Intrinsic apoptosis is evolutionary divergent among metazoans

Apoptosis is characterised by an analogous set of morphological features1 that depend on a proteolytic multigenic family, the caspases. Each apoptotic signalling pathway involves a specific initiator caspase, upstream of the pathway regulation, which finally converges to common executioner caspases. Intrinsic apoptosis, previously known as the mitochondrial apoptotic pathway, is often considered as ancestral and evolutionary conserved among animals. First identified in the nematode Caenorhabditis elegans, intrinsic apoptosis was next characterised in fruit fly Drosophila melanogaster and mammals. Intrinsic apoptosis depends on the key initiator caspase-9 (named Ced-3 and Dronc in Caenorhabditis and Drosophila, respectively), the activator Apaf-1 and the Bcl-2 multigenic family. Many functional studies have led to a deep characterisation of intrinsic apoptosis based on those classical models. Nevertheless, the biochemical role of mitochondria, the pivotal function of cytochrome c and the modality of caspases activation remain highly heterogeneous and hide profound molecular divergences among apoptotic pathways in animals. Independent of functional approaches, the phylogenetic history of the signal transduction actors, mostly the caspase family, is the Rosetta Stone to shed light on intrinsic apoptosis evolution. Here, after exhaustive research on CARD-caspases, we demonstrate by phylogenetic analysis that the caspase-9, the fundamental key of intrinsic apoptosis, is deuterostomes-specific, while it is the caspase-2 which is ancestral and common to bilaterians. Our analysis of Bcl-2 family and Apaf-1 confirm the high heterogeneity in apoptotic pathways elaboration in animals. Taken together, our results support convergent emergence of distinct intrinsic apoptotic pathways during metazoan evolution.

The gene repertoire of the main cysteine protease of Trypanosoma cruzi, cruzipain, reveals four sub-types with distinct active sites

Cruzipains are the main papain-like cysteine proteases of Trypanosoma cruzi, the protozoan parasite that causes Chagas disease. Encoded by a multigenic family, previous studies have estimated the presence of dozens of copies spread over multiple chromosomes in different parasite strains. Here, we describe the complete gene repertoire of cruzipain in three parasite strains, their genomic organization, and expression pattern throughout the parasite life cycle. Furthermore, we have analyzed primary sequence variations among distinct family members as well as structural differences between the main groups of cruzipains. Based on phylogenetic inferences and residue positions crucial for enzyme function and specificity, we propose the classification of cruzipains into two families (I and II), whose genes are distributed in two or three separate clusters in the parasite genome, according with the strain. Family I comprises nearly identical copies to the previously characterized cruzipain 1/cruzain, whereas Family II encompasses three structurally distinct sub-types, named cruzipain 2, cruzipain 3, and cruzipain 4. RNA-seq data derived from the CL Brener strain indicates that Family I genes are mainly expressed by epimastigotes, whereas trypomastigotes mainly express Family II genes. Significant differences in the active sites among the enzyme sub-types were also identified, which may play a role in their substrate selectivity and impact their inhibition by small molecules.

The gene repertoire of the main cysteine protease of Trypanosoma cruzi, cruzipain, reveals four sub-types with distinct active sites

Cruzipains are the main papain-like cysteine proteases of Trypanosoma cruzi, the protozoan parasite that causes Chagas disease. Encoded by a multigenic family, previous studies have estimated the presence of dozens of copies spread over multiple chromosomes in different parasite strains. Here, we describe the complete gene repertoire of cruzipain in three parasite strains, their genomic organization, and expression pattern throughout the parasite life cycle. Furthermore, we have analyzed primary sequence variations among distinct family members as well as structural differences between the main groups of cruzipains. Based on phylogenetic inferences and residue positions crucial for enzyme function and specificity, we propose the classification of cruzipains into two families (I and II), whose genes are distributed in two or three separate clusters in the parasite genome, according with the strain. Family I comprises nearly identical copies to the previously characterized cruzipain 1/cruzain, whereas Family II encompasses three structurally distinct sub-types, named cruzipain 2, cruzipain 3, and cruzipain 4. RNA-seq data derived from the CL Brener strain indicates that Family I genes are mainly expressed by epimastigotes, whereas trypomastigotes mainly express Family II genes. Significant differences in the active sites among the enzyme sub-types were also identified, which may play a role in their substrate selectivity and impact their inhibition by small molecules.

Nucleosome landscape reflects phenotypic differences in Trypanosoma cruzi life forms

Trypanosoma cruzi alternates between replicative and nonreplicative life forms, accompanied by a shift in global transcription levels and by changes in the nuclear architecture, the chromatin proteome and histone posttranslational modifications. To gain further insights into the epigenetic regulation that accompanies life form changes, we performed genome-wide high-resolution nucleosome mapping using two T. cruzi life forms (epimastigotes and cellular trypomastigotes). By combining a powerful pipeline that allowed us to faithfully compare nucleosome positioning and occupancy, more than 125 thousand nucleosomes were mapped, and approximately 20% of them differed between replicative and nonreplicative forms. The nonreplicative forms have less dynamic nucleosomes, possibly reflecting their lower global transcription levels and DNA replication arrest. However, dynamic nucleosomes are enriched at nonreplicative regulatory transcription initiation regions and at multigenic family members, which are associated with infective-stage and virulence factors. Strikingly, dynamic nucleosome regions are associated with GO terms related to nuclear division, translation, gene regulation and metabolism and, notably, associated with transcripts with different expression levels among life forms. Finally, the nucleosome landscape reflects the steady-state transcription expression: more abundant genes have a more deeply nucleosome-depleted region at putative 5’ splice sites, likely associated with trans-splicing efficiency. Taken together, our results indicate that chromatin architecture, defined primarily by nucleosome positioning and occupancy, reflects the phenotypic differences found among T. cruzi life forms despite the lack of a canonical transcriptional control context.

Characterization of an eutherian gene cluster generated after transposon domestication identifies Bex3 as relevant for advanced neurological functions

Background One of the most unusual sources of phylogenetically restricted genes is the molecular domestication of transposable elements into a host genome as functional genes. Although these kinds of events are sometimes at the core of key macroevolutionary changes, their origin and organismal function are generally poorly understood. Results Here, we identify several previously unreported transposable element domestication events in the human and mouse genomes. Among them, we find a remarkable molecular domestication that gave rise to a multigenic family in placental mammals, the Bex/Tceal gene cluster. These genes, which act as hub proteins within diverse signaling pathways, have been associated with neurological features of human patients carrying genomic microdeletions in chromosome X. The Bex/Tceal genes display neural-enriched patterns and are differentially expressed in human neurological disorders, such as autism and schizophrenia. Two different murine alleles of the cluster member Bex3 display morphological and physiopathological brain modifications, such as reduced interneuron number and hippocampal electrophysiological imbalance, alterations that translate into distinct behavioral phenotypes. Conclusions We provide an in-depth understanding of the emergence of a gene cluster that originated by transposon domestication and gene duplication at the origin of placental mammals, an evolutionary process that transformed a non-functional transposon sequence into novel components of the eutherian genome. These genes were integrated into existing signaling pathways involved in the development, maintenance, and function of the CNS in eutherians. At least one of its members, Bex3, is relevant for higher brain functions in placental mammals and may be involved in human neurological disorders.

Identification of Novel Interspersed DNA Repetitive Elements in the Trypanosoma cruzi Genome Associated with the 3′UTRs of Surface Multigenic Families

Trypanosoma cruzi is the etiological agent of Chagas disease, which affects millions of people in Latin America. No transcriptional control of gene expression has been demonstrated in this organism, and 50% of its genome consists of repetitive elements and members of multigenic families. In this study, we applied a novel bioinformatics approach to predict new repetitive elements in the genome sequence of T. cruzi. A new repetitive sequence measuring 241 nt was identified and found to be interspersed along the genome sequence from strains of different DTUs. This new repeat was mostly on intergenic regions, and upstream and downstream regions of the 241 nt repeat were enriched in surface protein genes. RNAseq analysis revealed that the repeat was part of processed mRNAs and was predominantly found in the 3′ untranslated regions (UTRs) of genes of multigenic families encoding surface proteins. Moreover, we detected a correlation between the presence of the repeat in the 3′UTR of multigenic family genes and the level of differential expression of these genes when comparing epimastigote and trypomastigote transcriptomes. These data suggest that this sequence plays a role in the posttranscriptional regulation of the expression of multigenic families.

Genome-wide analysis of the cupin superfamily in cowpea (Vigna unguiculata)

Cowpea [Vigna unguiculata (L.)Walp.] is an essential food crop that is cultivated in many important arid and semi-arid regions of the world. In this study the genome-wide database of cowpea genes was accessed in search of genomic sequences coding for globulins, specifically members of the cupin superfamily, a well-documented multigenic family belonging to the globulin protein class. A total of seventy-seven genes belonging to the cupin superfamily were found and divided into six families. We classify V. unguiculata genes into two subgroups: classical cupins with one cupin domain (fifty-nine proteins) and bicupins with two cupin domains (eighteen members). In addition, a search for cupin members in other closely related species of the fabaceae family [V. angularis, V. radiatam and Phaseolus vulgaris (common bean)] was performed. Based on those data, a detailed characterization and comparison of the cupin genes on these species was performed with the aim to better understand the connection and functions of cupin proteins from different, but related, plant species. This study was the first attempt to investigate the cupin superfamily in V. unguiculata, allowing the identification of six cupins families and better understand the structural features of those proteins, such as number of domains alternative splicing.

Eucalyptus grandis THIOREDOXINS, DIVERSITY AND GENE EXPRESSION

ABSTRACT Tree genomes have been sequenced in recent years providing a source of basic information on multigenic family characterization. Comparative genomics based on those complete genome sequences available in public database is an important tool providing useful information to progress on functional gene characterization. In this work, we focus on gene encoding for Thioredoxins (Trxs) in Eucalyptus grandis genome, which are oxidoreductase enzymes, involved in significant biochemical processes, above all the maintenance of cellular homeostasis. Here we investigate the diversity, structure and expression of these genes in eucalyptus. For this purpose, bioinformatics tools were employed, using public platforms data, to identify coding sequences and validate gene expression. Specific softwares were employed to characterize gene structure and expression. RT-PCR assays were carried out to specifically verify the expression of 4 cytoplasmic thioredoxin genes, observed in silico from leaf, phloem, xylem and apical meristem tissues. Twenty-two Trxs with characteristic and canonic active sites were identified, confirming the presence of all types of the three main groups already defined as plastidial (m, f, x, y, z) cytoplasmatic (h) and mitochondrial (o). However, differences in the number of genes per group were observed when compared with other tree genomes. The expression of these thioredoxin genes compared to some homologous genes presented divergent expression patterns compared to Arabidopis thaliana suggesting a functional specificity in eucalyptus, such as in the case of Eucgr.F01604 gene encoding an h1 cytoplasmic Trx, which presents a strong expression in conductor tissues.

Crystal Structure of Chloroplastic Thioredoxin f2 from Chlamydomonas reinhardtii Reveals Distinct Surface Properties

Protein disulfide reduction by thioredoxins (TRXs) controls the conformation of enzyme active sites and their multimeric complex formation. TRXs are small oxidoreductases that are broadly conserved in all living organisms. In photosynthetic eukaryotes, TRXs form a large multigenic family, and they have been classified in different types: f, m, x, y, and z types are chloroplastic, while o and h types are located in mitochondria and cytosol. In the model unicellular alga Chlamydomonas reinhardtii, the TRX family contains seven types, with f- and h-types represented by two isozymes. Type-f TRXs interact specifically with targets in the chloroplast, controlling photosynthetic carbon fixation by the Calvin–Benson cycle. We solved the crystal structures of TRX f2 and TRX h1 from C. reinhardtii. The systematic comparison of their atomic features revealed a specific conserved electropositive crown around the active site of TRX f, complementary to the electronegative surface of their targets. We postulate that this surface provides specificity to each type of TRX.

Metal transporter encoding gene families in Fabaceae: II. Cation/H+ exchanger (CAX) encoding genes

The plant CAtion/H+ eXchangers (CAX) proteins belong to Ca2+/cation antiporter (CaCA) superfamily. By using in silico methods, the CAX encoding genes in the genome of six legume species have been identified in this work. In examined legume genomes, the CAX genes belong to a small multigenic family. The number of the CAX genes in these legume species is 17 (soybean), 6 (common bean and C. cajan), 5 (M. truncatula and C. arietinum) and 3 genes (L. japonicus), respectively. The legume CAX genes vary in genomic full-length ranging from 1,213 to 11,561 base pairs. All of the genes exhibit introns (from 4 to 11 introns). Their deduced full-length protein sequences range from 248 to 718 amino acids. Theoretical pI values of most (39/42) of legume CAX proteins were less than 7. The secondary structure modelling of protein exhibit transmembrane helix region (from 3 to 11 regions). Half of all (23/42) included 11 transmembrane helix regions. Based on phylogeny analysis, all of the legume CAX were divided into two groups, A and B, each consisting of two subgroups. The phylogeny suggested an ancient gene duplication in the genome of legumes ancestry. The recent gene duplication even was only detected in the soybean genome after the speciation. The expression analysis showed that all of 3 L. japonicus CAX genes expressed in all examined tissues. However, the expression of C. cajan CAX genes was not detected. For each of 4 remaining legumes, the CAX genes were differed in their expression level depending on studied tissues. The tissue-specific expressions of some CAX genes were observed in 5 out of the 6 legume species, except C. cajan.