Although cell proliferation is an essential cell behavior for animal development, a detailed analysis of spatial and temporal patterns of proliferation in whole embryos are still lacking for most model organisms. Zebrafish embryos are particularly suitable for this type of analysis due to their transparency and size. Therefore, the main objective of the present work was to analyze the spatial and temporal patterns of proliferation during the first day of zebrafish embryo development by indirect immunofluorescence against phosphorylated histone H3, a commonly used mitotic marker. Several interesting findings were established. First, we found that mitosis metasynchrony among blastomeres could begin at the 2- to 4-cell stage embryos. Second, mitosis synchrony was lost before the midblastula transition (MBT). Third, we observed a novel pattern of mitotic clusters that coincided in time with the mitotic pseudo "waves" described to occur before the MBT. Altogether, our findings indicate that early development is less synchronic than anticipated and that synchrony is not a requirement for proper development in zebrafish.
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