Fig. 1.
Mx1 and Mx2 proteins were lost in toothed whales. (Top Left) The protein structure of human Mx1 is shown (PDB ID code 3SZR). The dotted line shows the predicted location of the L4 loop (17). BSE, bundle signaling element. (Left) Cladogram showing phylogentic relationship and approximate divergence times of five cetaceans relative to cow and human outgroups (29) (mya, millions of years ago). The proposed loss event of Mx1 and Mx2 is designated by a black arrow and a red dashed line. Solid red lines represent lineages with Mx1 and Mx2 loss. (Right) Columns: Ka/Ks ratio for Mx1 and Mx2 of each species relative to cow, the number of premature stop codons, frameshift mutations, deleted exons, and untranscribed exons of the Mx genes coding regions in all species. Asterisks indicate the transcription data are from a closely related Indo-Pacific humpback dolphin. N/A, not available. Note that the minke whale Mx1 and Mx2 show no signs of erosion.