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The aim of this work is to investigate the sequence conservation and the evolution of repeated DNA in related species. Satellite DNA is a component of eukaryotic genomes and is made up of tandemly repeated sequences. These sequences are affected by high rates of mutation that lead to the occurrence of species-specific satellite DNAs, which are different in terms of both quantity and quality. In this work, a novel repetitive DNA family, named PjHhaI sat, is described in Pecten jacobaeus. The quantitative analyses revealed a different abundance of this element in the molluscan species investigated in agreement with the "library hypothesis" even if, in this case, at a high taxonomic level. In addition, the qualitative analysis demonstrated an astonishing sequence conservation not only among scallops but also in six other molluscan species belonging to three classes. These findings suggest that the PjHhaI sat may be considered as the most ancients of DNA described so far, which remained "frozen" during molluscan evolution. The widespread distribution of this sat DNA in molluscs as well as its long evolutionary preservation open up questions on the functional role of this element. A future challenge might be the identification of proteins or molecules which interact with the PjHhaI sat.

Within the scope of a project on the characterization of satellite DNAs in polar mollusks, the Antarctic chiton Nuttallochitonmirandus (Thiele, 1906) was analyzed. Two novel families of tandemly repeated DNAs, namely NmH and NmP, are described in their structure and chromosomal localization, and, furthermore, their presence was analyzed in related species. Data reported here display a particular variability in the structural organization of DNA satellites within this species. Processes driving satellite evolution, which are likely responsible for the intriguing variability of the identified satellite DNAs, are discussed., (© 2015 S. Karger AG, Basel.)

The West Palearctic green toads, Bufo viridis , represent a species complex. Apart from tetraploid populations, which form at least one separate species, evidence exists for relevant differentiation among diploid populations. We present the results of a chromosomal (C-, Ag-NOR-, Replication pattern, DAPI and CMA3 banding) and molecular study (isolation and characterization of a satellite DNA family) carried out on a number of Central Asian, European and North African populations. For comparative purposes, our molecular analysis was also extended to specimens of three additional Bufo species (B. bufo, B. mauritanicus and B. cf. regularis ), as well as two rare African bufonids (Werneria mertensis and Wolterstoffina sp.). Our results demonstrate a remarkable karyological and molecular evolutionary stasis in the Bufo viridis complex. In fact, all chromatinic markers showed the same pattern and/or composition in all specimens, independently of their origin and ploidy levels. Even the NOR loci were invariably two and located on the telomeric regions of two chromosomes of the sixth pair, or quartet. Furthermore, very similar patterns of genomic hybridization of a monomeric unit of the Pst I satellite DNA family (named pBv) were observed in all diploid and tetraploid populations, as well as in B. bufo and B. mauritanicus . Finally, pBv hybridizes with monomeric units of Pst I satellite DNA in all species studied, including Werneria and Wolterstorffina, which are thought to have separated from Bufo as early as in the Mesozoic.

A PstI DNA family was isolated from the genome of a lacertid, Lacerta graeca. The 185-bp monomeric unit (pGPS) was cloned and hybridized to DNAs and chromosomes of several lacertid species. The data showed that pGPS hybridizes to the (1) centromeric or pericentromeric heterochromatin of almost all the chromosomes of L. graeca and (2) genomic DNA of species phylogenetically related and unrelated to L. graeca. The presence of pGPS even in species immunologically apart more than 30 million years suggests that this repeated family might be either very ancient or have been conserved during evolution due to its functional role. The latter hypothesis might be supported by the results of sequence analysis which showed some homology with both several alphoid sequences of primates and the CDEIII centromeric sequence of yeast. Segments of the satellite sequence are similar to the mammalian CENP-B box. These observations suggest that pGPS might have a role in determining the centromeric function in lacertid lizards.

This paper reports the isolation and characterization of two HindIII repetitive DNA families from the genome of two lacertid lizards, Podarcis sicula and Lacerta saxicola. These satellites did not appear to be related to each other. The consensus sequences of their monomeric units did not show any similarity, though both DNAs were A-T rich. Moreover, each of them was found only in closely related species. The monomeric unit of the HindIII DNA family isolated from P. sicula (pLHS) showed a close resemblance to pLCS, a centromeric satellite DNA previously isolated from the same species; it was, however, mainly localized at pericentromeric, interstitial and telomeric levels. The results also provide interesting information on the systematics of the lacertids studied.

1. The composition and phyletic distribution of a highly repetitive satellite DNA, isolated from Podarcis sicula, was studied. 2. This DNA was rich in adenine and thymine and displayed frequent adenine stretches. It was always located on the centromeric heterochromatin even in quite taxonomically distant species. 3. Southern blot hybridization of the Taq I satellite on various species of lacertid families showed a close affinity among Podarcis, Algyroides and Lacerta dugesii. 4. All the other taxa investigated did not seem to possess this repeated sequence.