Document Detail

Acoel development indicates the independent evolution of the bilaterian mouth and anus.
MedLine Citation:
PMID:  18806777     Owner:  NLM     Status:  MEDLINE    
Most bilaterian animals possess a through gut with a separate mouth and anus. It is commonly believed that during the transition from radial to bilateral symmetry, both openings evolved simultaneously by the lateral closure of a slit-like blastopore. Molecular phylogenies however, place the acoel flatworms, which have only one opening to their digestive system, as the sister group to all remaining Bilateria. To address how this single body opening is related to the mouth and anus of the protostomes and deuterostomes, we studied the expression of genes involved in bilaterian foregut and hindgut patterning during the development of the acoel Convolutriloba longifissura. Here we show that the genes brachyury and goosecoid are expressed in association with the acoel mouth, suggesting that this single opening is homologous to the mouth of other bilaterians. In addition, we find that the genes caudal, orthopedia and brachyury-which are expressed in various bilaterian hindguts-are expressed in a small region at the posterior end of the animal, separated from the anterior oral brachyury-expressing region by a dorsal domain of ectodermal bmp2/4 expression. These results contradict the hypothesis that the bilaterian mouth and anus evolved simultaneously from a common blastoporal opening, and suggest that a through gut might have evolved independently in different animal lineages.
Andreas Hejnol; Mark Q Martindale
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.     Date:  2008-09-17
Journal Detail:
Title:  Nature     Volume:  456     ISSN:  1476-4687     ISO Abbreviation:  Nature     Publication Date:  2008 Nov 
Date Detail:
Created Date:  2008-11-21     Completed Date:  2008-12-18     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0410462     Medline TA:  Nature     Country:  England    
Other Details:
Languages:  eng     Pagination:  382-6     Citation Subset:  IM    
Kewalo Marine Laboratory, PBRC, University of Hawaii, 41 Ahui Street, Honolulu, Hawaii 96813, USA.
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MeSH Terms
Anal Canal / anatomy & histology*,  embryology*,  growth & development
Gene Expression Regulation, Developmental
Genes, Helminth / genetics
Models, Biological
Mouth / anatomy & histology*,  embryology*,  growth & development
Turbellaria / anatomy & histology*,  embryology*,  genetics,  growth & development

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