A Novel Emx Gene in Petromyzon marinus Offers Insight into the Timing and Consequences of Gene Duplication in the Chordate Lineage

Abstract

Gene duplication is believed to have played a major role in the evolution of vertebrates. This has led to various hypotheses to explain the implications of gene duplication events, the fates of duplicate genes and what mechanism(s) are preserving duplicate genes. Conclusion Independent Duplication of EmxB Does Not Support Whole Genome Wide Duplication • Emx duplicated independently in lamprey, which fails to support the 2R hypothesis. • Duplication events leading to gnathostome Emx genes (Emx1, Emx2 and Emx3) suggests that the second genomic duplication event occurred after the lamprey-gnathostome split. Under the Classical Model (Ohno 1970), duplicates can be preserved if one copy accumulates selectively favorable mutations which confer novel function while an alternative model suggests genes coexist through degenerative mutations that lead to partitioning of gene function (figure 1). The phylogenetic position of the lamprey P. marinus, bridging protochordates and jawed gnathostomes, makes it a useful tool for studying vertebrate evolution, while the sheer diversity of the Emx gene family makes it a compelling family to study gene duplication. Two copies of Emx exist in amphioxus and three exist in some gnathostomes. In lamprey, only one Emx gene existed, but we have discovered a second Emx gene. The increase in Emx paralogs from t h d t t th t t tl tt E d li ti i hi t g p p yg p EmxB Expression Nests EmxA Expression • EmxA and EmxB expression in day 13 lamprey embryos suggests subfunctionalization outlined by the Duplication-Degeneration-Complementation model (Figure 6.). • DDC model support draws from spatial/ temporal separation in duplicate expression. a) EmxB expression is more dynamic, both spatially and temporally compared to EmxA. b) EmxA is expressed earlier, and for a longer period of time than EmxB. protochordates to gnathostomes suggests at least two Emx duplications in history, but exactly when these duplications occurred and how these Emx homologs are preserved still remains unclear. Experimental Objective: Map EmxB relative to other chordates to resolve the issue of Emx duplication timing and compare the expression of EmxB to its homolog EmxA to provide insight to the mechanism preserving Emx homologs.