Characterization and regulation of the hb9/mnx1 beta-cell progenitor specific enhancer in zebrafish.
; ; et al
in Developmental Biology (2012), 365(1), 290-302
Differentiation of insulin producing beta-cells is a genetically well defined process that involves functions of various conserved transcription factors. Still, the transcriptional mechanisms underlying ... [more ▼]
Differentiation of insulin producing beta-cells is a genetically well defined process that involves functions of various conserved transcription factors. Still, the transcriptional mechanisms underlying specification and determination of beta-cell fate are poorly defined. Here we provide the description of a beta-cell progenitor specific enhancer as a model to study initial steps of beta-cell differentiation. We show that evolutionary non-conserved upstream sequences of the zebrafish hb9 gene are required and sufficient for regulating expression in beta-cells prior to the onset of insulin expression. This enhancer contains binding sites for paired-box transcription factors and two E-boxes that in EMSA studies show interaction with Pax6b and NeuroD, respectively. We show that Pax6b is a potent activator of endodermal hb9 expression and that this activation depends on the beta-cell enhancer. Using genetic approaches we show that pax6b is crucial for maintenance but not induction of pancreatic hb9 transcription. As loss of Pax6b or Hb9 independently results in the loss of insulin expression, the data reveal a novel cross-talk between the two essential regulators of early beta-cell differentiation. While we find that the known pancreatic E-box binding proteins NeuroD and Ngn3 are not required for hb9 expression we also show that removal of both E-boxes selectively eliminates pancreatic specific reporter expression. The data provide evidence for an Ngn3 independent pathway of beta-cell specification that requires function of currently not specified E-box binding factors. [less ▲]Detailed reference viewed: 22 (3 ULg)
Fast Homozygosity Mapping and Identification of a Zebrafish ENU-Induced Mutation by Whole-Genome Sequencing.
Voz, Marianne ; Coppieters, Wouter ; Manfroid, Isabelle et al
in PLoS ONE (2012), 7(4), 34671
Forward genetics using zebrafish is a powerful tool for studying vertebrate development through large-scale mutagenesis. Nonetheless, the identification of the molecular lesion is still laborious and ... [more ▼]
Forward genetics using zebrafish is a powerful tool for studying vertebrate development through large-scale mutagenesis. Nonetheless, the identification of the molecular lesion is still laborious and involves time-consuming genetic mapping. Here, we show that high-throughput sequencing of the whole zebrafish genome can directly locate the interval carrying the causative mutation and at the same time pinpoint the molecular lesion. The feasibility of this approach was validated by sequencing the m1045 mutant line that displays a severe hypoplasia of the exocrine pancreas. We generated 13 Gb of sequence, equivalent to an eightfold genomic coverage, from a pool of 50 mutant embryos obtained from a map-cross between the AB mutant carrier and the WIK polymorphic strain. The chromosomal region carrying the causal mutation was localized based on its unique property to display high levels of homozygosity among sequence reads as it derives exclusively from the initial AB mutated allele. We developed an algorithm identifying such a region by calculating a homozygosity score along all chromosomes. This highlighted an 8-Mb window on chromosome 5 with a score close to 1 in the m1045 mutants. The sequence analysis of all genes within this interval revealed a nonsense mutation in the snapc4 gene. Knockdown experiments confirmed the assertion that snapc4 is the gene whose mutation leads to exocrine pancreas hypoplasia. In conclusion, this study constitutes a proof-of-concept that whole-genome sequencing is a fast and effective alternative to the classical positional cloning strategies in zebrafish. [less ▲]Detailed reference viewed: 41 (7 ULg)