The role of Down syndrome candidate region 1 (DSCR1) in neurotransmitter release, vesicle recycling and Down syndrome.

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Individuals with Down syndrome (DS) have three copies of human chromosome 21 (HSA21), rather than the normal two. The symptoms observed in DS individuals are therefore due to the overexpression of HSA21 genes. Since all individuals with DS develop symptoms in the brain similar to those see in Alzheimer's disease (AD), there may be a common mechanism that can be traced to the extra gene dosage from HSA21. We are interested in one of these genes, Down syndrome candidate region 1 (Dscr1), which is overexpressed in both DS and AD brains. We hypothesise that Dscr1 has a role in regulating exocytosis, a process in which chemical messengers are released from cells. Exocytosis is highly specialised in the brain where neurotransmitters are released from neuronal synapses in a process known as synaptic transmission. Reduced synaptic transmission is one of the earliest hallmark of DS and AD occurring long before the classical neurological traits of DS and AD such as plaque formation and dementia. We propose that alterations in Dscr1 expression are responsible for the reduced neuronal exocytosis observed in the early stages of DS and AD. We have generated mice in which Dscr1 expression is altered, as occurs in DS and AD brains, and our preliminary studies indicate that exocytosis is reduced in these mice. We now wish to find the intracellular changes responsible for regulating exocytosis when Dscr1 expression is altered. We also aim to compare this to exocytosis in classical DS mouse models which have an extra chromosome 21 and in similar DS mouse models which have normal levels of Dscr1. This project will uncover the currently unknown functions of Dscr1 in exocytosis in an animal model, allow us to gauge whether Dscr1 is solely responsible for altering exocytosis in DS amongst other HSA21 genes, enable us to better understand the mechanisms initiating DS and AD and possibly lead to new targets of early intervention in these diseases.