Evolutionary developmental biology (evolution of development or
informally, evo-devo) is a field of biology that compares the
developmental processes of different organisms to determine the ancestral
relationship between them, and to discover how developmental processes
evolved (source wikipedia).
Conservation and diversification of an ancestral chordate gene regulatory
network for dorsoventral patterning.
(Kozmikova I, Smolikova J, Vlcek C, Kozmik Z., PLoS One. 2011 Feb3;6(2):e14650.)
Formation of a dorsoventral axis is a key event in the early development
of most animal embryos. It is well established that bone morphogenetic
proteins (Bmps) and Wnts are key mediators of dorsoventral patterning in
vertebrates. In the cephalochordate amphioxus, genes encoding Bmps and
transcription factors downstream of Bmp signaling such as Vent are
expressed in patterns reminiscent of those of their vertebrate
orthologues. However, the key question is whether the conservation of
expression patterns of network constituents implies conservation of
functional network interactions, and if so, how an increased functional
complexity can evolve. Using heterologous systems, namely by reporter gene
assays in mammalian cell lines and by transgenesis in medaka fish, we have
compared the gene regulatory network implicated in dorsoventral patterning
of the basal chordate amphioxus and vertebrates. We found that Bmp but not
canonical Wnt signaling regulates promoters of genes encoding homeodomain
proteins AmphiVent1 and AmphiVent2. Furthermore, AmphiVent1 and AmphiVent2
promoters appear to be correctly regulated in the context of a vertebrate
embryo. Finally, we show that AmphiVent1 is able to directly repress
promoters of AmphiGoosecoid and AmphiChordin genes. Repression of genes
encoding dorsal-specific signaling molecule Chordin and transcription
factor Goosecoid by Xenopus and zebrafish Vent genes represents a key
regulatory interaction during vertebrate axis formation. Our data indicate
high evolutionary conservation of a core Bmp-triggered gene regulatory
network for dorsoventral patterning in chordates and suggest that
co-option of the canonical Wnt signaling pathway for dorsoventral
patterning in vertebrates represents one of the innovations through which
an increased morphological complexity of vertebrate embryo is achieved.
Gene regulatory network (GRN) architecture for early D/V mesoderm
specification in Xenopus and amphioxus.
Experimental data suggest high conservation of Bmp-Chordin signaling network in all chordates. In contrast, the role of Wnt/b-catenin signaling in D/V mesoderm specification seems to be limited to vertebrates. Dashed line indicates interactions, that are present in Xenopus but were shown to be absent in
Amphioxus GRN (this study). The question mark within the continuous line denotes presumed but not yet proven regulatory link. The question mark
within the dashed line denotes likely absence of the regulatory link in amphioxus.