RESUMO
There are several forms of hereditary human hair loss, known collectively as alopecias, the molecular bases of which are entirely unknown. A kindred with a rare, recessively inherited type of alopecia universalis was used to search for a locus by homozygosity mapping, and linkage was established in a 6-centimorgan interval on chromosome 8p12 (the logarithm of the odds favoring linkage score was 6.19). The human homolog of a murine gene, hairless, was localized in this interval by radiation hybrid mapping, and a missense mutation was found in affected individuals. Human hairless encodes a putative single zinc finger transcription factor protein with restricted expression in the brain and skin.
Assuntos
Alopecia/genética , Proteínas/genética , Dedos de Zinco , Sequência de Aminoácidos , Animais , Encéfalo/metabolismo , Mapeamento Cromossômico , Cromossomos Humanos Par 8 , Proteínas de Ligação a DNA/genética , Feminino , Fatores de Transcrição Forkhead , Expressão Gênica , Genes Recessivos , Homozigoto , Humanos , Masculino , Camundongos , Camundongos Pelados/genética , Repetições de Microssatélites , Dados de Sequência Molecular , Mutação , Linhagem , Proteínas/química , Ratos , Análise de Sequência de DNA , Homologia de Sequência de Aminoácidos , Pele/metabolismo , Fatores de Transcrição/genéticaRESUMO
Serotonin (5HT) transporters (SERTs) couple to existing ion gradients to transport 5HT into presynaptic terminals. In mammalian SERTs, the transport cycle is reported as electroneutral, with a translocation of zero net charge, and 5HT uptake is independent of membrane voltage. Yet mammalian SERTs exhibit 5HT-induced currents, and Drosophila SERTs (dSERTs) show voltage-dependent uptake. Thus, the relationship between uptake and current remains controversial; furthermore, the number of 5HT molecules translocated per ion channel event is unknown. To investigate this, we have used heterologous expression of cloned dSERTs to measure 5HT flux and dSERT currents concurrently under voltage clamp, and we have used fluctuation analysis to measure the size of the elementary ionic events in the same cells. RNA-injected Xenopus oocytes accumulate 5HT, and paroxetine or desipramine inhibit this uptake. RNA-injected oocytes also display paroxetine-sensitive 5HT-induced currents and 5HT-independent leak currents. Na replacement decreases the uptake and the induced currents. 5HT-induced current and 5HT uptake both increase at negative potentials, where 5HT carries approximately 5% of the induced current. Recently, several groups have reported similar phenomena for other transporters, in which transmitter-induced currents exceed the predictions of coupled transport. We now provide evidence that in dSERT, approximately 500 5HT molecules are translocated per channel opening, which, at -20 mV, carries approximately 10,000 electronic charges. These data support a model in which 500 SERT cycles occur for each 5HT-induced channel opening or a model in which 500 5HT molecules and 10,000 electronic charges pass through a common pore.