Noncanonical role of Hox14 revealed by its expression patterns in lamprey and shark

doi:10.1073/pnas.0710947105

Noncanonical role of Hox14 revealed by its expression patterns in lamprey and shark

*Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology, 2-2-3 Minatojima-minami, Chuo-ku, Kobe 650-0047, Japan;
^†Lehrstuhl für Zoologie und Evolutionsbiologie, Department of Biology, University of Konstanz, Universitätsstrasse 10, D-78457 Konstanz, Germany;
^§Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama Aoba-ku, Sendai 980-8578, Japan; and
^¶National Research Institute of Fisheries Science, 6-31-1 Nagai, Yokosuka, Kanagawa 238-0316, Japan

Edited by Masatoshi Nei, Pennsylvania State University, University Park, PA, and approved March 11, 2008 (received for review November 19, 2007)

Abstract

Hox genes are arranged in uninterrupted clusters in vertebrate genomes, and the nested patterns of their expression define spatial identities in multiple embryonic tissues. The ancestral Hox cluster of vertebrates has long been thought to consist of, maximally, 13 Hox genes. However, recently, Hox14 genes were discovered in three chordate lineages, the coelacanth, cartilaginous fishes, and amphioxus, but their expression patterns have not yet been analyzed. We isolated Hox14 cDNAs from the Japanese lamprey and cloudy catshark. These genes were not expressed in the central nervous systems, somites, or fin buds/folds but were expressed in a restricted cell population surrounding the hindgut. The lack of Hox14 expression in most of the embryonic axial elements, where nested Hox expressions define spatial identities, suggests a decoupling of Hox14 genes' regulation from the ancestral regulatory mechanism. The relaxation of preexisting constraint for collinear expression may have permitted the secondary losses of this Hox member in the tetrapod and teleost lineages.

Footnotes

^‡To whom correspondence should be sent at the ^† address. E-mail: shigehiro.kuraku{at}uni-konstanz.de
Author contributions: S. Kuraku and Y.T. contributed equally to this work; S. Kuraku and S. Kuratani designed research; S. Kuraku and Y.T. performed research; K.T. and H.A. contributed new reagents/analytic tools; S. Kuraku and Y.T. analyzed data; and S. Kuraku, A.M., and S. Kuratani wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. AB293596–AB293599).
This article contains supporting information online at www.pnas.org/cgi/content/full/0710947105/DCSupplemental.