title: Lmx1b-controlled isthmic organizer is essential for development of midbrain dopaminergic neurons.
abstract: The LIM homeodomain transcription factor Lmx1b has been suggested to be required for the differentiation of midbrain dopaminergic (mDA) neurons. However, whether the loss of mDA neurons in Lmx1b(-/-) mice is due to its intrinsic role in the mDA lineage or to a consequence of the malformations caused by the earlier mid/hindbrain patterning defects remains to be clarified. We report here that Lmx1b expression in mDA neurons is dispensable for their differentiation and maintenance, and the loss of mDA neurons in Lmx1b(-/-) mice is due to the disruption of inductive activity of the isthmic organizer (IsO) in the absence of Lmx1b at the mid/hindbrain boundary (MHB). We found that mDA neurons revealed by tyrosine hydroxylase (TH), Pitx3, Nurr1, and dopamine transporter were indistinguishable from wild-type controls during embryonic development as well as in adulthood in TH-Cre;Lmx1b(flox/-) and Dat(Cre/+);Lmx1b(flox/-) mice, in which Lmx1b was selectively deleted in differentiating mDA neurons. In addition, mDA neurons were recovered in Lmx1b(-/-) mice, when IsO activity was restored by Wnt1-Lmx1b transgene at MHB. The restored IsO activity was evidenced by apparently normal tectum and cerebellum and recurrence of expression of Fgf8 and Wnt1 at MHB in Wnt1(Lmx1b);Lmx1b(-/-). Furthermore, when Lmx1b was deleted in the whole brain after the formation of IsO by Nestin-Cre, mDA neurons were normal, whereas serotonergic neurons displayed defective development phenocopying what observed in Lmx1b(-/-) mice. Thus, our results indicate that the inductive activity of IsO is essential, but Lmx1b expression in mDA neurons is dispensable for their differentiation and maintenance.
authors.affiliation: Institute of Neuroscience, Key Laboratory of Neurobiology, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Guo
authors.forename: Hai-Yan
authors.initials: HY
authors.lastname: Qiu
authors.forename: Ming
authors.initials: M
authors.lastname: Shi
authors.forename: Ying
authors.initials: Y
authors.lastname: Huang
authors.forename: Randy L
authors.initials: RL
authors.lastname: Johnson
authors.forename: Marcelo
authors.initials: M
authors.lastname: Rubinstein
authors.forename: Sheng-Di
authors.initials: SD
authors.lastname: Chen
authors.forename: Yu-Qiang
authors.initials: YQ
authors.lastname: Ding
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D019521:Body Patterning / Q000235:genetics / Q000502:physiology*; D001973:Bromodeoxyuridine / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D004268:DNA-Binding Proteins / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D050483:Dopamine Plasma Membrane Transport Proteins / Q000235:genetics; D004622:Embryo, Mammalian; D005260:Female; D017353:Gene Deletion; D018507:Gene Expression Regulation, Developmental / Q000235:genetics / Q000502:physiology*; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D007381:Intermediate Filament Proteins / Q000235:genetics; D060850:LIM-Homeodomain Proteins; D008636:Mesencephalon / Q000166:cytology / Q000196:embryology / Q000254:growth & development; D051379:Mice; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000235:genetics; D064231:Nestin; D009474:Neurons / Q000502:physiology*; D057126:Nuclear Receptor Subfamily 4, Group A, Member 2; D011247:Pregnancy; D012249:Rhombencephalon / Q000502:physiology*; D013234:Stem Cells / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics; D051155:Wnt1 Protein / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; D050483:Dopamine Plasma Membrane Transport Proteins; D018398:Homeodomain Proteins; D007381:Intermediate Filament Proteins; C112149:LIM homeobox transcription factor 1 beta; D060850:LIM-Homeodomain Proteins; D009419:Nerve Tissue Proteins; C577485:Nes protein, mouse; D064231:Nestin; C539883:Nr4a2 protein, mouse; D057126:Nuclear Receptor Subfamily 4, Group A, Member 2; D014157:Transcription Factors; D051155:Wnt1 Protein; C495246:Wnt1 protein, mouse; C433629:homeobox protein PITX3; D014446:Tyrosine 3-Monooxygenase; D001973:Bromodeoxyuridine; D004298:Dopamine