Monofocal origin of telencephalic oligodendrocytes in the anterior entopeduncular area of the chick embryo

Oligodendrocytes are the myelin-forming cells in the central nervous system . In the brain, oligodendrocyte precursors arise in multiple restricted foc i, distributed along the caudorostral axis of the ventricular neuroepitheli um, In chick embryonic hind-, mid- and caudal forebrain, oligodendrocytes h ave a basoventral origin, while in the rostral fore-brain oligodendrocytes emerge from alar territories (Perez Villegas, E, M,, Olivier, C,, Spassky, N,, Poncet, C,, Cochard, P,, Zalc, B,, Thomas, J, L, and Martinez, S, (1999 ) Dev, Biol, 216, 98-113), To investigate the respective territories coloni zed by oligodendrocyte progenitor cells that originate from either the baso ventral or alar foci, we have created a series of quail-chick chimeras. Hom otopic chimeras demonstrate clearly that, during embryonic development, oli godendrocyte progenitors that emerge from the alar anterior entopeduncular area migrate tangentially to invade the entire telencephalon, whereas those from the basal rhombomeric foci show a restricted rostrocaudal distributio n and colonize only their rhombomere of origin. Heterotopic chimeras indica te that differences in the migratory properties of oligodendroglial cells d o not depend on their basoventral or alar ventricular origin. Irrespective of their origin (basal or alar), oligodendrocytes migrate only short distan ces in the hindbrain and long distances in the prosencephalon, Furthermore, we provide evidence that, in the developing chick brain, ail telencephalic oligodendrocytes originate from the anterior entopeduncular area and that the prominent role of anterior entopeduncular area in telencephalic oligode ndrogenesis is conserved between birds and mammals.