Abstract
Membrane channel connexin (Cx) forms gap junctions that are implicated in the homeostatic regulation of multicellular systems; thus, hematopoietic cells were assumed not to express Cxs. However, hematopoietic progenitors organize a multicellular system during the primitive stage; thus, the aim of the present study was to determine whether Cx32, a member of the Cx family, may function during the primitive steady-state hematopoiesis in the bone marrow (BM). First, the numbers of mononuclear cells in the peripheral blood and various hematopoietic progenitor compartments in the BM decreased in Cx32-knockout (KO) mice. Second, on the contrary, the number of primitive hematopoietic progenitor cells, specifically the Lin−/c-kit+/Scal+ fraction, the KSL progenitor cell compartment, also increased in Cx32-KO mice. Third, expression of Cx32 was detected in Lin−/c-kit+ hematopoietic progenitor cells of wild-type mice (0.27% in the BM), whereas it was not detected in unfractionated wild-type BM cells. Furthermore, cell-cycle analysis of the fractionated KSL compartment from Cx32-KO BM showed a higher ratio in the G2/M fraction. Taken together, all these results imply that Cx32 is expressed solely in the primitive stem cell compartment, which maintains the stemness of the cells, i.e., being quiescent and noncycling; and once Cx32 is knocked out, these progenitor cells are expected to enter the cell cycle, followed by proliferation and differentiation for maintaining the number of peripheral blood cells.
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Acknowledgment
The authors thank Dr. K. Sai, Ms. E. Tachihara, Ms. N. Moriyama, Ms. Y. Usami and Ms. M. Uchiyama for excellent technical assistance as well as Ms. N. Kikuchi, Ms. M. Yoshizawa and Ms. M. Hojo for secretarial assistance. Use of FACSAria (BD Biosciences) for flow-cytometric analysis was facilitated by Dr. H. Akiyama and Dr. T. Maitani, Division of Food Sciences, NIHS. This study was supported in part by a Grant-in-Aid for Scientific Research (B 11694334, C 16590329 and C 18510066), the Japan Society for the Promotion of Science Invitation Fellowship for Research in Japan (S01275), the Health Sciences Basic Project and the Integrated Study Project in Drug Innovation Science conducted by the Japan Health Sciences Foundation (KHC1204) and the Ministry of Health, Labour and Welfare (MHLW)-Research Fund (H18-Chemistry 001), National Institute of Health Sciences.
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Hirabayashi, Y., Yoon, BI., Tsuboi, I. et al. Membrane Channel Connexin 32 Maintains Lin−/c-kit+ Hematopoietic Progenitor Cell Compartment: Analysis of the Cell Cycle. J Membrane Biol 217, 105–113 (2007). https://doi.org/10.1007/s00232-007-9042-z
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DOI: https://doi.org/10.1007/s00232-007-9042-z