Genetic Tracing of Subpopulation Neurons in the Prethalamus of Mice (Mus musculus) DELPHINE DELAUNAY, 1,2 KATHARINA HEYDON, 1,2 ANDRES MIGUEZ, 1,2 MARKUS SCHWAB, 3 KLAUS-ARMIN NAVE, 3 JEAN LEON THOMAS, 1,2 NATHALIE SPASSKY, 1,2 SALVADOR MARTINEZ, 4 AND BERNARD ZALC 1,2 * 1 Inserm, U711, Ho ˆpital de la Salpe ˆtrie `re, 75013 Paris, France 2 Universite ´ Pierre et Marie Curie, Faculte ´ de me ´decine, IFR70, 75013 Paris, France 3 Max-Planck-Institute of Experimental Medicine, D-37075 Goettingen, Germany 4 Experimental Embryology Laboratory, Instituto de Neurociencias Alicante, Campus de San Juan, San Juan de Alicante, 03550, Spain ABSTRACT Genetic labeling based on the Cre/lox reporter system has allowed the creation of fate maps for progenitor cells and their offspring. In the diencephalon, pools of progenitors express the plp transcripts in the zona limitans intrathal- amica (ZLI), the basal plate of the diencephalon (bpD), and the posterior part of the hypothalamus. We used plp-Cre transgenics crossed with either Rosa26-lox-lacZ (R26R) or actin-lox gfp (Z/EG) reporter mice to investigate the progeny of plp-expressing ventricular cells in the diencephalon. We describe the subpopulations of prethalamic neurons de- rived from plp-activated progenitors, their possible migra- tory routes as development proceeds, and their final posi- tional identity. Neurons derived from plp-expressing progenitors issued from the ZLI contribute to GABAergic cells in the zona incerta, the subgeniculate nucleus, the ventral lateral geniculate, and the intergeniculate leaflet. Plp  progenitors in the bpD and posterior hypothalamus appear to generate glutamatergic neurons in the subtha- lamic nucleus and GABAergic neurons in the mammillary and retromammillary tegmentum derivatives. In all these nuclei the contribution of plp  progenitors is only partial, illustrating the heterogeneity of origin of neurons in pretha- lamic and caudal hypothalamic nuclei. J. Comp. Neurol. 512: 74 – 83, 2009. © 2008 Wiley-Liss, Inc. Indexing terms: diencephalon; hypothalamus; intergeniculate leaflet; subgeniculate nucleus; subthalamic nucleus; ventral lateral geniculate nucleus; zona incerta; zona limitans intrathalamica In the adult central nervous system (CNS), the proteolipid protein (PLP) is the major protein of myelin and oligodendro- cytes (Folch and Lees, 1951). During embryonic development, expression of the corresponding transcript is detectable as early as embryonic day (E)9.5, i.e., at least 10 –15 days before any myelin is deposited around axons. In the developing em- bryo, plp mRNA has been detected in discrete ventricular foci distributed along the neural tube (Timsit et al., 1992, 1995; Spassky et al., 1998) and the plp transcript has been reported as a marker of a subpopulation of oligodendrocyte precursor cells (at E12.5–E14.5), that do not depend on PDGFR signal- ing for their survival and proliferation (Spassky et al., 2001a,b). In the diencephalon, we have recently shown that plp is ex- pressed first (at E9.5) by neuroepithelial cells and later (at E13.5) by radial glial cells (Delaunay et al., 2008). Using in vitro and in vivo complementary approaches, we have provided evidence that the plp  progenitors of the diencephalon have a restricted neuronal fate of differentiation at E9.5, while they exhibit a restricted glial cell fate at E13.5. Therefore, we have proposed a two-step model for the specification of neural progenitors in the diencephalon, with neuronal progenitors (neuroblasts) segregating at E9.5 and glial progenitors (glio- blasts) appearing at E12.5–E13.5. Grant sponsor: DD was a fellow of the Ministe ` re de l’Enseignement Supe ´ rieur et de la Recherche and European Leukodystrophy Association; Grant sponsor: INSERM; Grant sponsor: Association de Recherche sur la Scle ´ rose En Plaques (to J.L.T.); Grant sponsor: National Multiple Sclerosis Society; Grant number: TR-3762-A-1 (to B.Z.); Grant sponsor: DFG (CMPB) and BMBF (to K.A.N.); Grant sponsor: EEC; Grant number: LSHG-CT-2004- 512003; Grant sponsor: EUREXPRESS; Grant numbers: ACOMP06/076, BFU2005-23722-E/BFI, MEC BFU2005-09085; Grant sponsor: ELA Fonda- tion de Recherche, France (to S.M.). The first two authors contributed equally to this work. *Correspondence to: B. Zalc, INSERM U711; UPMC, Biologie des Inter- actions Neurones/Glie, Hopital de la Salpetriere, 47, Bd de l’Hopital, 75651 Paris Cedex 13, France. E-mail: berzalc@ccr.jussieu.fr Received 16 February 2007; Revised 28 April 2008; Accepted 27 Sep- tember 2008 DOI 10.1002/cne.21904 Published online in Wiley InterScience (www.interscience.wiley.com). The Journal of Comparative Neurology 512:74 – 83 (2009) © 2008 Wiley-Liss, Inc.