May be required for posterior development and development of normal embryonic axial pattern. It is first expressed at the midblastula transition and is maximally expressed at the late gastrula-early neurula stage. It is expressed in two distinct periods, the early period is characterized by an anteroposterior graded expression in the mesoderm with the highest concentration at the posterior end. The late period begins at the tailbud stage and is characterized by new expression in the CNS, predominantly in the brain, and in addition it is also expressed in the tail bud at this stage. Belongs to the even-skipped homeobox family.