One major question in evolutionary biology is understanding the genes which underlie traits and where these genes come from. This project takes on special importance regarding the evolution of multicellularity, especially given the phenotypic and life history changes necessary for the evolution of multicellularity. During the evolution of multicellularity, the unit of selection shifts from the lower level (i.e., cells) to a group of cells; cells lose evolutionary fitness through specialization on fitness components of the group. When this happens, cells are integrated into the fitness of the group of cells, and adaptations occur at the group level to solidify individuality.
The unicellular and multicellular genomes of the volvocine algae have already been published (Merchant et al. 2007; Prochnik et al. 2010). The genome of Volvox carteri identified important transcription factors (i.e., cyclins and regA (Duncan et al. 2007; Prochnik et al. 2010)) and cell wall genes (pherophorins and metalloproteases) associated with the evolution of multicellularity. Working with Dr. Brad Olson at KSU, I have sequenced the genome of Gonium pectorale, an undifferentiated colonial volvocine algae with 8-16 cells.
This research aims to further identify which genes are associated with the evolution of multicellularity, as well as the order in which they evolved. After looking at a variety of genomic measures (including transcription factors, Pfam protein functional domains, gene family evolution, microRNA target genes, protein domain architecture, and de novo genes), we suggest that large scale, genomic modifications are not underlying the evolution of multicellularity in the volvocine algae. Instead, we looked to specific genes to explain the mechanistic basis for the evolution of multicellularity.
Substantial cell cycle regulation modifications such as expanded cyclin D gene familes and structural modifications of the tumor suppressor regulator, retinoblastoma (RB) correlate with multicellularity in Volvox. These differences are also shared with Gonium, suggesting they play an important role in the evolution of multicellularity. We tested this by transforming the RB gene into unicellular Chlamydomonas, which then developed as colonies! This demonstrates a causal link between cell cycle regulation and modification, very early in the evolution of multicellularity, and the origins of group formation.
If you want to know more, read the paper from my Publications page!