Collection and Cryopreservation of Hamster Oocytes and Mouse Embryos

Summary

In this video-article we present a step-by-step demonstration on how to collect and cryopreserve hamster oocytes with high post-thaw survival rates. The same procedure can also be applied to successfully freeze and thaw mouse embryos at different stages of preimplantation development.

Abstract

Embryos and oocytes were first successfully cryopreserved more than 30 years ago, when Whittingham et al. ¹ and Wilmut ² separately described that mouse embryos could be frozen and stored at -196 °C and, a few years later, Parkening et al. ³ reported the birth of live offspring resulting from in vitro fertilization (IVF) of cryopreserved oocytes. Since then, the use of cryopreservation techniques has rapidly spread to become an essential component in the practice of human and animal assisted reproduction and in the conservation of animal genetic resources. Currently, there are two main methods used to cryopreserve oocytes and embryos: slow freezing and vitrification. A wide variety of approaches have been used to try to improve both techniques and millions of animals and thousands of children have been born from cryopreserved embryos. However, important shortcomings associated to cryopreservation still have to be overcome, since ice-crystal formation, solution effects and osmotic shock seem to cause several cryoinjuries in post-thawed oocytes and embryos. Slow freezing with programmable freezers has the advantage of using low concentrations of cryoprotectants, which are usually associated with chemical toxicity and osmotic shock, but their ability to avoid ice-crystal formation at low concentrations is limited. Slow freezing also induces supercooling effects that must be avoided using manual or automatic seeding ⁴. In the vitrification process, high concentrations of cryoprotectants inhibit the formation of ice-crystals and lead to the formation of a glasslike vitrified state in which water is solidified, but not expanded. However, due to the toxicity of cyroprotectants at the concentrations used, oocytes/embryos can only be exposed to the cryoprotectant solution for a very short period of time and in a minimum volume solution, before submerging the samples directly in liquid nitrogen ⁵. In the last decade, vitrification has become more popular because it is a very quick method in which no expensive equipment (programmable freezer) is required. However, slow freezing continues to be the most widely used method for oocyte/embryo cryopreservation. In this video-article we show, step-by-step, how to collect and slowly freeze hamster oocytes with high post-thaw survival rates. The same procedure can also be applied to successfully freeze and thaw mouse embryos at different stages of preimplantation development.

Protocol

Animal care and procedures were conducted according to the guidelines and regulations approved by the Ethics Committee on Animal and Human Research of the Universitat Autònoma of Barcelona, Spain.

I. Oocyte collection

1. Check and select female hamsters (Mesocricetus auratus; 8-12 week’s old) of the Golden Syrian strain for the presence of a thick vaginal discharge (postovulatory discharge).
2. Induce selected females to superovulate by intraperitoneal injection of 40 IU of PMSG (Pregnant Mare Serum Gonadotropin) followed by 40 IU of hCG (human Chorionic Gonadotropin) 60 hours later.
3. Euthanize female....

Discussion

With this protocol hamster oocytes and mouse embryos can be successfully cryopreserved. Once frozen, oocytes/embryos can be stored in liquid nitrogen tanks indefinitely and recovered at any time or place desired. This offers the advantage of having samples almost ready to use whenever needed. On the other hand, this protocol can also be used to generate embryo cryobanks from valuable mouse strains (such as transgenic lines), as an economical and safer alternative to the maintenance of live animal colonies. It is importan.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Material Name	Type	Company	Catalogue Number	Comment
French type mini-straw 0.25 ml		Mini-tub	13407/0010
hCG		Farma-Lepori, Spain	749036.4
Hyaluronidase		Sigma	H-3884
KSOM-H medium				Ref. [11]
Liquid Nitrogen		Air Liquide
Plastic plugs		Mini-tub	19046
PMSG		Intervet, Spain	1.614/8447
Propilenglycol		Fluka	82280
Sucrose		Merck	107687
Surgical Scissors		Aesculap	BC-060R; BG-061R
Thermo-sealer		SIZ	220
35 and 90 mm culture dishes		Nunc	153066; 150350
10 ml tubes		Greiner Bio-one	163160
Nitrogen tank		MVE, Cryogenics	XC 43/28
Programmable Freezer		Planner Products Ltd.	Kryo-10 Series III
Forceps		Aesculap	BD-331R; BD-053R; OC-020R