Abstract
Organizers are regions of the embryo that can both induce new fates and impart pattern on other regions. So far, surprisingly few organizers have been discovered, considering the number of patterned tissue types generated during development. This may be because their discovery has relied on transplantation and ablation experiments. Here we describe a new approach, using chick embryos, to discover organizers based on a common gene expression signature, and use it to uncover the anterior intestinal portal (AIP) endoderm as a putative heart organizer. We show that the AIP can induce cardiac identity from non-cardiac mesoderm and that it can pattern this by specifying ventricular and suppressing atrial regional identity. We also uncover some of the signals responsible. The method holds promise as a tool to discover other novel organizers acting during development.
Highlights
Organizers are regions of the embryo that can both induce new fates and impart pattern on other regions
We tested this idea by comparing the transcriptomes of three known amniote organizers (Hensen’s node, the notochord/floor-plate and the ZPA). This defines a synexpression set of 48 transcripts that are either enriched or depleted in organizers, which we used to explore the embryo for other regions of synexpression. This suggested that the endoderm of the anterior intestinal portal (AIP) might be a new organizer
AIP does not induce AMHC1 (Fig. 2f,b0) or SHOX2 (Fig. 2g,e0), a marker of the sinoatrial node (Supplementary Fig. 6i0,p0). These results show that the AIP can induce ventricular cardiac identity in mesoderm not destined to this fate
Summary
Organizers are regions of the embryo that can both induce new fates and impart pattern on other regions. A graft of Hensen’s node from an early (primitive streak stage) embryo into the anterior limb bud of a much later embryo can mimic the action of the limb organizer, the ZPA, by inducing and patterning a full set of skeletal elements including the digits[8]. We tested this idea by comparing the transcriptomes of three known amniote organizers (Hensen’s node, the notochord/floor-plate and the ZPA) This defines a synexpression set of 48 transcripts that are either enriched or depleted in organizers, which we used to explore the embryo for other regions of synexpression. Title ‘Microarray analysis of chick embryonic tissues: gastrulation, neural tube/notochord and limb development’ and given accession number E-MTAB-4048) These lists were combined using a Boolean algorithm to find enriched or depleted transcripts common to all three organizers. This approach uncovers relative changes in expression between a b c d e f
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