DNA Template Strand Segregation in Whole Zebrafish

Asymmetric inheritance of sister chromatids has long been predicted to be linked to discordant fates of daughter cells and even hypothesized to minimize accumulation of mutations in stem cells. Here, we use (2'S)-2'-deoxy-2'-fluoro-5-ethynyluridine (F-ara-EdU), bromodeoxyuridine (BrdU), and light-sheet microscopy to track embryonic DNA in whole zebrafish. Larval development resulted in rapid depletion of older, template DNA strands from stem cell niches in retina, brain and intestine. Prolonged label retention occurred in quiescent progenitors that resumed replication in later development. Quantifying >100 daughter cell pairs throughout the body showed no evidence of asymmetric template strand segregation, making it improbable that asymmetric DNA segregation prevents mutational burden.