The nematode C. elegans expresses 26 Argonaute (AGO) proteins which interact with different small RNAs in the worm to regulate of gene expression1. Interestingly, only one AGO has been shown to be essential: CSR-1 (chromosome segregation and RNAi deficient)1. Loss of CSR-1 causes multiple defects in the animal: impaired ability to raise an RNAi response, abnormal germline morphology, chromosome mis-segregation, and embryonic lethality1,2,3.
Various studies have explored roles for CSR-1 in modulating centromeric chromatin2, RNAi1,2, histone mRNA maturation4, small RNA-independent translational regulation5 and meiotic silencing of unpaired chromsomes3. However, these studies have neglected to address the contributions of two distinct isoforms of CSR-1 to overall CSR-1 function.
Initially identified by Claycomb et al., the two CSR-1 isoforms differ by presence/absence of a 5'exon encoding an RG-rich motif and have differential expression across developmental stages2. We are currently using an integrated approach to examine isoform-specific functions across C. elegans tissues and development. Epitope tagged transgenes for each isoform will be used to characterize each form of CSR-1. Preliminary immunolocalization studies have revealed a differential localization pattern for the long isoform of CSR-1 in mitotic embryos distinct from the overall pattern of CSR-1 localization which was previously not appreciated. These observations will be further explored and supplemented with analysis of small RNA and protein binding partners of each isoform to determine the subset of isoform-specific cofactors functioning across C. elegans development.
1. Yigit, E. et al. Cell 127, 747-757 (2006). 2. Claycomb, J.M. et al. Cell 139, 123-134. (2009). 3. She, X., Xu, X., Fedotov, A., Kelly, W.G., & Maine, E.M. PLoS Genet. 5,
e1000624. (2009). 4. Avgousti, D.C., Palani, S., Sherman, U., & Grishok, A. EMBO J. 31, 3821-3832 (2012). 5. Friend, K. et al. Nat. Struct. Mol. Biol. 19, 176-184 (2012).