ニワトリのケアとメンテナンスの基本

Chicken embryos are excellent model organisms for studying early vertebrate development because they are easy and inexpensive to maintain compared to most laboratory organisms. Unlike mice or zebrafish bred in labs, fertilized chicken eggs are purchased from external suppliers, requiring minimal specialized equipment. Their accessibility and affordability make them ideal for undergraduate research and experimentation.

Fertilized chicken eggs can be stored at temperatures between 13-16°C for up to 5 days before incubation begins. Once you are ready for embryo development, allow the eggs to warm to room temperature, then transfer them to a rocking incubator maintained at 37°C with 60% humidity until they reach the desired developmental stage.

Candling is a technique that uses a bright light source or candler box to illuminate the egg and visualize internal structures like blood vessels, confirming embryo presence. Researchers use candling to identify the location of embryonic structures in intact eggs, such as locating the interface between the allantoic cavity and air sac for precise virus injection without damaging the embryo.

Windowing involves cutting a small, resealable hole in the eggshell to access the embryo while keeping it intact, improving chick survival. The process requires removing albumin to lower the embryo away from the shell, sterilizing with ethanol, and using tape to prevent shell fragments from contaminating the embryo. This technique permits direct access for microinjection and other experimental manipulations on developing tissues.

Diluted, non-toxic India ink is injected into the yolk beneath the embryo and allowed to diffuse, creating a dark background that increases contrast. This technique is especially useful for visualizing transparent early-stage embryos that are difficult to see due to their small size and lack of pigmentation, enabling precise microinjection of DNA into refined tissue domains.

During in ovo electroporation, DNA is first delivered into specific embryonic tissues via microinjection. Electrodes are then placed around the tissue of interest, and an electric field is applied to temporarily permeabilize cell membranes and drive nucleic acids into cells. This technique allows researchers to label individual cells for monitoring cell divisions and tracking developmental processes over time.

The extraembryonic membranes of chicken embryos, particularly the allantoic membrane, are commonly used for virus propagation. Researchers use candling to locate the allantoic cavity, then inject virus directly into it without damaging the embryo. After several days of incubation, large numbers of viral particles can be harvested from the allantoic fluid for research purposes.