Neurogenetic Compartments of the Mouse Diencephalon and some Characteristic Gene Expression Patterns

Abstract

In the last 10 years our concept of the developing diencephalon has changed dramatically. This is a consequence of an increasing number of morphological, chemoarchitectural, gene expression and experimental data that resist a satisfactory interpretation within the usual morphological schema suggested by textbooks, represented by the so-called columnar view of the vertebrate forebrain. The columnar paradigm was instaurated by Herrick (1910), who divided the vertebrate diencephalon into four superposed columns separated by ventricular sulci. This schema was later supported by numerous adherents, among which Kuhlenbeck played a singular role (Kuhlenbeck 1973, and earlier work reviewed therein). The four columns were called epithalamus, thalamus dorsalis, thalamus ventralis and hypothalamus (from dorsal to ventral). They were held to be longitudinal parts of the neural tube, though this view is only possible by arbitrary disregard of the notorius axial bending of the rostral neural tube at the cephalic flexure (Keyser 1972; Puelles and Rubenstein 1993; Puelles 1995). Among other problems (see Puelles 1995), this schema typically dealt poorly with the pretectum, causing many authors to fail to distinguish it adequately from the dorsal thalamus, the epithalamus or the midbrain roof. Various descriptive embryologists noticed over the years the difficulties of the columnar approach, favoring a segmental paradigm, but did not achieve a substantial impact with their alternative interpretations (Rendahl 1924; Tello 1934; Bergquist 1954; Coggeshall 1964; Keyser 1972; Gribnau and Geijsberts 1985). These, nevertheless, finally constituted the base of the present conceptions, together with parallel work on non-mammalian vertebrates.