Culturing and Measuring Fetal and Newborn Murine Long Bones

Summary

Here, we present a method for ex vivo culture of long murine bones at both fetal and newborn stages, suitable for analyzing bone and cartilage development and homeostasis in controlled conditions while recapitulating the in vivo process.

Abstract

Long bones are complex and dynamic structures, which arise from endochondral ossification via a cartilage intermediate. The limited access to healthy human bones makes particularly valuable the use of mammalian models, such as mouse and rat, to look into different aspects of bone growth and homeostasis. Additionally, the development of sophisticated genetic tools in mice allows more complex studies of long bone growth and asks for an expansion of techniques used to study bone growth. Here, we present a detailed protocol for ex vivo murine bone culture, which allows the study of bone and cartilage in a tightly controlled manner while recapitulating most of the in vivo process. The method described allows the culture of a range of bones, including tibia, femur, and metatarsal bones, but we have focused mainly on tibial culture here. Moreover, it can be used in combination with other techniques, such as time-lapse live imaging or drug treatment.

Introduction

Organ growth has to be tightly tuned to prevent the appearance of growth disorders, and involves the regulation of multiple cell types, molecular pathways and crosstalk among different parts of the body. Imaging techniques are essential to address the changes occurring over time in a growing embryo, both in normal conditions, as well as after a perturbation is induced in the system. Embryos with intrauterine development, such as the widely used rodent models, present an additional challenge for live imaging and drug treatment, which can be partially overcome by using ex vivo culture techniques. To successfully recapitulate the in vivo processes and obtain meaningful r....

Protocol

All the experiments should be carried out following the local governmental and institutional guidelines of ethical handling of laboratory animals.

1. Preparations Prior to the Day of Bone Culture

1. Set up timed mouse matings to obtain fetuses and pups from embryonic day 14.5 (E14.5) and onward.
   NOTE: The culture of long bones can be successfully applied to different mouse strains; in the present protocol, outbred Swiss Webster wild-type mice are used.
2. Prepare dissection medium (adapted from Houston et al.¹⁵): dilute α-minimum essential medium (α-MEM) or Dulbecco&#....

Results

Bone culture can be performed starting from different stages. In Figure 1A-D, a comparison between cultured tibia and freshly extracted ones at equivalent stages is shown. The first observation is that up to two days of culture the size achieved is comparable to the in vivo bone growth for both cartilage and mineralized bone (Figure 1A,B,D). Longer culture periods lead to bigger differences betwe.......

Discussion

Bone ex vivo culture methods have been used for some time to assess the biology of bone growth²⁸, but have been seldom applied to murine long bones. With the development of imaging techniques, ex vivo bone culture offers an attractive way to study bone growth in real time in a setting closely resembling the in vivo conditions. In this scenario, it is important to define the conditions in which the growth of long bones is comparable to their growth in vivo.

In the presen.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
5-Ethynyl-2'-deoxyuridine	Santa Cruz	CAS 61135-33-9
5-Bromo-2′-deoxyuridine	Sigma	B5002
50 mL Conical Centrifuge Tubes	Falcon	352070
60 mm TC-treated Center Well Organ Culture Dish, 20/Pack, 500/Case, Sterile	Falcon	353037
Adobe Photoshop	Adobe	CS4
Ascorbic acid	Sigma	A92902
Base unit for the scope	Zeiss	435425-9100-000
Betaglycerophosphate	Sigma	G9422
Binocular scope	Zeiss	STEMI-2000
Bovine Serum Albumin (BSA) fraction v	Roche/Sigma	10735086001
DigiRetina 500 camera	Aunet
Dissection kit	Cumper Robbins	PFS00034
DMEM	Gibco	11960044
DMSO	Sigma	D8418
Eppendorf 2 mL tubes	Eppendorf	0030120094
Ethanol 96%	Merk	159010
Forceps Dumont#5 Inox08	Fine Science Tools	T05811
Heracell 150 CO2 incubator	Thermo Fisher	51026282
Minimum Essential Medium Eagle	Sigma	M2279
Multiwell 24 well	Falcon	353047
Paraformaldehyde	Sigma	158127
Penicillin-Streptomycin (10,000 U/mL)	Gibco	15140-122
Plastic pipettes 1 mL Sterile Individually wrapped	Thermo	273
Syringe filter 0.2 um	Life Sciences	PN4612
Terumo syringe 20 mL	Terumo	DVR-5174
Tretinoin (retinoic acid)	Sigma	PHR1187-3X
Trinocular scope	Aunet	AZS400T