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<p>Despite the long history of <i>Daphnia</i> hemocytes studies, it is not known whether the hemocytes are produced throughout the lifespan, and if yes, whether they are generated in a specialized hemopoietic tissue or represent a reproducing population. We detected de novo DNA synthesis by EdU staining in a significant portion of circulating hemocytes in adult <i>D. magna.</i> This portion did not vary among phases of molting cycle and showed only a slight decrease with age. There was no matching DNA synthesis elsewhere, inconsistent with the existence of hemopoietic stem cells in solid tissues of adult daphnids. Rather, it appears that circulating hemocytes are proliferating with mitoses continuing throughout life. Hemocytes showed average ploidy of 4, with a considerable variation around that value indicating that either some endomitoses were also present or a significant portion of hemocytes were sampled in G2. However, there was a positive correlation between total DNA content and EdU fluorescence among EdU-positive hemocytes, indicating that many cells were sampled during S-phase. It is not known whether the total number of hemocytes increases with age or the observed proliferation compensates for their losses, as well as whether the EdU-positive hemocytes represent a separate mitotically active stem subpopulation.</p>

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Circulating hemocytes continue to proliferate throughout lifespan in Daphnia

  • 期刊论文

  • 发表日期：

    2026年6月20日

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  • S. C. Cuthrell,
  • L. Y. Yampolsky

摘要

Despite the long history of Daphnia hemocytes studies, it is not known whether the hemocytes are produced throughout the lifespan, and if yes, whether they are generated in a specialized hemopoietic tissue or represent a reproducing population. We detected de novo DNA synthesis by EdU staining in a significant portion of circulating hemocytes in adult D. magna. This portion did not vary among phases of molting cycle and showed only a slight decrease with age. There was no matching DNA synthesis elsewhere, inconsistent with the existence of hemopoietic stem cells in solid tissues of adult daphnids. Rather, it appears that circulating hemocytes are proliferating with mitoses continuing throughout life. Hemocytes showed average ploidy of 4, with a considerable variation around that value indicating that either some endomitoses were also present or a significant portion of hemocytes were sampled in G2. However, there was a positive correlation between total DNA content and EdU fluorescence among EdU-positive hemocytes, indicating that many cells were sampled during S-phase. It is not known whether the total number of hemocytes increases with age or the observed proliferation compensates for their losses, as well as whether the EdU-positive hemocytes represent a separate mitotically active stem subpopulation.