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Method Article
This protocol describes using cultured Aorta-Gonad-Mesonephros for expression analyses, colony-forming units in the culture and spleen, and long-term reconstitution to determine the effect of regulatory factors and signaling pathways on hematopoietic stem cell development. This has been demonstrated as an effective system for studying hematopoietic stem cell biology and function.
The limitation of using mouse embryos for hematopoiesis studies is the added inconvenience in operations, which is largely due to the intrauterine development of the embryo. Although genetic data from knockout (KO) mice are convincing, it is not realistic to generate KO mice for all genes as needed. In addition, performing in vivo rescue experiments to consolidate the data obtained from KO mice is not convenient. To overcome these limitations, the Aorta-Gonad-Mesonephros (AGM) explant culture was developed as an appropriate system to study hematopoietic stem cell (HSC) development. Especially for rescue experiments, it can be used to recover the impaired hematopoiesis in KO mice. By adding the appropriate chemicals into the medium, the impaired signaling can be reactivated or up-regulated pathways can be inhibited. With the use of this method, many experiments can be performed to identify the critical regulators of HSC development, including HSC related gene expression at mRNA and protein levels, colony formation ability, and reconstitution capacity. This series of experiments would be helpful in defining the underlying mechanisms essential for HSC development in mammals.
Hematopoietic stem cells (HSCs) are tissue-specific adult stem cells that possess multilineage potential including erythroid, myeloid, and lymphoid cells as well as the ability to self-renew. Recent studies have shown that the earliest HSCs arose from a specialized endothelial population, known as hemogenic endothelium (HE), through the endothelial to hematopoietic transition (EHT) at the ventral wall of dorsal aorta1,2,3,4. Once formed in the aorta-gonad-mesonephros (AGM) region from embryonic (E) 10.5 to E12.5 in the mouse embryo, HSCs will migrate into the fetal liver for expansion and finally colonize the bone marrow to maintain adult hematopoiesis throughout an individual's life5,6. Although this has been studied for many years, the underlying mechanisms of HSC emergence and development remain incompletely understood.
Unlike in vitro fertilization and development of zebrafish embryos, intrauterine development of mouse embryos makes the study of definitive hematopoiesis during embryogenesis much more inconvenient. Although genetic experiments using knockout (KO) mice are commonly utilized, the lack of certain KO mice also limits their use in the hematopoietic research field. In addition, in vivo rescue experiments are not easily performed in KO mice. Since 1996, the AGM explant culture has been developed for hematopoietic studies by the pioneers in the field7. With the help of this culture system, ventral tissues of the AGM region have been identified to promote HSC activity, while dorsal tissues exert an opposite effect8,9. The AGM explant culture system has also been applied to determine the roles of Serotonin, Mpl, SCF, BMP, and Hedgehog signaling in HSC development10,11,12,13,14. Importantly, it is also a popular method used to rescue hematopoietic defects in mutant embryos13,15.
All the procedures including animal subjects have been approved by the Ethical Review Committee in the Institute of Zoology, Chinese Academy of Sciences, Beijing, China.
1. Material Preparation
2. AGM Explant Culture
3. Expression Analyses
4. Colony-Forming Units in the Culture (CFU-C) Assay
5. In Vivo Transplantation Assay
A recent publication reported endothelial cell-derived serotonin promotes the survival of HSCs by inhibiting the pro-apoptotic pathway in the AGM13. To confirm the promoting effect of serotonin on HSC development, Fluoxetine was included. As a selective serotonin re-uptake inhibitor (SSRI), Fluoxetine has been demonstrated to inhibit serotonin re-absorption in peripheral tissues16,17,
It is well known that mature HSCs in the bone marrow can repopulate the blood system of irradiated recipients. Unlike these functional HSCs, the emerging HSCs in the AGM of mouse embryos are immature. Direct transplantation results showed that type I (VE-cad+ CD45- CD41+) and type II (VE-cad+ CD45+) pre-HSCs possess no reconstitution ability20. Taking advantage of the AGM explant culture system, the nascent HSCs in the AGM region can reconstit...
The authors have no conflicting financial interests.
We thank Suwei Gao for help in figure preparation. This work was supported by grants from the National Natural Science Foundation of China (81530004, 31425016) and the Ministry of Science and Technology of China (2016YFA0100500). J.L. performed the experiments and drafted the manuscript; F.L. edited the manuscript. Both authors read and approved the final manuscript.
Name | Company | Catalog Number | Comments |
durapore 0.65 µm filters | Millipore | R5BA63787 | AGM explant culture |
M5300 long-term culture medium | Stem Cell Technologies | 5300 | AGM explant culture |
Trizol | Tiangen | 5829 | RNA extration |
M-MLV reverse transcriptase | Promega | 90694 | reverse transcription |
SYBR Green | Qiagen | A6002 | quantatitive real-time PCR |
protease inhibitor | Roche | 55622 | Protein extration |
collagenase | Sigma | C2674 | digestion of AGM tissues |
MethoCult GF M3434 medium | Stem Cell Technologies | 3434 | CFU-C assay |
ultra-low attachment 24-well plates | Costar | 3473 | CFU-C assay |
C57BL/6 CD45.2 mice | Beijing HFK Bioscience Co. Ltd | CFU-S assay | |
C57BL/6 CD45.1 mice | Beijing HFK Bioscience Co. Ltd | Long-term transplantation | |
phosphate buffered saline | Life Technologines | 8115284 | AGM Collection |
Penicillin-Streptomycin solution | HyClone | SV30010 | AGM explant culture |
anti-CD45.2-PE-CY7 | eBioscience | 25-0454-80 | Long-term transplantation |
anti-CD45-FITC | eBioscience | 11-0451-81 | Long-term transplantation |
UV lamp | Beijing jiangmorning yuan bio-technology co., LTD | 039-14402 | power: 30W |
stainless steel mesh | AS ONE SHANGHAI Corporation | 2-9817-10 | aperture diameter: 2.5 mm |
hydrocortisone | Sigma | H0396 | selectively diluted into M5300 medium |
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