Main description:

Recently, new genes and their proteins that revealed striking new insights into the early evolution of multicellular animals have been identified and characterized from members of the lowest metazoan phylum, the porifera (sponges). The unexpected result was that the sequences obtained from sponge displayed high similarity to those found in higher metazoa; in consequence, it was concluded that during the transition from protozoa to metazoa the major structural and regulatory proteins evolved only once. The data gathered are now powerful arguments to establish monophyly of metazoa; in addition, new insights on the evolutionary diversification of metazoa were obtained.

Contents:

The Question of Metazoan Monophyly and the Fossil Record.- 1 Introduction.- 2 The Rise of Metazoans.- 2.1 Are Metazoans Monophyletic?.- 2.1.1 Primitive Metazoans.- 3 Fossil Evidence for the Early Evolution of Metazoans.- 4 The Search for Pre-Ediacaran Metazoans.- 5 Where Do We Go from Here?.- 5.1 What is the Sister Group (or Sister Groups) of the Metazoans, and Will the Fossil Record Yield any Insights?.- 5.2 What Are the Inter-Relationships of the "Primitive" Metazoans, Notably the Sponges, Cnidarians, and Perhaps the Ctenophores?.- 5.3 Metazoan Evolution and Convergence: What Are the Constraints?.- References.- The Evolution of the Lower Metazoa: Evidence from the Phenotype.- 1 Introductionn.- 2 Origin of Multicellular Organization.- 3 Organization, Life Cycle and Lifestyle of the Ancestral Metazoa.- 4 The Origin of the Diploblastic Eumetazoa.- 4.1 Structural Innovations of the Eumetazoa.- 4.2 Models for the Most Primitive Organism with Diploblastic Organization.- Conclusions.- References.- Origin and Phylogeny of Metazoans as Reconstructed with rDNA Sequences.- 1 Introduction.- 2 Data and Methods.- 3 Theoretical Considerations: Sources of Errors in Phylogeny Inferrence.- 3.1 Species Errors.- 3.2 Character Errors.- 3.3 Algorithm Errors.- 3.4 Other Sources of Error.- 4 The rDNA Molecules.- 5 The Utility of rDNA Sequences Depends on Their Information Content.- 6 Monophyly of Metazoans.- 7 Relationships of Larger Groups of Metazoans.- 8 Determination of the Phylogenetical Signal Conserved in 18S-rDNA Sequences.- 9 Discussion.- References.- Sponges (Porifera) Molecular Model Systems to Study Cellular Differentiation in Metazoa.- 1 Introduction: Constituent Characters of Metazoa.- 2 Porifera and the Origin of Metazoan Evolution.- 3 Reproduction in Porifera.- 3.1 Sexual Reproduction: Gametes.- 3.2 Asexual Propagation.- 3.2.1 Gemmules.- 3.2.2 Buds.- 3.2.3 "Primordial Buds".- 4 Telomerase.- 4.1 Telomerase Assay.- 4.2 Telomerase Activity in Tissue from S. domuncula.- 4.3 Telomerase Activity in Tissue from G. cydonium.- 4.4 Telomerase Activity in Cells from G. cydonium.- 4.5 Comparison of Telomerase Activity Between Sponges and Mammalian Tumor Cells.- 5 Control of Cell Homeostasis in Sponges: Apoptosis.- 5.1 Induction of Apoptosis in Sponges.- 5.1.1 Cadmium-Induced Apoptosis.- 5.1.2 Induction of Apoptosis by Feeding the Animals with E. coli.- 5.2 Gemmule Formation.- 5.3 Induction of Expression of SDMA3 Gene.- 5.4 Telomerase Activity in Tissue from S. domuncula in Response to the Apoptotic Stimuli.- 6 Conclusion.- 6.1 Marker: Telomerase.- 6.2 Marker: Apoptosis.- 6.3 Shift from Immortal to Senescent Cells: Telomerase Activity as a Marker.- References.- The Notion of the Cambrian Pananimalia Genome and a Genomic Difference that Separated Vertebrates from Invertebrates.- 1 Introduction.- 2 Cyanobacteria in the Archean Ocean.- 3 Archaezoa as the First Animal in the Early Anaerobic Environment?.- 4 The Acquisition of Mitochondria Derived from an Endosymbiotic Paracoccus-Like Purple, Nonsulfur Bacterium as a Conditio Sine Qua Non to the Cambrian Explosion.- 5 Ediacaran Emergence of Porifera and Cnidaria as a Prelude to the Cambrian Explosion.- 6 Animals of the Cambrian Explosion and the Simultaneous Emergence of Three Subphyla of the Phylum Chordata.- 7 Genes in the Cambrian Pananimalia Genome.- 7.1 Pax 6 Genes and Eye Formation.- 7.2 The Universal Control of Anterior-To-Posterior Body Segment Differentiation by a Closely Linked Set of Hox Genes.- 7.3 The Antiquity of Ftz-F1, COUP and Other Genes Encoding Nuclear Receptor Proteins.- 8 Two Successive Rounds of Tetraploidization Events at the Beginning of Vertebrate Evolution and the Invariable Presence of Tetralogous Genes in the Vertebrate Genome.- 8.1 Four Sets of Hox Genes on Tetralogous Regions of Human Chromosomes 7pl2, 17q11.2-12, 12q13 and 2q34.- 8.2 Inevitable Degeneration of Tetralogous Genes to Trilogues, Dilogues and Even to Monologues.- 8.3 Tetralogues, Trilogues and Dilogues that Still Contribute to Functional Redundancy.- 8.4 The Emergence of New Genes from Some of the Tetralogues Trilogues and Dilogues.- 9 Conclusions.- References.- Evolution of Metazoan Collagens.- 1 Introduction: An Up-To-Date Definition of Collagen.- 1.1 The Collagen Molecule.- 1.2 The Collagen Family.- 2 Collagen Fibrils: From Sponges to Humans.- 2.1 The Homogeneous Subgroup of Fibrillar Collagen in Vertebrates.- 2.2 The Primitive Fibrillar Collagens.- 2.3 The Vertebrate-Type Fibrillar Collagens.- 3 Basement Membrane Collagen: The Marker of Tissue Differentiation.- 3.1 The Basement Membrane Collagens of Vertebrates.- 3.2 The Basement Membrane Collagens of Invertebrates.- 3.3 The Origin of Basement Membrane Collagens.- 4 The Species-Specific Collagens.- 4.1 The Mini-Collagens in Cnidarians.- 4.2 The "Externally-Secreted" Collagens.- 4.2.1 Annelid Cuticles.- 4.2.2 Nematode Cuticles.- 4.2.3 Invertebrate Exoskeletons.- 5 Conclusion: From a Sticky Membrane Protein to an Extracellular Matrix Component.- References.- Evolution of Early Metazoa: Phylogenetic Status of the Hexactinellida Within the Phylum of Porifera (Sponges).- 1 Introduction.- 2 Hexactinellida.- 3 Problem of Classification of Hexactinellida.- 4 A Rational Solution: The Deduced Amino Acid Sequence of Protein Kinase C.- 5 The Sponge cPKC Sequences.- 5.1 cDNAs.- 5.2 Cloning of the cDNA Encoding a "Conventional" PKC from R. dawsoni.- 5.3 Phylogenetic Position of R. dawsoni: Analysis of the Catalytic Domain.- 5.4 Phylogenetic Position of R. dawsoni: Analysis of the Regulatory Region.- 6 The Heat Shock Proteins: Hsp70s.- 6.1 The Sequences.- 6.2 Phylogenetic Analysis.- 7 Conclusion.- References.- Structure and Evolution of Genes Encoding Polyubiquitin in Marine Sponges.- 1 Introduction.- 2 Ubiquitin.- 2.1 Role in Protein Degradation.- 2.2 Occurrence in Nature.- 2.3 Conservation of the Primary Structure.- 3 Ubiquitin Genes.- 3.1 Class I and II: Ubiquitin Fusion Genes.- 3.2 Class III: Polyubiquitin Genes.- 3.3 Molecular Evolution of Ubiquitin Genes.- 4 Ubiquitin in Marine Sponges.- 4.1 Polyubiquitin Gene from Geodia cydonium.- 4.1.1 Expression of the Polyubiquitin Gene in Geodia cydonium.- 4.1.2 Phylogenetic Relationships of Ubiquitin Repeats in the Polyubiquitin Gene from Geodia cydonium.- 4.1.2.1 Enigma with Serine Codons.- 4.1.2.2 Homology Comparison of the Repeated Genes.- 4.1.2.3 Codon Usage in the G. cydonium Polyubiquitin Gene.- 4.1.2.4 Time Scale for Evolution of G. cydonium Polyubiquitin Gene.- 4.1.3 Is There One Additional Polyubiquitin Gene in Geodia cydonium?.- 4.2 Diubiquitin Gene from Suberites domuncula.- 4.3 Polyubiquitin Gene from Sycon raphanus.- 4.4 Phylogenetic Relationships of Sponge Ubiquitin Genes.- 5 Phylogenetic Tree of Metazoa Based on Polyubiquitin Genes.- 6 Concluding Remarks.- References.