DSCAM

DSCAM and Dscam are both abbreviations for Down syndrome cell adhesion molecule. The case difference between the two abbreviations is significant as DSCAM refers to the gene that encodes for the Dscam protein.

Down syndrome (DS), caused by trisomy 21, is the most common birth defect associated with intellectual disability. Recently, the novel gene DSCAM has been identified in the DS critical region. DSCAM is predicted to be a transmembrane protein with a very high structural and sequence homology to the immunoglobulin (Ig) superfamily of cell adhesion molecules. It is expressed in the developing nervous system with the highest level of expression occurring in the fetal brain. When this gene is over-expressed in the developing fetal central nervous system, it leads to Down syndrome. Diverse glycoproteins of cell surfaces and extracellular matrices, operationally termed as 'adhesion molecules' are important in the specification of cell interactions during development as well as maintenance and regeneration of the nervous system.

A homologue of the Dscam protein in Drosophila melanogaster has 38,016 isoforms arising from four variable exon clusters (12, 48, 33 and 2 alternatives, respectively). By comparison, the entire Drosophila melanogaster genome only has 15,016 genes. The diversity of isoforms from alternative splicing of the Dscam1 gene in D. melanogaster allows every neuron in the fly to display a unique set of Dscam proteins on its cell surface. Dscam interaction stimulates self-avoidance mechanisms that are essential for normal neural circuit development.

The DSCAM protein structure is conserved, with roughly more than 20% amino acid identity across the deuterostomes and protostomes, and assuming an ancestral homologous gene, places the origin of the DSCAM gene at >600 million years ago. Since then, the DSCAM gene has been duplicated at least once in vertebrates and insects.

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