Application of Aorta-gonad-mesonephros Explant Culture System in Developmental Hematopoiesis

Summary

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.

Abstract

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.

Introduction

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 aorta^1,2,3,4. Once formed in the aorta-gonad-mesonephros (AGM) region from embryonic (E) 10.5 to E12.5 in the mouse embryo, HSCs wil....

Protocol

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

1. Sterilize the 0.65 µm filters with ultraviolet rays produced under the ultraviolet ray lamp on the clean bench for 4 h and turn the filters over after the 2 h mark.
   NOTE: When working with UV light, wear appropriate protection.
2. Sterilize the stainless steel meshes with the autoclave sterilizer at 121 °C for 30 mins.
   NOTE: A certain height of stainless steel mesh is needed to support the filters at the air....

Results

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 tissues^16,17,

Discussion

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.......

Materials

List of materials used in this article

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