A search for primitive Purkinje cells: zebrin II expression in sea lampreys (Petromyzon marinus).

Zebrin II/aldolase C is a 36 kDa polypeptide expressed by Purkinje cells in the cerebellum of elasmobranchs, teleosts, birds, and mammals, and by octavolateralis pyramidal cells in developing teleosts. To better understand the evolution of these two systems we determined if zebrin II is expressed (1) in previously described primitive Purkinje cells, and (2) in octavolateralis pyramidal cells of sea lampreys (Petromyzon marinus). Ammocete and adult stages were reacted with mab anti-zebrin II. In ammocetes the large pyramidal cells of the anterior octavomotor nucleus (AON) were mab anti-zebrin II immunoreactive, but immunoreactivity was not detected in the cerebellar plate. In adults there was no immunoreactivity in any portion of the brain, including the cerebellar plate and the AON. The data indicate that zebrin II immunoreactivity may prove valuable in studying the development of the octavolateralis system across vertebrates. Three explanations are proposed to account for the absence of zebrin II+ Purkinje cells: aldolase C is expressed in Purkinje cells but the zebrin II epitope has not yet evolved; the zebrin II epitope was present in ancestral lampreys but has since been lost; or sea lampreys do not have Purkinje cells. The evolutionary implications of these results are briefly reviewed.