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Panopoulou, GD, Clark MD, Holland LZ, Lehrach H, Holland ND.  1998.  AmphiBMP2/4, an amphioxus bone morphogenetic protein closely related to Drosophila decapentaplegic and vertebrate BMP2 and BMP4: Insights into evolution of dorsoventral axis specification. Developmental Dynamics. 213:130-139.   10.1002/(sici)1097-0177(199809)213:1<130::aid-aja13>;2-z   AbstractWebsite

Amphioxus AmphiBMP2/4 appears to be a single gene closely related to vertebrate BMP2 and BMP4. In amphioxus embryos, the expression patterns of AmphiBMP2/4 suggest patterning roles in the ectodermal dorsoventral axis (comparable to dorsoventral axis establishment in the ectoderm by Drosophila decapentaplegic and vertebrate BMP4). In addition AmphiBMP2/4 may be involved in somite evagination, tail bud growth, pharyngeal differentiation (resulting in club-shaped gland morphogenesis), hindgut regionalization, differentiation of olfactory epithelium, patterning of the anterior central nervous system, and establishment of the heart primordium, One difference between the developmental role of amphioxus AmphiBMP2/4 and vertebrate BMP4 is that the former does not appear to be involved in the initial establishment of the dorsoventral polarity of the mesoderm, Dev. Dyn. 1998;213:130-139. (C) 1998 Wiley-Liss, Inc.

Holland, ND, Holland LZ, Kozmik Z.  1995.  An Amphioxus Pax Gene, Amphipax-1, Expressed in Embryonic Endoderm, but Not in Mesoderm - Implications for the Evolution of Class-I Paired Box Genes. Molecular Marine Biology and Biotechnology. 4:206-214. AbstractWebsite

Class I paired box genes are widely distributed through the animal phyla but only fruitfly Pox meso and vertebrate Pax-1 and Pax-9 have been adequately characterized. These vertebrate genes have several developmental functions, but their role in patterning the axial skeleton has received the most attention. Because axial skeletons appear after the origin of the vertebrates, special interest attaches to the possible functions of the precursors of Pax-1 and Pax-g in the invertebrate ancestor of the vertebrates. As a proxy for this ancestor, we studied amphioxus, which is widely thought to be the closest living invertebrate relative of the vertebrates. A cDNA library from developing amphioxus yielded an unequivocal class I paired box gene, AmphiPax-1, that is 2.5 kb long. The gene encodes a 337 amino acid protein that includes a paired domain in which the amino acids are 92% identical to the paired domain amino acids of mouse and human Pax-1 and Pax-g. In situ hybridization detects AmphiPax-1 expression only in the endoderm of the developing pharynx; within this tissue, expression becomes strikingly down-regulated in regions that will fuse with the overlying ectoderm to form gill slits. No transcripts of AmphiPax-1 ever become detectable in any mesodermal structures. We think it likely that, during animal evolution, class I paired box genes originally functioned in endoderm development and were only later co-opted for other roles in mesoderm development; however, other scenarios cannot be ruled out until homologues of these genes are studied in more invertebrate phyla and in the lower vertebrates.