[Mouse centromeric tandem repeats in silico and in situ]

The search for all sequences containing centromeric (CEN) minor satellite (MiSat) or pericentromeric (peri-CEN) mouse major satellite (MaSat) was conducted in the whole genome shotgun (WGS) database. The sequences were checked for the presence of the known dispersed repeats using the Censor software. The presence of tandem repeats was tested using Tandem Repeat Finder (TRF). Monotonous MiSat and MaSat arrays and MaSat to MiSat array transitions were detected. Moreover, two other types of contacts were revealed: (1) MiSat transition to fragments of retroelements LINE and IAP (ERV family, intracisternal A-type particles), mainly to ORF2 and 5'-LTR containing elements; (2) MaSat transition to two tandem repeats with monomers 21 bp and 31 bp in size. The presence of the MiSat/IAP transition could be checked experimentally. The common DNA motif among the IAP fragments close to MiSat was isolated. IAP-specific primers were constructed and the fragments obtained in PCR with LAP and MiSat primers compiled the plasmid vector library. Clone n51 with the maximum length of the possible insertion (approximately no. 800 bp) was selected from the library. FISH on extended chromatin fibers (fiberFISH) carried out on the n51 clone demonstrated that the main signal definitely belonged to CEN. However, the signals on the chromosome arms were also detected that could be due to the partial homology of n51 to the dispersed repeats. The duplicated fiberFISH with MiSat and n51 allowed to measure the distances between the fragments. The previously obtained MS3 sequence has some homology to IAP and CEN localization. Accordingly, the regular associations of MiSat with IAP retroelements were shown in silico and in situ. Together with the published data, the present findings suggest that retroelements or their fragments may be essential components of the normal centromere of higher eukaryotes.