Hair Cell Genes Research Articles

Positional information and mobile transcriptional regulators determine cell pattern in the Arabidopsis root epidermis

The root epidermis is a model system for deciphering the mechanism underpinning the formation of cellular pattern in planar groups of cells. The epidermis comprises rows of hair cells (H) and non-hair-bearing epidermal cells (N). Laser ablation and clonal analysis have shown that the fates of epidermal cells are flexible through development and that positional information which may be located in the cell wall or extracellular matrix determines cell fate. A leucine-rich repeat protein called SCRAMBLED is required for the development of cell pattern which may be involved in the perception of positional information. It is proposed that positional signals then initiate the cell-specific expression of a number of transcription factors that complete the patterning process, resulting in the expression of hair-promoting genes in hair cells (H) and their repression in the hairless cells (N).

Transgenic and gene targeting studies of hair cell function in mouse inner ear.

Despite the rapid discovery of a large number of genes in sensory hair cells of the inner ear, the functional roles of these genes in hair cells remain largely undetermined. Recent advances in transgenic and gene targeting technologies in mice have offered unprecedented opportunities to genetically manipulate the expression of these genes and to study their functional roles in hair cells in vivo. Transgenic analyses have revealed the presence of hair-cell-specific promoters in the genes encoding Math1, myosin VIIa, Pou4f3, and the alpha9 subunit of the acetylcholine receptor (alpha9 AChR). Targeted inactivation using embryonic stem cell technology and transgenic expression studies have revealed the roles of several genes involved in hair cell lineage (Math1), differentiation (Pou4f3), mechanotransduction (Myo1c, and Myo7a), electromotility (Prestin), and efferent modulation (Chrna9, encoding alpha9 AChR). Although many of these genes also play roles in other tissues, inactivation of these genes in hair cells alone will soon be possible by using the Cre-loxP system. Also imminent is the development of genetic methods to inactivate genes specifically in mouse hair cells at a desired time, by using inducible systems established in other types of neurons. Combining these types of manipulation of gene expression will enable hearing researchers to elucidate some of the fundamental and unique features of hair cell function such as mechanotransduction, frequency tuning, active mechanical amplification, and efferent modulation.

An inner ear gene expression database.

Microarray technology has provided an unprecedented opportunity to study gene expression profiles at a whole-genome level. As a first step toward a comprehensive understanding of inner ear gene expression, mouse cochleas were examined at two developmental stages (P2 and P32) using GeneChip oligonucleotide arrays. A large number of genes and ESTs (> 10,000) were found to be expressed in the cochlea. Expression profiles derived from duplicate samples at the same developmental stages showed general agreement and indicated the reproducibility of the assay. The expression of many known hair-cell genes was detected in the whole-cochlea samples, demonstrating the relatively high sensitivity of the assay. Genes highly expressed only at P2 or P32 were also identified and their expression patterns correlate with their functions in the cochlea. A web-based database with external links was set up for public access, which should facilitate the discovery of genes important in the development and function of the inner ear and should aid the identification of additional deafness genes.

Functional expression of exogenous proteins in mammalian sensory hair cells infected with adenoviral vectors.

To understand the function of specific proteins in sensory hair cells, it is necessary to add or inactivate those proteins in a system where their physiological effects can be studied. Unfortunately, the usefulness of heterologous expression systems for the study of many hair cell proteins is limited by the inherent difficulty of reconstituting the hair cell's exquisite cytoarchitecture. Expression of exogenous proteins within hair cells themselves may provide an alternative approach. Because recombinant viruses were efficient vectors for gene delivery in other systems, we screened three viral vectors for their ability to express exogenous genes in hair cells of organotypic cultures from mouse auditory and vestibular organs. We observed no expression of the genes for beta-galactosidase or green fluorescent protein (GFP) with either herpes simplex virus or adeno-associated virus. On the other hand, we found robust expression of GFP in hair cells exposed to a recombinant, replication-deficient adenovirus that carried the gene for GFP driven by a cytomegalovirus promoter. Titers of 4 x 10(7) pfu/ml were sufficient for expression in 50% of the approximately 1,000 hair cells in the utricular epithelium; < 1% of the nonhair cells in the epithelium were GFP positive. Expression of GFP was evident as early as 12 h postinfection, was maximal at 4 days, and continued for at least 10 days. Over the first 36 h there was no evidence of toxicity. We recorded normal voltage-dependent and transduction currents from infected cells identified by GFP fluorescence. At longer times hair bundle integrity was compromised despite a cell body that appeared healthy. To assess the ability of adenovirus-mediated gene transfer to alter hair cell function we introduced the gene for the ion channel Kir2.1. We used an adenovirus vector encoding Kir2.1 fused to GFP under the control of an ecdysone promoter. Unlike the diffuse distribution within the cell body we observed with GFP, the ion channel-GFP fusion showed a pattern of fluorescence that was restricted to the cell membrane and a few extranuclear punctate regions. Patch-clamp recordings confirmed the expression of an inward rectifier with a conductance of 43 nS, over an order of magnitude larger than the endogenous inward rectifier. The zero-current potential in infected cells was shifted by -17 mV. These results demonstrate an efficient method for gene transfer into both vestibular and auditory hair cells in culture, which can be used to study the effects of gene products on hair cell function.