SMA-10 Is a Non-Canonical Member of the TGF-ß Sma/Mab Pathway and Immunity Regulator via the DAF-2 Insulin Receptor in Caenorhabditis elegans.

Transforming growth factor ß (TGF-ß) signalling pathways are highly conserved across metazoa and play essential roles not only during development but also in adult tissue maintenance. Alterations of these pathways usually result in a plethora of pathologies. In the nematode Caenorhabditis elegans, the TGF-ß Sma/Mab (small/male abnormal) pathway regulates various worm phenotypes such as body size, immune response, ageing, matricide and reproductive span. SMA-10 has been described as a positive modulator of worm body size through the TGF-ß Sma/Mab pathway. To better understand if SMA-10 is a core component of the pathway, we use gene epistatic analysis to assess the contribution of SMA-10 to various phenotypes regulated by TGF-ß Sma/Mab. We confirm that SMA-10 controls body size and find that it also affects the matricide and reproductive span of the nematodes. However, neither male tail formation (previously reported) nor ageing appeared altered. Lastly, although null sma-10 worms are more susceptible to Pseudomonas aeruginosa infections than wild-types, this response does not depend on TGF-ß Sma/Mab but on the insulin receptor DAF-2. We also show that the expression of sma-10 in either hypodermis or intestine fully rescues the wild-type immune response. Our results contribute to understanding the role of SMA-10 as a context-dependent component of TGF-ß Sma/Mab, and reveal a function of SMA-10 in immunity in association to the Insulin/insulin-like growth factor signalling (IIS) pathway.

sta-1 is repressed by mir-58 family in Caenorhabditis elegans.

The miR-58 family comprises 6 microRNAs with largely shared functions, and with an overall high expression, because one of its members, miR-58, is the most abundant microRNA in Caenorhabditis elegans. We recently found that 2 TGF-ß signaling pathways, Sma/Mab and Dauer, responsible for body size and dauer formation respectively, among other phenotypes, are downregulated by the miR-58 family. Here, we further explore this family by showing that it also acts through the sta-1 3'UTR. sta-1 encodes a transcription factor, homologous to mammalian STATs, that inhibits dauer formation in association with the TGF-ß Dauer pathway. We also observe that mutants with a constitutively active TGF-ß Dauer pathway express higher levels of sta-1 mRNA. Our results reinforce the view of the miR-58 family and STA-1 as regulators of dauer formation in coordination with the TGF-ß Dauer pathway.

miR-58 family and TGF-ß pathways regulate each other in Caenorhabditis elegans.

Despite the fact that microRNAs (miRNAs) modulate the expression of around 60% of protein-coding genes, it is often hard to elucidate their precise role and target genes. Studying miRNA families as opposed to single miRNAs alone increases our chances of observing not only mutant phenotypes but also changes in the expression of target genes. Here we ask whether the TGF-ß signalling pathways, which control many animal processes, might be modulated by miRNAs in Caenorhabditis elegans. Using a mutant for four members of the mir-58 family, we show that both TGF-ß Sma/Mab (controlling body size) and TGF-ß Dauer (regulating dauer, a stress-resistant larval stage) are upregulated. Thus, mir-58 family directly inhibits the expression of dbl-1 (ligand), daf-1, daf-4 and sma-6 (receptors) of TGF-ß pathways. Epistasis experiments reveal that whereas the small body phenotype of the mir-58 family mutant must invoke unknown targets independent from TGF-ß Sma/Mab, its dauer defectiveness can be rescued by DAF-1 depletion. Additionally, we found a negative feedback loop between TGF-ß Sma/Mab and mir-58 and the related mir-80. Our results suggest that the interaction between mir-58 family and TGF-ß genes is key on decisions about animal growth and stress resistance in C. elegans and perhaps other organisms.

Functional characterization of thioredoxin 3 (TRX-3), a Caenorhabditis elegans intestine-specific thioredoxin.

Thioredoxins are a class of evolutionarily conserved proteins that have been demonstrated to play a key role in many cellular processes involving redox reactions. We report here the genetic and biochemical characterization of Caenorhabditis elegans TRX-3, the first metazoan thioredoxin with an intestine-specific expression pattern. By using green fluorescent protein reporters we have found that TRX-3 is expressed in both the cytoplasm and the nucleus of intestinal cells, with a prominent localization at the apical membrane. Although intestinal function, reproductive capacity, longevity, and resistance of trx-3 loss-of-function mutants to many stresses are indistinguishable from those of wild-type animals, we have observed a slight reduction in size and a minor reduction in the defecation cycle timing of trx-3 mutants. Interestingly, trx-3 is induced upon infection by Photorhabdus luminescens and Candida albicans, and TRX-3 overexpression provides a modest protection against these pathogens. Together, our data indicate that TRX-3 function in the intestine is dispensable for C. elegans development but may be important to fight specific bacterial and fungal infections.

Evolutionary history of Na,K-ATPases and their osmoregulatory role.

The Na/K pump, or Na,K-ATPase, is a key enzyme to the homeostasis of osmotic pressure, cell volume, and the maintenance of electrochemical gradients. Its alpha subunit, which holds most of its functions, belongs to a large family of ATPases known as P-type, and to the subfamily IIC, which also includes H,K-ATPases. In this study, we attempt to describe the evolutionary history of IIC ATPases by doing phylogenetic analysis with most of the currently available protein sequences (over 200), and pay special attention to the relationship between their diversity and their osmoregulatory role. We include proteins derived from many completed or ongoing genome projects, many of whose IIC ATPases have not been phylogenetically analyzed previously. We show that the most likely origin of IIC proteins is prokaryotic, and that many of them are present in non-metazoans, such as algae, protozoans or fungi. We also suggest that the pre-metazoan ancestor, represented by the choanoflagellate Monosiga brevicollis, whose genome has been sequenced, presented at least two IIC-type proteins. One of these proteins would have given rise to most current animal IIC ATPases, whereas the other apparently evolved into a lineage that, so far, has only been found in nematodes. We also propose that early deuterostomes presented a single IIC gene, from which all the extant diversity of vertebrate IIC proteins originated by gene and genome duplications.

Evolution of the parasitic wasp subfamily Rogadinae (Braconidae): phylogeny and evolution of lepidopteran host ranges and mummy characteristics.

BACKGROUND: The braconid subfamily Rogadinae is a large, cosmopolitan group of endoparasitoid wasps characterised by 'mummifying' their lepidopteran host larvae, from which the adult subsequently emerges. Rogadines attack a variety of both macro- and microlepidopteran taxa, although the speciose genus Aleiodes almost exclusively attacks macrolepidopterans. Here, we investigate the phylogenetic history of the Rogadinae, revise their higher-level classification and assess the evolution of their host ranges and mummy types. We also assess the divergence times within the subfamily and discuss the reasons for the extraordinary evolutionary diversification of Aleiodes. RESULTS: Our Bayesian analyses weakly support the monophyly of the subfamily. A clade comprising all Aleiodes species and some other taxa is not nested within the tribe Rogadini as previously supposed, but instead is recovered as sister to the Yeliconini, with the remaining Rogadini genera being recovered as sister to the Stiropiini. The Rogadinae is estimated to have originated during the mid to late Eocene, 36.1-51.62 MYA. Molecular dating gives a more recent origin for the Aleiodes clade (17.98-41.76 MYA) compared to the origins proposed for two of its principal lepidopteran host groups (Noctuidae: 60.7-113.4 MYA; Geometridae 48-62 MYA). The Bayesian ancestral reconstruction of the emergence habits from the mummified hosts weakly recovered an anterior emergence as the ancestral condition for the subfamily. Producing a hard mummy has evolved at various times independently, though most of the species with this biology belong to the Aleiodes clade. CONCLUSION: Based on our results, we erect the tribe Aleiodini nov. to include Aleiodes and Heterogamus stat. rev. Cordylorhogas, Pholichora and Hemigyroneuron are synonymised with Aleiodes. The molecular dating of clades and the ancestral reconstruction of host ranges support the hypothesis that radiation within Aleiodes s. s. was due to host recruitment leading to host range expansion followed by speciation, and not to parasitoid-host coevolution. Within the Rogadinae, variation in the site of emergence from the mummified host probably evolved as a consequence of the mummy's site and mode of formation, and the extent of mummy tanning/hardness to the degree of protection needed in relation to the cost of providing it.

Dietary regulation of hypodermal polyploidization in C. elegans.

BACKGROUND: Dietary restriction (DR) results in increased longevity, reduced fecundity and reduced growth in many organisms. Though many studies have examined the effects of DR on longevity and fecundity, few have investigated the effects on growth. RESULTS: Here we use Caenorhabditis elegans to determine the mechanisms that regulate growth under DR. We show that rather than a reduction in cell number, decreased growth in wild type C. elegans under DR is correlated with lower levels of hypodermal polyploidization. We also show that mutants lacking wild type sensory ciliated neurons are small, exhibit hypo-polyploidization and more importantly, when grown under DR, reduce their levels of endoreduplication to a lesser extent than wild type, suggesting that these neurons are required for the regulation of hypodermal polyploidization in response to DR. Similarly, we also show that the cGMP-dependent protein kinase EGL-4 and the SMA/MAB signalling pathway regulate polyploidization under DR. CONCLUSION: We show C. elegans is capable of actively responding to food levels to regulate adult ploidy. We suggest this response is dependent on the SMA/MAB signalling pathway.

Regulation of growth by ploidy in Caenorhabditis elegans.

Some animals, such as the larvae of Drosophila melanogaster, the larvae of the Appendicularian chordate Oikopleura, and the adults of the nematode Caenorhabditis elegans, are unusual in that they grow largely by increases in cell size. The giant cells of such species are highly polyploid, having undergone repeated rounds of endoreduplication. Since germline polyploid strains tend to have large cells, it is often assumed that endoreduplication drives cell growth, but this remains controversial. We have previously shown that adult growth in C. elegans is associated with the endoreduplication of nuclei in the epidermal syncitium, hyp 7. We show here that this relationship is causal. Manipulation of somatic ploidy both upwards and downwards increases and decreases, respectively, adult body size. We also establish a quantitative relationship between ploidy and body size. Finally, we find that TGF-beta (DBL-1) and cyclin E (CYE-1) regulate body size via endoreduplication. To our knowledge, this is the first experimental evidence establishing a cause-and-effect relationship between somatic polyploidization and body size in a metazoan.

Pseudo-cryptic speciation in coccolithophores.

Coccolithophores are a group of calcifying unicellular algae that constitute a major fraction of oceanic primary productivity, play an important role in the global carbon cycle, and are key biostratigraphic marker fossils. Their taxonomy is primarily based on the morphology of the minute calcite plates, or coccoliths, covering the cell. These are diverse and include widespread fine scale variation, of which the biological/taxonomic significance is unknown. Do they represent phenotypic plasticity, genetic polymorphisms, or species-specific characters? Our research on five commonly occurring coccolithophores supports the hypothesis that such variation represents pseudocryptic speciation events, occurring between 0.3 and 12.9 million years ago from a molecular clock estimation. This finding suggests strong stabilizing selection acting on coccolithophorid phenotypes. Our results also provide strong support for the use of fine scale morphological characters of coccoliths in the fossil record to improve biostratigraphic resolution and paleoceanographic data retrieval.

Patterns of DNA sequence polymorphism at Sod vicinities in Drosophila melanogaster: unraveling the footprint of a recent selective sweep.

We survey DNA sequence polymorphisms at the Sod locus and four neighboring regions of Drosophila melanogaster, spanning 55,513 base pairs (bp), in 15 strains from a natural population, plus one reference laboratory strain and one strain of Drosophila simulans. Our objective is to characterize a proposed selective sweep that occurred at a locus close to Sod in D. melanogaster and to characterize the strength of the selection event, its time, and the size of the hitchhiked region. Two regions, 1819 and 6kbr3r, show a pattern of polymorphism very similar to the one of Sod, implying that they have been affected by the same evolutionary process that impacted Sod. A third fragment, 2021 seems unaffected by the event. A fourth one, 4039, on the opposite flank of Sod in relation to 2021, is only partially affected. We estimate that the length of the chromosomal segment impacted by the selective sweep is 41-54 kb, the age of the selective sweep is 2,600-22,000 years, and the selective advantage is 0.020 < s < 0.103.

Genetic polymorphism at two linked loci, Sod and Est-6, in Drosophila melanogaster.

We have examined the patterns of polymorphism at two linked loci, Sod and Est-6, separated by nearly 1000 kb on the left arm of chromosome 3 of Drosophila melanogaster. The evidence suggests that natural selection has been involved in shaping the polymorphisms. At the Sod locus, a fairly strong (s>0.01) selective sweep, started >or=2600 years ago, increased the frequency of a rare haplotype, F(A), to about 50% frequency in populations of Europe, Asia, and the Americas. More recently, an F(A) allele mutated to an S allele, which has increased to frequencies 5-15% in populations of Europe, Asia and North America. All S alleles are identical (or very nearly) in sequence and differ by one nucleotide substitution (which accounts for the F-->S electrophoretic difference) from F(A) alleles. At the Est-6 locus, the evidence indicates both directional and balancing selection impacting separately the promoter and the coding regions of the gene, with linkage disequilibrium occurring within each region. Some linkage disequilibrium also exists between the two genes.