Agarose/gelatin immobilisation of tissues or embryo segments for orientated paraffin embedding and sectioning.

The technique described in this protocol allows the user to position small tissues in the optimal orientation for paraffin embedding and sectioning by first immobilising the tissue in an agarose/gelatin cube. This method is an adaptation of methods used for early embryos and can be used for any small tissues or embryo segments. Processing of larger tissue sections using molds to create agarose/gelatin blocks has been described previously; this detailed protocol provides a method for dealing with much smaller tissues or embryos (≤5 mm). The tissue is briefly fixed then an agarose/gelatin drop is created to surround the tissue. The tissue can be orientated as per the user's preference in the drop before it sets as is carved into a cube with a domed top. The cube is then dehydrated and goes through the embedding and sectioning process. The domed cube is easy to orientate when embedding the tissue in a wax block giving the user assured orientation of the small tissue for sectioning. Additionally, the agarose/gelatin cube is easy to see in the unmolded wax once embedded, making the region of interest easy to identify.