title: Zebrafish Lmx1b.1 and Lmx1b.2 are required for maintenance of the isthmic organizer.
abstract: The mesencephalic and metencephalic region (MMR) of the vertebrate central nervous system develops in response to signals produced by the isthmic organizer (IsO). We have previously reported that the LIM homeobox transcription factor Lmx1b is expressed within the chick IsO, where it is sufficient to maintain expression of the secreted factor wnt1. In this paper, we show that zebrafish express two Lmx1b orthologs, lmx1b.1 and lmx1b.2, in the rostral IsO, and demonstrate that these genes are necessary for key aspects of MMR development. Simultaneous knockdown of Lmx1b.1 and Lmx1b.2 using morpholino antisense oligos results in a loss of wnt1, wnt3a, wnt10b, pax8 and fgf8 expression at the IsO, leading ultimately to programmed cell death and the loss of the isthmic constriction and cerebellum. Single morpholino knockdown of either Lmx1b.1 or Lmx1b.2 has no discernible effect on MMR development. Maintenance of lmx1b.1 and lmx1b.2 expression at the isthmus requires the function of no isthmus/pax2.1, as well as Fgf signaling. Transient misexpression of Lmx1b.1 or Lmx1b.2 during early MMR development induces ectopic wnt1 and fgf8 expression in the MMR, as well as throughout much of the embryo. We propose that Lmx1b.1- and Lmx1b.2-mediated regulation of wnt1, wnt3a, wnt10b, pax8 and fgf8 maintains cell survival in the isthmocerebellar region.
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
authors.forename: F Patrick
authors.initials: FP
authors.lastname: O'Hara
authors.forename: Ernestine
authors.initials: E
authors.lastname: Beck
authors.forename: Lauren K
authors.initials: LK
authors.lastname: Barr
authors.forename: Lily L
authors.initials: LL
authors.lastname: Wong
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Kessler
authors.forename: Robert D
authors.initials: RD
authors.lastname: Riddle
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004268:DNA-Binding Proteins / Q000378:metabolism; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis / Q000235:genetics; D060850:LIM-Homeodomain Proteins; D008636:Mesencephalon / Q000196:embryology*; D020540:Metencephalon / Q000196:embryology*; D008969:Molecular Sequence Data; D051762:PAX2 Transcription Factor; D020033:Protein Isoforms / Q000235:genetics / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051153:Wnt Proteins; D051155:Wnt1 Protein; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics; D029961:Zebrafish Proteins
chemical_list: D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D036341:Intercellular Signaling Peptides and Proteins; C112149:LIM homeobox transcription factor 1 beta; D060850:LIM-Homeodomain Proteins; D051762:PAX2 Transcription Factor; D020033:Protein Isoforms; D014157:Transcription Factors; D051153:Wnt Proteins; D051155:Wnt1 Protein; D029961:Zebrafish Proteins; C497320:pax2a protein, zebrafish; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors