Inhibition of neurogenesis at the zebrafish midbrain-hindbrain boundary by the combined and dose-dependent activity of a new hairy/E(spl) gene pair.
The intervening zone (IZ) is a pool of progenitor cells located at the midbrain-hindbrain boundary (MHB) and important for MHB maintenance, midbrain-hindbrain growth and the generation of midbrain-hindbrain neurons. Recently, we implicated the Hairy/E(spl) transcription factor Her5 in the formation of the medial (most basal) part of the IZ (MIZ) in zebrafish; the molecular bases for lateral IZ (LIZ) formation, however, remain unknown. We now demonstrate that her5 is physically linked to a new family member, him, displaying an identical MHB expression pattern. Using single and double knockdowns of him and her5, as well as a him+her5 deletion mutant background (b404), we demonstrate that Him and Her5 are equally necessary for MIZ formation, and that they act redundantly in LIZ formation in vivo. We show that these processes do not involve cross-regulation between Him and Her5 expression or activities, although Him and Her5 can heterodimerize with high affinity. Increasing the function of one factor when the other is depleted further shows that Him and Her5 are functionally interchangeable. Together, our results demonstrate that patterning and neurogenesis are integrated by the her5-him gene pair to maintain a progenitor pool at the embryonic MHB. We propose a molecular mechanism for this process where the global 'Him+Her5' activity inhibits ngn1 expression in a dose-dependent manner and through different sensitivity thresholds along the medio-lateral axis of the neural plate.
Ninkovic
Jovica
J
Zebrafish Neurogenetics Junior Research Group, Institute of Virology, Technical University-Munich, Trogerstrasse 4b, D-81675 Munich, Germany. ninkovic@gsf.de
Tallafuss
Alexandra
A
Leucht
Christoph
C
Topczewski
Jacek
J
Tannhäuser
Birgit
B
Solnica-Krezel
Lilianna
L
Bally-Cuif
Laure
L
D000595:Amino Acid Sequence; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D015153:Blotting, Western; D019521:Body Patterning; D003001:Cloning, Molecular; D017931:DNA Primers / Q000737:chemistry; D018507:Gene Expression Regulation, Developmental; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D017403:In Situ Hybridization; D008636:Mesencephalon / Q000196:embryology*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000502:physiology*; D009474:Neurons / Q000378:metabolism / Q000473:pathology* / Q000502:physiology; D010802:Phylogeny; D011485:Protein Binding; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012249:Rhombencephalon / Q000196:embryology*; D014157:Transcription Factors / Q000096:biosynthesis / Q000502:physiology*; D019076:Transgenes; D020798:Two-Hybrid System Techniques; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000096:biosynthesis / Q000502:physiology*
D051792:Basic Helix-Loop-Helix Proteins; D017931:DNA Primers; D009419:Nerve Tissue Proteins; D012313:RNA; D012333:RNA, Messenger; D014157:Transcription Factors; D029961:Zebrafish Proteins; C496678:Her11 protein, zebrafish; C474186:Her5 protein, zebrafish; C486337:neurog1 protein, zebrafish