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On the monophyletic evolution of the metazoa
W E Müller1, I M Müller, V Gamulin
1Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität, Mainz, Germany.
Summary
Adhesion proteins, crucial for multicellular life, were found in sponges, the earliest animals. These ancient proteins, including lectins and receptor tyrosine kinases, share features with those in higher vertebrates, suggesting early origins for complex animal structures.
Area of Science:
- Evolutionary Biology
- Molecular Biology
- Zoology
Background:
- Multicellular organisms rely on adhesion proteins for integration.
- Marine sponges (Geodia cydonium) represent early multicellular animals.
Purpose of the Study:
- To investigate the presence and characteristics of adhesion protein genes in sponges.
- To understand the evolutionary origins of adhesion molecules and developmental genes.
Main Methods:
- Cloning and characterization of cDNAs for sponge lectins (LECT-1, LECT-2) and a receptor tyrosine kinase (GCTK).
- Sequence analysis to identify conserved domains and homologies with vertebrate and other animal proteins.
- Investigation of homeodomain-containing genes in G. cydonium.
Main Results:
- Sponge lectins (LECT-1, LECT-2) possess conserved amino acid sequences characteristic of vertebrate S-type lectin binding sites.
- A sponge receptor tyrosine kinase (GCTK) contains tyrosine kinase and immunoglobulin-like domains homologous to vertebrate counterparts.
- A homeodomain sequence in G. cydonium shows high homology to chicken and Drosophila melanogaster sequences.
- These findings indicate that key domains of adhesion proteins and developmental genes existed in animals diverging ~800 million years ago.
Conclusions:
- Adhesion protein domains are not recent evolutionary developments but are ancient, present in early diverging animals like sponges.
- The presence of homologous genes for lectins, receptor tyrosine kinases, and homeodomains supports the monophyletic origin of the kingdom Animalia.