Heteroplasmy in the mtDNA control region of sturgeon (Acipenser, Huso and Scaphirhynchus)

Data from 1238 fishes from 19 sturgeon species and 1 paddlefish were used t o analyze heteroplasmy in sturgeon. Lengths of central repeat units ranged from 74 to 83 bp among sturgeon species. No repeat sequence was found in th e paddlefish, Polyodon spathula. A general feature of the repeat units was the presence of termination associated sequence (TAS) motifs. About 50% of 138 interspecific mutations observed among the D-loop sequences are located 10 bp down- and upstream from these TAS motifs. Interestingly, most homopl asmic species showed deletions upstream to the TAS motifs, whereas deletion s downstream to the TAS motifs: observed in two species do not seem to prec lude heteroplasmy. Calculations of secondary structures and thermal stabili ties of repeat units showed DeltaG values for all heteroplasmic species to be <-8 and for most homoplasmic species <Delta>G value to be >-8. Most hete roplasmic fishes had two and/or three repeat units. No homoplasmic sturgeon with >2 repeat units were observed. Molecular phylogeny based on the entir e cytochrome b showed that heteroplasmy probably resulted fr om a single ev olutionary event. Our data demonstrate that heteroplasmy is present in most sturgeon species and suggest that the thermal stability of the secondary s tructure of the repeat unit in combination with mutations downstream of the TAS sequences influences heteroplasmy.