Similarity and variation in the insulin-like growth factor 2 - H19 locus in primates

Imprinting of canine IGF2 and H19

Genomic imprinting occurs in therian mammals and is a phenomenon whereby the two alleles of a gene are differentially expressed, based on the sex of the parent from whom the alleles were inherited. The allelic differences in expression are the consequence of different epigenetic modifications that are established in the sperm or oocyte during gametogenesis and transmitted at fertilization to offspring. A small minority of genes is regulated in this way but they have important biological functions, and aberrant regulation of imprinted genes contributes to disease aetiology in humans and other animals. The factors driving the evolution of imprinted genes are also of considerable interest, as these genes appear to forego the benefits of diploidy. To broaden the phylogenetic analysis of genomic imprinting, we began a study of imprinted genes in the domestic dog, Canis familiaris. In this report, we show that canine IGF2 and H19 are imprinted, with parent-of origin-dependent monoallelic expression patterns in neonatal umbilical cord. We identify a putative imprint control region associated with the genes, and provide evidence for differential methylation of this region in a somatic tissue (umbilical cord) and for its hypermethylation in the male germline. Canis familiaris is fast becoming a highly informative system for elucidating disease processes and evolution, and the study of imprinted genes in this species may help in understanding how these genes contribute to the generation of morphological and behavioral diversity.

Regulation of gene expression by growth hormone

Growth hormone (GH) plays a pivotal role in many physiological processes in humans, and in other mammalian and non-mammalian vertebrate species, through actions on somatic growth, tissue development and repair, and intermediary metabolism. This review will focus on mechanisms of GH actions on gene expression, primarily from the perspective of the genes that encode proteins stimulated by GH to regulate somatic growth, especially insulin-like growth factor 1 (IGF-I), but also others that are induced or repressed by GH. Topics to be discussed will include a brief overview of GH-mediated signal transduction pathways and how these cascades alter the functions of responsive transcription factors, with a specific focus on STAT5B, a key member of the signal transducers and activators of transcription family, characterization of essential GH-regulated genes, and elucidation of mechanisms of their regulation from biochemical, genetic, and genomic perspectives.

Insulin-Like Growth Factor 2 (IGF2) Signaling in Colorectal Cancer-From Basic Research to Potential Clinical Applications

Colorectal cancer (CRC) is one of the most common cancers in men and women worldwide as well as is the leading cause of death in the western world. Almost a third of the patients has or will develop liver metastases. While genetic as well as epigenetic mechanisms are important in CRC pathogenesis, the basis of the most cases of cancer is unknown. High spatial and inter-patient variability of the molecular alterations qualifies this cancer in the group of highly heterogeneous tumors, which makes it harder to elucidate the mechanisms underlying CRC progression. Determination of highly sensitive and specific early diagnosis markers and understanding the cellular and molecular mechanism(s) of cancer progression are still a challenge of the current era in oncology of solid tumors. One of the accepted risk factors for CRC development is overexpression of insulin-like growth factor 2 (IGF2), a 7.5-kDa peptide produced by liver and many other tissues. IGF2 is the first gene discovered to be parentally imprinted. Loss of imprinting (LOI) or aberrant imprinting of IGF2 could lead to IGF2 overexpression, increased cell proliferation, and CRC development. IGF2 as a mitogen is associated with increased risk of developing colorectal neoplasia. Higher serum IGF2 concentration as well as its tissue overexpression in CRC compared to control are associated with metastasis. IGF2 protein was one of the three candidates for a selective marker of CRC progression and staging. Recent research indicates dysregulation of different micro- and long non-coding RNAs (miRNAs and lncRNAs, respectively) embedded within the IGF2 gene in CRC carcinogenesis, with some of them indicated as potential diagnostic and prognostic CRC biomarkers. This review systematises the knowledge on the role of genetic and epigenetic instabilities of IGF2 gene, free (active form of IGF2) and IGF-binding protein (IGFBP) bound (inactive form), paracrine/autocrine secretion of IGF2, as well as mechanisms of inducing dysplasia in vitro and tumorigenicity in vivo. We have tried to answer which molecular changes of the IGF2 gene and its regulatory mechanisms have the most significance in initiation, progression (including liver metastasis), prognosis, and potential anti-IGF2 therapy in CRC patients.

Long non-coding RNA H19 is associated with polycystic ovary syndrome in Chinese women: a preliminary study

Polycystic ovary syndrome (PCOS) represents a serious reproductive and endocrine condition and is associated with high incidence rates. H19 is a compelling long noncoding RNA (lncRNA) which carries out a range of biological functions. However, prior to this study, little was known as to whether there was an association between lncRNA H19 and PCOS. In the current study, we used quantitative real-time polymerase chain reaction (qRT-PCR) to determine lncRNA H19 expression levels in peripheral blood leukocytes from patients with PCOS and compared this data with that derived from normal controls. We also screened data for potential relationships between lncRNA H19 and a range of endocrine variables in PCOS. The expression of lncRNA H19 was significantly higher in cases of PCOS than in controls. Individuals exhibiting higher expression levels of lncRNA H19 were associated with a significantly higher risk of PCOS than those with lower expression levels. Moreover, lncRNA H19 expression was positively correlated with fasting plasma glucose levels; this was the case with both raw data, and after adjustment for age and BMI in the PCOS group. However, lncRNA H19 expression showed no significant correlation with total testosterone or insulin resistance in either PCOS cases or the controls. In conclusion, we demonstrate the first evidence to indicate that lncRNA H19 is associated with PCOS, suggesting that elevated lncRNA H19 levels are a risk factor for PCOS. For susceptible individuals, lncRNA H19 may represent a useful biomarker of the early stages of endocrine and metabolic disorders in PCOS.

The insulin-like growth factor 2 gene in mammals: Organizational complexity within a conserved locus

The secreted protein, insulin-like growth factor 2 (IGF2), plays a central role in fetal and prenatal growth and development, and is regulated at the genetic level by parental imprinting, being expressed predominantly from the paternally derived chromosome in mice and humans. Here, IGF2/Igf2 and its locus has been examined in 19 mammals from 13 orders spanning ~166 million years of evolutionary development. By using human or mouse DNA segments as queries in genome analyses, and by assessing gene expression using RNA-sequencing libraries, more complexity was identified within IGF2/Igf2 than was annotated previously. Multiple potential 5’ non-coding exons were mapped in most mammals and are presumably linked to distinct IGF2/Igf2 promoters, as shown for several species by interrogating RNA-sequencing libraries. DNA similarity was highest in IGF2/Igf2 coding exons; yet, even though the mature IGF2 protein was conserved, versions of 67 or 70 residues are produced secondary to species-specific maintenance of alternative RNA splicing at a variable intron-exon junction. Adjacent H19 was more divergent than IGF2/Igf2, as expected in a gene for a noncoding RNA, and was identified in only 10/19 species. These results show that common features, including those defining IGF2/Igf2 coding and several non-coding exons, were likely present at the onset of the mammalian radiation, but that others, such as a putative imprinting control region 5’ to H19 and potential enhancer elements 3’ to H19, diversified with speciation. This study also demonstrates that careful analysis of genomic and gene expression repositories can provide new insights into gene structure and regulation.

Quantifying promoter-specific Insulin-like Growth Factor 1 gene expression by interrogating public databases

The actions of insulin-like growth factor 1 (IGF1), a small, secreted protein, are essential for normal somatic growth in children and are important for tissue regeneration and repair in adults. Similar functions are conserved in other mammalian species. IGF1 gene regulation is complicated in mammals, with transcription being controlled by different hormonal, nutritional, and tissue-specific inputs. Quantifying IGF1 gene expression in different organs and tissues also has been difficult because of the variable contributions of its two promoters and because of the lack of standard platforms for analysis. Here, I have taken advantage of the wealth of information found in publicly accessible RNA-sequencing libraries to measure steady-state levels of IGF1 mRNAs from human and macaque, species chosen because they are not readily tractable experimental organisms, yet retain similar IGF1 gene organization. Results demonstrate that IGF1 transcripts are highly expressed in fat and liver in both species, and are induced during human adipocyte differentiation. IGF1 mRNAs also are increased in macaque skeletal muscle after selected dietary manipulations. In the organs and tissues examined, IGF1 promoter 1 appears to be far more active than promoter 2. Collectively, these observations show that interrogating large-scale public genomic resources is an effective strategy for quantifying gene expression across different tissues and species.

The insulin-like growth factor 2 gene and locus in nonmammalian vertebrates: Organizational simplicity with duplication but limited divergence in fish

The small, secreted peptide, insulin-like growth factor 2 (IGF2), is essential for fetal and prenatal growth in humans and other mammals. Human IGF2 and mouse Igf2 genes are located within a conserved linkage group and are regulated by parental imprinting, with IGF2/Igf2 being expressed from the paternally derived chromosome, and H19 from the maternal chromosome. Here, data retrieved from genomic and gene expression repositories were used to examine the Igf2 gene and locus in 8 terrestrial vertebrates, 11 ray-finned fish, and 1 lobe-finned fish representing >500 million years of evolutionary diversification. The analysis revealed that vertebrate Igf2 genes are simpler than their mammalian counterparts, having fewer exons and lacking multiple gene promoters. Igf2 genes are conserved among these species, especially in protein-coding regions, and IGF2 proteins also are conserved, although less so in fish than in terrestrial vertebrates. The Igf2 locus in terrestrial vertebrates shares additional genes with its mammalian counterparts, including tyrosine hydroxylase (Th), insulin (Ins), mitochondrial ribosomal protein L23 (Mrpl23), and troponin T3, fast skeletal type (Tnnt3), and both Th and Mrpl23 are present in the Igf2 locus in fish. Taken together, these observations support the idea that a recognizable Igf2 was present in the earliest vertebrate ancestors, but that other features developed and diversified in the gene and locus with speciation, especially in mammals. This study also highlights the need for correcting inaccuracies in genome databases to maximize our ability to accurately assess contributions of individual genes and multigene families toward evolution, physiology, and disease.