Although its great importance on Primates genomes the LINE 1 elements were much less characterized than the Alu elements. Analyzing the New World monkey genus Saguinus Serfaty et al 2017 carried out a comparative mapping of LINE 1 in S bicolor and S midas to understand the contribution of this element to their genomic organization and karyotype evolution. Although both species have the same diploid number and similar GTG banding patterns the authors showed that LINE 1 distribution may be used as diagnosis in species differentiation as well as in natural hybrids identification. Their results as well as those of Boissinot et al 2004 for S oedipus suggested a recent expansion and diversification of LINE 1 in the genome of species of Saguinus. Another important class of repetitive sequences that compose the Primates genome is the satellite DNAs characterized by long arrays of tandem head to tail arranged repeats frequently rich in A T. The size of each repeat unit monomer may differ in nucleotide sequence length ranging from five nucleotides for human satellite III up to several hundreds of base pairs abundance and complexity. The monomers form long and homogeneous arrays which compose the constitutive heterochromatin of centromeric pericentromeric subtelomeric and interstitial regions Plohl et al 2008 2012 Garrido Ramos 2017. Satellite DNAs families represent abundant fractions of the genomes of most eukaryotic species Plohl et al 2012;
In Primates, for example, they may constitute 2 7 of Callithrix jacchus Araújo et al 2017a 5 of human Miga 2015 10 of Gorilla gorilla Gordon et al 2016 and 12 of Aotus nancymaae Araújo et al in press genomes. This variation may be attributed to differential amplification deletion of several families in each lineage in which they can contribute to the extensive heterochromatic variation observed even among phylogenetically close species. In contrast to the high interspecific nucleotide divergence, intraspecific copies of the satellite DNAs are very homogeneous low variability due to a phenomenon known as Concerted Evolution Dover 1986. In this process mutations in the monomer sequences of satellite, DNAs can be eliminated or scattered in the array which leads to the homogenization of the repeats with consequent fixation in the individuals of the population Plohl et al 2012.
Thus satellite DNA sequences are rapidly evolving sequences that might cause reproductive barriers between organisms and promote speciation Plohl et al 2014. Satellite DNAs were included within the useless fraction of the genome along with the so-called junk DNAs. It had long been believed that this hypothesis was true since these highly diverse sequences are noncoding repeats associated with heterochromatin and especially because they were believed to perform no biological function Orgel and Crick 1980. In recent years, however, satellite DNAs have gained special attention as a growing number of studies have shown that sequences from several organisms can play important roles in various biological functions such as the formation of centromere locus and the heterochromatin of the pericentromeric area and chromosome organization pairing and segregation Plohl et al 2008 2012 2014. Furthermore, their transcripts may be involved in the assembly of the kinetochore in the control of telomere elongation capping and replication in the modulation of chromatin and in the regulation of heterochromatin establishment and maintenance Plohl et al 2012 Biscotti et al 2015. In addition to the centromeric satellite DNAs the subtelomeric families also have been related to genomic stability chromosomal replication pairing and segregation cell cycle regulation aging and immortalization chromosome location within the nucleus transcriptional regulation of subtelomeric genes among others revision in Garrido Ramos 2017.
Concerning Primates satellite DNAs it is now well appreciated that the alpha satellite DNA is the most studied repetitive sequence. This satellite DNA was firstly isolated in the genome of the African green monkey Cercopithecus aethiops in 1971 by Maio Maio 1971 and latter characterized by Rosenberg and colleagues Rosenberg et al 1978. Since then alpha satellite DNA has been identified throughout the order Primates including great apes Old World monkeys and New World monkeys Tables Y and X with the exception of the suborder Strepsirrhini Table Z Maio et al 1981 In Strepsirrhini, for instance, the centromeres are composed by the DMA1 146 bp motifs and DMA2 268 bp monomers satellite DNAs in Daubentonia Lee et al 2011 and Mn53 53 bp satellite DNA in Microcebus Larsen et al 2017 all unrelated to alpha satellite DNAs. The alpha satellite DNA consists of repeat units of around 171 bp in the infraorder Catarrhini and of about 340 bp in Platyrrhini with the exception of Chiropotes satanas Pithecia irrorata and Cacajao melanocephalus which have alpha satellite repeat motifs of 539 bp 559 bp and higher than 550 bp respectively Fanning et al 1993. Alves et al 1994 1998 Alkan et al 2007 Cellamare et al 2009 Alpha satellite DNA repetitive units form homogeneous arrays usually composing the constitutive heterochromatin of primary constrictions and consequently related to the maintenance of centromeric function. Willard 1991 Additional alpha sequences were also detected at telomeres and interstitial regions of the Owl World monkeys Symphalangus Baicharoen et al 2012 2014 Koga et al 2012 and Nomascus Cellamare et al 2009 Baicharoen et al 2012 2014 Koga et al 2014 in which these loci might represent regions of evolutionary genomic instability and may be involved in the high rates of evolutionary rearrangements of their karyotypes Cellamare et al 2009.
