title: The Enhancer of split transcription factor Her8a is a novel dimerisation partner for Her3 that controls anterior hindbrain neurogenesis in zebrafish.
abstract: BACKGROUND
  Neurogenesis control and the prevention of premature differentiation in the vertebrate embryo are crucial processes, allowing the formation of late-born cell types and ensuring the correct shape and cytoarchitecture of the brain. Members of the Hairy/Enhancer of Split (Hairy/E(spl)) family of bHLH-Orange transcription factors, such as zebrafish Her3, 5, 9 and 11, are implicated in the local inhibition of neurogenesis to maintain progenitor pools within the early neural plate. To better understand how these factors exert their inhibitory function, we aimed to isolate some of their functional interactors.
  
  
  RESULTS
  We used a yeast two-hybrid screen with Her5 as bait and recovered a novel zebrafish Hairy/E(spl) factor--Her8a. Using phylogenetic and synteny analyses, we demonstrate that her8a evolved from an ancient duplicate of Hes6 that was recently lost in the mammalian lineage. We show that her8a is expressed across the mid- and anterior hindbrain from the start of segmentation. Through knockdown and misexpression experiments, we demonstrate that Her8a is a negative regulator of neurogenesis and plays an essential role in generating progenitor pools within rhombomeres 2 and 4--a role resembling that of Her3. Her8a co-purifies with Her3, suggesting that Her8a-Her3 heterodimers may be relevant in this domain of the neural plate, where both proteins are co-expressed. Finally, we demonstrate that her8a expression is independent of Notch signaling at the early neural plate stage but that SoxB factors play a role in its expression, linking patterning information to neurogenesis control. Overall, the regulation and function of Her8a differ strikingly from those of its closest relative in other vertebrates--the Hes6-like proteins.
  
  
  CONCLUSIONS
  Our results characterize the phylogeny, expression and functional interactions involving a new Her factor, Her8a, and highlight the complex interplay of E(spl) proteins that generates the neurogenesis pattern of the zebrafish early neural plate.
authors.affiliation: Zebrafish Neurogenetics Department, Helmholtz Zentrum München, German Research Center for Environmental Health, Ingolstädter Landstr, 1, D-85764 Neuherberg, Germany. webb@helmholtz-muenchen.de
authors.forename: Katharine J
authors.initials: KJ
authors.lastname: Webb
authors.forename: Marion
authors.initials: M
authors.lastname: Coolen
authors.forename: Christian J
authors.initials: CJ
authors.lastname: Gloeckner
authors.forename: Christian
authors.initials: C
authors.lastname: Stigloher
authors.forename: Brigitte
authors.initials: B
authors.lastname: Bahn
authors.forename: Stefanie
authors.initials: S
authors.lastname: Topp
authors.forename: Marius
authors.initials: M
authors.lastname: Ueffing
authors.forename: Laure
authors.initials: L
authors.lastname: Bally-Cuif
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009024:Morphogenesis / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D055495:Neurogenesis / Q000502:physiology*; D010802:Phylogeny; D011485:Protein Binding; D055503:Protein Multimerization; D051880:Receptors, Notch / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012249:Rhombencephalon / Q000166:cytology / Q000196:embryology*; D015398:Signal Transduction / Q000502:physiology; D020798:Two-Hybrid System Techniques; D015027:Zebrafish / Q000033:anatomy & histology* / Q000196:embryology*; D029961:Zebrafish Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism*
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D009419:Nerve Tissue Proteins; D051880:Receptors, Notch; D012097:Repressor Proteins; D029961:Zebrafish Proteins; C488362:Her3 protein, zebrafish; C560436:Her8a protein, zebrafish