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Abstract

We have characterized two novel, complex, heterochromatic repeat sequences, MS3 and MS4, isolated from Microtus rossiaemeridionalis genomic DNA. Sequence analysis indicates that both repeats consist of unique sequences interrupted by repeat elements of different origin and can be classified as long complex repeat units (LCRUs). A unique feature of both repeat units is the presence of short interspersed repeat elements (SINEs), which are usually characteristic of the euchromatic part of the genome. Comparative analysis revealed no significant stretches of homology in the nucleotide sequences between the two repeats, suggesting that the repeats originated independently during the course of vole genome evolution. Fluorescence in situ hybridization analysis demonstrates that MS3 and MS4 occupy distinct domains in the heterochromatic regions of the sex chromosomes in M. transcaspicus and M. arvalis but collocalize in M. rossiaemeridionalis and M. kirgisorum heterochromatic blocks. The localization pattern of the repeats on the vole chromosomes confirms the independent origin of the two repeats and suggests that expansion of the heterochromatic blocks has occurred subsequent to speciation.

Dynamics of the Two Heterochromatin Types during Imprinted X Chromosome Inactivation in Vole Microtus levis

“…In vole extraembryonic tissues, the paternal X-chromosome is inactivated [21], [22] and the vole TS cells, like these of mice, demonstrate imprinted XCI and Xist RNA accumulation on Xi (Figure 1A) [19]. The X-chromosome of M. levis is acrocentric and has a giant block of constitutive heterochromatin consisting of two repetitive sequences: MS3 (3265 bp) and MS4 (4088 bp), which contain mobile element fragments [23].…”

“…It is easily revealed by strong telomeric and narrow pericentromeric bands of MS4 repeat [23]. uH2A immunostaining combined with DNA FISH (MS4 repeat) showed that the Y-chromosome was enriched with uH2A distributed uniformly along the entire chromosome (Figure 5).…”

FGF4 Independent Derivation of Trophoblast Stem Cells from the Common Vole

“…5C). The heterochromatin-specific repeat MS4 [40] was used as a marker of the maternal M. rossiaemeridionalis X, thereby allowing us to establish unequivocally if Xist was being transcribed from the maternal, or paternal X chromosome. If the Xist domain localises together with the MS4 domain, then the X inactivation pattern is somatic-type, in which the M. rossiaemeridionalis X is preferentially inactivated.…”

Structural and Evolutionary Relationships in the Giant Sex Chromosomes of Three Microtus Species

“…Moreover, diversity in the type of sequences that compose these chromosomes is extraordinary, even in the same species [ 13 ]. The list of sequences that are currently known includes satellite DNAs [ 14 , 17 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ], non-tandem complex repeats [ 7 , 20 , 30 , 31 ], L1-related retroelements [ 21 , 32 , 33 ], Long Terminal Repeats (LTRs) retrotransposons [ 34 , 35 , 36 ], interstitial telomeric sequences (ITSs) [ 37 ] and pseudogenes [ 18 , 36 ].…”