Nuclear-localized plastid DNA fragments in protozoa, metazoa and fungi

We analyzed nuclear-localized plastid-like DNA (nupDNA) fragments in protozoa, metazoa and fungi. Most eukaryotes that do not have plastids contain 40-5000 bp nupDNAs in their nuclear genomes. These nupDNA fragments are mainly derived from repeated regions of plastids and distribute through the whole genomes. A majority of nupDNA fragments is located on coding regions with very important functions. Similar to plastids, these nupDNAs most possibly originate from cyanobacteria. Analysis of them suggests that through millions of years of universal endosymbiosis and gene transfer they may have occurred in ancient protists before divergence of plants and animals/fungi, and some transferred fragments have been reserved till now even in modern mammals.     

Heterotrophic protozoa and small metazoa: feeding rates and prey-consumer interactions

A common approach to divide zooplankton into groups has beenby size or size fractionation (micro-, meso- and macrozooplankton).Whereas almost all zooplankton retained by 200 µm meshare metazoa, those not retained are proto- and metazoa. Evenso, the variability of major taxa among those retained by 200µm mesh can range widely between samples, that of passing200 pm can vary even more when considering the grazing impact.If heavily weighted towards protozoa, the <200 µm communityfeeding rate on small phytoplankton could be several times therate when most animals would be metazoa. Also, the interactionbetween proto- and metazooplankton passing 200 µm meshought to be considered, as should be that among protozoa. Usingpublished data from the North Atlantic Ocean, the potentialimpact of small metazooplankton on the chlorophyll standingstock and primary productivity as well as on protozooplanktonwas evaluated. It was found that metazoo plankton passing <200µm mesh removed a much larger part of the primary productivitythan those retained by 200 µm mesh. Although the biomassof the 200 µm mesh metazoa was close to that of protozoapassing the same mesh, their ration was only a relatively smallpart of the primary productivity ingested by the latter. Yet,due to their unusually high abundance in these oceanic waters,the overall metazooplankton appeared to come close to controllingprotozooplankton >50 µm³ in volume, i.e. those whichcould be actively perceived. It is hypothesized that in theabsence of control by meta zooplankton, protozoa control theirown abundance by predation/cannibalism.     

Use of protozoa and metazoa for decreasing sludge production in aerobic wastewater treatment

Summary A new approach to decreasing sludge production in aerobic biological wastewater treatment involving use of protozoa and metazoa was tested. The dissolved organics in the two synthetic wastewaters (based on acetic acid and methanol, respectively) tested were decomposed to >90% and the biomass production was decreased by 60–80%. The total sludge yield, expressed as total suspended solids per gram chemical oxygen demand removed, was 0.17 g TSS/g COD in the system fed acetic acid, whereas it was 0.05 g TSS/g COD in the system fed methanol. The explanation for this difference was that in the system fed methanol, dispersed bacteria were obtained that were easily grazed by the protozoa and metazoa in the predator stage. In the system fed acetic acid, the bacteria formed zoogloeal flocs, which protected them from grazing in the predator stage. With both carbon sources a significant release of nitrate (> 7 mg N/l) and of phosphate (> 2.5 mg P/l) was observed in the effluent.     

Spliced leader RNA trans-splicing in metazoa

Spliced leader trans-splicing is a form of RNA processing originally described and studied in parasitic kinetoplastida. This mechanism of gene expression also occurs in parasitic and free-living metazoa. In this review, Dick Davis describes current knowledge of the distribution, substrates, specificity and functional significance of trans-splicing in metazoa.     

Cycling through development in Drosophila and other metazoa

The cell-division cycle is an orchestrated sequence of events that results in the duplication of a cell. In metazoa, cell proliferation is regulated in response to differentiation signals and body-size parameters, which either induce cell duplication or arrest the cell cycle, to ensure that organs develop to the correct size. In addition, the cell cycle may be altered to meet specialized requirements. This can be seen in the rapid cleavage cycles of vertebrates and insects that lack gap phases, in the nested S phases of Drosophila, and in the endocycles of nematodes, insects, plants and mammals that lack mitosis. Here we present the various modes of cell-cycle regulation in metazoa and discuss their possible generation by a combination of universally conserved molecules and new regulatory circuits.     

Regulation of heme biosynthesis and transport in metazoa

Heme is an iron-containing tetrapyrrole that plays a critical role in regulating a variety of biological processes including oxygen and electron transport, gas sensing, signal transduction, biological clock, and micro RNA processing. Most metazoan cells synthesize heme via a conserved pathway comprised of eight enzyme-catalyzed reactions. Heme can also be acquired from food or extracellular environment. Cellular heme homeostasis is maintained through the coordinated regulation of synthesis, transport, and degradation. This review presents the current knowledge of the synthesis and transport of heme in metazoans and highlights recent advances in the regulation of these pathways.     

Preventing DNA re-replication--divergent safeguards in yeast and metazoa

Eukaryotes employ redundant mechanisms to limit the replication of genomic DNA to only once per cycle. These mechanisms prevent DNA re-replication by restricting the assembly of the pre-replication complex to the cell cycle stages of late mitosis and G1 phase so that the re-initiation of DNA replication cannot occur during S phase. Here we discuss the conserved yet divergent mechanisms of replication control employed in yeast and metazoan species, including a perspective on the newly uncovered role of the CUL-4 ubiquitin ligase as a central regulator of DNA replication in the nematode Caenorhabditis elegans.     

Comparative aspects of DNA organization in metazoa

Data on sequence organization in metazoa are reviewed and tabulated. It is shown that the features of sequence organization previously observed in Xenopus DNA are extremely widespread. At least 70% of DNA fragments 2,000-3,000 nucleotides long contain both single copy and repetitive sequence in all the organisms examined except Drosophila.     

A review of FMRFamide- and RFamide-like peptides in metazoa

Neuropeptides are a diverse class of signalling molecules that are widely employed as neurotransmitters and neuromodulators in animals, both invertebrate and vertebrate. However, despite their fundamental importance to animal physiology and behaviour, they are much less well understood than the small molecule neurotransmitters. The neuropeptides are classified into families according to similarities in their peptide sequence; and on this basis, the FMRFamide and RFamide-like peptides, first discovered in molluscs, are an example of a family that is conserved throughout the animal phyla. In this review, the literature on these neuropeptides has been consolidated with a particular emphasis on allowing a comparison between data sets in phyla as diverse as coelenterates and mammals. The intention is that this focus on the structure and functional aspects of FMRFamide and RFamide-like neuropeptides will inform understanding of conserved principles and distinct properties of signalling across the animal phyla.     

Molecular evidence of regression in evolution of metazoa

Molecular data permit to construct phylogenetic trees independently of morphological characters. It allows to consider their evolution without the frames of a priori hypothesis of regularities of morphological evolution and independently of palaeontological data. Cladistic analysis of elements of secondary structure of varible areas V7 and V2 in 18S rRNA with different Protozoa as "external" groups shows that Bilateria + Cnidaria are monophyletic, Ctenophora and Porifera are early derivatives of Metazoa, Trichoplax (Placozoa) is a form related to Cnidaria, while Rhombozoa, Orthonectida and Myxozoa were branched within Bilateria. Morphological reduction with losses of any organs and tissues took place many times in early evolution of Metazoa and Bilateria not only in parasitic species. It occurred both at early and late stages of embryonic development and differentiation. Two alternative scenario of morphological degeneration in Trichoplax and the way of their testing are suggested. The similarity of Ctenophora and Calcarea is discussed. Meridional or oblique position of the third cleavage furrow of ovule can be considered as an evidence of their origin from common ancestor.     

Evolution of sensory structures in basal metazoa

Cnidaria have traditionally been viewed as the most basal animalswith complex, organ-like multicellular structures dedicatedto sensory perception. However, sponges also have a surprisingrange of the genes required for sensory and neural functionsin Bilateria. Here, we: (1) discuss "sense organ" regulatorygenes, including; sine oculis, Brain 3, and eyes absent, thatare expressed in cnidarian sense organs; (2) assess the sensoryfeatures of the planula, polyp, and medusa life-history stagesof Cnidaria; and (3) discuss physiological and molecular datathat suggest sensory and "neural" processes in sponges. We thendevelop arguments explaining the shared aspects of developmentalregulation across sense organs and between sense organs andother structures. We focus on explanations involving divergentevolution from a common ancestral condition. In Bilateria, distinctsense-organ types share components of developmental-gene regulation.These regulators are also present in basal metazoans, suggestingevolution of multiple bilaterian organs from fewer antecedentsensory structures in a metazoan ancestor. More broadly, wehypothesize that developmental genetic similarities betweensense organs and appendages may reflect descent from closelyassociated structures, or a composite organ, in the common ancestorof Cnidaria and Bilateria, and we argue that such similaritiesbetween bilaterian sense organs and kidneys may derive froma multifunctional aggregations of choanocyte-like cells in ametazoan ancestor. We hope these speculative arguments presentedhere will stimulate further discussion of these and relatedquestions.     

Bridging morphological transitions to the metazoa

Our inability to answer many questions regarding the developmentof metazoan complexity may be due in part to the prevailingidea that most eukaryote "phyla" originated within a short periodof geologic time from simple unicellular ancestors. This view,however, is contradicted by evidence that larger groups of eukaryotesshare characters, suggesting that these assemblages inheritedcharacters from a common ancestor. Because molecular analyseshave had limited success in resolving the relationships of highereukaryote taxa, we have undertaken a phylogenetic analysis basedprimarily on morphological characters. The analysis emphasizescharacters considered to have a high probability of having evolvedonly once. Transitions between taxa are evaluated for the likelihoodof character-state transformations. The analysis indicates thatthe evolutionary history of the clade containing the Metazoahas been complex, encompassing the gain and loss of a secondaryand perhaps a primary photosynthetic endosymbiont with accompanyingchanges in trophic level. The history also appears to have includeda hetero-autotrophic ancestor that possessed a "conoid" feedingapparatus and may have involved a transformation from a flagellateto an amoeboid body form, a trend toward increased intracellularcompartmentation, and the development of complex social behavior.Such changes could have been critical for establishing the underlyingcomplexity required for a rapid diversification of cell andtissue types in the early stages of metazoan evolution.     

Heat-shock response in Archaea

The Archaea are one of the three phylogenetic domains into which all organisms have been classified, and include extreme halophiles, extreme thermophiles and methanogens. Some of these organisms inhabit inhospitable environments on Earth, and thus have evolved stress responses to cope with the extremes of heat, pH and salinity that they encounter. Although the archaeal stress or heat-shock response bears some similarity to the heat-shock responses of other organisms, it possesses some unique features. A better understanding of this response would facilitate its exploitation in the biotechnological industries; for example, in engineering cells that exhibit an improved ability to withstand, or recover from, stress.