The mouse DXZ4 homolog retains Ctcf binding and proximity to Pls3 despite substantial organizational differences compared to the primate macrosatellite

Here we extend our comparative genome analysis and report the identification and characterization of the mouse homolog of the macrosatellite. Furthermore, we provide evidence of DXZ4 in a conserved location downstream of the PLS3 gene in a diverse group of mammals, and reveal that DNA sequence conservation is restricted to the CTCF binding motif, supporting a central role for this protein at this locus. However, many features that characterize primate DXZ4 differ in mouse, including the overall size of the array, the mode of transcription, the chromatin organization and conservation between adjacent repeat units of DNA sequence and length. Ctcf binds Dxz4 but is not exclusive to the inactive X chromosome, as evidenced by association in some males and equal binding to both X chromosomes in trophoblast stem cells.Characterization of Dxz4 reveals substantial differences in the organization of DNA sequence, chromatin packaging, and the mode of transcription, so the potential roles performed by this sequence in mouse have probably diverged from those on the primate X chromosome.Over two-thirds of the human genome is likely to be composed of repetitive DNA [1], of which a significant proportion is tandem repeat DNA [2]. The tandem repeats consist of homologous DNA sequences arranged head to tail, and the number of repeat units is invariably polymorphic from one individual to the next [3]. The size of the individual repeat unit varies substantially, from the simple microsatellite composed of individual repeat units of 1 to 6 bp spanning tens to hundreds of base pairs [4] to those consisting of individual repeat units of several kilobases that can cover hundreds to thousands of kilobases [5]. For some tandem repeat DNA, deciphering of function is assisted by location, such as the alpha satellite DNA that defines active centromeres [6] to the telomeric minisatellite [7], but the roles of others in our genome remain unknown, resulting in opinions in the past that they serve n