Isolation of repetitive sequence elements from the genome of a mayfly Rhithrogena japonica (Ephemeroptera: Heptageniidae)

Isolation of short, tandem repeat sequences from mayfly Rhithrogena japonica Uéno 1928 has been carried out by probing the multicopy DNA regions using labeled total genomic DNA. Several microsatellites comprised of pyrimidine/purine-biased (Pyr/Pur) repeating units (CT, TCTG, and TCTCTG) and two minisatellites were identified. No locus containing (CA) n repeat has been identified so far by screening with total genomic DNA and (CA) 25 probes. The Pur/Pyr microsatellites may be more abundant than (CA) n microsatellite in the R. japonica genome. Both minisatellite sequences, termed Rja66 family (107bp repeating unit) and Taq I-family (repeating unit about 160bp), have self-complementary regions within the repeating units, thereby conforming to stem-loop structures in single-stranded DNA. As for microsatellite loci, a preliminary analysis on two microsatellites Rja18-1 (CT repeat, FJ827088) and Rja130F (TCTCTG repeat, FJ826512) was done for a local population of R. japonica , showing that they were highly polymorphic. Characterization of genetic structures of local R. japonica populations using Rja18-1 locus, demonstrated significant differences between geographically distant populations indicating an impaired genetic flow between such populations.