Hdhex4/5/Hdhex4/5 embryos also fail to restrict the expression of goosecoid (Gsc). Normally, Gsc is initially expressed in the visceral endoderm and proximal, posterior streak where the primitive streak will form prior to gastrulation. As the primitive streak forms and extends, Gsc is expressed in the distal streak, the node, and the axial mesoderm extending anteriorly from the node (Fig. 3I,K, [31,32]). However, in the mutant Hdhex4/5/Hdhex4/5 embryos, high levels of Gsc expression remain unrestricted in the endoderm overlying the entire embryo and ectopically in cells adjacent to the ectoplacental cone (Fig. 3J,L). These results suggest that, in contrast to proper Hnf3β regulation, Gsc remains inappropriately activated in mutant visceral and definitive endoderm, implicating huntingtin in the proper restriction of this homeodomain transcription factor.