Jcr

However, as Rieger et al. point out, a different relationship is suggested by the expression of an anterior Hox gene in the hydrozoan jellyfish Podocoryne: cnoxl-Pc is expressed in a region of the planula larva corresponding to the future aboral end of the adult polyp (2). The evolutionary significance of this finding is unclear because (i) the expression patterns of Hox and Hox-related genes vary among hydrozoans (1, 2), and (ii), in one instance, a Hox-related gene undergoes an axial reversal during the course of development in Podocoryne itself (3). This variability within and between hydrozoan cnidarians makes it difficult to reconstruct the spatial expression of Hox-related genes in the ancestral hydrozoan. It is therefore impossible to reliably extrapolate these hydrozoan data to the ancestral cnidarian or the cnidarian-bilaterian ancestor. In contrast, orthologous genes in Nematostella and the coral Acropora, two anthozoan cnidarians, tend to exhibit highly similar and presumably conserved patterns of spatial expression [our Report, (4)].

We argue that the mouth of most bilateri-ans is formed "in a region" close to the anterior end of the adult body plan. On the basis of paleontological evidence, an anterior terminal mouth is likely to be the ancestral condition for all ecdysozoans (5), and a compos ite circum-oral "brain" is a feature of virtually all invertebrate animals (6). With regard to the position of the mouth in acoels, the development of the primary muscle grid may or may not be associated with the position of the anterior pole. The only way to make such a statement about the embryological origin of any structure is to perform a detailed fate map, but such a fate map has been performed only for a single species of acoelomorph (7).

Finally, it is not clear if our data can distinguish whether triploblastic bilaterians arose from larval or adult diploblasts. Diploblasts (cnidarians and ctenophores) do not generate feeding larvae and the adult mouth arises only once, at the animal pole (also the site of first cleavage). In cnidarians, the mouth arises at the posterior pole of the swimming stage (planula). If Nematostella reflects the ancestral condition for the cnidarian-bilaterian ancestor, then most descendant organisms modified an axial system in which the mouth forms at the anterior pole.

MARK Q. MARTINDALE1 AND JOHN R. FINNERTY2 1Kewalo Marine Laboratory, Pacific Biomedical Research Center, University of Hawaii, 41 Ahui Street, Honolulu, HI 96813, USA. 2Department of Biology, Boston University, 5 Cummington Street, Boston, MA 02215, USA.

References

1. J. R. Finnerty, D. Paulson, P. Burton, K. Pang, M. Q. Martindale, Evol.Dev. 5,331 (2003).

2. N. Yanze, J. Spring, C. Schmidli, V. Schmid, Dev. Biol. 236,89 (2001).

3. L. M. Masuda-Nakagawa, H. Groger, B. L. Aerne, V. Schmid, Dev. GenesEvol. 210,151 (2000).

4. D. C. Hayward et al., Proc. Natl. Acad. Sci. U.S.A. 99, 8106 (2002).

5. G. E. Budd, S. Jensen, Biol. Rev. 75,253 (2000).

6. E. E. Ruppert, R. S. Fox, R. D. Barnes, Invertebrate Zoology. A Functional Evolutionary Approach (Brooks/Cole-Thompson Learning, Belmont, CA, ed. 7, 2004).

7. J. Q. Henry, M. Q. Martindale, B. C. Boyer, Dev. Biol. 220, 285 (2000).

CORRECTIONS AND CLARIFICATIONS:

Essays: "The scientific consensus on climate change" by N. Oreskes (3 Dec. 2004, p. 1686).The final sentence of the fifth paragraph should read "That hypothesis was tested by analyzing 928 abstracts, published in refereed scientific journals between 1993 and 2003, and listed in the ISI database with the keywords 'global climate change' (9)." The keywords used were "global climate change," not "climate change."

News of the Week: "Science agencies caught in postelection spending squeeze" (3 Dec. 2004, p.1662).The article contains an incorrect reference to Michael Marx's institutional affiliation. He is a professor of physics at Stony Brook University in New York.

Innovation has its Rewards

Discover New Solutions for Tomorrow...

The Alternatives Research & Development Foundation, a leader in the funding and promotion of alternatives to the use of laboratory animals in research, testing, and education, announces that it is currently soliciting research proposals to its Alternatives Research Grant Program. For 15 years, this innovative program has rewarded scientists who have an interest and expertise in alternative research investigation.

Up to $40,000 in funding available to support individual projects with preference given to U.S. universities and research institutions.

Downloadable application and instructions at www.ardf-online.org.

Deadline: April 30, 2005.

Announcement of recipients: July 15, 2005.

www.ardf-online.org [email protected]"/>
801 Old York Road, #316 Jenkintown, PA 19046 fax: (215)887-0771 www.ardf-online.org [email protected]

BooksE-

Supplements For Diabetics

Supplements For Diabetics

All you need is a proper diet of fresh fruits and vegetables and get plenty of exercise and you'll be fine. Ever heard those words from your doctor? If that's all heshe recommends then you're missing out an important ingredient for health that he's not telling you. Fact is that you can adhere to the strictest diet, watch everything you eat and get the exercise of amarathon runner and still come down with diabetic complications. Diet, exercise and standard drug treatments simply aren't enough to help keep your diabetes under control.

Get My Free Ebook


Post a comment