Gene Maps and Related Histogenetic Domains in the Forebrain and Midbrain

Rodent brain gene patterns are readily comparable with counterparts in the human, avian, reptilian, amphibian, teleost, shark and agnathan species. This scenario provides substantial novel evidence for comparative neuroanatomy, both corroborating some earlier conclusions and calling for revision of other concepts. In recent years accumulated observations have shown that gene expression patterns frequently display reproducible boundaries; these tend to be aligned with the axial and dorsoventral dimensions of the neural tube and are topologically invariant during ontogenesis. Many early molecular patterns are remarkably resistant to evolutionary change. Accumulated comparative results over the last decade strongly indicate that there is a common pattern of differentially-specified neural regions among all vertebrates. This chapter studies the molecular approaches to understanding the structural and functional organization of the nervous system which promise new insights into modular brain domains conserved among various species. Fate-map analysis suggests that early differential molecular specification of progenitor regions and subregions in the neural plate and neural tube eventually correlates with specific prospective fates via patterned proliferation, neurogenesis and differentiation.