1: Brain Res Brain Res Rev. 2005 Sep;49(2):120-6. Epub 2005 Jan 21. Isthmus organizer for midbrain and hindbrain development. Nakamura H, Katahira T, Matsunaga E, Sato T. Department of Molecular Neurobiology, Graduate School of Life Sciences and Institute of Development, Aging and Cancer, Tohoku University, Seiryo-machi 4-1, Aoba-ku, Sendai 980-8575, Japan. nakamura@idac.tohoku.ac.jp Classical transplantation studies showed that the isthmus has an organizing activity upon the tectum and cerebellum. Since Fgf8 is expressed in the isthmus and mimics functionally isthmic grafts, it is accepted that Fgf8 plays pivotal role in the isthmic organizing activity. The fate of brain vesicles is determined by the combinations of transcription factors. The neural tube region where Otx2, Pax2, and En1 are expressed early on acquires midbrain identity. Pax3/7 forces the midbrain to differentiate into tectum. En1/2, Pax2/5, and Fgf8 form a positive feedback loop for their expression, thus misexpression of one of these molecules turns on the loop and forces presumptive diencephalon to differentiate into tectum. The isthmic organizer signal, Fgf8, stabilizes or changes the expression of the transcription factors in mid/hindbrain region. A strong Fgf8 signal activates the Ras-ERK signaling pathway, which in turn activates Irx2 in a rostrodorsal part of the hindbrain, and forces this tissue to differentiate into cerebellum. Publication Types: Review PMID: 16111543 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 2: FASEB J. 2005 Sep;19(11):1537-9. Epub 2005 Jun 21. Serotonergic-like progenitor cells propagated from neural stem cells in vitro: survival with SERT protein expression following implantation into brains of mice lacking SERT. Ren-Patterson RF, Kim DK, Zheng X, Sherrill S, Huang SJ, Tolliver T, Murphy DL. Laboratory of Clinical Science, National Institute of Mental Health, NIH, Bethesda, MD 20892-1264, USA. renpatr@intra.nimh.nih.gov Neural stem cells (NSCs) obtained from the midbrain region of embryonic (E14) mice were initially cultured with basic fibroblast growth factor (bFGF), Sonic hedgehog, and FGF-8 in a serum-free N-2 culture medium to foster differentiation into a serotonergic-like phenotype. During the initial differentiating phase, these progenitor cells expressed En1, Pax3, and Pax5 mRNA. Subsequently, a single serotonin [5-hydroxytryptamine (5-HT)] and tryptophan hydroxylase-positive clone was isolated, which gave rise to cells that developed serotonergic properties. Sixty percent of these progenitor cells expressed the serotonin transporter (SERT), as indicated by specific ligand binding of [125I]-RTI-55. To further evaluate SERT functionality, we showed that these progenitor cells possessed specific [3H]-5-HT uptake activity. Implantation of the serotonergic-like progenitors into the hippocampus of adult mice genetically lacking SERT was followed by migration of these cells into adjacent brain regions, and survival of the cells at 8 weeks was accompanied by a gradual increase in density of SERT protein expression, which was not found in vehicle-injected, control mice. These findings suggest that this serotonergic-like NSC model will be a useful contribution to the development of cell biotechnology in regard to the expression of missing genes such as SERT in the adult brain. PMID: 15972295 [PubMed - in process] --------------------------------------------------------------- 3: Int J Dev Biol. 2005;49(2-3):231-5. Isthmus organizer and regionalization of the mesencephalon and metencephalon. Nakamura H, Watanabe Y. Department of Molecular Neurobiology, Graduate School of Life Sciences and Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan. nakamura@idac.tohoku.ac.jp The brain vesicles that are formed at an early stage of neural development are the fundamentals of the brain plan. Heterotopic transplantation revealed that the diencephalon could change its fate when juxtaposed to the isthmus (mes-metencephalic boundary), which indicated that the isthmus functions as an organizer for the mesencephalon and metencephalon. Fgf8 is identified as an isthmus organizing signal. Misexpression of Fgf8a and Fgf8b indicated that a strong Fgf8 signal organizes cerebellar development. The transcription factors define the fate of the region. Overlapping expression of Otx2, En1 and Pax2 may define the mesencephalic region and additional expression of Pax3/7 may instruct the mesencephalic region to differentiate into the tectum. The di-mesencephalic boundary is determined by repressive interaction between Pax6 and En1/Pax2 and the mes-metencephalic boundary is defined by repressive interaction between Otx2 and Gbx2. Fgf8 is induced at the border of the Otx2 and Gbx2 expression domain, overlapping with Gbx2 expression. Publication Types: Review Review, Tutorial PMID: 15906236 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 4: Development. 1999 Oct;126(19):4247-55. Transplacental delivery of the Wnt antagonist Frzb1 inhibits development of caudal paraxial mesoderm and skeletal myogenesis in mouse embryos. Borello U, Coletta M, Tajbakhsh S, Leyns L, De Robertis EM, Buckingham M, Cossu G. Istituto Pasteur-Cenci Bolognetti, Dipartimento di Istologia ed Embriologia Medica, Universita di Roma 'La Sapienza', Via A. Scarpa 14, Italy. Axial structures (neural tube/notochord) and surface ectoderm activate myogenesis in the mouse embryo; their action can be reproduced, at least in part, by several molecules such as Sonic hedgehog and Wnts. Recently, soluble Wnt antagonists have been identified. Among those examined only Frzb1 was found to be expressed in the presomitic mesoderm and newly formed somites and thus its possible role in regulating myogenesis was investigated in detail. When presomitic mesoderm or newly formed somites were cultured with axial structures and surface ectoderm on a feeder layer of C3H10T1/2 cells expressing Frzb1, myogenesis was abolished or severely reduced in presomitic mesoderm and the three most recently formed somites. In contrast, no effect was observed on more mature somites. Inhibition of myogenesis did not appear to be associated with increased cell death since the final number of cells in the explants grown in the presence of Frzb1 was only slightly reduced in comparison with controls. In order to examine the possible function of Frzb1 in vivo, we developed a method based on the overexpression of the soluble antagonist by transient transfection of WOP cells with a Frzb1 expression vector and injection of transfected cells into the placenta of pregnant females before the onset of maternofoetal circulation. Frzb1, secreted by WOP cells, accumulated in the embryo and caused a marked reduction in size of caudal structures. Myogenesis was strongly reduced and, in the most severe cases, abolished. This was not due to a generalized toxic effect since only several genes downstream of the Wnt signaling pathway such as En1, Noggin and Myf5 were downregulated; in contrast, Pax3 and Mox1 expression levels were not affected even in embryos exhibiting the most severe phenotypes. Taken together, these results suggest that Wnt signals may act by regulating both myogenic commitment and expansion of committed cells in the mouse mesoderm. PMID: 10477293 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 5: Mech Dev. 1998 Nov;78(1-2):171-8. Pax3 and Pax7 are expressed in commissural neurons and restrict ventral neuronal identity in the spinal cord. Mansouri A, Gruss P. Max-Planck Institute for Biophysical Chemistry, Department of Molecular Cell Biology, Am Fassberg 11, 37077, Gottingen, Germany. Pax3 and Pax7 are transcription factors sharing high sequence identity and overlapping patterns of expression in particular in the dorsal spinal cord. Analysis of Pax3 and Pax7 double mutant mice demonstrates that both genes share redundant functions to restrict ventral neuronal identity in the spinal cord. In their absence, the En1 expression domain is expanded dorsally but that of Evx1 is not affected. In addition, Pax3 and Pax7 are expressed in commissural neurons and double mutant embryos exhibit highly reduced ventral commissure. Our findings reveal two distinct regulatory pathways for spinal cord neurogenesis, only one of which is dependent on Pax3/7 and 6. Copyright 1998 Elsevier Science Ireland Ltd. All Rights Reserved PMID: 9858722 [PubMed - indexed for MEDLINE] ---------------------------------------------------------------