One of the major mechanisms by which stem cells maintain tissue homeostasis is by the asymmetric division of stem cells such that one daughter cell remains a stem cell and another daughter cell differentiates. The loss of asymmetric stem cell division could contribute to a wide variety of diseases such as cancer, tissue degeneration, and infertility. Despite its critical importance, little is understood about the epigenetic mechanisms underlying asymmetric cell division. Previously, our lab found that preexisting (old) and newly synthesized (new) histones H3, a major carrier of epigenetic information in Drosophila, are segregated asymmetrically during the asymmetric division of the Drosophila male Germline Stem Cell (GSC), and that the disruption of proper asymmetric histone segregation leads to defects in GSC maintenance and proper spermatogenesis. We recently obtained data suggesting that old and new histones are differentially incorporated during DNA replication, wherein old histones are preferentially incorporated on the leading strand while new histones are incorporated on the lagging strand. However, this explanation alone is not sufficient for creating a global asymmetry old and new histone incorporation on the two sets of sister chromatids. If DNA replication forks fire bidirectionally, it would create a patchwork of old and new histone-enriched chromosomal domains, but not a global asymmetry. We have preliminary data suggesting that the initiation of DNA replication in GSCs is tightly regulated temporally and precisely regulated spatially. We found that GSCs have a unique nuclear architecture and replication initiation pattern: Heterochromatin is localized to a perinucleolar domain where centromeres cluster. DNA replication apparently initiates near this perinucleolar region and progresses outwards. By contrast, in the differentiating GB daughter cell DNA replication initiates stochastically throughout the nucleus prior to the reformation of the nucleolus. This perinucleolar heterochromatin could potentially serve as a fork block for DNA replication, and thereby coordinate DNA replication fork to progress unidirectionally resulting in the establishment of global asymmetric histone incorporation onto the two sets of sister chromatids, in preparation for their asymmetric segregation during mitosis.