AflaSAT-1, a Satellite DNA in the Grasshopper Abracris flavolineata: Sequence and Chromosomal Evolution in A and B Chromosomes

DIOGO MILANI, E RAMOS, V LORETO, DARDO A. MARTI, A CARDOSO, CESAR MARTINS & DIOGO C CABRAL-DE-MELLO

Foz do Iguacu

Congreso; 21st International Chromosome Conference (ICC); 2016

Satellite DNAs (satDNA) are sequences repeated a hundred to thousand times and are tandemly arrayed. They are enriched mainly in heterochromatin located in centromeres and telomeres, or in intercalary regions, and moreover, they can spread out in specific chromosomes, such as B chromosomes. Here, we isolatedthe first satDNA in the grasshopper Abracris flavolineata , named AflaSAT-1, by restriction enzyme digestion. The sequence was characterized combining cytogenetic, molecular and genomic approaches, aiming to understand the structural organization, evolution in A and B chromosomes, and the possible functionality of this sequence. The AflaSAT-1 is a satDNA shared with other grasshopper species, but our data suggests that it is exclusively enriched in the genome of A. flavolineata . The AflaSAT-1 monomers recovered from individuals belonging to 6 populations and from the microdissected B chromosomes (μB-DNA) presented almost no variation between populations, but 4 exclusive mutations in μB-DNA were noticed, reflecting the common higher mutational rate in B chromosomes. The analysis using the sequenced genome revealed distinct organization for the satDNA with occurrence of clusters containing only the AflaSAT-1 or containing the AflaSAT-1 associated with other satDNA, named AflaSAT-2, but AflaSAT-2 was never found alone. Regarding the chromosomes, in the population from Rio Claro/SP, the AflaSAT-1 and AflaSAT-2 were interlinked with each other forming large blocks in the centromeres of almost all chromosomes, except in the smallest element (pair 11). In the B chromosome, only a small centromeric signal was noticed. At the level of population, the chromosomal distribution for AflaSAT-1 showed slight variations, such as absence of some marks, additional clusters, and heteromorphism. These variations were reflected in AflaSAT-1 copy number estimated by qPCR, suggesting a dynamic expansion or elimination of this satDNA. Finally, the cDNA analysis revealed constitutive transcription signals for AflaSAT-1 in distinct tissues of adults, and in distinct life cycle phases in individuals harboring B chromosomes.