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Reactive oxygen species (ROS) play a major role in drug-, noise-, and age-dependent hearing loss, but the source of ROS in the inner ear remains largely unknown. Herein, we demonstrate that NADPH oxidase (NOX) 3, a member of the NOX/dual domain oxidase family of NADPH oxidases, is highly expressed in specific portions of the inner ear. As assessed by real-time PCR, NOX3 mRNA expression in the inner ear is at least 50-fold higher than in any other tissues where its expression has been observed (e.g. fetal kidney, brain, skull). Microdissection and in situ hybridization studies demonstrated that NOX3 is localized to the vestibular and cochlear sensory epithelia and to the spiral ganglions. Transfection of human embryonic kidney 293 cells with NOX3 revealed that it generates low levels of ROS on its own but produces high levels of ROS upon co-expression with cytoplasmic NOX subunits. NOX3-dependent superoxide production required a stimulus in the absence of subunits and upon co-expression with phagocyte NADPH oxidase subunits p47 phox and p67 phox , but it was stimulus-independent upon co-expression with colon NADPH oxidase subunits NOX organizer 1 and NOX activator 1. Pre-incubation of NOX3-transfected human embryonic kidney 293 cells with the ototoxic drug cisplatin markedly enhanced superoxide production, in both the presence and the absence of subunits. Our data suggest that NOX3 is a relevant source of ROS generation in the cochlear and vestibular systems and that NOX3-dependent ROS generation might contribute to hearing loss and balance problems in response to ototoxic drugs.The inner ear is a highly complex structure involved in hearing and balancing. The conversion of sound into electrical signals occurs within the cochlea, in the organ of Corti, and the electrical signals are conducted by the axons of spiral ganglion neurons to the brain. The linear movement of the head is sensed by the otolith organs (utricle and saccule) and the rotation movements by the ampulla of the semicircular canals. The signals generated in the vestibular system are transmitted by the vestibular ganglion neurons to the central nervous system.Hearing impairment caused by loss of cochlear function occurs frequently, if not invariably, over a lifetime. Noise and ototoxic chemicals may lead to a precocious, rapid hearing loss, whereas aging leads to a more insidious, chronic loss of hearing. Research over the last decades has identified reactive oxygen species (ROS) 1 as the major factor mediating hearing loss (1). ROS is generated within the cochlea after exposure to ototoxic drugs (e.g. cisplatin (2, 3), aminoglycoside antibiotics (3)) or to noise (4). Signs of oxidative stress, such as DNA damage and lipid peroxidation, have been documented in vivo in response to those challenges (5, 6), as well as in cochlear aging (7). The vestibular system is also damaged by ototoxic drugs (8, 9) in a process that includes excessive ROS production (10, 11).Although the role of oxidative stress in inner ear damage is well established, its source ...

The primary event in mammalian sexual development is the differentiation of the bipotential gonads into either testes or ovaries. Our understanding of the molecular pathways specifying gonadal differentiation is still incomplete. To identify the initial molecular changes accompanying gonadal differentiation in mice, we have performed a large-scale transcriptional analysis of XX and XY Sf1-positive gonadal cells during sex determination. In both male and female genital ridges, a robust genetic program is initiated pre-dating the first morphological changes of the differentiating gonads. Between E10.5 and E13.5, 2306 genes were expressed in a sex-specific manner in the somatic compartment of the gonads; 1223 were overexpressed in XX embryos and 1083 in XY embryos. Although sexually dimorphic genes were scattered throughout the mouse genome, we identified chromosomal regions hosting clusters of genes displaying similar expression profiles. The cyclin-dependent kinase inhibitors Cdkn1a and Cdkn1c are overexpressed in XX gonads at E11.5 and E12.5, suggesting that the increased proliferation of XY gonads relative to XX gonads may result from the overexpression of cell cycle inhibitors in the developing ovaries. These studies define the major characteristics of testicular and ovarian transcriptional programs and reveal the richness of signaling processes in differentiation of the bipotential gonads into testes and ovaries.

Mutations in the gene encoding copper/zinc superoxide dismutase enzyme produce an animal model of familial amyotrophic lateral sclerosis (FALS), a fatal disorder characterized by paralysis. Overexpression of the proto-oncogene bcl-2 delayed onset of motor neuron disease and prolonged survival in transgenic mice expressing the FALS-linked mutation in which glycine is substituted by alanine at position 93. It did not, however, alter the duration of the disease. Overexpression of bcl-2 also attenuated the magnitude of spinal cord motor neuron degeneration in the FALS-transgenic mice.