Dynamic regulation of glutamate decarboxylase 67 gene expression by alternative promoters and splicing during rat testis maturation

Abstract

Glutamate decarboxylase produces GABA, the main inhibitory neurotransmitter in adult mammalian brain. Two homologous forms of GAD encoded by separate genes have been identified in mammalian brain, with molecular weight of 67 kDa (GAD67) and 65 kDa (GAD65). Here, we studied the transcriptional regulation of GAD67. Three transcript variants (GAD67A, GAD67B, and GAD67C) transcribed from distinct categories of transcriptional start sites were identified. RT-PCR revealed these transcripts have distinct tissues distributions. Though GAD67A and GAD67B were co-expressed in brain and many nonneural tissues, in heart, only GAD67A was expressed. GAD67C was specifically expressed in testis. These transcripts also showed distinct developmental expression patterns during testis maturation. GAD67A was expressed at all age points examined. GAD67B was only detected at postnatal day 1 and day 5, while GAD67C was expressed from postnatal day 30. Characterizing the genome sequence upstream of transcriptional start sites of these transcripts revealed the presence of TATA-less promoters. Potential promoter activities were analyzed by coupling these promoter sequences to the open reading frame of a luciferase reporter gene in transient expression experiments. Moreover, our results showed GAD67 gene expression was also regulated by alternative splicing in postnatal day 1 and day 5 testis. The above results suggested GAD67 gene expression was dynamically regulated by alternative promoters and splicing during postnatal rat testis maturation.