Partial mitochondrial gene arrangements support a close relationship between Tardigrada and Arthropoda.
Regions (about 3.7-3.8 kb) of the mitochondrial genomes (rrnL-cox1) of two tardigrades, a heterotardigrade, Batillipes pennaki, and a eutardigrade, Pseudobiotus spinifer, were sequenced and characterized. The gene order in Batillipes was rrnL-V-rrnS-Q-I-M-nad2-W-C-Y-cox1, and in Pseudobiotus it was rrnL-V-rrnS-Q-M-nad2-W-C-Y-cox1. With the exception of the trnI gene, the two tardigrade regions have the same gene content and order. Their gene orders are strikingly similar to that of the chelicerate Limulus polyphemus (rrnL-V-rrnS-CR-I-Q-M-nad2-W-C-Y-cox1), which is considered to be ancestral for arthropods. Although the tardigrades do not have a distinct control region (CR) within this segment, the trnI gene in Pseudobiotus is located between rrnL-trnL1 and trnL2-nad1, and the trnI gene in Batillipes is located between trnQ and trnM. In addition, the 106-bp region between trnQ and trnM in Batillipes not only contains two plausible trnI genes with opposite orientations, but also exhibits some CR-like characteristics. The mitochondrial gene arrangements of 183 other protostomes were compared. 60 (52.2%) of the 115 arthropods examined have the M-nad2-W-C-Y-cox1 arrangement, and 88 (76.5%) the M-nad2-W arrangement, as found in the tardigrades. In contrast, no such arrangement was seen in the 70 non-arthropod protostomes studied. These are the first non-sequence molecular data that support the close relationship of tardigrades and arthropods.
Ryu
Shi Hyun
SH
Department of Biology, Teachers College, Kyungpook National University, Daegu 702-701, Korea.
Lee
Ji Min
JM
Jang
Kuem-Hee
KH
Choi
Eun Hwa
EH
Park
Shin Ju
SJ
Chang
Cheon Young
CY
Kim
Won
W
Hwang
Ui Wook
UW
D000818:Animals; D001181:Arthropods / Q000145:classification / Q000235:genetics*; D001483:Base Sequence; D019143:Evolution, Molecular; D050259:Genes, Mitochondrial / Q000235:genetics*; D054629:Genome, Mitochondrial / Q000235:genetics*; D007448:Invertebrates / Q000145:classification / Q000235:genetics; D010802:Phylogeny