Systematic Functional Characterization Of Human 21st Chromosome Orthologs In Caenorhabditis elegans

Abstract

Individuals with Down syndrome have neurological and muscle impairments due to an additional copy of the human 21st chromosome (HSA21). Only a few of ~200 HSA21 genes encoding protein have been linked to specific Down syndrome phenotypes, while the remainder are understudied. To identify poorly characterized HSA21 genes required for nervous system function, we studied behavioral phenotypes caused by loss-of-function mutations in conserved HSA21 orthologs in the nematode Caenorhabditis elegans. We identified ten HSA21 orthologs that are required for neuromuscular behaviors: cle-1 (COL18A1), cysl-2 (CBS), dnsn-1 (DONSON), eva-1 (EVA1C), mtq-2 (N6ATM1), ncam-1 (NCAM2), pad-2 (POFUT2), pdxk-1 (PDXK), rnt-1 (RUNX1), and unc-26 (SYNJ1). We also found that three of these genes are required for normal release of the neurotransmitter acetylcholine. This includes a known synaptic gene unc-26 (SYNJ1), as well as uncharacterized genes pdxk-1 (PDXK) and mtq-2 (N6ATM1). As the first systematic functional analysis of HSA21 orthologs, this study may serve as a platform to understand genes that underlie phenotypes associated with Down syndrome.\n\nARTICLE SUMMARYDown syndrome causes neurological and muscle dysfunction due to an extra 21st chromosome. This chromosome has over 200 genes, most of which are understudied. To address this, we studied whether reducing function of these gene equivalents in the worm C. elegans caused neuronal or muscle defects. We identified ten genes conserved between human and worm that mediate function of behaviors. Among these, we show the uncharacterized genes mtq-2 and pdxk-1 are important for synaptic transmission and are exclusively expressed in nervous system. Our analysis may reveal functions of poorly studied genes that affect nervous system function in Down syndrome.