MBE Advance Access published online on April 9, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn087
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The Dscam Homologue of the Crustacean Daphnia is Diversified by Alternative Splicing Like in Insects
1 Zoologisches Institut, Evolutionsbiologie, Universität Basel, Vesalgasse 1, CH-4051 Basel, Switzerland
2 Institut for Evolutionary Biology, School of Biological Sciences, Kings Buildings, University of Edinburgh, Edinburgh, EH9 3JT, UK
3 Hubbard Center for Genome Studies, University of New Hampshire, 35 Colovos Road, Durham NH 03824, USA
Daniela Brites d.brites{at}unibas.ch
Received for publication December 3, 2007. Revision received March 13, 2008. Accepted for publication April 6, 2008.
In insects, the homologue of the Down syndrome cell adhesion molecule (Dscam) is a unique case of a single-locus gene whose expression has extensive somatic diversification in both the nervous and immune systems. How this situation evolved is best understood through comparative studies. We describe structural, expression and evolutionary aspects of a Dscam homolog in 2 species of the crustacean Daphnia. The Dscam of Daphnia generates up to 13,000 different transcripts by the alternative splicing of variable exons. This extends the taxonomic range of a highly diversified Dscam beyond the insects. Additionally, we have identified 4 alternative forms of the cytoplasmic tail that generate isoforms with or without inhibitory or activating immunoreceptor tyrosine-based motifs (ITIM-ITAM), something not previously reported in insect's Dscam. In Daphnia, we detected exon usage variability in both the brain and hemocytes (the effector cells of immunity), suggesting that Dscam plays a role in the nervous and immune systems of crustaceans, as it does in insects. Phylogenetic analysis shows a high degree of amino acid conservation between Daphnia and insects except in the alternative exons, which diverge greatly between these taxa. Our analysis shows that the variable exons diverged before the split of the two Daphnia species and is in agreement with the nearest-neighbour model for the evolution of the alternative exons. The genealogy of the Dscam gene family from vertebrates and invertebrates confirmed that the highly diversified form of the gene evolved from a non-diversified form before the split of insects and crustaceans.
Key Words: Dscam evolution • Immunoglobulin domains • Somatic diversity • Immunity • Nervous system • Arthropoda
* These authors contributed equally to this work
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  H.-H. Yu, J. S. Yang, J. Wang, Y. Huang, and T. Lee Endodomain Diversity in the Drosophila Dscam and Its Roles in Neuronal Morphogenesis J. Neurosci., February 11, 2009; 29(6): 1904 - 1914. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. Schmucker and B. Chen Dscam and DSCAM: complex genes in simple animals, complex animals yet simple genes Genes & Dev., January 15, 2009; 23(2): 147 - 156. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Schulenburg, J. Kurtz, Y. Moret, and M. T Siva-Jothy Introduction. Ecological immunology Phil Trans R Soc B, January 12, 2009; 364(1513): 3 - 14. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 O. Roth, B. M Sadd, P. Schmid-Hempel, and J. Kurtz Strain-specific priming of resistance in the red flour beetle, Tribolium castaneum Proc R Soc B, January 7, 2009; 276(1654): 145 - 151. [Abstract] [Full Text] [PDF]
|
|