Abstract
Actins are a small family of ubiquitous proteins that are essential cytoskeletal components and are highly conserved during evolution. Actins are usually divided into two classes, the cytoplasmic and muscle actins, which have different functional roles. Here we systematically analyzed the actin genes in the genome of the primitive chordate amphioxus (Branchiostoma floridae). We found that amphioxus contains more than 30 actin genes, many of which are linked. Phylogenetic analysis suggests the amphioxus actin genes have clearly undergone extensive expansion through tandem duplications. The actin genes’ structure also varies a lot, containing 2 to 7 exons. We also cloned two muscle type of actin genes from the amphioxus（B. belcheri）and compared their expression patterns during early development. The slight difference in their expression suggests functional diversification of these actin genes. Our results shed light on the evolution both of actin genes themselves and their functional roles in chordate development.
Highlights
Actins are a small family of ubiquitous proteins that are essential cytoskeletal components and are highly conserved during evolution
The cytoplasmic actin gene BfCA1 is widely expressed while the muscle actin BfMA1 is expressed strongly in somatic muscle and weakly in smooth muscle associated with gill slits
Phylogenetic analysis (Fig.2) of the 27 predicted full length actin proteins showed that they fell into three different groups: the muscle type, the cytoplasmic type and those that showed similar homology to both muscle and cytoplasmic types
Summary
Actins are a small family of ubiquitous proteins that are essential cytoskeletal components and are highly conserved during evolution. Phylogenetic analysis suggests the amphioxus actin genes have clearly undergone extensive expansion through tandem duplications. We cloned two muscle type of actin genes from the amphioxus(B. belcheri)and compared their expression patterns during early development. With the nearly complete genome sequencing of the Florida amphioxus (B. floridae, Putnam et al, 2008), we can systematically study the actin genes in this primitive chordate species. Phylogenetic analysis suggests that the amphioxus actin genes have clearly undergone expansion through tandem and clusteral duplications. We cloned two muscle type of actin genes from the amphioxus and compared their expression patterns during early development. Our results shed light on the evolution both of actin genes themselves and their functional roles in chordate development
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