Retention of Latent Centromeres in the Mammalian Genome

Abstract

The centromere is a cytologically defined entity that possesses a conserved and restricted function in the cell: it is the site of kinetochore assembly and spindle attachment. Despite its conserved function, the centromere is a highly mutable portion of the chromosome, carrying little sequence conservation across taxa. This divergence has made studying the movement of a centromere, either within a single karyotype or between species, a challenging endeavor. Several hypotheses have been proposed to explain the permutability of centromere location within a chromosome. This permutability is termed "centromere repositioning" when described in an evolutionary context and "neocentromerization" when abnormalities within an individual karyotype are considered. Both are characterized by a shift in location of the functional centromere within a chromosome without a concomitant change in linear gene order. Evolutionary studies across lineages clearly indicate that centromere repositioning is not a rare event in karyotypic evolution and must be considered when examining the evolution of chromosome structure and syntenic order. This paper examines the theories proposed to explain centromere repositioning in mammals. These theories are interpreted in light of evidence gained in human studies and in our presented data from the marsupial model species Macropus eugenii, the tammar wallaby.

Genomic Instability Within Centromeres of Interspecific Marsupial Hybrids

“…The first sequence, sat23, is a 178-bp satellite that is capable of binding the centromere protein CENP-B both in vitro and in vivo and most likely represents the primary satellite dictating centromere function within this group of mammals (Bulazel et al 2006). The second, KERV-1, is a retrovirus that is found in the genomes of a wide range of marsupials (Ferreri et al 2005). It is found at higher copy number at the active centromere (O'Neill et al 1998;Ferreri et al 2004) as well as in low copy number at breaks of synteny between the conserved chromosome segments within marsupials (Ferreri et al 2004).…”

“…Blots were prehybridized and hybridized according to Ferreri et al (2005) at 65°overnight, washed in 13 SSC, 0.1% SDS at 65°, and exposed to film overnight at À80°. Cytb probe was produced by PCR as per Bulazel et al (2007) and hybridized as for sat23 and KERV.…”

Fast Diploidization in Close Mesopolyploid Relatives ofArabidopsis

“…The centromere inactivation will ensure regular meiotic segregation of the fusion chromosome and can result in evolutionary fixed reduction of chromosome number. Several cases of inactivated ancestral centromeres as well as the emergence of neocentromeres (centromere repositioning) were reported in mammalian species (e.g., Ferreri et al, 2005;Ventura et al, 2007), but only a few examples of centromere inactivation (and reactivation; F. ) in plants, including dicentric chromosomes of Trititiceae (Sears and Camara, 1952;Luo et al, 2009), maize (Zea mays) B chromosomes (F. Han et al, 2006, and potentially also chromosomes of two cucurbit species (Y. . Except for the heterochromatic knob on chromosome SN3 corresponding to the AK5 centromere, no heterochromatin was observed at sites of the other 17 presumably inactivated centromeres.…”

Centromere repositioning in cucurbit species: Implication of the genomic impact from centromere activation and inactivation

“…Thus, neocentromeres do not seem to have any evolutionary advantage over existing native centromeres. However, comparative mapping among closely related mammalian species has revealed position changes of some centromeres during evolution, most likely via neocentromere formation (5,(10)(11)(12)(13)(14)(15). Centromere repositioning (CR) events have occurred frequently in some mammalian lineages.…”