Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2009 Jul 29:9:178.
doi: 10.1186/1471-2148-9-178.

Differential expression of three galaxin-related genes during settlement and metamorphosis in the scleractinian coral Acropora millepora

Alejandro Reyes-Bermudez  1 , Zhiyi Lin, David C Hayward, David J Miller, Eldon E Ball
Affiliations

Differential expression of three galaxin-related genes during settlement and metamorphosis in the scleractinian coral Acropora millepora

Alejandro Reyes-Bermudez et al. BMC Evol Biol. .

Abstract

Background: The coral skeleton consists of CaCO3 deposited upon an organic matrix primarily as aragonite. Currently galaxin, from Galaxea fascicularis, is the only soluble protein component of the organic matrix that has been characterized from a coral. Three genes related to galaxin were identified in the coral Acropora millepora.

Results: One of the Acropora genes (Amgalaxin) encodes a clear galaxin ortholog, while the others (Amgalaxin-like 1 and Amgalaxin-like 2) encode larger and more divergent proteins. All three proteins are predicted to be extracellular and share common structural features, most notably the presence of repetitive motifs containing dicysteine residues. In situ hybridization reveals distinct, but partially overlapping, spatial expression of the genes in patterns consistent with distinct roles in calcification. Both of the Amgalaxin-like genes are expressed exclusively in the early stages of calcification, while Amgalaxin continues to be expressed in the adult, consistent with the situation in the coral Galaxea.

Conclusion: Comparisons with molluscs suggest functional convergence in the two groups; lustrin A/pearlin proteins may be the mollusc counterparts of galaxin, whereas the galaxin-like proteins combine characteristics of two distinct proteins involved in mollusc calcification. Database searches indicate that, although sequences with high similarity to the galaxins are restricted to the Scleractinia, more divergent members of this protein family are present in other cnidarians and some other metazoans. We suggest that ancestral galaxins may have been secondarily recruited to roles in calcification in the Triassic, when the Scleractinia first appeared. Understanding the evolution of the broader galaxin family will require wider sampling and expression analysis in a range of cnidarians and other animals.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Diagrammatic summary of the morphological changes involved in Acropora settlement, metamorphosis and the initiation of calcification. (A) Initially the planula swims horizontally, well away from the bottom. (B) After it has become competent to settle it explores the substratum with its aboral end. (C) If it encounters appropriate chemical cues it rounds up into a sphere, which then flattens against the substratum. As this is happening the cells against the substratum change their morphology and begin to secrete a disc of organic material. (D) Perpendicular walls, the protosepta, are then secreted on the plate in multiples of six. (E) The protosepta become more elaborate and more are added. (F) The walls become joined laterally and grow upward, forming a crown shaped structure upon which the polyp sits. In all stages the skeleton is external to, but enveloped by, the living tissue which secretes it. By the stages shown in (E) and (F) a polyp has formed, initially with tentacle buds and then with tentacles. However, these have been omitted from the drawing in order to focus on the skeleton. The drawings are based on drawings in Goreau and Hayes [34].
Figure 2
Figure 2
Inferred protein sequences of Amgalaxin and the Amgalaxin-like molecules. Amgalaxin differs from the galaxin-like molecules in that it lacks an acidic domain. The signal peptide is marked in green, the acidic domain in yellow, and the di-Cys repeats in red. Potential N-linked glycosylation sites in Amgalaxin and Amgalaxin-like-1 are shown in blue.
Figure 3
Figure 3
Alignments of the Cys rich repeats of the three proteins. Numbers on the left indicate the position in the predicted protein. A consensus sequence for the repeats from each protein is shown beneath the alignments. Residues are included in the consensus if they are represented in at least 50% of the repeats.
Figure 4
Figure 4
Virtual northern blots of the three genes arranged in the order in which they are expressed. The various stages represented on each blot are labelled across the bottom of the blot. Amgalaxin-like 1 expression first appears weakly even before gastrulation and is strong both before and after settlement, but is not apparent in the adult. Amgalaxin-like 2 is expressed exclusively immediately after settlement. Amgalaxin apparently has two isoforms both of which are expressed weakly immediately after settlement and more strongly in the adult. Abbreviations: PC = prawn chip, D = donut, Pre = presettlement planula larva, Post = polyp immediately after settlement.
Figure 5
Figure 5
Developmental expression of Amgalaxin-like 1. (A-C) Expression begins in a zone of strong expression at the aboral end of the planula. At the margins of this zone the expressing cells are no longer contiguous (arrows). (D-F) After settlement the zone of expression on the aboral side of the polyp expands as the polyp ages. (G-H) The zone of expression then begins to fragment segmentally, eventually leaving a few traces of expression centrally as well as a submarginal ring of expression (I). Planulae are shown in lateral view with the aboral end to the right. (D-I) are aboral views.
Figure 6
Figure 6
Developmental expression of Amgalaxin-like 2. There is no expression in the planula larva (A-B). Expression first appears as a ring on the aboral side of the planula as it shortens to form a sphere (C-D). Expression continues aborally, sometimes in a zone (E) and sometimes in a submarginal ring (F-J) as the polyp ages. In (F)(H) and (J) the polyp is viewed orally and the aboral expression is seen through the cleared tissue.
Figure 7
Figure 7
Developmental expression of Amgalaxin. Expression begins as an aboral submarginal ring (A-B) Septal expression is then added (arrows) as the polyp grows older (C-F). There is also sometimes aboral granular expression between the septa (E). Septal expression continues in the oldest polyp studied (F). (A), (C) and (E) are viewed aborally, (B), (D) and (F) are viewed orally.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Muscatine L, Goiran C, Land L, Jaubert J, Cuif JP, Allemand D. Stable isotopes (delta13C and delta15N) of organic matrix from coral skeleton. Proc Natl Acad Sci USA. 2005;102:1525–1530. doi: 10.1073/pnas.0408921102. - DOI - PMC - PubMed
    1. Moya A, Tambutte S, Tambutte E, Zoccola D, Caminiti N, Allemand D. Study of calcification during a daily cycle of the coral Stylophora pistillata: implications for 'light-enhanced calcification'. J Exp Biol. 2006;209:3413–3419. doi: 10.1242/jeb.02382. - DOI - PubMed
    1. Cuif JP, Dauphin Y. The two-step mode of growth in the scleractinian coral skeletons from the micrometre to the overall scale. J Struct Biol. 2005;150:319–331. doi: 10.1016/j.jsb.2005.03.004. - DOI - PubMed
    1. Puverel S, Tambutte E, Zoccola D, Domart-Coulon I, Bouchot A, Lotto S, Allemand D, Tambutte S. Antibodies against the organic matrix in scleractinians: a new tool to study coral biomineralization. Coral Reefs. 2005;24:149–156. doi: 10.1007/s00338-004-0456-0. - DOI
    1. Helman Y, Natale F, Sherrell RM, Lavigne M, Starovoytov V, Gorbunov MY, Falkowski PG. Extracellular matrix production and calcium carbonate precipitation by coral cells in vitro. Proc Natl Acad Sci USA. 2008;105:54–58. doi: 10.1073/pnas.0710604105. - DOI - PMC - PubMed

Publication types

LinkOut - more resources