Analysis of the mechanism underlying the pathway formation using mutant animals.

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We have examined the brain development in both normal and mutant animals by chiefly using the morphological technique. Recent findings obtained are as follows.1) Calbindin D-28k, a calsium-binding protein, is localized in neurons migrating from the nascent vomeronasal organ to the brain in rats (Toba et al., 2001). N-syndecan, a heparansulfate proteoglycan, is expressed in the migratory route from the rat olfactory placode (Toba et al., 2002).2) Defects of the development and pathway formation of hypothalamic neurosecretory neurons were found in animals lacking transcription factors Brn-2, Nkx2.1 and Pax-6 (Kawano et al., 2002).3) The abnormal development of cerebral neocortex is observed in double-knockout mice lacking both Brn-1 and Brn-2 (Sugitani et al., 2002).4) InPax-6 mutant rats, precerebellar neurons of the medulla oblongata exhibit a delayed migration and aberrant migratory route (Horie et al., 2003).5) Ascending dopaminergic axons of the mesencephalon abnormally cross the midline in knochout mice lacking Nkx2.1 (Kawano et al., 2003).6) The motor function of mice lackingNB3, a cell recognition molecule, is abnormal (Takeda et al., 2003).