The Evolution of Mammalian Gene Families

Gene families are groups of homologous genes that are likely to have highly similar functions. Differences in family size due to lineage-specific gene duplication and gene loss may provide clues to the evolutionary forces that have shaped mammalian genomes. Here we analyze the gene families contained within the whole genomes of human, chimpanzee, mouse, rat, and dog. In total we find that more than half of the 9,990 families present in the mammalian common ancestor have either expanded or contracted along at least one lineage. Additionally, we find that a large number of families are completely lost from one or more mammalian genomes, and a similar number of gene families have arisen subsequent to the mammalian common ancestor. Along the lineage leading to modern humans we infer the gain of 689 genes and the loss of 86 genes since the split from chimpanzees, including changes likely driven by adaptive natural selection. Our results imply that humans and chimpanzees differ by at least 6% (1,418 of 22,000 genes) in their complement of genes, which stands in stark contrast to the oft-cited 1.5% difference between orthologous nucleotide sequences. This genomic “revolving door” of gene gain and loss represents a large number of genetic differences separating humans from our closest relatives

Cutaneous nociception and neurogenic inflammation evoked by PACAP38 and VIP

Pituitary adenylate cyclase-activating peptide-38 (PACAP38) and vasoactive intestinal peptide (VIP) belong to the same secretin–glucagon superfamily and are present in nerve fibers in dura and skin. Using a model of acute cutaneous pain we explored differences in pain perception and vasomotor responses between PACAP38 and VIP in 16 healthy volunteers in a double-blind, placebo-controlled, crossover study. All participants received intradermal injections of 200 pmol PACAP38, 200 pmol VIP and placebo into the volar forearm. Measurements included pain intensity on a visual analog scale (VAS), blood flow by laser Doppler flowmetry, visual flare and wheal. Pain intensities after PACAP38 and VIP were mild and limited to a short time of about 100 s after injection. The area under the VAS-time curve was larger following PACAP38 (P = 0.004) and VIP (P = 0.01) compared to placebo. We found no statistical difference in pain perception between PACAP38 and VIP. Skin blood flow increase, flare and wheal were larger after both PACAP38 (P = 0.011) and VIP (P = 0.001) compared to placebo. VIP induced a considerably larger increase in skin blood flow, flare and wheal than PACAP38 (P = 0.002). In conclusion, we found that peripheral nociceptive cutaneous responses elicited by PACAP38 and VIP are similar in healthy volunteers. This suggests that acute pain and vasomotor responses following intradermal injections of PACAP38 and VIP are primarily mediated by VPAC receptors

Extensive Evolutionary Changes in Regulatory Element Activity during Human Origins Are Associated with Altered Gene Expression and Positive Selection

Understanding the molecular basis for phenotypic differences between humans and other primates remains an outstanding challenge. Mutations in non-coding regulatory DNA that alter gene expression have been hypothesized as a key driver of these phenotypic differences. This has been supported by differential gene expression analyses in general, but not by the identification of specific regulatory elements responsible for changes in transcription and phenotype. To identify the genetic source of regulatory differences, we mapped DNaseI hypersensitive (DHS) sites, which mark all types of active gene regulatory elements, genome-wide in the same cell type isolated from human, chimpanzee, and macaque. Most DHS sites were conserved among all three species, as expected based on their central role in regulating transcription. However, we found evidence that several hundred DHS sites were gained or lost on the lineages leading to modern human and chimpanzee. Species-specific DHS site gains are enriched near differentially expressed genes, are positively correlated with increased transcription, show evidence of branch-specific positive selection, and overlap with active chromatin marks. Species-specific sequence differences in transcription factor motifs found within these DHS sites are linked with species-specific changes in chromatin accessibility. Together, these indicate that the regulatory elements identified here are genetic contributors to transcriptional and phenotypic differences among primate species

Epigenetic management of major psychosis

Epigenetic mechanisms are thought to play a major role in the pathogenesis of the major psychoses (schizophrenia and bipolar disorder), and they may be the link between the environment and the genome in the pathogenesis of these disorders. This paper discusses the role of epigenetics in the management of major psychosis: (1) the role of epigenetic drugs in treating these disorders. At present, there are three categories of epigenetic drugs that are being actively investigated for their ability to treat psychosis: drugs inhibiting histone deacetylation; drugs decreasing DNA methylation; and drugs targeting microRNAs; and (2) the role of epigenetic mechanisms in electroconvulsive therapy in these disorders

Live Cell Monitoring of hiPSC Generation and Differentiation Using Differential Expression of Endogenous microRNAs

Human induced pluripotent stem cells (hiPSCs) provide new possibilities for regenerative therapies. In order for this potential to be achieved, it is critical to efficiently monitor the differentiation of these hiPSCs into specific lineages. Here, we describe a lentiviral reporter vector sensitive to specific microRNAs (miRNA) to show that a single vector bearing multiple miRNA target sequences conjugated to different reporters can be used to monitor hiPSC formation and subsequent differentiation from human fetal fibroblasts (HFFs). The reporter vector encodes EGFP conjugated to the targets of human embryonic stem cell (hESC) specific miRNAs (miR-302a and miR-302d) and mCherry conjugated to the targets of differentiated cells specific miRNAs (miR-142-3p, miR-155, and miR-223). The vector was used to track reprogramming of HFF to iPSC. HFFs co-transduced with this reporter vector and vectors encoding 4 reprogramming factors (OCT4, SOX2, KLF4 and cMYC) were mostly positive for EGFP (67%) at an early stage of hiPSC formation. EGFP expression gradually disappeared and mCherry expression increased indicating less miRNAs specific to differentiated cells and expression of miRNAs specific to hESCs. Upon differentiation of the hiPSC into embryoid bodies, a large fraction of these hiPSCs regained EGFP expression and some of those cells became single positive for EGFP. Further differentiation into neural lineages showed distinct structures demarcated by either EGFP or mCherry expression. These findings demonstrate that a miRNA dependent reporter vector can be a useful tool to monitor living cells during reprogramming of hiPSC and subsequent differentiation to lineage specific cells

Patterns of Positive Selection and Neutral Evolution in the Protein-Coding Genes of Tetraodon and Takifugu

Recent genome-wide analyses have revealed patterns of positive selection acting on protein-coding genes in humans and mammals. To assess whether the conclusions drawn from these analyses are valid for other vertebrates and to identify mammalian specificities, I have investigated the selective pressure acting on protein-coding genes of the puffer fishes Tetraodon and Takifugu. My results indicate that the strength of purifying selection in puffer fishes is similar to previous reports for murids but stronger in hominids, which have a smaller population size. Gene ontology analyses show that more than half of the biological processes targeted by positive selection in mammals are also targeted in puffer fishes, highlighting general patterns for vertebrates. Biological processes enriched with positively selected genes that are shared between mammals and fishes include immune and defense responses, signal transduction, regulation of transcription and several of their descendent terms. Mammalian-specific processes displaying an excess of positively selected genes are related to sensory perception and neurological processes. The comparative analyses also revealed that, for both mammals and fishes, genes encoding extracellular proteins are preferentially targeted by positive selection, indicating that adaptive evolution occurs more often in the extra-cellular environment rather than inside the cell. Moreover, I present here the first genome-wide characterization of neutrally-evolving regions of protein-coding genes. This analysis revealed an unexpectedly high proportion of genes containing both positively selected motifs and neutrally-evolving regions, uncovering a strong link between neutral evolution and positive selection. I speculate that neutrally-evolving regions are a major source of novelties screened by natural selection

The neurogenic potential of astrocytes is regulated by inflammatory signals

Although the adult brain contains neural stem cells (NSCs) that generate new neurons throughout life, these astrocyte-like populations are restricted to two discrete niches. Despite their terminally differentiated phenotype, adult parenchymal astrocytes can re-acquire NSC-like characteristics following injury, and as such, these 'reactive' astrocytes offer an alternative source of cells for central nervous system (CNS) repair following injury or disease. At present, the mechanisms that regulate the potential of different types of astrocytes are poorly understood. We used in vitro and ex vivo astrocytes to identify candidate pathways important for regulation of astrocyte potential. Using in vitro neural progenitor cell (NPC)-derived astrocytes, we found that exposure of more lineage-restricted astrocytes to either tumor necrosis factor alpha (TNF-α) (via nuclear factor-κB (NFκB)) or the bone morphogenetic protein (BMP) inhibitor, noggin, led to re-acquisition of NPC properties accompanied by transcriptomic and epigenetic changes consistent with a more neurogenic, NPC-like state. Comparative analyses of microarray data from in vitro-derived and ex vivo postnatal parenchymal astrocytes identified several common pathways and upstream regulators associated with inflammation (including transforming growth factor (TGF)-β1 and peroxisome proliferator-activated receptor gamma (PPARγ)) and cell cycle control (including TP53) as candidate regulators of astrocyte phenotype and potential. We propose that inflammatory signalling may control the normal, progressive restriction in potential of differentiating astrocytes as well as under reactive conditions and represent future targets for therapies to harness the latent neurogenic capacity of parenchymal astrocytes

A Downstream CpG Island Controls Transcript Initiation and Elongation and the Methylation State of the Imprinted Airn Macro ncRNA Promoter

A CpG island (CGI) lies at the 5′ end of the Airn macro non-protein-coding (nc) RNA that represses the flanking Igf2r promoter in cis on paternally inherited chromosomes. In addition to being modified on maternally inherited chromosomes by a DNA methylation imprint, the Airn CGI shows two unusual organization features: its position immediately downstream of the Airn promoter and transcription start site and a series of tandem direct repeats (TDRs) occupying its second half. The physical separation of the Airn promoter from the CGI provides a model to investigate if the CGI plays distinct transcriptional and epigenetic roles. We used homologous recombination to generate embryonic stem cells carrying deletions at the endogenous locus of the entire CGI or just the TDRs. The deleted Airn alleles were analyzed by using an ES cell imprinting model that recapitulates the onset of Igf2r imprinted expression in embryonic development or by using knock-out mice. The results show that the CGI is required for efficient Airn initiation and to maintain the unmethylated state of the Airn promoter, which are both necessary for Igf2r repression on the paternal chromosome. The TDRs occupying the second half of the CGI play a minor role in Airn transcriptional elongation or processivity, but are essential for methylation on the maternal Airn promoter that is necessary for Igf2r to be expressed from this chromosome. Together the data indicate the existence of a class of regulatory CGIs in the mammalian genome that act downstream of the promoter and transcription start

Regulated Fluctuations in Nanog Expression Mediate Cell Fate Decisions in Embryonic Stem Cells

The notion that the differentiated state of a cell population is determined simply by expression of specific marker genes is changing. In this work, the authors reveal that a pluripotent cell population comprises cells with temporal fluctuations in the expression of Nanog