Cell Labeling and Injection in Developing Embryonic Mouse Hearts

Summary

We describe a series of methods to inject dyes, DNA vectors, virus, and cells in order to monitor both cell fate and phenotype of endogenous and grafted cells derived from embryonic or pluripotent cells within mouse embryos at embryonic day (E)9.5 and later stages of development.

Abstract

Testing the fate of embryonic or pluripotent stem cell-derivatives in in vitro protocols has led to controversial outcomes that do not necessarily reflect their in vivo potential. Preferably, these cells should be placed in a proper embryonic environment in order to acquire their definite phenotype. Furthermore, cell lineage tracing studies in the mouse after labeling cells with dyes or retroviral vectors has remained mostly limited to early stage mouse embryos with still poorly developed organs. To overcome these limitations, we designed standard and ultrasound-mediated microinjection protocols to inject various agents in targeted regions of the heart in mouse embryos at E9.5 and later stages of development.  Embryonic explant or embryos are then cultured or left to further develop in utero. These agents include fluorescent dyes, virus, shRNAs, or stem cell-derived progenitor cells. Our approaches allow for preservation of the function of the organ while monitoring migration and fate of labeled and/or injected cells. These technologies can be extended to other organs and will be very helpful to address key biological questions in biology of development.

Introduction

More than a decade ago, human embryonic stem cells (HuESCs) have been derived from human blastocysts¹. Since then, these cells have become the subject of an important field of research which addresses unmet questions in human developmental biology. HuESCs have furthermore provided hopes in regenerative medicine. In recent years, human induced pluripotent stem cells (iPSCs) have been generated from patient-specific somatic cells, providing models of genetic disease². Many in vitro protocols for differentiation of embryonic or induced pluripotent stem cells towards various cell lineages, including heart lineages³, have been repo....

Protocol

1. Preparation

Animal procedures

Obtain approval from an animal ethical committee and follow institutional guidelines for work with virus, HuESC and/or iPSC (when applicable), as well as mouse handling, obtaining mouse embryos, and performing mouse surgery. For timed matings, the day of the plug is considered embryonic day (E)0.5 / 0.5 days post-coitum.

1. Microinjection needles:
   For ex utero microinjection, pull glass pipettes (1.2 mm external diameter borosilicate capillary tubes) using a pipette puller/beveller to get a 1 or 10 μm internal tip diameter and a sharp and conic tip sh....

Results

Using the injection protocols described above, cells can be labeled and/or injected into the embryonic mouse heart. As proof of concept, several examples are shown in which the injection protocol and the ex vivo AVC explant, isolated heart, or whole embryo culture were combined (Figure 1).

Figure 1 shows the preparation of the embryo before cell injection. The E9.5 embryo is removed from its decidua while maintaining integrity of the yolk sac (

Discussion

The intra-cardiac ex vivo injection protocols described above are designed to preserve myocardial function for at least 48 hr in mid-stage (E9.5- E11.5) mouse embryos. These injection approaches allow for spatially targeted injection of DNA or cells. The few examples shown in Figures 1-3 provide proof of concept for delineating ex vivo and in vivo molecular mechanisms of developmental processes that take place in restricted cardiac regions, such as EMT of endocardial or epicard.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Setups/Hardware
40 MHz Transducer	VisualSonics	MS550S
Microinjector	VisualSonics
Microinjector	Eppendorf	5242
Micromanipulator	Eppendorf	5171
Nitrogen			required to pressurize the injector
Rail system	VisualSonics
rotator			to rotate glass tube with embryos inside the incubator
Standard incubator			5% CO2, 37 °C
stereomicroscope	Zeiss	Discovery. V8
Vevo 2100	VisualSonics
Microinjection
Borosilicate capillary tubes	World Precision Instrument	KTW-120-6	1.2-μm external diameter
Pipette puller	Sutter	Model P87
Microinjection needles	Origio-Humagen	C060609	OD/ID 1.14 mm/53 mm, with 50/35 μm OD/ID tip
Hamilton syringes
Petri dishes			10-cm diameter
Mineral oil	Sigma	M8410
Silicon membrane	Visualsonics		4.3 x 4.3 cm
Play-Doh
Isoflurane	Vet One
hair removal agent	Nair
Eye lubricant	Optixcare	31779
Electrode gel (Signa)	Parker
Suture	Sofsilk 5-0	S1173
Ultrasound gel	Aquasonic
Buprenex Buprenex (buprenorphine hydrochloride)	Reckitt Benckiser Pharmaceuticals Inc.	NDC 12496-0757-1	0.05-0.1 mg/kg in saline
Other
Silicone Elastomer	Dow Corning	Sylgard 184
Glass petridishes	Fine Science Tools		60-mm diameter
Insect pins	Fine Science Tools	26002-20
Media and culture reagents
Optimem medium	Life Technologies	51985026
M2 medium	Sigma	M7167
Dulbecco’s Eagle Medium	Lonza	BE12-640F	high glucose and 50% rat serum
M16 medium	Sigma	M7292
Rat serum	Janvier	ODI 7158
Pennicilin/streptomycin	Life Technologies	15140-12
oxygen 40%	Air liquid		required to oxygenate the embryo culture medium
Fetal calf serum	Fisher	RVJ35882
Matrigel	BD	356230
Collagen type I	BD	354236	to coat culture dishes for explant culture
Culture dishes	Dutcher /Orange	131020
Injectates
CDCFDA-SE	Invitrogen/Molecular Probes	C1165	25 mg/ml DMSO. Store at -20 °C. Dilute 1:100-200 in saline before use.
PGK-GFP-expressing lentivirus			~8E9 transducing units/ml DMEM
Lipofectamine 2000	Life Technologies	11668019