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Metazoan Evolution (metazoan + evolution)

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Life Sciences	100%

Selected Abstracts

Basolateral junctions are sufficient to suppress epithelial invasion during Drosophila oogenesis

DEVELOPMENTAL DYNAMICS, Issue 2 2007
Przemyslaw Szafranski
Abstract Epithelial junctions play crucial roles during metazoan evolution and development by facilitating tissue formation, maintenance, and function. Little is known about the role of distinct types of junctions in controlling epithelial transformations leading to invasion of neighboring tissues. Discovering the key junction complexes that control these processes and how they function may also provide mechanistic insight into carcinoma cell invasion. Here, using the Drosophila ovary as a model, we show that four proteins of the basolateral junction (BLJ), Fasciclin-2, Neuroglian, Discs-large, and Lethal-giant-larvae, but not proteins of other epithelial junctions, directly suppress epithelial tumorigenesis and invasion. Remarkably, the expression pattern of Fasciclin-2 predicts which cells will invade. We compared the apicobasal polarity of BLJ tumor cells to border cells (BCs), an epithelium-derived cluster that normally migrates during mid-oogenesis. Both tumor cells and BCs differentiate a lateralized membrane pattern that is necessary but not sufficient for invasion. Independent of lateralization, derepression of motility pathways is also necessary, as indicated by a strong linear correlation between faster BC migration and an increased incidence of tumor invasion. However, without membrane lateralization, derepression of motility pathways is also not sufficient for invasion. Our results demonstrate that spatiotemporal patterns of basolateral junction activity directly suppress epithelial invasion by organizing the cooperative activity of distinct polarity and motility pathways. Developmental Dynamics 236:364,373, 2007. © 2006 Wiley-Liss, Inc. [source]

Choanoflagellates, choanocytes, and animal multicellularity

INVERTEBRATE BIOLOGY, Issue 1 2004
Manuel Maldonado
Abstract. It is widely accepted that multicellular animals (metazoans) constitute a monophyletic unit, deriving from ancestral choanoflagellate-like protists that gave rise to simple choanocyte-bearing metazoans. However, a re-assessment of molecular and histological evidence on choanoflagellates, sponge choanocytes, and other metazoan cells reveals that the status of choanocytes as a fundamental cell type in metazoan evolution is unrealistic. Rather, choanocytes are specialized cells that develop from non-collared ciliated cells during sponge embryogenesis. Although choanocytes of adult sponges have no obvious homologue among metazoans, larval cells transdifferentiating into choanocytes at metamorphosis do have such homologues. The evidence reviewed here also indicates that sponge larvae are architecturally closer than adult sponges to the remaining metazoans. This may mean that the basic multicellular organismal architecture from which diploblasts evolved, that is, the putative planktonic archimetazoan, was more similar to a modern poriferan larva lacking choanocytes than to an adult sponge. Alternatively, it may mean that other metazoans evolved from a neotenous larva of ancient sponges. Indeed, the Porifera possess some features of intriguing evolutionary significance: (1) widespread occurrence of internal fertilization and a notable diversity of gastrulation modes, (2) dispersal through architecturally complex lecithotrophic larvae, in which an ephemeral archenteron (in dispherula larvae) and multiciliated and syncytial cells (in trichimella larvae) occur, (3) acquisition of direct development by some groups, and (4) replacement of choanocyte-based filter-feeding by carnivory in some sponges. Together, these features strongly suggest that the Porifera may have a longer and more complicated evolutionary history than traditionally assumed, and also that the simple anatomy of modern adult sponges may have resulted from a secondary simplification. This makes the idea of a neotenous evolution less likely than that of a larva-like choanocyte-lacking archimetazoan. From this perspective, the view that choanoflagellates may be simplified sponge-derived metazoans, rather than protists, emerges as a viable alternative hypothesis. This idea neither conflicts with the available evidence nor can be disproved by it, and must be specifically re-examined by further approaches combining morphological and molecular information. Interestingly, several microbial lin°Cages lacking choanocyte-like morphology, such as Corallochytrea, Cristidiscoidea, Ministeriida, and Mesomycetozoea, have recently been placed at the boundary between fungi and animals, becoming a promising source of information in addition to the choanoflagellates in the search for the unicellular origin of animal multicellularity. [source]

The phylogeography of the Placozoa suggests a taxon-rich phylum in tropical and subtropical waters

MOLECULAR ECOLOGY, Issue 11 2010
M. EITEL
Abstract Placozoa has been a key phylum for understanding early metazoan evolution. Yet this phylum is officially monotypic and with respect to its general biology and ecology has remained widely unknown. Worldwide sampling and sequencing of the mitochondrial large ribosomal subunit (16S) reveals a cosmopolitan distribution in tropical and subtropical waters of genetically different clades. We sampled a total of 39 tropical and subtropical locations worldwide and found 23 positive sites for placozoans. The number of genetically characterized sites was thereby increased from 15 to 37. The new sampling identified the first genotypes from two new oceanographic regions, the Eastern Atlantic and the Indian Ocean. We found seven out of 11 previously known haplotypes as well as five new haplotypes. One haplotype resembles a new genetic clade, increasing the number of clades from six to seven. Some of these clades seem to be cosmopolitan whereas others appear to be endemic. The phylogeography also shows that different clades occupy different ecological niches and identifies several euryoecious haplotypes with a cosmopolitic distribution as well as some stenoecious haplotypes with an endemic distribution. Haplotypes of different clades differ substantially in their phylogeographic distribution according to latitude. The genetic data also suggest deep phylogenetic branching patterns between clades. [source]

Origin and evolution of chromosomal sperm proteins

BIOESSAYS, Issue 10 2009
José M. Eirín-López
Abstract In the eukaryotic cell, DNA compaction is achieved through its interaction with histones, constituting a nucleoprotein complex called chromatin. During metazoan evolution, the different structural and functional constraints imposed on the somatic and germinal cell lines led to a unique process of specialization of the sperm nuclear basic proteins (SNBPs) associated with chromatin in male germ cells. SNBPs encompass a heterogeneous group of proteins which, since their discovery in the nineteenth century, have been studied extensively in different organisms. However, the origin and controversial mechanisms driving the evolution of this group of proteins has only recently started to be understood. Here, we analyze in detail the histone hypothesis for the vertical parallel evolution of SNBPs, involving a "vertical" transition from a histone to a protamine-like and finally protamine types (H,,,PL,,,P), the last one of which is present in the sperm of organisms at the uppermost tips of the phylogenetic tree. In particular, the common ancestry shared by the protamine-like (PL)- and protamine (P)-types with histone H1 is discussed within the context of the diverse structural and functional constraints acting upon these proteins during bilaterian evolution. [source]

My favorite animal, Trichoplax adhaerens

BIOESSAYS, Issue 12 2005
Bernd Schierwater
Trichoplax adhaerens is more simply organized than any other living metazoan. This tiny marine animal looks like a irregular "hairy plate" ("tricho plax") with a simple upper and lower epithelium and some loose cells in between. After its original description by F.E. Schulze 1883, it attracted particular attention as a potential candidate representing the basic and ancestral state of metazoan organization. The lack of any kind of symmetry, organs, nerve cells, muscle cells, basal lamina and extracellular matrix originally left little doubt about the basal position of T. adhaerens. Nevertheless, the interest of zoologists and evolutionary biologists suddenly vanished for more than half a century when Trichoplax was claimed to be an aberrant hydrozoan planula larva. Recently, Trichoplax has been rediscovered as a key species for unraveling early metazoan evolution. For example, research on regulatory genes and whole genome sequencing promise insights into the genetics underlying the origin and development of basal metazoan phyla. Trichoplax offers unique potential for understanding the minimal requirements of metazoan animal organization. BioEssays 27:1294,1302, 2005. © 2005 Wiley Periodicals, Inc. [source]