Ancestral Role Research Articles

Anteroposterior axis patterning by early canonical Wnt signaling during hemichordate development.

The Wnt family of secreted proteins has been proposed to play a conserved role in early specification of the bilaterian anteroposterior (A/P) axis. This hypothesis is based predominantly on data from vertebrate embryogenesis as well as planarian regeneration and homeostasis, indicating that canonical Wnt (cWnt) signaling endows cells with positional information along the A/P axis. Outside of these phyla, there is strong support for a conserved role of cWnt signaling in the repression of anterior fates, but little comparative support for a conserved role in promotion of posterior fates. We further test the hypothesis by investigating the role of cWnt signaling during early patterning along the A/P axis of the hemichordate Saccoglossus kowalevskii. We have cloned and investigated the expression of the complete Wnt ligand and Frizzled receptor complement of S. kowalevskii during early development along with many secreted Wnt modifiers. Eleven of the 13 Wnt ligands are ectodermally expressed in overlapping domains, predominantly in the posterior, and Wnt antagonists are localized predominantly to the anterior ectoderm in a pattern reminiscent of their distribution in vertebrate embryos. Overexpression and knockdown experiments, in combination with embryological manipulations, establish the importance of cWnt signaling for repression of anterior fates and activation of mid-axial ectodermal fates during the early development of S. kowalevskii. However, surprisingly, terminal posterior fates, defined by posterior Hox genes, are unresponsive to manipulation of cWnt levels during the early establishment of the A/P axis at late blastula and early gastrula. We establish experimental support for a conserved role of Wnt signaling in the early specification of the A/P axis during deuterostome body plan diversification, and further build support for an ancestral role of this pathway in early evolution of the bilaterian A/P axis. We find strong support for a role of cWnt in suppression of anterior fates and promotion of mid-axial fates, but we find no evidence that cWnt signaling plays a role in the early specification of the most posterior axial fates in S. kowalevskii. This posterior autonomy may be a conserved feature of early deuterostome axis specification.

Expression of a carotenoid-modifying gene and evolution of red coloration in weaverbirds (Ploceidae).

Red carotenoid colours in birds are widely assumed to be sexually selected quality indicators, but this rests on a very incomplete understanding of genetic mechanisms and honesty-mediating costs. Recent progress was made by the implication of the gene CYP2J19 as an avian carotenoid ketolase, catalysing the synthesis of red C4-ketocarotenoids from yellow dietary precursors, and potentially a major mechanism behind red coloration in birds. Here, we investigate the role of CYP2J19 in the spectacular colour diversification of African weaverbirds (Ploceidae), represented by five genera and 16 species: eight red, seven yellow and one without carotenoid coloration. All species had a single copy of CYP2J19, unlike the duplication found in the zebra finch, with high expression in the retina, confirming its function in colouring red oil droplets. Expression was weak or undetected in skin and follicles of pigment-depositing feather buds, as well as in beaks and tarsi, including those of the red-billed quelea. In contrast, the hepatic (liver) expression of CYP2J19 was consistently higher (>14-fold) in seven species with C4-ketocarotenoid coloration than in species without (including one red species), an association strongly supported by a phylogenetic comparative analysis. The results suggest a critical role of the candidate ketolase, CYP2J19, in the evolution of red C4-ketocarotenoid colour variation in ploceids. As ancestral state reconstruction suggests that ketocarotenoid coloration has evolved twice in this group (once in Euplectes and once in the Quelea/Foudia clade), we argue that while CYP2J19 has retained its ancestral role in the retina, it has likely been co-opted for red coloration independently in the two lineages, via increased hepatic expression.

Amphioxus SYCP1: a case of retrogene replacement and co-option of regulatory elements adjacent to the ParaHox cluster

Retrogenes are formed when an mRNA is reverse-transcribed and reinserted into the genome in a location unrelated to the original locus. If this retrocopy inserts into a transcriptionally favourable locus and is able to carry out its original function, it can, in rare cases, lead to retrogene replacement. This involves the original, often multi-exonic, parental copy being lost whilst the newer single-exon retrogene copy ‘replaces’ the role of the ancestral parent gene. One example of this is amphioxus SYCP1, a gene that encodes a protein used in synaptonemal complex formation during meiosis and which offers the opportunity to examine how a retrogene evolves after the retrogene replacement event. SYCP1 genes exist as large multi-exonic genes in most animals. AmphiSYCP1, however, contains a single coding exon of ~ 3200 bp and has inserted next to the ParaHox cluster of amphioxus, whilst the multi-exonic ancestral parental copy has been lost. Here, we show that AmphiSYCP1 has not only replaced its parental copy, but also has evolved additional regulatory function by co-opting a bidirectional promoter from the nearby AmphiCHIC gene. AmphiSYCP1 has also evolved a de novo, multi-exonic 5′untranslated region that displays distinct regulatory states, in the form of two different isoforms, and has evolved novel expression patterns during amphioxus embryogenesis in addition to its ancestral role in meiosis. The absence of ParaHox-like expression of AmphiSYCP1, despite its proximity to the ParaHox cluster, also suggests that this gene is not influenced by any potential pan-cluster regulatory mechanisms, which are seemingly restricted to only the ParaHox genes themselves.

Deciphering the Origin, Evolution, and Physiological Function of the Subtelomeric Aryl-Alcohol Dehydrogenase Gene Family in the Yeast Saccharomyces cerevisiae.

ABSTRACTHomology searches indicate that Saccharomyces cerevisiae strain BY4741 contains seven redundant genes that encode putative aryl-alcohol dehydrogenases (AAD). Yeast AAD genes are located in subtelomeric regions of different chromosomes, and their functional role(s) remain enigmatic. Here, we show that two of these genes, AAD4 and AAD14, encode functional enzymes that reduce aliphatic and aryl-aldehydes concomitant with the oxidation of cofactor NADPH, and that Aad4p and Aad14p exhibit different substrate preference patterns. Other yeast AAD genes are undergoing pseudogenization. The 5′ sequence of AAD15 has been deleted from the genome. Repair of an AAD3 missense mutation at the catalytically essential Tyr73 residue did not result in a functional enzyme. However, ancestral-state reconstruction by fusing Aad6 with Aad16 and by N-terminal repair of Aad10 restores NADPH-dependent aryl-alcohol dehydrogenase activities. Phylogenetic analysis indicates that AAD genes are narrowly distributed in wood-saprophyte fungi and in yeast that occupy lignocellulosic niches. Because yeast AAD genes exhibit activity on veratraldehyde, cinnamaldehyde, and vanillin, they could serve to detoxify aryl-aldehydes released during lignin degradation. However, none of these compounds induce yeast AAD gene expression, and Aad activities do not relieve aryl-aldehyde growth inhibition. Our data suggest an ancestral role for AAD genes in lignin degradation that is degenerating as a result of yeast's domestication and use in brewing, baking, and other industrial applications.IMPORTANCE Functional characterization of hypothetical genes remains one of the chief tasks of the postgenomic era. Although the first Saccharomyces cerevisiae genome sequence was published over 20 years ago, 22% of its estimated 6,603 open reading frames (ORFs) remain unverified. One outstanding example of this category of genes is the enigmatic seven-member AAD family. Here, we demonstrate that proteins encoded by two members of this family exhibit aliphatic and aryl-aldehyde reductase activity, and further that such activity can be recovered from pseudogenized AAD genes via ancestral-state reconstruction. The phylogeny of yeast AAD genes suggests that these proteins may have played an important ancestral role in detoxifying aromatic aldehydes in ligninolytic fungi. However, in yeast adapted to niches rich in sugars, AAD genes become subject to mutational erosion. Our findings shed new light on the selective pressures and molecular mechanisms by which genes undergo pseudogenization.

Pan-arthropod analysis reveals somatic piRNAs as an ancestral defence against transposable elements.

Summary ParagraphIn animals, small RNA molecules termed PIWI-interacting RNAs (piRNAs) silence transposable elements (TEs), protecting the germline from genomic instability and mutation. piRNAs have been detected in the soma in a few animals, but these are believed to be specific adaptations of individual species. Here, we report that somatic piRNAs were likely present in the ancestral arthropod more than 500 million years ago. Analysis of 20 species across the arthropod phylum suggests that somatic piRNAs targeting TEs and mRNAs are common among arthropods. The presence of an RNA-dependent RNA polymerase in chelicerates (horseshoe crabs, spiders, scorpions) suggests that arthropods originally used a plant-like RNA interference mechanism to silence TEs. Our results call into question the view that the ancestral role of the piRNA pathway was to protect the germline and demonstrate that small RNA silencing pathways have been repurposed for both somatic and germline functions throughout arthropod evolution.

Conserved redox-dependent DNA binding of ROXY glutaredoxins with TGA transcription factors.

The Arabidopsis thaliana CC‐type glutaredoxin (GRX) ROXY1 and the bZIP TGA transcription factor (TF) PERIANTHIA (PAN) interact in the nucleus and together regulate petal development. The CC‐type GRXs exist exclusively in land plants, and in contrast to the ubiquitously occurring CPYC and CGFS GRX classes, only the CC‐type GRXs expanded strongly during land plant evolution. Phylogenetic analyses show that TGA TFs evolved before the CC‐type GRXs in charophycean algae. MpROXY1/2 and MpTGA were isolated from the liverwort Marchantia polymorpha to analyze regulatory ROXY/TGA interactions in a basal land plant. Homologous and heterologous protein interaction studies demonstrate that nuclear ROXY/TGA interactions are conserved since the occurrence of CC‐type GRXs in bryophytes and mediated by a conserved ROXY C‐terminus. Redox EMSA analyses show a redox‐sensitive binding of MpTGA to the cis‐regulatory as‐1‐like element. Furthermore, we demonstrate that MpTGA binds together with MpROXY1/2 to this motif under reducing conditions, whereas this interaction is not observed under oxidizing conditions. Remarkably, heterologous complementation studies reveal a strongly conserved land plant ROXY activity, suggesting an ancestral role for CC‐type GRXs in modulating the activities of TGA TFs. Super‐resolution microscopy experiments detected a strong colocalization of ROXY1 with the active form of the RNA polymerase II in the nucleus. Together, these data shed new light on the function of ROXYs and TGA TFs and the evolution of redox‐sensitive transcription regulation processes, which likely contributed to adapt land plants to novel terrestrial habitats.

Tangential migration of corridor guidepost neurons contributes to anxiety circuits.

In mammals, thalamic axons are guided internally toward their neocortical target by corridor (Co) neurons that act as axonal guideposts. The existence of Co-like neurons in non-mammalian species, in which thalamic axons do not grow internally, raised the possibility that Co cells might have an ancestral role. Here, we investigated the contribution of corridor (Co) cells to mature brain circuits using a combination of genetic fate-mapping and assays in mice. We unexpectedly found that Co neurons contribute to striatal-like projection neurons in the central extended amygdala. In particular, Co-like neurons participate in specific nuclei of the bed nucleus of the stria terminalis, which plays essential roles in anxiety circuits. Our study shows that Co neurons possess an evolutionary conserved role in anxiety circuits independently from an acquired guidepost function. It furthermore highlights that neurons can have multiple sequential functions during brain wiring and supports a general role of tangential migration in the building of subpallial circuits.

AMP-activated protein kinase - not just an energy sensor.

Orthologues of AMP-activated protein kinase (AMPK) occur in essentially all eukaryotes as heterotrimeric complexes comprising catalytic α subunits and regulatory β and γ subunits. The canonical role of AMPK is as an energy sensor, monitoring levels of the nucleotides AMP, ADP, and ATP that bind competitively to the γ subunit. Once activated, AMPK acts to restore energy homeostasis by switching on alternate ATP-generating catabolic pathways while switching off ATP-consuming anabolic pathways. However, its ancestral role in unicellular eukaryotes may have been in sensing of glucose rather than energy. In this article, we discuss a few interesting recent developments in the AMPK field. Firstly, we review recent findings on the canonical pathway by which AMPK is regulated by adenine nucleotides. Secondly, AMPK is now known to be activated in mammalian cells by glucose starvation by a mechanism that occurs in the absence of changes in adenine nucleotides, involving the formation of complexes with Axin and LKB1 on the surface of the lysosome. Thirdly, in addition to containing the nucleotide-binding sites on the γ subunits, AMPK heterotrimers contain a site for binding of allosteric activators termed the allosteric drug and metabolite (ADaM) site. A large number of synthetic activators, some of which show promise as hypoglycaemic agents in pre-clinical studies, have now been shown to bind there. Fourthly, some kinase inhibitors paradoxically activate AMPK, including one (SU6656) that binds in the catalytic site. Finally, although downstream targets originally identified for AMPK were mainly concerned with metabolism, recently identified targets have roles in such diverse areas as mitochondrial fission, integrity of epithelial cell layers, and angiogenesis.

Nitric Oxide regulates mouth development in amphioxus

The development of the mouth in animals has fascinated researchers for decades, and a recent study proposed the modern view of recurrent evolution of protostomy and deuterostomy. Here we expanded our knowledge about conserved traits of mouth formation in chordates, testing the hypothesis that nitric oxide (NO) is a potential regulator of this process. In the present work we show for the first time that NO is an essential cell signaling molecule for cephalochordate mouth formation, as previously shown for vertebrates, indicating its conserved ancestral role in chordates. The experimental decrease of NO during early amphioxus Branchiostoma lanceolatum development impaired the formation of the mouth and gill slits, demonstrating that it is a prerequisite in pharyngeal morphogenesis. Our results represent the first step in the understanding of NO physiology in non-vertebrate chordates, opening new evolutionary perspectives into the ancestral importance of NO homeostasis and acquisition of novel biological roles during evolution.

Iron metabolism: State of the art

Iron homeostasis relies on the amount of its absorption by the intestine and its release from storage sites, the macrophages. Iron homeostasis is also dependent on the amount of iron used for the erythropoiesis. Hepcidin, which is synthesized predominantly by the liver, is the main regulator of iron metabolism. Hepcidin reduces serum iron by inhibiting the iron exporter, ferroportin expressed both tissues, the intestine and the macrophages. In addition, in the enterocytes, hepcidin inhibits the iron influx by acting on the apical transporter, DMT1. A defect of hepcidin expression leading to the appearance of a parenchymal iron overload may be genetic or secondary to dyserythropoiesis. The exploration of genetic hemochromatosis has revealed the involvement of several genes, including the recently described BMP6. Non-transfusional secondary hemochromatosis is due to hepcidin repression by cytokines, in particular the erythroferone factor that is produced directly by the erythroid precursors. Iron overload is correlated with the appearance of a free form of iron called NTBI. The influx of NTBI seems to be mediated by ZIP14 transporter in the liver and by calcium channels in the cardiomyocytes. Beside the liver, hepcidin is expressed at lesser extent in several extrahepatic tissues where it plays its ancestral role of antimicrobial peptide. In the kidney, hepcidin modulates defense barriers against urinary tract infections. In the heart, hepcidin maintains tissue iron homeostasis by an autocrine regulation of ferroprotine expression on the surface of cardiomyocytes. In conclusion, hepcidin remains a promising therapeutic tool in various iron pathologies.

Dopamine signaling tunes spatial pattern selectivity in C. elegans.

Animals with complex brains can discriminate the spatial arrangement of physical features in the environment. It is unknown whether such sensitivity to spatial patterns can be accomplished in simpler nervous systems that lack long-range sensory modalities such as vision and hearing. Here we show that the nematode Caenorhabditis elegans can discriminate spatial patterns in its surroundings, despite having a nervous system of only 302 neurons. This spatial pattern selectivity requires touch-dependent dopamine signaling, including the mechanosensory TRP-4 channel in dopaminergic neurons and the D2-like dopamine receptor DOP-3. We find that spatial pattern selectivity varies significantly among C. elegans wild isolates. Electrophysiological recordings show that natural variations in TRP-4 reduce the mechanosensitivity of dopaminergic neurons. Polymorphic substitutions in either TRP-4 or DOP-3 alter the selectivity of spatial patterns. Together, these results demonstrate an ancestral role for dopamine signaling in tuning spatial pattern preferences in a simple nervous system.

Gene regulatory network plasticity predates a switch in function of a conserved transcription regulator.

The rewiring of gene regulatory networks can generate phenotypic novelty. It remains an open question, however, how the large number of connections needed to form a novel network arise over evolutionary time. Here, we address this question using the network controlled by the fungal transcription regulator Ndt80. This conserved protein has undergone a dramatic switch in function-from an ancestral role regulating sporulation to a derived role regulating biofilm formation. This switch in function corresponded to a large-scale rewiring of the genes regulated by Ndt80. However, we demonstrate that the Ndt80-target gene connections were undergoing extensive rewiring prior to the switch in Ndt80's regulatory function. We propose that extensive drift in the Ndt80 regulon allowed for the exploration of alternative network structures without a loss of ancestral function, thereby facilitating the formation of a network with a new function.

Mitochondrial control through nutritionally regulated global histone H3 lysine-4 demethylation.

Histone demethylation by Jumonji-family proteins is coupled with the decarboxylation of α-ketoglutarate (αKG) to yield succinate, prompting hypotheses that their activities are responsive to levels of these metabolites in the cell. Consistent with this paradigm we show here that the Saccharomyces cerevisiae Jumonji demethylase Jhd2 opposes the accumulation of H3K4me3 in fermenting cells only when they are nutritionally manipulated to contain an elevated αKG/succinate ratio. We also find that Jhd2 opposes H3K4me3 in respiratory cells that do not exhibit such an elevated αKG/succinate ratio. While jhd2∆ caused only limited gene expression defects in fermenting cells, transcript profiling and physiological measurements show that JHD2 restricts mitochondrial respiratory capacity in cells grown in non-fermentable carbon in an H3K4me-dependent manner. In association with these phenotypes, we find that JHD2 limits yeast proliferative capacity under physiologically challenging conditions as measured by both replicative lifespan and colony growth on non-fermentable carbon. JHD2’s impact on nutrient response may reflect an ancestral role of its gene family in mediating mitochondrial regulation.

Multiplicity of Buc copies in Atlantic salmon contrasts with loss of the germ cell determinant in primates, rodents and axolotl

BackgroundThe primordial germ cells (PGCs) giving rise to gametes are determined by two different mechanisms in vertebrates. While the germ cell fate in mammals and salamanders is induced by zygotic signals, maternally delivered germ cell determinants specify the PGCs in birds, frogs and teleost fish. Assembly of the germ plasm in the oocyte is organized by the single Buc in zebrafish, named Velo1 in Xenopus, and by Oskar in Drosophila. Secondary loss of oskar in several insect lineages coincides with changes in germline determination strategies, while the presence of buc in mammals suggests functions not associated with germline formation.ResultsTo clarify the evolutionary history of buc we searched for the gene in genomes available from various chordates. No buc sequence was found in lamprey and chordate invertebrates, while the gene was identified in a conserved syntenic region in elephant shark, spotted gar, teleosts, Comoran coelacanth and most tetrapods. Rodents have probably lost the buc gene, while a premature translation stop was found in primates and in Mexican axolotl lacking germ plasm. In contrast, several buc and buc-like (bucL) paralogs were identified in the teleosts examined, including zebrafish, and the tetraploid genome of Atlantic salmon harbors seven buc and bucL genes. Maternal salmon buc1a, buc2a and buc2b mRNAs were abundant in unfertilized eggs together with dnd and vasa mRNAs. Immunostained salmon Buc1a was restricted to cleavage furrows in 4-cell stage embryos similar to a fluorescent zebrafish Buc construct injected in salmon embryos. Salmon Buc1a and Buc2a localized together with DnD, Vasa and Dazl within the Balbiani body of early oocytes.ConclusionsBuc probably originated more than 400 million years ago and might have played an ancestral role in assembling germ plasm. Functional redundancy or subfunctionalization of salmon Buc paralogs in germline formation is suggested by the maternally inherited mRNAs of three salmon buc genes, the localized Buc1a in the cleavage furrows and the distribution of Buc1a and Buc2a in the Balbiani body during oogenesis. The extra-ovarian expression of salmon buc genes and the presence of a second zebrafish bucL gene suggest additional functions not related to germ cell specification.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0809-7) contains supplementary material, which is available to authorized users.

Expression of segment polarity genes in brachiopods supports a non-segmental ancestral role of engrailed for bilaterians.

The diverse and complex developmental mechanisms of segmentation have been more thoroughly studied in arthropods, vertebrates and annelids—distantly related animals considered to be segmented. Far less is known about the role of “segmentation genes” in organisms that lack a segmented body. Here we investigate the expression of the arthropod segment polarity genes engrailed, wnt1 and hedgehog in the development of brachiopods—marine invertebrates without a subdivided trunk but closely related to the segmented annelids. We found that a stripe of engrailed expression demarcates the ectodermal boundary that delimits the anterior region of Terebratalia transversa and Novocrania anomala embryos. In T. transversa, this engrailed domain is abutted by a stripe of wnt1 expression in a pattern similar to the parasegment boundaries of insects—except for the expression of hedgehog, which is restricted to endodermal tissues of the brachiopod embryos. We found that pax6 and pax2/5/8, putative regulators of engrailed, also demarcate the anterior boundary in the two species, indicating these genes might be involved in the anterior patterning of brachiopod larvae. In a comparative phylogenetic context, these findings suggest that bilaterians might share an ancestral, non-segmental domain of engrailed expression during early embryogenesis.

Transcriptome Profiling of the Green Alga Spirogyra pratensis (Charophyta) Suggests an Ancestral Role for Ethylene in Cell Wall Metabolism, Photosynthesis, and Abiotic Stress Responses.

It is well known that ethylene regulates a diverse set of developmental and stress-related processes in angiosperms, yet its roles in early-diverging embryophytes and algae are poorly understood. Recently, it was shown that ethylene functions as a hormone in the charophyte green alga Spirogyra pratensis Since land plants evolved from charophytes, this implies conservation of ethylene as a hormone in green plants for at least 450 million years. However, the physiological role of ethylene in charophyte algae has remained unknown. To gain insight into ethylene responses in Spirogyra, we used mRNA sequencing to measure changes in gene expression over time in Spirogyra filaments in response to an ethylene treatment. Our analyses show that at the transcriptional level, ethylene predominantly regulates three processes in Spirogyra: (1) modification of the cell wall matrix by expansins and xyloglucan endotransglucosylases/hydrolases, (2) down-regulation of chlorophyll biosynthesis and photosynthesis, and (3) activation of abiotic stress responses. We confirmed that the photosynthetic capacity and chlorophyll content were reduced by an ethylene treatment and that several abiotic stress conditions could stimulate cell elongation in an ethylene-dependent manner. We also found that the Spirogyra transcriptome harbors only 10 ethylene-responsive transcription factor (ERF) homologs, several of which are regulated by ethylene. These results provide an initial understanding of the hormonal responses induced by ethylene in Spirogyra and help to reconstruct the role of ethylene in ancestral charophytes prior to the origin of land plants.

Coelimination and Survival in Gene Network Evolution: Dismantling the RA-Signaling in a Chordate.

The bloom of genomics is revealing gene loss as a pervasive evolutionary force generating genetic diversity that shapes the evolution of species. Outside bacteria and yeast, however, the understanding of the process of gene loss remains elusive, especially in the evolution of animal species. Here, using the dismantling of the retinoic acid metabolic gene network (RA-MGN) in the chordate Oikopleura dioica as a case study, we combine approaches of comparative genomics, phylogenetics, biochemistry, and developmental biology to investigate the mutational robustness associated to biased patterns of gene loss. We demonstrate the absence of alternative pathways for RA-synthesis in O. dioica, which suggests that gene losses of RA-MGN were not compensated by mutational robustness, but occurred in a scenario of regressive evolution. In addition, the lack of drastic phenotypic changes associated to the loss of RA-signaling provides an example of the inverse paradox of Evo-Devo. This work illustrates how the identification of patterns of gene coelimination-in our case five losses (Rdh10, Rdh16, Bco1, Aldh1a, and Cyp26)-is a useful strategy to recognize gene network modules associated to distinct functions. Our work also illustrates how the identification of survival genes helps to recognize neofunctionalization events and ancestral functions. Thus, the survival and extensive duplication of Cco and RdhE2 in O. dioica correlated with the acquisition of complex compartmentalization of expression domains in the digestive system and a process of enzymatic neofunctionalization of the Cco, while the surviving Aldh8 could be related to its ancestral housekeeping role against toxic aldehydes.

An ancestral role for the mitochondrial pyruvate carrier in glucose-stimulated insulin secretion

ObjectiveTransport of pyruvate into the mitochondrial matrix by the Mitochondrial Pyruvate Carrier (MPC) is an important and rate-limiting step in its metabolism. In pancreatic β-cells, mitochondrial pyruvate metabolism is thought to be important for glucose sensing and glucose-stimulated insulin secretion. MethodsTo evaluate the role that the MPC plays in maintaining systemic glucose homeostasis, we used genetically-engineered Drosophila and mice with loss of MPC activity in insulin-producing cells. ResultsIn both species, MPC deficiency results in elevated blood sugar concentrations and glucose intolerance accompanied by impaired glucose-stimulated insulin secretion. In mouse islets, β-cell MPC-deficiency resulted in decreased respiration with glucose, ATP-sensitive potassium (KATP) channel hyperactivity, and impaired insulin release. Moreover, treatment of pancreas-specific MPC knockout mice with glibenclamide, a sulfonylurea KATP channel inhibitor, improved defects in islet insulin secretion and abnormalities in glucose homeostasis in vivo. Finally, using a recently-developed biosensor for MPC activity, we show that the MPC is rapidly stimulated by glucose treatment in INS-1 insulinoma cells suggesting that glucose sensing is coupled to mitochondrial pyruvate carrier activity. ConclusionsAltogether, these studies suggest that the MPC plays an important and ancestral role in insulin-secreting cells in mediating glucose sensing, regulating insulin secretion, and controlling systemic glycemia.

Challenging the paradigms of leaf evolution: Class III HD-Zips in ferns and lycophytes.

Despite the extraordinary significance leaves have for life on Earth, their origin and development remain vigorously debated. More than a century of paleobotanical, morphological, and phylogenetic research has still not resolved fundamental questions about leaves. Developmental genetic data are sparse in ferns, and comparative studies of lycophytes and seed plants have reached opposing conclusions on the conservation of a leaf developmental program. We performed phylogenetic and expression analyses of a leaf developmental regulator (Class III HD-Zip genes; C3HDZs) spanning lycophytes and ferns. We show that a duplication and neofunctionalization of C3HDZs probably occurred in the ancestor of euphyllophytes, and that there is a common leaf developmental mechanism conserved between ferns and seed plants. We show C3HDZ expression in lycophyte and fern sporangia and show that C3HDZs have conserved expression patterns during initiation of lateral primordia (leaves or sporangia). This expression is maintained throughout sporangium development in lycophytes and ferns and indicates an ancestral role of C3HDZs in sporangium development. We hypothesize that there is a deep homology of all leaves and that a sporangium-specific developmental program was coopted independently for the development of lycophyte and euphyllophyte leaves. This provides molecular genetic support for a paradigm shift in theories of lycophyte leaf evolution.

Expression of GATA and POU transcription factors during the development of the planktotrophic trochophore of the polychaete serpulid Hydroides elegans.

The expression of transcription factors with endodermal and mesodermal roles in bilaterians is characterized during the development of Hydroides elegans, a serpulid polychaete with planktotrophic trochophore. GATA 4/5/6 is expressed in endodermal and mesodermal precursors during embryogenesis and in the midgut of trochophore larvae. HeGATA1/2/3a is expressed in animal hemisphere blastomeres 1d121 and 1d122, in dorsal ectoderm and in 4d endomesodermal derivatives that maintain their expression in trochophore larvae. HeGATA1/2/3b is not expressed during embryogenesis, but in several regions of the larva during postembryonic development. During very early gastrulation, Brn1/2/4 is first expressed in cells associated with the prospective oral/foregut side of the blastopore, and during larval development in 4d blastomere descendants. Comparison with orthologs in other metazoans suggests ancestral expression of GATA4/5/6 in the midgut of the last common ancestor of protostomes and deuterostomes. The conserved expression of Brn1/2/4 in the foregut precursors of Hydroides and sea urchins suggests an ancestral role in patterning the tripartite gut of planktotrophic larvae. Broader analysis of these and other regulatory genes reveals variability of developmental gene expression among polychaetes with lecithotrophic larvae, suggesting that they are evolutionarily derived from polychaetes with planktotrophic larvae.