Repetitive sequences in the lamprey mitochondrial DNA control region and speciation of Lethenteron

The sequence of the mitochondrial DNA control region was examined in four species of lamprey in the genus Lethenteron. The 3′ half of the control region contains highly variable repeat sequences, showing variation in both copy number and nucleotide sequence, even within local populations. Detailed analyses of the sequences of the repeats allowed us to deduce that slipped-strand mispairing during DNA replication, accompanied by a high rate of substitutions and indels, was primarily responsible for the variation in the repeats. We also found that some cases might be better explained by gene conversion, due to intermolecular recombination. Based on the observed variable nature of the mitochondrial control region, we searched for molecular markers in mitochondrial DNA, because there are few fixed genetic markers for distinguishing between Lethenteron japonicum and Lethenteron kessleri. However, we found no reliable markers in the control region. No fixed substitution was observed in intron sequences of the nuclear gene SoxD. Thus, these two species likely diverged quite recently and may possess only a limited number of fixed genetic loci

Characterization and phylogenetic position of two sympatric sister species of toxic flatworms Planocera multitentaculata and Planocera reticulata (Platyhelminthes: Acotylea)

The complete mitochondrial genomes of two toxic flatworm species of the genus Planocera were determined. The total length of mitochondrial DNA (mtDNA) was 15,657 bp in Planocera multitentaculata and 15,486 bp in Planocera reticulata and included 12 protein-coding genes, 2 ribosomal RNA (rRNA) genes, 22 transfer RNA (tRNA) genes, and 4 non-coding regions. The mitochondrial gene arrangement of these planocerid species was identical to that of previously described acotylean species, Hoploplana elisabelloi, and also to those of other polyclads. Maximum likelihood analysis against 14 Platyhelminthes showed that a tree was robustly constructed using 12 protein-coding genes than COI gene

The possible interplanetary transfer of microbes: assessing the viability of Deinococcus spp. under the ISS environmental conditions for performing exposure experiments of microbes in the Tanpopo mission

To investigate the possible interplanetary transfer of life, numerous exposure experiments have been carried out on various microbes in space since the 1960s. In the Tanpopo mission, we have proposed to carry out experiments on capture and space exposure of microbes at the Exposure Facility of the Japanese Experimental Module of the International Space Station (ISS). Microbial candidates for the exposure experiments in space include Deinococcus spp.: Deinococcus radiodurans, D. aerius and D. aetherius. In this paper, we have examined the survivability of Deinococcus spp. under the environmental conditions in ISS in orbit (i.e., long exposure to heavy-ion beams, temperature cycles, vacuum and UV irradiation). A One-year dose of heavy-ion beam irradiation did not affect the viability of Deinococcus spp. within the detection limit. Vacuum (10−1 Pa) also had little effect on the cell viability. Experiments to test the effects of changes in temperature from 80 °C to −80 °C in 90 min (±80 °C/90 min cycle) or from 60 °C to −60 °C in 90 min (±60 °C/90 min cycle) on cell viability revealed that the survival rate decreased severely by the ±80 °C/90 min temperature cycle. Exposure of various thicknesses of deinococcal cell aggregates to UV radiation (172 nm and 254 nm, respectively) revealed that a few hundred micrometer thick aggregate of deinococcal cells would be able to withstand the solar UV radiation on ISS for 1 year. We concluded that aggregated deinococcal cells will survive the yearlong exposure experiments. We propose that microbial cells can aggregate as an ark for the interplanetary transfer of microbes, and we named it ‘massapanspermia’