The Barx-1 gene in the embryonic head

A frontal section of a stage 23 chick embryo head showing the distribution of transcripts of the Barx-1 gene. This has been visualised by in situ hybridisation with an RNA probe labelled with 35S. This binds to the Barx-1 mRNA and its presence is detected as silver grains after autoradiography. These grains appear as white dots under darkfield illumination and can be seen in the proximal regions of the branchial arch mesenchyme. The developing eyes can be seen at the top of the picture.