MOLECULAR CHARACTERIZATION OF A CENTROMERIC SATELLITE DNA IN THE HEMICLONAL HYBRID FROG RANA-ESCULENTA AND ITS PARENTAL SPECIES

Hybrid water frogs Rana esculenta reproduce by hybridogenesis: one par ental genome (of Rana lessonae) is excluded in the germ line, the othe r (of Rana ridibunda) is clonally transmitted to haploid gametes. The two parental species differ in that the amount of centromeric heteroch romatin revealed by differential staining is much higher in Rana ridib unda. An abundant, tandemly arrayed, centromeric satellite DNA, design ated RrS1, is revealed in Rana ridibunda genomes by the restriction en donuclease Stul, which generates a major repetitive sequence fragment of 300 and a minor one of 200 bp. This AT-rich (68%) satellite family is located at the centromeres of the five largest chromosomes (1-5) an d of a medium to small heterobrachial one (8 or 9); it thus constitute s only part of the centromeric heterochromatin that characterizes all Rana ridibunda chromosomes. RrS1 represents about 2.5% of the genome o f Rana ridibunda; it may represent as little as 0.2% of the genome of Rana lessonae, and cannot be detected in Xenopus laevis frogs or Salam andra salamandra and Triturus carnifex salamanders. Segments of the sa tellite sequence are similar to sequences of yeast centromeric DNA ele ment CDEIII and of the mammalian CENP-B box. A role for RrS1 and other centromeric satellite DNAs in the germ line genome exclusion of the h ybridogenetic frog hybrids, although suggested, has not yet been demon strated.