Alpha cells are glucagon producing endocrine cells which reside in the Islets of Langerhans. In mice, the alpha cells are the first to mature, (as determined by immunofluorescence) and are detectable as early as E9.5 in the dorsal pancreatic bud and one day later in the ventral pancreatic bud.
In the pancreas the differentiation of endocrine cells is non-synchronous and lasts from the secondary transition period (which is the major time of endocrine cell differentiation) to the postnatal period.