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1Department of Neurobiology and Behaviour, University of California, Irvine (UCI)
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A variety of growth factors and proteins interact to induce cells to take on different cell fates during development. Here we demonstrate the use of an in ovo preparation to address possible interactions between different proteins in development by placing beads on E2.5 chick embryos.
J. Korn, M., S. Cramer, K. Placing Growth Factor-Coated Beads on Early Stage Chicken Embryos. J. Vis. Exp. (8), e307, doi:10.3791/307 (2007).
The neural tube expresses many proteins in specific spatiotemporal patterns during development. These proteins have been shown to be critical for cell fate determination, cell migration, and formation of neural circuits. Neuronal induction and patterning involve bone morphogenetic protein (BMP), sonic hedgehog (SHH), fibroblast growth factor (FGF), among others. In particular, the expression pattern of Fgf8 is in close proximity to regions expressing BMP4 and SHH. This expression pattern is consistent with developmental interactions that facilitate patterning in the telencephalon.
Here we provide a visual demonstration of a method in which an in ovo preparation can be used to test the effects of Fgfs in the formation of the forebrain. Beads are coated with protein and placed in the developing neural tube to provide sustained exposure. Because the procedure uses small, carefully placed beads, it is minimally invasive and allows several beads to be placed within a single neural tube. Moreover, the method allows for continued development so that embryos can be analyzed at a more mature stage to detect changes in anatomy and in neural patterning. This simple but useful protocol allows for real time imaging. It provides a means to make spatially and temporally limited changes to endogenous protein levels.
1. Remove eggs from the incubator
At E2-2.5 (~ St. 17 HH), remove the eggs and prepare them accordingly. They can be worked on immediately or returned to the incubator for a couple hours. The eggs can be placed at room temperature safely for over an hour. Eggs can stay out for the duration of the manipulations. Sometimes these can take an hour or more.
Note: The longer they sit at room temperature, the less likely they are to survive.
2. Preparation of India ink
3. Opening the eggs and injection of India ink
4. Opening the neural tube
Note: Depending on the age, a fine tungsten probe can be used to do the same thing.
5. Retrieving a coated heparin-acrylic bead
6. Placing the bead
7. Closing the egg
Depending on the protein you wish to use, there are different protocols on how to prepare the beads. In these experiments, we use heparin-acrylic beads, but affi-gel beads can also be used. We have found that the heparin-acrylic beads are easier to manipulate in the aqueous environment of the egg albumin. Beads are soaked in 5 l of protein overnight at 4°C. Control beads are placed in sterile PBS until the time of placement. The advantage in using an in ovo preparation is that the embryo is still alive and free to develop normally 1. Although the environment in which an explant is kept can be controlled for particular variables, the live embryo allows for an accurate representation of the affect of a protein on developmental patterns 2-3. All assays that you can perform on an explant, you can with an embryo.
The authors have nothing to disclose.
|Eggs||Animal||Fertilized, E2-2.5 (~ St. 17 HH)|
|India Ink||Tool||Higgins||Prepare a 4% solution in sterile PBS.|
|Sterile PBS||Alternatively, an antibody cocktail can be used|
|27G 1/2 needles||Tool||BD Biosciences||305109||Angled at 90 degrees|
|Forceps||Tool||World Precision Instruments, Inc.||size 55|
|Dissection scissors||Tool||World Precision Instruments, Inc.||500086||vannas, 8.5cm|
|Parafilm tape||to seal eggs|
|Tungsten Probe||Tool||Electron Microscopy Sciences||62091||Tool #24. Handle optional.|
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