Figure 1.
Expression of ERK proteins in animals. ERK1 and ERK2 proteins were classified as such upon phylogenic study of amino-acid coding sequences (same conclusions were reached with nucleotide sequences; Busca et al., 2015). In invertebrates only one erk gene was identified so far. Ancestral ERK corresponds to ERK protein sequence that cannot be classified into ERK1 or ERK2 group. Protein expression in vertebrate brains was described in the same study. Animal silhouettes are from phylopic (http://phylopic.org/).