bHLH transcription factor Her5 links patterning to regional inhibition of neurogenesis at the midbrain-hindbrain boundary.
The midbrain-hindbrain (MH) domain of the vertebrate embryonic neural plate displays a stereotypical profile of neuronal differentiation, organized around a neuron-free zone ('intervening zone', IZ) at the midbrain-hindbrain boundary (MHB). The mechanisms establishing this early pattern of neurogenesis are unknown. We demonstrate that the MHB is globally refractory to neurogenesis, and that forced neurogenesis in this area interferes with the continued expression of genes defining MHB identity. We further show that expression of the zebrafish bHLH Hairy/E(spl)-related factor Her5 prefigures and then precisely delineates the IZ throughout embryonic development. Using morpholino knock-down and conditional gain-of-function assays, we demonstrate that Her5 is essential to prevent neuronal differentiation and promote cell proliferation in a medial compartment of the IZ. We identify one probable target of this activity, the zebrafish Cdk inhibitor p27Xic1. Finally, although the her5 expression domain is determined by anteroposterior patterning cues, we show Her5 does not retroactively influence MH patterning. Together, our results highlight the existence of a mechanism that actively inhibits neurogenesis at the MHB, a process that shapes MH neurogenesis into a pattern of separate neuronal clusters and might ultimately be necessary to maintain MHB integrity. Her5 appears as a partially redundant component of this inhibitory process that helps translate early axial patterning information into a distinct spatiotemporal pattern of neurogenesis and cell proliferation within the MH domain.
Geling
Andrea
A
Zebrafish Neurogenetics Junior Research Group, Institute of Virology, Technical University-Munich, Trogerstrasse 4b, D-81675 Munich, Germany.
Itoh
Motoyuki
M
Tallafuss
Alexandra
A
Chapouton
Prisca
P
Tannhäuser
Birgit
B
Kuwada
John Y
JY
Chitnis
Ajay B
AB
Bally-Cuif
Laure
L
D000818:Animals; D030801:Animals, Genetically Modified; D016590:Aphidicolin / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins; D015415:Biomarkers; D019521:Body Patterning; D018797:Cell Cycle Proteins / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004791:Enzyme Inhibitors / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D018257:Helix-Loop-Helix Motifs; D017403:In Situ Hybridization; D008636:Mesencephalon / Q000166:cytology / Q000254:growth & development*; D009474:Neurons / Q000502:physiology*; D012249:Rhombencephalon / Q000166:cytology / Q000254:growth & development*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D015027:Zebrafish / Q000033:anatomy & histology / Q000196:embryology / Q000378:metabolism; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
D016590:Aphidicolin; D051792:Basic Helix-Loop-Helix Proteins; D015415:Biomarkers; D018797:Cell Cycle Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004791:Enzyme Inhibitors; D018840:HSP70 Heat-Shock Proteins; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D029961:Zebrafish Proteins; C474186:Her5 protein, zebrafish