The olig family: phylogenetic analysis and early gene expression in Xenopus tropicalis
The olig genes form a small subfamily of basic helix-loop-helix transcription factors. They were discovered in 2000 as genes required for oligodendrocyte lineage specification. Since then, olig genes have been identified in various vertebrate species and corresponding sequences accumulated within genomic databases. Until now, three groups of olig genes have been characterized. Our phylogenetic analysis demonstrates the existence of a fourth group, which we named olig4. Genes of the four olig groups are present in actinopterygians and amphibians, whereas mammals only possess olig1, 2, and 3. We also found one olig gene in hemichordates, urochordates, and cephalochordates. Our expression study during Xenopus tropicalis embryogenesis shows that the four olig genes have very distinct expression patterns. Olig1 is very faintly expressed before the tadpole stage, whereas olig2, 3, and 4 are expressed from the gastrula stage onward. The olig3 expression during neurulation suggests a role in early anteroposterior patterning of the brain. All these results indicate that olig genes are involved in several developmental processes during early development.
KeywordsOlig bHLH Xenopus Oligodendrocytes Phylogeny
We would like to thank Chantal Ballagny, Albert Chesneau, Laure-Hélène Jestin, Christophe De Medeiros, and Claudia Bevilacqua for their technical assistance and contributions to the work.
We are grateful to Muriel Perron and Morgane Locker for valuable discussions and critical reading of the manuscript and to James Richardson for correcting the English.
This work was supported by the Centre National de la Recherche Scientifique, the Université Paris-Sud XI, the Ministère de l’Education Nationale, de la Recherche et de la Technologie, the European Community FP6 (X-omics coordinated action no. 512065).
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