Sequence comparison of mariner-like elements among the populations of Bombyx mandarina inhabiting China, Korea and Japan

Mariner-like elements (MLEs) were isolated from Chinese, Korean and Japanese individuals of Bombyx mandarina by the long PCR methods using the inverted terminal repeat of the Hyalophora cecropia MLE as a primer. The amplified clones of about 1.3 kbp in size were regarded to be full-length MLEs and termed Cecropia-ITR-MLEs. The sequences of the elements were determined, trimmed to eliminate any insertions and used to construct a phylogenetic tree. As a result, the Cecropia-ITR-MLE sequences of B. mandarina could be divided into major groups here called the Continental type and the Japanese type. Chinese and Korean specimens mostly belonged to the former group, which is very diverse and may well consist of subgroups. A majority of Honshu (the main island of Japan) specimens belonged to the latter, which is a much more closely related group of sequences. Interestingly, Tsushima (south of Korea) and Hokkaido (close to Russia) specimens mainly fell into the former type, whereas Fukuoka (south of Tsushima) individuals included both.