José A. Carrillo

Comparative study of satellite DNA in ants of the Messor genus

The satellite DNA of ants Messor barbarus and Messor bouvieri is analysed. The results are compared with the satellite DNA data from Messor structor previously reported and with new data obtained from the genome of geographically distinct M. structor population, which have shown that this satellite DNA is highly conserved within the species. The satellite DNA is organized as tandemly repeated 79 bp monomers in all species. The sampled sequences of the three species show a high similarity and all belong to the same family of satellite DNA. Sequence comparisons suggested the occurrence of highly effective homogenization mechanism acting upon the ant genomes. In accordance with this hypothesis, putative gene conversion tracts are identified when the different monomers of the same species are compared. The highest sequence conservation in all species corresponds to a single region with inverted repeats. A CENP-B-like motif was found in this region. The possibility that it may be involved in the homogenization of satellite DNA is discussed.

Characterization and evolutionary dynamics of a complex family of satellite DNA in the leaf beetle Chrysolina carnifex (Coleoptera, Chrysomelidae)

The present study characterizes the complex satellite DNA from the specialized phytophagous beetle species Chrysolina carnifex. The satellite DNA is formed by six monomer types, partially homologous but having diverged enough to be separate on the phylogenetic trees, since each monomer type is located on a different branch, having statistically significant bootstrap values. Its analysis suggests a common evolutionary origin of all monomers from the same 211-bp sequence mainly by means of base-substitution mutations evolutionarily fixed to each monomer type and duplications and/or deletions of pre-existing segments in the 211-bp sequence. The analysis of the sequences and Southern hybridizations suggest that the monomers are organized in three types of repeats: monomers (211-bp) and higher-order repeats in the form of dimers (477-bp) or even trimers (633-bp). These repetitive units are not isolated from others, and do not present the pattern characteristic for the regular tandem arrangement of satellite DNA. In-situ hybridization with biotinylated probes corresponding to the three types of repeats showed the pericentromeric location of these sequences in all meiotic bivalents, coinciding with the heterochromatic blocks revealed by C-banding, indicating in addition that each type of repeat is neither isolated from others nor located in specific chromosomes but rather that they are intermixed in the heterochromatic regions. The presence of this repetitive DNA in C. haemoptera, C. bankii and C. americana was also tested by Southern analysis. The results show that this satellite DNA sequence is specific to the C. carnifex genome but has not been found in three other species of Chrysolina occupying similar or different host plants.

Satellite DNA in the elm leaf beetle, Xanthogaleruca luteola (Coleoptera, Chrysomelidae): characterization, interpopulation analysis, and chromosome location

In this paper the satellite DNA (stDNA) of the phytophagous beetle Xanthogaleruca luteola is analyzed. It is organized in a tandem repeat of 149-bp-long monomers, has an AT content of 59%, and presents inverted internal repeats. Restriction analysis of the total DNA with methylation-sensitive enzymes suggests that this repetitive DNA is not methylated. Analysis of the electrophoretic mobility of stDNA on non-denaturing polyacrylamide gels showed that this stDNA is not curved. In situ hybridization with a biotinylated probe of the stDNA revealed a pericentromeric localization of these sequences in the majority of the meiotic bivalents. We have studied the stDNA of X. luteola from two populations with very distinct geographical origins. The sequence and phylogenetic analysis of monomers from these two populations showed that the repetitive element is conserved within the species. Putative gene conversion tracts are identified when the different monomers of the same population are compared. These results could indicate the existence of processes of homogenization that would extend these mutations to all the satellite repeats.

Isolation and characterization of two families of satellite DNA with repetitive units of 135 bp and 2.5 kb in the ant Monomorium subopacum (Hymenoptera, Formicidae)

Analyzing the satellite DNA in the ant species Monomorium subopacum we found two unrelated families of satellite DNA. Because these satellite DNA families were isolated using the two enzymes HaeIII and EcoRI we called the two families HaeIII and EcoRI family, respectively. The HaeIII family proved to be organized in a 135-bp basic unit repeat, the EcoRI family in a 2.5-kb basic unit repeat. The latter represents perhaps the longest satellite DNA isolated up to now in insects. The HaeIII family apparently comprises about 10% of the total genomic DNA whereas the EcoRI family represents only about 1–2%. A comparative analysis of the two satellite DNA sequences showed no homology between the two families although both sequences possessed long A and T stretches. Eight of the 34 chromosomes showed hybridization with the HaeIII family and hybridization signals are visible in six chromosomes with the EcoRI family. Analysis of the electrophoretic mobility of satellite DNA on non-denaturing polyacrylamide showed that the HaeIII family is only slightly curved. However, the unit of the EcoRI satellite DNA family has curvature, especially the first 1000 bp of the monomeric repeat, in which this DNA is AT rich and has numerous A and T stretches. There are also internal inverted subrepeats in each family. The sequences of satellite DNA families found in Monomorium subopacum are different from the sequences of other satellite DNAs cloned in insects, including other species of ants.