The overall goals of this procedure are to isolate and culture metanephric rudiments from mouse embryos and to observe the effects of specific treatments on ureteric bud branching morphology. This method can help answer key questions in kidney organogenesis about the control of tubular branching morphogenesis, about epithelial mesenchyme interactions, and about the origin of congenital malformations. The main advantages with this technique are that it facilitates direct access to the organ;that it is simple, inexpensive, and easily modified.
Before beginning the dissection, use sterile forceps to carefully place one polycarbonate membrane filter with a five-micrometer pore size into each well of a four-well plate containing 500 microliters of fresh culture medium. Transfer the plate into a cell culture incubator. Then use a razor blade to cut approximately 30 100-microliter micropipette tips approximately one millimeter from the tip to widen the tip openings and return the tips to the pipette tip rack.
When the tips are ready, place an embryonic day 11 1/2 embryo in PBS under a dissecting microscope. Use a fresh dish for each embryo. And with number five watchmaker forceps, cut the embryo directly under the forelegs.
Next, hold the legs with one pair of forceps using a second forceps to remove the leg tissue. Remove the tail in the same manner, and use the tips of the forceps to laterally and superficially open the body wall of the embryo in a rostral and caudal direction parallel to the dorsal aorta. Cutting superficially, make an incision along the dorsal aorta and use the tips of the closed forceps to carefully separate the ventral part of the body wall from the dorsal body wall.
Flip the embryo over and cut the body wall laterally in a rostral-to-caudal direction using the dorsal aorta for orientation as just demonstrated. Once the ventral body wall has been separated from the dorsal body, grasp the ventral body wall with the forceps, and carefully pull to remove the wall and the ventral organ mass. Holding the dorsal body wall with one forceps with the ventral side facing up, use the other forceps to grasp the dorsal aorta at its rostral end and carefully peel the dorsal aorta from the dorsal body wall.
Using one forceps, cut rostrally to the kidney anlagen to remove the aorta. And use the tips of the forceps to carefully separate the two anlagen. Use the tips of the forceps to carefully peel the unwanted tissue from the kidney anlagen.
And use a microliter pipette and a modified pipette tip to transfer one anlagen and 10 microliters of PBS into the center of one half of a single polycarbonate membrane filter in the four-well plate. Then return the plate to the incubator until the metanephric rudiments from the next embryo are ready to be placed on the filter. After three days at 37 degrees Celsius and 5%carbon dioxide, use a micropipette to carefully replace the culture medium in each well with 500 microliters of 4%paraformaldehyde and PBS dropwise to submerge the filters.
After 30 minutes at room temperature, remove the fixative and rinse the filters two times with 500 microliters of PBS submerging the filters with each wash. Then add 500 microliters of permeabilization solution to each well for a one-hour incubation at room temperature. At the end of the permeabilization incubation, rinse the filters two times as just demonstrated, and add 500 microliters of blocking solution to each well, After one hour at room temperature, replace the blocking solution with 250 microliters of biotinylated Dolichos biflorus agglutinin and blocking solution, and place the tissues at four degrees Celsius for 24 hours.
The next day, wash the filters two times with 500 microliters of PBS per well. And label the tissue with 250 microliters of Alexa 488 conjugated streptavidid and blocking solution for 24 hours at four-degree Celsius. The next day, wash the tissues two times with 500 microliters of PBS per well and use forceps to transfer the filters to prepared glass slides with the explants facing up.
Mount the explants with 50 to 100 microliters of embedding medium and cover the tissues with 60-millimeter long number 1.5 coverslips. Then allow the embedding medium to solidify for two hours at room temperature in the dark, and image the metanephric kidney samples. After three days of culture, the ureteric bud of the metanephric kidney anlagen branches up to five times, resulting in a ramification of the initially T-shaped ureteric bud.
In the presence of clustered ephrin-B2, the branching complexity has decreased, as compared to control explants incubated with clustered human Fc.Indeed, ureteric bud branching in the majority of the ephrin-B2 treated explants, does not exceed third generation. And the fourth generation is reached in only 8%of the treated explants. Accordingly, the number of endpoints per branch and endpoints per millimeter squared is reduced in the explants treated with clustered ephrin-B2.
Further, a third of the explants demonstrate an unusual morphology in the ureteric bud tips, suggesting that ephrin-B2 might have a restricting effect on ureteric bud branching process, most likely by activating FA4 and FB2 forward signaling. Any injury of the mesenchyme decreases the inductive potential leading to a reduced or absent ureteric bud branching. For example, in this explant with an almost-missing mesenchyme, the ureteric bud did not branch beyond the T stage.
In this experiment, the metanephric mesenchyme was damaged, leading to poor growth and branching. After it's development in the 1960s, this technique paved the way for researchers in the field of developmental biology to explore kidney organogenesis. After watching this video, you should have a good understanding of how to isolate and culture metanephric rudiments from E11.5 mouse embryo.
Once mastered, the dissection can be completed in less than five minutes if performed properly.
