Cell- and gene-therapy approaches to inner ear repair.

Sensorineural hearing loss is the most common sensory disorder in humans. It is primarily due to the degeneration of highly specialised mechanosensory cells in the cochlea, the so-called hair cells. Hearing problems can also be caused or further aggravated by the death of auditory sensory neurons that convey the information from the hair cells to the brain stem. Despite the discovery of stem/progenitor cells in the mammalian cochlea, no regeneration of either damaged hair cells or auditory neurons has been observed in mammals, in contrast to what is seen in avians and non-mammalian vertebrates. The reasons for this divergence have not yet been elucidated, although loss of stem cells and/or loss of their phenotypic plasticity in adult mammals have been put forward as possible explanations. Given the high incidence of this disorder and its economic and social implications, a considerable number of research lines have been set up aimed towards the regeneration of cochlear sensory cell types. This review summarizes the various routes that have been explored, ranging from the genetic modification of endogenous cells remaining in the inner ear in order to promote their transdifferentiation, to the implantation of exogenous stem or progenitor cells and their subsequent differentiation within the host tissue. Prophylactic treatments to fight against progressive sensory cell degeneration in the inner ear are also discussed.

Robust reporter system based on chalcone synthase rppA gene from Saccharopolyspora erythraea.

Industrial overproducing strains present unique hosts for expression of heterologous gene clusters encoding secondary metabolite biosynthesis. For this purpose, efficient gene expression tools and methods are needed. A robust and versatile reporter system based on the rppA gene from Saccharopolyspora erythraea is presented as the method of choice when studying gene expression in actinomycete hosts. The method is easily scalable to accommodate high-throughput procedure, and collected samples can be easily stored and re-tested when needed. The product of RppA is an inert 1,3,6,8-tetrahydroxynaphthalene which spontaneously oxidises to a dark-red quinone flaviolin providing a qualitative visual assessment of gene expression on an agar plate as well as a quantitative spectrophotometric measurement in liquid broth without the need for invasive procedures or external substrate addition. The applicability of the reporter system has been demonstrated by expressing the rppA gene under the control of the heterologous promoters actII-ORF4/PactI, ermE and its upregulated variant ermE*. The model streptomycete Streptomyces coelicolor, and three industrially important species, Streptomyces tsukubaensis (FK506), Streptomyces cinnamonensis (monensin) and Streptomyces rimosus (oxytetracycline) were used as hosts. The reporter system has shown its utility independently of cultivation conditions or composition of growth medium, from simple laboratory to complex industrial media. The simplicity and robustness of the system, demonstrated even in industrial settings, shows great potential for wider use in different microbial hosts and applications, and may thus represent a new generic and versatile tool useful to a wider scientific community.