Diane Lipscombe, PhD
Department of Neuroscience and Brown Institute for Brain Science (BIBS)
Brown University
(February 4, 2015)
Neuronal Calcium Channel Cell Specific Splicing: Patterns & Properties
Neurons fire in response to changes in the levels of ions such as sodium, potassium, and calcium. The ions enter the cells though channels that open and close in response to changes in the neuron, for instance, changes in voltage across the cell’s membrane. Dysfunction in any of these channels can lead to problems, including neurologic or psychiatric disorders. Dr. Lipscombe explores the genesis of differences in calcium channels, by pinpointing how these channels are created at the genetic level — at the level of an early process known as alternative RNA splicing. Alternative splicing can lead to variations in calcium channels that could affect both the behavior of an organism and its response to different substances and medications.
Voltage-gated calcium channels generate rapid, transient intracellular calcium signals in response to membrane depolarization. Neuronal CaV channels regulate a range of cellular functions and are implicated in a variety of neurological and psychiatric diseases. Each of the 10 mammalian Cacna1 genes that encode the main subunits of CaV channels has the potential to generate tens to thousands of CaV channels by alternative pre-mRNA splicing. Alternative pre-mRNA splicing may enrich the pool of CaV channel structures and functions used by cells. The coordinated expression and activity of available nuclear splicing factors determines the composition of the pool of CaV channel isoforms in a given cell type. The activity of splicing factors are in turn regulated by other molecules that regulate various cellular features, including cell-type, activity, metabolic states, developmental state, and other factors.
We study the cellular and behavioral consequences of individual CaV splice isoforms and the cell-specific splicing factors that control exon selection. Altered patterns of alternative splicing of CaV pre-mRNAs can impact the behavior of an organism in subtle but measurable ways, with the potential in humans to influence drug efficacy and disease severity. The composition of the pool of CaV mRNA splice isoforms varies with cell-type, stage of development, and possibly neuronal activity. Thus, anticipated functional differences among splice isoforms within a given CaV family are either individually or collectively contributing to neuronal processes.
Alternatively spliced exons are present in >95% of multi-exon genes suggesting that cellular control over exon selection must play a critical role in normal development and
cell function. But, the cellular and behavioral consequences of only a few CaV splice isoforms are known. I discuss our approaches to determine them. I show that at least for certain sites of alternative splicing in Cacna1 genes, exon choice and the resultant changes in CaV channel activity affect behavior. Specifically, the enrichment of an alternatively spliced exon of Cacna1b in capsaicin-responsive nociceptors of dorsal root ganglia impacts the cellular and the analgesic actions of morphine in vivo.