Phenotypic alterations in keratinocyte behavior are essential for maintaining epidermal integrity during growth and wound repair and rely on co-ordinated cell signaling events. Numerous growth factors and cytokines have been shown to be instrumental in guiding such changes in keratinocyte activity; here we provide evidence which proposes a novel epidermal signaling pathway mediated by the excitatory amino acid glutamate. Glutamate is the major excitatory neurotransmitter at synaptic junctions within the central nervous system; however, we have identified expression in vivo of several regulatory molecules associated with glutamate signaling in keratinocytes. In resting rat skin epidermis, different classes of glutamate receptors, transporters, and a recently described clustering protein were shown to display distinct distribution patterns, supportive of a multifunctional cellular communication pathway. Immunoreactive N-methyl-D-aspartate-type, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate-type, and metabotropic-type glutamate receptors were colocalized with the specific glutamate transporter EAAC1 in basal layer keratinocytes, and GLT-1, a related transporter, was expressed suprabasally. In full-thickness rat skin wounds, marked modifications in the distribution of N-methyl-D-aspartate receptors and EAAC1 were observed during re-epithelialization, and alterations in N-methyl-D-aspartate receptor expression accompanied embryonic epidermal development, implicating glutamate signaling in these important biologic events. Furthermore, we provide evidence that these receptors are functional in vitro. These data provide strong evidence to support a role for glutamate in the control of epidermal renewal, and therefore suggest potentially novel therapeutic targets for the treatment of skin disease and enhancement of wound healing.

Of 311 expressed sequenced tags (ESTs) mapped to single human chromosomes by analysis of a monochromosome somatic cell hybrid panel, 29 were localized to chromosome 3. Analysis of somatic cell hybrid lines containing different regions of chromosome 3 has enabled the regional assignment of these 29 ESTs to 13 of 23 intervals covering chromosome 3. Northern analysis of 25 of the EST clones has provided information on the pattern of expression of potential genes represented by these transcripts in 16 human tissue types. Nine of the clones hybridized solely to a transcript(s) in the testis, 12 hybridized to transcripts in testis and other tissues, and 4 hybridized with transcripts in testis and other tissues but in addition have testis-specific transcript sizes. These ESTs will provide useful markers throughout chromosome 3 for the development of physical and transcription maps. In addition, they provide candidate genes for disease loci mapping to the intervals defined by the chromosome 3 deletion panel.