Evolution of Antp-class genes and differential expression of Hydra Hox/paraHox genes in anterior patterning

Evolution of Antp-class genes and differential expression of Hydra Hox/paraHox genes in anterior patterning

^*Department of Zoology and Animal Biology, University of Geneva, 30 Quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland; ^†Station de Zoologie, 154 Route de Malagnou, CH-1224 Chêne-Bougeries, Switzerland; and ^‡Zentrum für Molecular Biologie, University of Heidelberg, INF 282, D-69120 Heidelberg, Germany

Edited by Walter J. Gehring, University of Basel, Basel, Switzerland, and approved February 22, 2000 (received for review January 5, 2000)

Abstract

The conservation of developmental functions exerted by Antp-class homeoproteins in protostomes and deuterostomes suggested that homologs with related functions are present in diploblastic animals. Our phylogenetic analyses showed that Antp-class homeodomains belong either to non-Hox or to Hox/paraHox families. Among the 13 non-Hox families, 9 have diploblastic homologs, Msx, Emx, Barx, Evx, Tlx, NK-2, and Prh/Hex, Not, and Dlx, reported here. Among the Hox/paraHox, poriferan sequences were not found, and the cnidarian sequences formed at least five distinct cnox families. Two are significantly related to the paraHox Gsx (cnox-2) and the mox (cnox-5) sequences, whereas three display some relatedness to the Hox paralog groups 1 (cnox-1), 9/10 (cnox-3) and the paraHox cdx (cnox-4). Intermediate Hox/paraHox genes (PG 3 to 8 and lox) did not have clear cnidarian counterparts. In Hydra, cnox-1, cnox-2, and cnox-3 were not found chromosomally linked within a 150-kb range and displayed specific expression patterns in the adult head. During regeneration, cnox-1 was expressed as an early gene whatever the polarity, whereas cnox-2 was up-regulated later during head but not foot regeneration. Finally, cnox-3 expression was reestablished in the adult head once it was fully formed. These results suggest that the Hydra genes related to anterior Hox/paraHox genes are involved at different stages of apical differentiation. However, the positional information defining the oral/aboral axis in Hydra cannot be correlated strictly to that characterizing the anterior–posterior axis in vertebrates or arthropods.

Footnotes

↵ § Present address: Box 357730, Department of Molecular Biotechnology, University of Washington, Seattle, WA 98195.
↵ ¶ To whom reprint requests should be addressed. E-mail: brigitte.galliot{at}zoo.unige.ch.
This paper was submitted directly (Track II) to the PNAS office.
The sequences reported in this paper have been deposited in the GenBank database (accession nos. cnox-1 Hv, AJ252181; cnox-2 Hv, AJ277388; cnox-3 Hv, AJ252182; dlx Hv, AJ252183; cnot Hv, AJ252184; cnHex Hv, AJ252185; msh Hv, AJ271008).
Abbreviations:

Cv, Chlorohydra viridissima,

Hv, Hydra vulgaris;

HD,

homeodomain;

ML,

maximum likelihood;

NJ,

neighbor joining;

PFGE,

pulse field gel electrophoresis