Background
Circadian rhythms are known to influence a variety of biological phenomena such as cell cycle, sleep-wake rhythm, hormone release and other important physiological functions. Given that cell cycle entry of hibernating hematopoietic stem cells (HSCs) plays a critical role in controlling hematopoiesis, we asked functional significance of the clock gene Bmal1, which plays a central role in regulating circadian rhythms as a transcription factor. Here we investigated the necessity of Bmal1 for HSC functions using Bmal1 deficient (Bmal1⁻/⁻) mice. Findings: Using colony-forming assays in vitro, we found that the frequency of mixed colony formation between Bmal1⁺/⁺ and Bmal1⁻/⁻ CD34-KSL cells does not differ significantly. Competitive bone marrow assays also revealed that Bmal1⁻/⁻ bone marrow cells competed normally with wild-type cells and displayed long-term multi-hematopoietic lineage reconstitution. In addition, there were no significant differences in the frequencies and hibernation state of bone marrow HSCs between Bmal1⁺/⁺ and Bmal1⁻/⁻ mice, suggesting that they are independent of circadian rhythms. Conclusions: This paper discusses the necessity of circadian rhythms for HSC functions. Our data clearly shows that a key circadian clock gene Bmal1 is dispensable for intrinsic functions of HSCs, such as differentiation, proliferation and repopulating ability.
Conclusions
This paper discusses the necessity of circadian rhythms for HSC functions. Our data clearly shows that a key circadian clock gene Bmal1 is dispensable for intrinsic functions of HSCs, such as differentiation, proliferation and repopulating ability.