In Vivo Regulation of the Zebrafish Endoderm Progenitor Niche by T-Box Transcription Factors

Publication date: 27 June 2017
Source:Cell Reports, Volume 19, Issue 13
Author(s): Andrew C. Nelson, Stephen J. Cutty, Saule N. Gasiunas, Isabella Deplae, Derek L. Stemple, Fiona C. Wardle
T-box transcription factors T/Brachyury homolog A (Ta) and Tbx16 are essential for correct mesoderm development in zebrafish. The downstream transcriptional networks guiding their functional activities are poorly understood. Additionally, important contributions elsewhere are likely masked due to redundancy. Here, we exploit functional genomic strategies to identify Ta and Tbx16 targets in early embryogenesis. Surprisingly, we discovered they not only activate mesodermal gene expression but also redundantly regulate key endodermal determinants, leading to substantial loss of endoderm in double mutants. To further explore the gene regulatory networks (GRNs) governing endoderm formation, we identified targets of Ta/Tbx16-regulated homeodomain transcription factor Mixl1, which is absolutely required in zebrafish for endoderm formation. Interestingly, we find many endodermal determinants coordinately regulated through common genomic occupancy by Mixl1, Eomesa, Smad2, Nanog, Mxtx2, and Pou5f3. Collectively, these findings augment the endoderm GRN and reveal a panel of target genes underlying the Ta, Tbx16, and Mixl1 mutant phenotypes.

Graphical abstract

Teaser

Endoderm contributes to the respiratory and gastrointestinal tracts and all associated organs. How transcription factors control endodermal progenitor specification and expansion is not completely understood. Here, Nelson et al. identify a key redundant requirement for T-box factors Ta and Tbx16 in zebrafish endoderm formation and explore the downstream transcriptional programs.


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