Although non-random sister chromatid segregation has been proposed to underlie asymmetric cell divisions, the underlying biological significance or mechanisms remained elusive. Here we show that non-random sister chromatid segregation during asymmetric division of Drosophila male germline stem cells is mediated by ribosomal DNA (rDNA) loci, consisting of hundreds of tandemly repeated rDNA units. We identify a novel zinc-finger protein CG2199/Indra that binds to rDNA and control non-random sister chromatid segregation. Our data indicate that non-random sister chromatid segregation may reflect the segregation of sister chromatids with different rDNA copy numbers after unequal sister chromatid exchange to maintain rDNA copy number through generations. To our knowledge, this is the first study to provide mechanistic insights into the mechanism of non-random sister chromatid segregation.
Nonrandom sister chromatid segregation of sex chromosomes in Drosophila male germline stem cells
