Figure 5

Dual growth phase model of miRNA gene cluster in intron 10 of the Sfmbt2 gene. A) During the first extension phase of the cluster in the last common ancestor of mouse and rat a 0.3 kb SHORT1 (yellow box) was copied by gene conversion. Ancestral SHORT1 contains the self-complementary microsatellite which may (mice) or may not (rats) evolve to miRNA genes (red arrow); this sequence is preceded by the 3' half of a B1F3-SINE (green arrow). A B1F3 full-length copy marks the 3' borders of both examined clusters. The initial unit diverged into MSHORT1 (0.3 kb) and RSHORT1 (0.2 kb), which are both detected in rat, while only MSHORT1 is found in mouse. B) Diversification of MSHORT1 in mouse caused a fixation of ten adjacent elements in the head-to-tail arrangement to create one 2.5 kb MLONG1 element (gray arrow), which was further amplified. Fixation involved sequence loss (dashed area) and mutation based element alienation beyond recognition of B1F3-elements and microsatellites (white arrow).