Elongation capacity of polyunsaturated fatty acids in the annelid Platynereis dumerilii
Marc Ramos-LlorensKhalida BainourLeonie AdelmannFrancisco HontoriaJuan Carlos NavarroFlorian RaibleÓscar Monroig
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Abstract:
Elongation of very long-chain fatty acid (Elovl) proteins plays pivotal functions in the biosynthesis of the physiologically essential long-chain polyunsaturated fatty acids (LC-PUFA). Polychaetes have important roles in marine ecosystems, contributing not only to nutrient recycling but also exhibiting a distinctive capacity for biosynthesizing LC-PUFA. To expand our understanding of the LC-PUFA biosynthesis in polychaetes, this study conducted a thorough molecular and functional characterization of Elovl occurring in the model organism Platynereis dumerilii . We identify six Elovl in the genome of P. dumerilii . The sequence and phylogenetic analyses established that four Elovl, identified as Elovl2/5, Elovl4 (two genes) and Elovl1/7, have putative functions in LC-PUFA biosynthesis. Functional characterization confirmed the roles of these elongases in LC-PUFA biosynthesis, demonstrating that P. dumerilii possesses a varied and functionally diverse complement of Elovl that, along with the enzymatic specificities of previously characterized desaturases, enables P. dumerilii to perform all the reactions required for the biosynthesis of the LC-PUFA. Importantly, we uncovered that one of the two Elovl4-encoding genes is remarkably long in comparison with any other animals' Elovl, which contains a C terminal KH domain unique among Elovl. The distinctive expression pattern of this protein in photoreceptors strongly suggests a central role in vision.Keywords:
Annelid
Examining polychaetous annelids collected from Chinhae Bay in the southeastern part of Korea, I found three species which should be added in the list as new to the polychaetous annelid fauna of Korea. In the present study three species are reported with morphological descriptions. Consquently, it totals 133 species of polychaetous annelids from Korea including those previously reported.
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Chemical detection is key to various behaviours in both marine and terrestrial animals. Marine species, though highly diverse, have been underrepresented so far in studies on chemosensory systems, and our knowledge mostly concerns the detection of airborne cues. A broader comparative approach is therefore desirable. Marine annelid worms with their rich behavioural repertoire represent attractive models for chemosensory studies. Here, we study the marine worm Platynereis dumerilii to provide the first comprehensive study of head chemosensory organ physiology in an annelid. By combining microfluidics and calcium imaging, we record neuronal activity in the entire head of early juveniles upon chemical stimulation. We find that Platynereis uses four types of organs to detect stimuli such as alcohols, esters, amino acids and sugars. Antennae, but not nuchal organs or palps as generally hypothesised in annelids, are the main chemosensory organs. We report chemically-evoked activity in possible downstream brain regions including the mushroom bodies, which are anatomically and molecularly similar to insect mushroom bodies. We conclude that chemosensation is a major sensory modality for marine annelids, and propose early Platynereis juveniles as a model to study annelid chemosensory systems.
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Commensalism
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This chapter contains sections titled: Introduction Genes Molecular Annelid Phylogeny Choosing Model Organisms Branch Lengths Problems in Inferring Annelid Phylogeny Conclusions
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Molecular Phylogenetics
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Abstract Annelids, like many other invertebrate animals, replace lost body parts in a process called regeneration. However, the ability to regenerate lost segments is present in some groups and not others; for example, leeches do not regenerate lost segments. Anterior and posterior regeneration involves the formation of a bud containing stem cells that differentiate into the new head or tail segments. Annelid regeneration also involves remodelling of surviving body fragments. The ability of annelids to regenerate tail segments appears to be nearly universal among species capable of regeneration. The ability to regenerate head segments, although common, is not universal and can depend on the number of segments lost. The absence and presence of regeneration across annelid groups, including closely related species, suggests that regeneration ability may be an ancient trait that has been lost in some species during annelid evolution. Key Concepts Annelids vary in their capability for regenerating body segments, including among closely related species. The ability of annelids to regenerate posterior segments appears to be nearly universal. The ability of annelids to regenerate anterior segments, although common, is not universal and is often limited depending on the number of segments lost. Annelid regeneration may involve both epimorphic and morphallactic mechanisms. Multiple losses and gains of regeneration ability have likely occurred during annelid evolution. Why regenerative ability among annelids varies extensively remains unclear. With development of new techniques for genetic analysis and microscopy, annelids are becoming important model systems for the study of regeneration.
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Coelom
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Abstract: Polyunsaturated fatty acids are needed for normal neonatal brain development, but the degree of conversion of the 18‐carbon polyunsaturated fatty acid precursors consumed in the diet to their respective 20‐and 22‐carbon polyunsaturates accumulating in the brain is not well known. In the present study, in vivo 13 C nuclear magnetic resonance spectroscopy was used to monitor noninvasively the brain uptake and metabolism of a mixture of uniformly 13 C‐enriched 16‐and 18‐carbon polyunsaturated fatty acid methyl esters injected intragastrically into neonatal rats. In vivo NMR spectra of the rat brain at postnatal days 10 and 17 had larger fatty acid signals than in uninjected controls, but changes in levels of individual fatty acids could not be distinguished. One day after injection of the U‐ 13 C‐polyunsaturated fatty acid mixture, 13 C enrichment (measured by isotope ratio mass spectrometry) was similar in brain phospholipids, free fatty acids, free cholesterol, and brain aqueous extract; 13 C enrichment remained high in the phospholipids and cholesterol for 15 days. 13 C enrichment was similar in the main fatty acids of the brain within 1 day of injection but 15 days later had declined in all except arachidonic acid while continuing to increase in docosahexaenoic acid. These changes in 13 C enrichment in brain fatty acids paralleled the developmental changes in brain fatty acid composition. We conclude that, in the neonatal rat brain, dietary 16‐and 18‐carbon polyunsaturates are not only elongated and desaturated but are also utilized for de novo synthesis of long‐chain saturated and monounsaturated fatty acids and cholesterol.
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Annelida is a very diverse group of segmented worms with over 16,500 described
species. They play an important role in both terrestrial and aquatic environments. Despite
this, their phylogenetic and evolutionary relationships of many groups within annelids are
still poorly understood. This study focused on Terebelliformia annelids, a group of tubedwelling
worms used for investigation, comprises five recognized families with
ambiguous phylogeny and a myzostomid worm, whose annelid affinity has been debated
in recent years. In view of the conserved composition across bilaterians and the
hypothesis of conserved gene order pattern across annelids, the mitochondrial genomic
data have been becoming increasingly useful for applications to resolve this issue. The main aim of this research is to characterize the mtDNA genomes in above annelids
and resolve certain relationships within annelids with mitochondrial genome to evaluate
their applicability to annelid phylogeny. Additionally, two group II introns that
unexpectedly discovered in the myzostomid mtDNA drew our attentions to explore the
evolution of such introns as they are rarely found in bilaterian genomes.
This study showed that the mitochondrial gene arrangement pattern is
evolutionarily conserved as previously hypothesized, especially for protein-coding genes.
Phylogenetic analyses based on the mitochondrial genome data indicated a well-resolved
phylogeny within Terebelliformia group: Pectinariidae was placed as a basal clade to all
other Terebelliformia families; Ampharetidae and Alvinellidae were sister to each other;
Trichobranchidae and Terebellidae were sister clade with strong support. This suggests
the great potential applicability of mitochondrial genomes which could likely be applied
to the phylogenetic reconstruction of other annelid clades.
Two group II introns (divergent Mintron1 and degenerated Mintron2) which are
characterized here in a partial mitochondrial genome of Endomyzostoma sp.
(Myzostomida), is the first report of multiple introns in bilaterian genomes. The study
implicated that both introns belong to the mitochondrial class and they could have
independent origins given the dissimilarity between their RNA structures. It offers an
important basis for the future studies in regard to the evolution and function of bilaterian
group II introns.
Overall, the study implies an increasingly potential applicability to explore the
mitochondrial genomes of annelids in terms of the phylogenetic and evolutionary
examinations.
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Sister group
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Distributional patterns of Ulnung-do's Polychaetous annelid worms comprising 64 species out of 53 genera were divided into four zoogeographical groups with reference to the distribution of the world's polychaetous annelid worms; cosmopolitan, northern, temperate and tropical types. It was found out that there were 25 species of cosmopolitan type taking up , 20 species of northern type, , and 19 species of temperate type, , but tropical type was not found. When compared with the polychaetous annelid worms of the neighboring coastal areas of the Yellow Sea, the east coast of U.S.S.R., Korea and Japan, those of Ulnung-do island were shown to have highest similarity to those of Yellow Sea follwed by the areas in the order named.
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Integumentary system
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Two peptides, H-Ala-Lys-Ser-Gly-Phe-Val-Arg-Ile-NH2 (AKSGFVRIamide), and H-Val-Ser-Ser-Phe-Val-Arg-Ile-NH2 (VSSFVRIamide) were isolated from a polychaete annelid, Perinereis vancaurica. Both the peptides evoked rhythmic contractions in the esophagus of Perinereis with a threshold as low as 10-10-10-9 M, suggesting that the peptides may be involved in the regulation of gut motility of the animal. The sequences of these peptides are very similar to those of other S-Iamide family peptides which have been previously isolated from an echiuroid worm and some molluses. In particular, the sequence of VSSFVRIamide is identical to that of an echiuroid S-Iamide peptide. All of the molluscan and echiuroid S-Iamide peptides, as well as the annelid peptides, were found to produce contractions in the esophagus of Perinereis. On the other hand, the annelid S-Iamide peptides, as well as the molluscan and echiuroid peptides, were found to inhibit or potentiate contractions elicited by electrical stimulation in echiuroid and molluscan muscles. S-Iamide peptides may be a typical neuropeptide family distributed interphyletically in the Protostomia.
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