<Emphasis Type="Italic">Wnt</Emphasis> gene loss in flatworms |
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Authors: | Nick Riddiford Peter D Olson |
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Institution: | (1) Department of Zoology, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK; |
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Abstract: | Wnt genes encode secreted glycoproteins that act in cell–cell signalling to regulate a wide array of developmental processes,
ranging from cellular differentiation to axial patterning. Discovery that canonical Wnt/β-catenin signalling is responsible
for regulating head/tail specification in planarian regeneration has recently highlighted their importance in flatworm (phylum
Platyhelminthes) development, but examination of their roles in the complex development of the diverse parasitic groups has
yet to be conducted. Here, we characterise Wnt genes in the model tapeworm Hymenolepis microstoma and mine genomic resources of free-living and parasitic species for the presence of Wnts and downstream signalling components.
We identify orthologs through a combination of BLAST and phylogenetic analyses, showing that flatworms have a highly reduced
and dispersed complement that includes orthologs of only five subfamilies (Wnt1, Wnt2, Wnt4, Wnt5 and Wnt11) and fewer paralogs
in parasitic flatworms (5–6) than in planarians (9). All major signalling components are identified, including antagonists
and receptors, and key binding domains are intact, indicating that the canonical (Wnt/β-catenin) and non-canonical (planar
cell polarity and Wnt/Ca2+) pathways are functional. RNA-Seq data show expression of all Hymenolepis Wnts and most downstream components in adults and larvae with the notable exceptions of wnt1, expressed only in adults, and wnt2 expressed only in larvae. The distribution of Wnt subfamilies in animals corroborates the idea that the last common ancestor
of the Cnidaria and Bilateria possessed all contemporary Wnts and highlights the extent of gene loss in flatworms. |
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