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Mazet, F, Yu JK, Liberles DA, Holland LZ, Shimeld SM.  2003.  Phylogenetic relationships of the Fox (Forkhead) gene family in the Bilateria. Gene. 316:79-89.   10.1016/s0378-1119(03)00741-8   AbstractWebsite

The Forkhead or Fox gene family encodes putative transcription factors. There are at least four Fox genes in yeast, 16 in Drosophila melanogaster (Dm) and 42 in humans. Recently, vertebrate Fox genes have been classified into 17 groups named FoxA to FoxQ [Genes Dev. 14 (2000) 142]. Here, we extend this analysis to invertebrates, using available sequences from D. melanogaster, Anopheles gambiae (Ag), Caenorhabditis elegans (Ce), the sea squirt Ciona intestinalis (Ci) and amphioxus Branchiostoma floridae (Bf), from which we also cloned several Fox genes. Phylogenetic analyses lend support to the previous overall subclassification of vertebrate genes, but suggest that four subclasses (FoxJ, L, N and Q) could be further subdivided to reflect their relationships to invertebrate genes. We were unable to identify orthologs of Fox subclasses E, H, I, J, M and Q1 in D. melanogaster, A. gambiae or C. elegans, suggesting either considerable loss in ecdysozoans or the evolution of these subclasses in the deuterostome lineage. Our analyses suggest that the common ancestor of protostomes and deuterostomes had a minimum complement of 14 Fox genes. (C) 2003 Elsevier B.V. All rights reserved.

Holland, LZ, Kene M, Williams NA, Holland ND.  1997.  Sequence and embryonic expression of the amphioxus engrailed gene (AmphiEn): The metameric pattern of transcription resembles that of its segment-polarity homolog in Drosophila. Development. 124:1723-1732. AbstractWebsite

Vertebrate segmentation has been proposed as an evolutionary inheritance either from some metameric protostome or from a more closely related deuterostome, To address this question, we studied the developmental expression of AmphiEn, the engrailed gene of amphioxus, the closest living invertebrate relative of the vertebrates, In neurula embryos of amphioxus, AmphiEn is expressed along the anteroposterior axis as metameric stripes, each located in the posterior part of a nascent or newly formed segment, This pattern resembles the expression stripes of the segment-polarity gene engrailed, which has a key role in establishing and maintaining the metameres in embryos of Drosophila and other metameric protostomes, Later, amphioxus embryos express AmphiEn in non-metameric patterns - transiently in the embryonic ectoderm and dorsal nerve cord. Nerve cord expression occurs in a few cells approximately midway along the rostrocaudal axis and also in a conspicuous group of anterior cells in the cerebral vesicle at a level previously identified as corresponding to the vertebrate diencephalon. Compared to vertebrate engrailed expression at the midbrain/hindbrain boundary, AmphiEn expression in the cerebral vesicle is relatively late, Thus, it is uncertain whether the cerebral vesicle expression marks the rostral end of the amphioxus hindbrain; if it does, then amphioxus may have little or no homolog of the vertebrate midbrain, The segmental expression of AmphiEn in forming somites suggests that the functions of engrailed homologs in establishing and maintaining a metameric body plan may have arisen only once during animal evolution, If so, the protostomes and deuterostomes probably shared a common segmented ancestor.