Sex and age differences in the expression of liver microRNAs during the life span of F344 rats

Female-to-male differential transcription patterns of miRNA-mRNA networks in the livers of dioxin-exposed mice

Non-coding microRNAs (miRNAs) have important roles in regulating the expression of liver mRNAs in response to xenobiotic-exposure, but their roles concerning dioxins such as TCDD (2,3,7,8-Tetrachlorodibenzo-p-dioxin) are less clear. This report concerns the potential implication of liver (class I) and circulating (class II) miRNAs in hepatotoxicity of female and male mice after acute exposure to TCDD. The data show that, of a total of 38 types of miRNAs, the expression of eight miRNAs were upregulated in both female and male mice exposed to TCDD. Inversely, the expression of nine miRNAs were significantly downregulated in both animal genders. Moreover, certain miRNAs were preferentially induced in either females or males. The potential downstream regulatory effects of miRNAs on their target genes was evaluated by determining the expression of three group of genes that are potentially involved in cancer biogenesis, other diseases and in hepatotoxicity. It was found that certain cancer-related genes were more highly expressed females rather than males after exposure to TCDD. Furthermore, a paradoxical female-to-male transcriptional pattern was found for several disease-related and hepatotoxicity-related genes. These results suggest the possibility of developing of new miRNA-specific interfering molecules to address their dysfunctions as caused by TCDD.

Human pancreatic islet microRNAs implicated in diabetes and related traits by large-scale genetic analysis

Genetic studies have identified ≥240 loci associated with the risk of type 2 diabetes (T2D), yet most of these loci lie in non-coding regions, masking the underlying molecular mechanisms. Recent studies investigating mRNA expression in human pancreatic islets have yielded important insights into the molecular drivers of normal islet function and T2D pathophysiology. However, similar studies investigating microRNA (miRNA) expression remain limited. Here, we present data from 63 individuals, the largest sequencing-based analysis of miRNA expression in human islets to date. We characterized the genetic regulation of miRNA expression by decomposing the expression of highly heritable miRNAs into cis- and trans-acting genetic components and mapping cis-acting loci associated with miRNA expression [miRNA-expression quantitative trait loci (eQTLs)]. We found i) 84 heritable miRNAs, primarily regulated by trans-acting genetic effects, and ii) 5 miRNA-eQTLs. We also used several different strategies to identify T2D-associated miRNAs. First, we colocalized miRNA-eQTLs with genetic loci associated with T2D and multiple glycemic traits, identifying one miRNA, miR-1908, that shares genetic signals for blood glucose and glycated hemoglobin (HbA1c). Next, we intersected miRNA seed regions and predicted target sites with credible set SNPs associated with T2D and glycemic traits and found 32 miRNAs that may have altered binding and function due to disrupted seed regions. Finally, we performed differential expression analysis and identified 14 miRNAs associated with T2D status-including miR-187-3p, miR-21-5p, miR-668, and miR-199b-5p-and 4 miRNAs associated with a polygenic score for HbA1c levels-miR-216a, miR-25, miR-30a-3p, and miR-30a-5p.

Sex Differences in Molecular Mechanisms of Cardiovascular Aging

Cardiovascular disease (CVD) is still the leading cause of illness and death in the Western world. Cardiovascular aging is a progressive modification occurring in cardiac and vascular morphology and physiology where increased endothelial dysfunction and arterial stiffness are observed, generally accompanied by increased systolic blood pressure and augmented pulse pressure. The effects of biological sex on cardiovascular pathophysiology have long been known. The incidence of hypertension is higher in men, and it increases in postmenopausal women. Premenopausal women are protected from CVD compared with age-matched men and this protective effect is lost with menopause, suggesting that sex-hormones influence blood pressure regulation. In parallel, the heart progressively remodels over the course of life and the pattern of cardiac remodeling also differs between the sexes. Lower autonomic tone, reduced baroreceptor response, and greater vascular function are observed in premenopausal women than men of similar age. However, postmenopausal women have stiffer arteries than their male counterparts. The biological mechanisms responsible for sex-related differences observed in cardiovascular aging are being unraveled over the last several decades. This review focuses on molecular mechanisms underlying the sex-differences of CVD in aging.

Sexual dimorphism in liver cell cycle and senescence signalling pathways in young and old rats

At the molecular level, cellular ageing involves changes in multiple gene pathways. Cellular senescence is both an important initiator and a consequence of natural ageing. Senescence results in changes in multiple cellular mechanisms that result in a natural decrease in cell cycle activity. Liver senescence changes impair hepatic function. Given the well-established sexual dimorphism in ageing, we hypothesized that the natural hepatic ageing process is driven by sex-dependent gene mechanisms. We studied our well-characterized normal, chow-fed rat ageing model, lifespan ∼850 days, in which we have reported ageing of metabolism, reproduction and endocrine function. We performed liver RNA-seq on males and females at 110 and 650 days to determine changes in the cell cycle and cellular senescence signalling pathways. We found that natural liver ageing shows sexual dimorphism in these pathways. RNA-seq revealed more male (3967) than female (283) differentially expressed genes between 110 and 650 days. Cell cycle pathway signalling changes in males showed decreased protein and expression of key genes (Cdk2, Cdk4, Cycd and PCNA) and increased expression ofp57 at 650 vs 110 days. In females, protein and gene expression of cell growth regulators, e.g. p15 and p21, which inhibit cell cycle G1 progression, were increased. The cell senescence pathway also showed sexual dimorphism. Igfbp3, mTOR and p62 gene and protein expression decreased in males while those ofTgfb3 increased in females. Understanding the involvement of cell cycling and cellular senescence pathways in natural ageing will advance evaluation of mechanisms associated with altered ageing and frailty trajectories. KEY POINTS: In rats RNA-seq analysis showed sexual dimorphism in gene expression across the life-course between 110 and 650 days of life. Fourteen times more liver transcriptome and six times more pathway changes were observed in males compared with females. Significant changes were observed in several signalling pathways during ageing. Bioinformatic analysis were focused on changes in genes and protein products related to cell cycle and cellular senescence pathways. Males showed decreased protein product and expression of the key genes Cdk2 and Cdk4 responsible for cell cycle progression while females increased protein product and expression of p21 and p15, key genes responsible for cell cycle arrest. In conclusion, normative rat hepatic ageing involves changes in cellular pathways that control cell cycle arrest but through changes in different genes in males and females. These findings identify mechanisms that underlie the well-established sexual dimorphism in ageing.

Roles of microRNAs in carbohydrate and lipid metabolism disorders and their therapeutic potential

MicroRNAs (miRNAs) are small (∼21 nucleotides), endogenous, non-coding RNA molecules implicated in the post-transcriptional gene regulation performed through target mRNA cleavage or translational inhibition. In recent years, several investigations have demonstrated that miRNAs are involved in regulating both carbohydrate and lipid homeostasis in humans and other organisms. Moreover, it has been observed that the dysregulation of these metabolism-related miRNAs leads to the development of several metabolic disorders, such as type 2 diabetes, obesity, nonalcoholic fatty liver, insulin resistance, and hyperlipidemia. Hence, in this current review, with the aim to impulse the research arena of the micro-transcriptome implications in vital metabolic pathways as well as to highlight the remarkable potential of miRNAs as therapeutic targets for metabolic disorders in humans, we provide an overview of the regulatory roles of metabolism-associated miRNAs in humans and murine models.

Variation of microRNA expression in the human placenta driven by population identity and sex of the newborn

BACKGROUND

Analysis of lymphocyte cell lines revealed substantial differences in the expression of mRNA and microRNA (miRNA) among human populations. The extent of such population-associated differences in actual human tissues remains largely unexplored. The placenta is one of the few solid human tissues that can be collected in substantial numbers in a controlled manner, enabling quantitative analysis of transient biomolecules such as RNA transcripts. Here, we analyzed microRNA (miRNA) expression in human placental samples derived from 36 individuals representing four genetically distinct human populations: African Americans, European Americans, South Asians, and East Asians. All samples were collected at the same hospital following a unified protocol, thus minimizing potential biases that might influence the results.

RESULTS

Sequence analysis of the miRNA fraction yielded 938 annotated and 70 novel miRNA transcripts expressed in the placenta. Of them, 82 (9%) of annotated and 11 (16%) of novel miRNAs displayed quantitative expression differences among populations, generally reflecting reported genetic and mRNA-expression-based distances. Several co-expressed miRNA clusters stood out from the rest of the population-associated differences in terms of miRNA evolutionary age, tissue-specificity, and disease-association characteristics. Among three non-environmental influenced demographic parameters, the second largest contributor to miRNA expression variation after population was the sex of the newborn, with 32 miRNAs (3% of detected) exhibiting significant expression differences depending on whether the newborn was male or female. Male-associated miRNAs were evolutionarily younger and correlated inversely with the expression of target mRNA involved in neuron-related functions. In contrast, both male and female-associated miRNAs appeared to mediate different types of hormonal responses. Demographic factors further affected reported imprinted expression of 66 placental miRNAs: the imprinting strength correlated with the mother's weight, but not height.

CONCLUSIONS

Our results showed that among 12 assessed demographic variables, population affiliation and fetal sex had a substantial influence on miRNA expression variation among human placental samples. The effect of newborn-sex-associated miRNA differences further led to expression inhibition of the target genes clustering in specific functional pathways. By contrast, population-driven miRNA differences might mainly represent neutral changes with minimal functional impacts.

Genetic factors contributing to extensive variability of sex-specific hepatic gene expression in Diversity Outbred mice

Sex-specific transcription characterizes hundreds of genes in mouse liver, many implicated in sex-differential drug and lipid metabolism and disease susceptibility. While the regulation of liver sex differences by growth hormone-activated STAT5 is well established, little is known about autosomal genetic factors regulating the sex-specific liver transcriptome. Here we show, using genotyping and expression data from a large population of Diversity Outbred mice, that genetic factors work in tandem with growth hormone to control the individual variability of hundreds of sex-biased genes, including many long non-coding RNA genes. Significant associations between single nucleotide polymorphisms and sex-specific gene expression were identified as expression quantitative trait loci (eQTLs), many of which showed strong sex-dependent associations. Remarkably, autosomal genetic modifiers of sex-specific genes were found to account for more than 200 instances of gain or loss of sex-specificity across eight Diversity Outbred mouse founder strains. Sex-biased STAT5 binding sites and open chromatin regions with strain-specific variants were significantly enriched at eQTL regions regulating correspondingly sex-specific genes, supporting the proposed functional regulatory nature of the eQTL regions identified. Binding of the male-biased, growth hormone-regulated repressor BCL6 was most highly enriched at trans-eQTL regions controlling female-specific genes. Co-regulated gene clusters defined by overlapping eQTLs included sets of highly correlated genes from different chromosomes, further supporting trans-eQTL action. These findings elucidate how an unexpectedly large number of autosomal factors work in tandem with growth hormone signaling pathways to regulate the individual variability associated with sex differences in liver metabolism and disease.

Loss of TSC complex enhances gluconeogenesis via upregulation of Dlk1-Dio3 locus miRNAs

Loss of the tumor suppressor tuberous sclerosis complex 1 (Tsc1) in the liver promotes gluconeogenesis and glucose intolerance. We asked whether this could be attributed to aberrant expression of small RNAs. We performed small-RNA sequencing on liver of Tsc1-knockout mice, and found that miRNAs of the delta-like homolog 1 (Dlk1)-deiodinase iodothyronine type III (Dio3) locus are up-regulated in an mTORC1-dependent manner. Sustained mTORC1 signaling during development prevented CpG methylation and silencing of the Dlk1-Dio3 locus, thereby increasing miRNA transcription. Deletion of miRNAs encoded by the Dlk1-Dio3 locus reduced gluconeogenesis, glucose intolerance, and fasting blood glucose levels. Thus, miRNAs contribute to the metabolic effects observed upon loss of TSC1 and hyperactivation of mTORC1 in the liver. Furthermore, we show that miRNA is a downstream effector of hyperactive mTORC1 signaling.

miRMap: Profiling 14q32 microRNA Expression and DNA Methylation Throughout the Human Vasculature

Aims: MicroRNAs are regulators of (patho)physiological functions with tissue-specific expression patterns. However, little is known about inter-vascular differences in microRNA expression between blood vessel types or vascular beds. Differences in microRNA expression could influence cardiovascular pathophysiology at specific sites in the vasculature. Therefore, we aimed to map expression profiles of vasoactive 14q32 microRNAs throughout the human vasculature, as well as expression of vasoactive target genes of the 14q32 microRNAs. Furthermore, we aimed to map the DNA methylation status of the 14q32 locus, which has been linked to cardiovascular disease. Methods and Results: We collected 109 samples from different blood vessels, dissected during general surgery. Expression of a representative set of 17 14q32 microRNAs was measured in each sample. All 17 microRNAs showed a unique expression pattern throughout the vasculature. 14q32 microRNA expression was highest in lower limb vessels and lowest in head and neck vessels. All 17 microRNAs were expressed more abundantly in arteries than in veins. Throughout the human vasculature, we observed trends toward an inverse correlation between expression levels of the 14q32 microRNAs and their vasoactive target genes. DNA methylation of the 3 Differentially Methylated Regions (DMRs) along the 14q32 locus did not associate with primary or mature microRNA expression. However, hyper-methylation in venous coronary artery bypass grafts compared to arterial bypass grafts was observed in the Intergenic-DMR and MEG3-DMR. In patients with end-stage peripheral arterial disease we found differential DNA methylation throughout all DMRs in their lower limb veins. These findings were confirmed in a mouse model for vein-graft disease in which we found regulated 14q32 DNA methylation during the active phase of vascular remodeling. In ischemic tissues of a murine hind limb ischemia model we observed an increase in DNA methylation associated with increased ischemia over time. Conclusions: We show that 14q32 microRNAs are abundantly expressed in the human vasculature and that expression differs significantly between different blood vessels. 14q32 DNA methylation also varies throughout the vasculature and is associated with vascular health, independently of microRNA levels. These findings could have important implications for future research and for future site-specific targeting of epigenetics-based therapeutics.

Microarray analysis of genes from animals treated with a traditional formulation ChandraprabhaVati reveals its therapeutic targets

Background

Traditional medicinal preparations have not received global acceptance, and their therapeutic benefits remain disputed due to lack of scientific evidence on their mechanism of action. Microarray analysis has emerged as a powerful technique that can aid in understanding the complex signaling networks activated by these formulations and thereby assess their beneficial as well as adverse effects.

Aim

The present work aims to investigate the differential influence of ChandraprabhaVati, Ayurvedic formulation used in the treatment of diabetes, anemia, urinary, respiratory, skin and liver disorders.

Materials and methods

The RNA from the liver of rats treated with different doses of ChandraprabhaVati for 28 days was isolated and studied for the genome-wide changes in the expression.

Results

The results revealed several molecular targets that could contribute to the therapeutic effects of ChandraprabhaVati. Several genes have been differentially expressed, among those miRNAs miR-434, miR877, and miRlet7e contribute to the anti-diabetic, anti-fibrotic and anti-inflammatory of CPV. The rejuvenative activity of CPV may be due to the MeOX1 and Upf3b genes. Up-regulation of Hbaa2 gene facilitates the anti-anemic effect. Interestingly gender-specific differential expressions of genes were also observed. Rab3d were found to be altered in female when compared to male animals.

Conclusion

Thus the microarray data for the CPV treated animals has revealed molecular targets that may be responsible for the various known therapeutic effects and also identified new beneficial effects of CPV.

Microarray Profiling of Circular RNA Identifies hsa_circ_0126991 as a Potential Risk Factor for Essential Hypertension

Essential hypertension (EH), a major cause of cardiovascular diseases, is an important public health issue. However, the molecular mechanisms involved in EH remain unknown. Circular RNA (circRNA) is a novel promising biomarker for the disease. The purpose of the present study was to determine the expression of circRNAs in the blood of EH patients and to evaluate the performance of circRNA for early diagnosis of EH. A total of 178 subjects were recruited in the case-control study. Initial screening was done by using the Agilent human circRNA microarray followed by qRT-PCR validation. Finally, miRNAs were combined with circRNAs to create a new early prediction model for EH. The expression level of hsa_circ_0126991 in EH patients was significantly higher in comparison with healthy controls (p < 0.0001). Using the interaction of miR-10a-5p in combination with hsa_circ_0126991 led to a sensitivity of 0.708, a specificity of 0.764, and combined area under the curve of 0.774 (95% CI: 0.705-0.843) for early diagnosis of EH. In summary, the present study uncovered a novel perspective that hyperexpression of hsa_circ_0126991 is correlated with the risk of EH and may serve as a stable biomarker for early diagnosis of EH.

Gene-by-Sex Interactions in Mitochondrial Functions and Cardio-Metabolic Traits

We studied sex differences in over 50 cardio-metabolic traits in a panel of 100 diverse inbred strains of mice. The results clearly showed that the effects of sex on both clinical phenotypes and gene expression depend on the genetic background. In support of this, genetic loci associated with the traits frequently showed sex specificity. For example, Lyplal1, a gene implicated in human obesity, was shown to underlie a sex-specific locus for diet-induced obesity. Global gene expression analyses of tissues across the panel implicated adipose tissue "beiging" and mitochondrial functions in the sex differences. Isolated mitochondria showed gene-by-sex interactions in oxidative functions, such that some strains (C57BL/6J) showed similar function between sexes, whereas others (DBA/2J and A/J) showed increased function in females. Reduced adipose mitochondrial function in males as compared to females was associated with increased susceptibility to obesity and insulin resistance. Gonadectomy studies indicated that gonadal hormones acting in a tissue-specific manner were responsible in part for the sex differences.

Sex differences in metabolism and cardiometabolic disorders

PURPOSE OF REVIEW

Sex differences are pervasive in metabolic and cardiovascular traits, yet they have often been ignored in human and animal model research. Sex differences can arise from reversible hormonal effects, from irreversible organizational (developmental) processes, and from gene expression differences from the X and Y chromosomes. We briefly review our current understanding of the impact of these factors in metabolic traits and disorders, with an emphasis on the recent literature.

RECENT FINDINGS

Novel sex differences continue to be identified for metabolic and cardiovascular traits. For example, it is now clear that gut microbiota tend to differ between men and women, with potentially large implications for disease susceptibility. Also, tissue-specific gene regulation differs between men and women, contributing to differential metabolism. These new insights will open up personalized therapeutic avenues for cardiometabolic diseases.

SUMMARY

Sex differences in body fat distribution, glucose homeostasis, insulin signaling, ectopic fat accumulation, and lipid metabolism during normal growth and in response to hormonal or nutritional imbalance are mediated partly through sex hormones and the sex chromosome complement. Most of these differences are mediated in a tissue-specific manner. Important future goals are to better understand the interactions between genetic variation and sex differences, and to bring an understanding of sex differences into clinical practice.

Combined seven miRNAs for early hepatocellular carcinoma detection with chronic low-dose exposure to microcystin-LR in mice

Aberrant miRNA expression has been detected in various tumor tissues, which may be considered as a marker for early cancer diagnosis. One miRNA has multiple downstream target genes, which can be regulated by multiple upstream other miRNAs. Hence, this dynamic regulation is likely characterized by volatility, and thus, finding the appropriate time point for tests becomes essential for the use of miRNAs as an early marker of tumor diagnosis. In this study, we established a chronic liver cancer progression model in mice by using low doses of the harmful substance microcystin-LR (MC-LR). On the basis of miRNAs microarray assay, we further tested seven miRNAs that showed characteristic expression changes in pre-hepatocarcinogenesis. Our results showed that the levels of four miRNAs (miR-122-5p, miR-125-5p, miR-199a-5p, and miR-503-5p) decreased dramatically, whereas those of two miRNAs (miR-222-5p and miR-590-5p) increased significantly in the early stages, which were all accompanied by an increase in atypia of hepatocytes. MiR-490-5p was a sensitive molecular, suitable only for evaluation of pathological changes in young mice. Therefore the combination the seven of miRNAs for a set may prove to be an effective method in healthy assessment of environmental toxicants for detection of hepatocarcinogenesis caused by hazardous materials.

Functional Roles of Sex-Biased, Growth Hormone-Regulated MicroRNAs miR-1948 and miR-802 in Young Adult Mouse Liver

Sex-specific temporal patterns of pituitary growth hormone (GH) secretion determine the sex-biased transcription of hundreds of genes in the liver and impart important sex differences in liver physiology, metabolism, and disease. Sex differences in hepatic gene expression vary widely, ranging from less than twofold to >1000-fold in the mouse. Here, we use small RNA sequencing to discover 24 sex-biased mouse liver microRNAs (miRNAs), and then investigate the roles of two of these miRNAs in GH-regulated liver sex differences. Studies in prepubertal and young adult mice, and in mice in which pituitary hormones are ablated or where sex-specific hepatic GH signaling is dysregulated, demonstrated that the male-biased miR-1948 and the female-biased miR-802 are both regulated by sex-specific pituitary GH secretory patterns, acquire sex specificity at puberty, and are dependent on the GH-activated transcription factor STAT5 for their sex-specific expression. Both miRNAs are within genomic regions characterized by sex-biased chromatin accessibility. miR-1948, an uncharacterized miRNA, has essential features for correct Drosha/Dicer processing, generates a bona fide mature miRNA with strong strand bias for the 5p arm, and is bound by Argonaute in liver tissue, as is miR-802. In vivo studies using inhibitory locked nucleic acid sequences revealed that miR-1948-5p preferentially represses female-biased messenger RNAs (mRNAs) and induces male-biased mRNAs in male liver; conversely, miR-802-5p preferentially represses male-biased mRNAs and increases levels of female-biased mRNAs in female liver. Cytochrome P450 mRNAs were strongly enriched as targets of both miRNAs. Thus, miR-1948-5p and miR-802-5p are functional components of the GH regulatory network that shapes sex-differential gene expression in mouse liver.

Sex-specific differences in hypertension and associated cardiovascular disease

Although intrinsic mechanisms that regulate arterial blood pressure (BP) are similar in men and women, marked variations exist at the molecular, cellular and tissue levels. These physiological disparities between the sexes likely contribute to differences in disease onset, susceptibility, prevalence and treatment responses. Key systems that are important in the development of hypertension and cardiovascular disease (CVD), including the sympathetic nervous system, the renin-angiotensin-aldosterone system and the immune system, are differentially activated in males and females. Biological age also contributes to sexual dimorphism, as premenopausal women experience a higher degree of cardioprotection than men of similar age. Furthermore, sex hormones such as oestrogen and testosterone as well as sex chromosome complement likely contribute to sex differences in BP and CVD. At the cellular level, differences in cell senescence pathways may contribute to increased longevity in women and may also limit organ damage caused by hypertension. In addition, many lifestyle and environmental factors - such as smoking, alcohol consumption and diet - may influence BP and CVD in a sex-specific manner. Evidence suggests that cardioprotection in women is lost under conditions of obesity and type 2 diabetes mellitus. Treatment strategies for hypertension and CVD that are tailored according to sex could lead to improved outcomes for affected patients.

Sex-biased microRNA expression in mammals and birds reveals underlying regulatory mechanisms and a role in dosage compensation

Sexual dimorphism depends on sex-biased gene expression, but the contributions of microRNAs (miRNAs) have not been globally assessed. We therefore produced an extensive small RNA sequencing data set to analyze male and female miRNA expression profiles in mouse, opossum, and chicken. Our analyses uncovered numerous cases of somatic sex-biased miRNA expression, with the largest proportion found in the mouse heart and liver. Sex-biased expression is explained by miRNA-specific regulation, including sex-biased chromatin accessibility at promoters, rather than piggybacking of intronic miRNAs on sex-biased protein-coding genes. In mouse, but not opossum and chicken, sex bias is coordinated across tissues such that autosomal testis-biased miRNAs tend to be somatically male-biased, whereas autosomal ovary-biased miRNAs are female-biased, possibly due to broad hormonal control. In chicken, which has a Z/W sex chromosome system, expression output of genes on the Z Chromosome is expected to be male-biased, since there is no global dosage compensation mechanism that restores expression in ZW females after almost all genes on the W Chromosome decayed. Nevertheless, we found that the dominant liver miRNA, miR-122-5p, is Z-linked but expressed in an unbiased manner, due to the unusual retention of a W-linked copy. Another Z-linked miRNA, the male-biased miR-2954-3p, shows conserved preference for dosage-sensitive genes on the Z Chromosome, based on computational and experimental data from chicken and zebra finch, and acts to equalize male-to-female expression ratios of its targets. Unexpectedly, our findings thus establish miRNA regulation as a novel gene-specific dosage compensation mechanism.

Splicing regulatory factors, ageing and age-related disease

Alternative splicing is a co-transcriptional process, which allows for the production of multiple transcripts from a single gene and is emerging as an important control point for gene expression. Alternatively expressed isoforms often have antagonistic function and differential temporal or spatial expression patterns, yielding enormous plasticity and adaptability to cells and increasing their ability to respond to environmental challenge. The regulation of alternative splicing is critical for numerous cellular functions in both pathological and physiological conditions, and deregulated alternative splicing is a key feature of common chronic diseases. Isoform choice is controlled by a battery of splicing regulatory proteins, which include the serine arginine rich (SRSF) proteins and the heterogeneous ribonucleoprotein (hnRNP) classes of genes. These important splicing regulators have been implicated in age-related disease, and in the ageing process itself. This review will outline the important contribution of splicing regulator proteins to ageing and age-related disease.

Comparative microRNAome analysis of the testis and ovary of the Chinese giant salamander

MicroRNAs (miRNAs) are 18-24 nucleotides non-coding RNAs that regulate gene expression by post-transcriptional suppression of mRNA. The Chinese giant salamander (CGS, Andrias davidianus), which is an endangered species, has become one of the important models of animal evolution; however, no miRNA studies on this species have been conducted. In this study, two small RNA libraries of CGS ovary and testis were constructed using deep sequencing technology. A bioinformatics pipeline was developed to distinguish miRNA sequences from other classes of small RNAs represented in the sequencing data. We found that many miRNAs and other small RNAs such as piRNA and tsRNA were abundant in CGS tissue. A total of 757 and 756 unique miRNAs were annotated as miRNA candidates in the ovary and testis respectively. We identified 145 miRNAs in CGS ovary and 155 miRNAs in CGS testis that were homologous to those in Xenopus laevis ovary and testis respectively. Forty-five miRNAs were more highly expressed in ovary than in testis and 21 miRNAs were more highly expressed in testis than in ovary. The expression profiles of the selected miRNAs (miR-451, miR-10c, miR-101, miR-202, miR-7a and miR-499) had their own different roles in other eight tissues and different development stages of testis and ovary, suggesting that these miRNAs play vital regulatory roles in sexual differentiation, gametogenesis and development in CGS. To our knowledge, this is the first study to reveal miRNA profiles that are related to male and female CGS gonads and provide insights into sex differences in miRNA expression in CGS.