Fig. 2. hdl and tcf3b show redundant and unique domains of expression during development. (A,B) Shield stage, animal pole view, dorsal towards the right. Expression of hdl is much higher than tcf3b throughout the epiblast at this stage. (C,D) Bud stage, rostral view, dorsal is towards the right. Both genes are expressed in the presumptive forebrain and midbrain and at the ventral midline. (E,F) Bud stage, caudal view, dorsal towards the left. Both genes are expressed at a low level in the notochord, but only hdl is expressed in the tailbud (tb). (G,H) Closer view of head region at six somites. Both genes are expressed throughout the CNS, but tcf3b levels are higher in stripes corresponding to telencephalon and midbrain (mb). (I,J) Six somites, caudal view, dorsal towards the left. Only hdl is expressed in the tailbud and presomitic mesoderm (psm). (K,L) Eighteen somites. Both genes continue to be expressed throughout the brain, with tcf3b showing more specific domains of localization. There is a noticeable gap in tcf3b expression at the midbrain-hindbrain boundary (mhb). sh, shield.