Maternally expressed in oocytes and after fertilization, expressed in early embryos. Expression is activated at, or just after the midblastula stage, about 2 hours before the appearance of the embryonic shield. In early gastrulation, expression marks the anterior shield and by late gastrulation, expression is restricted to the rostral crescent and medial strip. Levels of GSC then decline and disappear at 12 hours post-fertilization. Belongs to the paired homeobox family. Bicoid subfamily.