Hoxa-2 in situ hybridisation in chick embryo

A stage 16 chick embryo showing where the Hoxa-2 gene is switched on (purple). This is done by labelling an RNA copy of the Hoxa-2 gene with digoxygenin. This then binds to the Hoxa-2 mRNA and can be detected using the purple dye. This technique shows that the Hoxa-2 gene is on in the hindbrain from rhombomere 2 posteriorly and in all the other tissues behind this point apart from the heart. Hoxa-2 is a transcription factor, binding to DNA and affecting the action of other genes.