinase 1 Is Essential for Normal Sensory Hair Cell Development

Proneural basic helix-loop-helix transcription factor, Atoh1, plays a key role in the development of sensory hair cells. We show here that the level of Atoh1 must be accurately controlled by degradation of the protein in addition to the regulation of Atoh1 gene expression to achieve normal cellular patterning during development of the cochlear sensory epithelium. The stability of Atoh1 was regulated by the ubiquitin proteasome system through the action of Huwe1, a HECT-domain, E3 ubiquitin ligase. An interaction between Huwe1 and Atoh1 could be visualized by a proximity ligation assay and was confirmed by co-immunoprecipitation and mass spectrometry. Transfer of a lysine 48-linked polyubiquitin chain to Atoh1 by Huwe1 could be demonstrated both in intact cells and in a cell-free system, and proteasome inhibition or Huwe1 silencing increased Atoh1 levels. The interaction with Huwe1 and polyubiquitylation were blocked by disruption of casein kinase 1 (CK1) activity, and mass spectrometry and mutational analysis identified serine 334 as an important phosphorylation site for Atoh1 ubiquitylation and subsequent degradation. Phosphorylation by CK1 thus targeted the protein for degradation. Development of an extra row of inner hair cells in the cochlea and an approximate doubling in the number of afferent synapses was observed after embryonic or early postnatal deletion of Huwe1 in cochlear-supporting cells, and hair cells died in the early postnatal period when Huwe1 was knocked out in the developing cochlea. These data indicate that the regulation of Atoh1 by the ubiquitin proteasome pathway is necessary for hair cell fate determination and survival.