Insulin-like growth factor signaling regulates zebrafish embryonic growth and development by promoting cell survival and cell cycle progression

The Critical Balance Between Quiescence and Reactivation of Neural Stem Cells

Neural stem cells (NSC) are multipotent, self-renewing cells that give rise to all neural cell types within the central nervous system. During adulthood, most NSCs exist in a quiescent state which can be reactivated in response to metabolic and signalling changes, allowing for long-term continuous neurogenesis and response to injury. Ensuring a critical balance between quiescence and reactivation is required to maintain the limited NSC reservoir and neural replenishment throughout lifetime. The precise mechanisms and signalling pathways behind this balance are at the focus of current research. In this review, we highlight and discuss recent studies using Drosophila, mammalian and zebrafish models contributing to the understanding of molecular mechanisms underlying quiescence and reactivation of NSCs.

Thyroid and growth hormone endocrine disruption and mechanisms of homosalate and octisalate using wild-type, thrαa-/-, and dre-miR-499-/- zebrafish embryo/larvae

Homosalate (HS) and octisalate (OS), which are used in sunscreen for the purpose of blocking ultraviolet rays, are frequently detected in water environment. Although effects on estrogens and androgens have been reported, studies on thyroid and growth hormone endocrine disruption are limited. In the present study, larval mortality was compared in wild-type and two knockout fish (thyroid hormone receptor alpha a knockout (thrαa-/-) and dre-miR-499 knockout (dre-miR-499-/-)) after 96 h of exposure to HS and OS (0, 0.003, 0.03, 0.3, 3, 30 and 300 µg/L). To investigate the mechanisms of thyroid and growth hormone endocrine disruption, we measured the levels of triiodothyronine (T3), thyroxine (T4), thyroid stimulating hormone (TSH), growth hormone (GH), and insulin-like growth factor-1 (IGF-1), and the regulation of representative genes related to the hypothalamus-pituitary-thyroid (HPT) and GH/IGF axis in wild-type zebrafish exposed to target chemicals. The significantly lower larval survival rate of thrαa-/- and dre-miR-499-/- fish exposed to 300 μg/L of HS and OS suggest that thyroid hormone receptors and dre-miR-499 play a crucial role in the toxic effects of HS and OS. The finding of a significant increase in T3 and T4 in zebrafish larvae exposed to HS and OS supports a significant decrease in the crh gene. The reduction of GH and IGF-1 in fish exposed to HS and OS is well supported by the regulation of genes involved in the GH/IGF axis. Our observations suggest that exposure to HS and OS affects not only thyroid hormone receptors and their associated miRNAs, but also the feedback routes of HPT and GH/IGF axes, ultimately leading to growth reduction.

Insulin signaling in development

Nutrient intake is obligatory for animal growth and development, but nutrients alone are not sufficient. Indeed, insulin and homologous hormones are required for normal growth even in the presence of nutrients. These hormones communicate nutrient status between organs, allowing animals to coordinate growth and metabolism with nutrient supply. Insulin and related hormones, such as insulin-like growth factors and insulin-like peptides, play important roles in development and metabolism, with defects in insulin production and signaling leading to hyperglycemia and diabetes. Here, we describe the insulin hormone family and the signal transduction pathways activated by these hormones. We highlight the roles of insulin signaling in coordinating maternal and fetal metabolism and growth during pregnancy, and we describe how secretion of insulin is regulated at different life stages. Additionally, we discuss the roles of insulin signaling in cell growth, stem cell proliferation and cell differentiation. We provide examples of the role of insulin in development across multiple model organisms: Caenorhabditis elegans, Drosophila, zebrafish, mouse and human.

IGF-1 receptor inhibitor OSI-906 reduces growth in nestlings of a wild passerine

Young animals need to grow to a large body size fast to maximise their survival prospects until sexual maturity. However, body size varies substantially in wild populations, and neither the selection pressures maintaining this variation, nor the regulatory mechanisms are well understood. IGF-1 administration has been shown to accelerate growth, but this does not necessarily imply that natural variation in growth rate is IGF-1 dependent. To test the latter we administered OSI-906 to pied flycatcher Ficedula hypoleuca nestlings, which has an inhibitory effect on IGF-1 receptor activity. We performed the experiment in two breeding seasons to test the prediction that blocking the IGF-1 receptor downregulates growth. As predicted, OSI-906 treated nestlings had lower body mass and reached a smaller structural size than siblings receiving a vehicle only, with the mass difference being most profound at the age preceding the highest body mass growth rate. The IGF-1 receptor inhibition effect on growth varied with age and year of study, and we discuss possible explanations. The OSI-906 administration results indicate that natural variation in growth rate is regulated by IGF-1, and constitutes a novel tool to study causes and consequences of growth variation, but details of the underlying mechanism still need to be resolved.

The neurobiology of insulin-like growth factor I: From neuroprotection to modulation of brain states

After decades of research in the neurobiology of IGF-I, its role as a prototypical neurotrophic factor is undisputed. However, many of its actions in the adult brain indicate that this growth factor is not only involved in brain development or in the response to injury. Following a three-layer assessment of its role in the central nervous system, we consider that at the cellular level, IGF-I is indeed a bona fide neurotrophic factor, modulating along ontogeny the generation and function of all the major types of brain cells, contributing to sculpt brain architecture and adaptive responses to damage. At the circuit level, IGF-I modulates neuronal excitability and synaptic plasticity at multiple sites, whereas at the system level, IGF-I intervenes in energy allocation, proteostasis, circadian cycles, mood, and cognition. Local and peripheral sources of brain IGF-I input contribute to a spatially restricted, compartmentalized, and timed modulation of brain activity. To better define these variety of actions, we consider IGF-I a modulator of brain states. This definition aims to reconcile all aspects of IGF-I neurobiology, and may provide a new conceptual framework in the design of future research on the actions of this multitasking neuromodulator in the brain.

Chronic estrone exposure affects spermatogenesis and sperm quality in zebrafish (Danio rerio)

Estrone (E1) is a common environmental contaminant found in rivers and streams due to the farming of animals, such as swine and cattle. Our study evaluated the effects of chronic E1 exposure at environmentally relevant concentrations on spermatogenesis and the semen quality of zebrafish (Danio rerio). We exposed the fish to E1 at concentrations of 20, 200, and 2000 ng/L diluted in 0.001% ethanol (v/v) for 49 days. There were two control groups: one was exposed to water only and the other to ethanol at the same concentration used in the E1 groups. Following exposure, we analyzed the proportion of testicular cell types and other components (%), rate of cell proliferation and death, and sex steroid concentrations. Furthermore, we analyzed the expression of insulin-like growth factor 1 (IGF1), IGF2, IGF1 receptor (IGF1R), and inducible nitric oxide synthase and assessed the semen quality. E1 exposure increased spermatogonia, spermatids, Sertoli cells, Leydig cells, and the proportion of inflammatory infiltrate but decreased the spermatozoa amount. These changes were reflected by reductions in the gonadosomatic index and levels of 11-ketotestosterone in the testes. On the other hand, E1 exposure increased testicular estradiol, IGF1R expression, and nitric oxide production. After an evaluation using a computer-assisted sperm analysis (CASA) system, we observed reduced progressive motility, curvilinear velocity, and beat cross frequency of 20 and 2000 ng/L E1 groups. Our findings support that E1 causes deleterious effects on the testicular function and semen quality of D. rerio even at environmental concentrations. Thus, E1 concentrations should be monitored in surface waters for the purposes of fish conservation.

Concordant patterns of morphological, stable isotope, and genetic variation in a recent ecological radiation (Salmonidae: Coregonus spp.)

Groups of sympatric taxa with low inter-specific genetic differentiation, but considerable ecological differences, offer great opportunities to study the dynamics of divergence and speciation. This is the case of ciscoes (Coregonus spp.) in the Laurentian Great Lakes, which are characterized by a complex evolutionary history and are commonly described as having undergone an adaptive radiation. In this study, morphometrics, stable isotopes and transcriptome sequencing were used to study the relationships within the Coregonus artedi complex in western Lake Superior. We observed general concordance for morphological, ecological and genomic variation, but the latter was more taxonomically informative as it showed less overlap among species in multivariate space. Low levels of genetic differentiation were observed between individuals morphologically identified as C. hoyi and C. zenithicus, which could be evidence of incomplete lineage sorting or recent hybridization between the two groups. Transcriptome-based single nucleotide polymorphisms exhibited significant divergence for genes associated with vision, development, metabolism and immunity among species that occupy different habitats. This study highlights the importance of using an integrative approach when studying groups of taxa with a complex evolutionary history, as individual-level analyses of multiple independent datasets can provide a clearer picture of the patterns and processes associated with the origins of biodiversity.

Thyroid disruption and growth inhibition of zebrafish embryos/larvae by phenanthrene treatment at environmentally relevant concentrations

Phenanthrene induces reproductive and developmental toxicity in fish, but whether it can disrupt the thyroid hormone balance and inhibit growth had not been determined to date. In this study, zebrafish embryos were exposed to phenanthrene (0, 0.1, 1, 10 and 100 μg/L) for 7 days. The results of this experiment demonstrated that phenanthrene induced thyroid disruption and growth inhibition in zebrafish larvae. Phenanthrene significantly decreased the concentration of l-thyroxine (T4) but increased that of 3,5,3'-l-triiodothyronine (T3). The expression of genes related to the hypothalamic-pituitary-thyroid (HPT) axis was altered in zebrafish larvae exposed to phenanthrene. Moreover, phenanthrene exposure significantly increased the malformation rate and significantly reduced the survival rate and the body length of zebrafish larvae. Furthermore, phenanthrene significantly decreased the concentrations of growth hormone (GH) and insulin-like growth factor-1 (IGF-1). Changes observed in gene expression patterns further support the hypothesis that these effects may be related to alterations along the GH/IGF-1 axis. In conclusion, our study indicated that exposure to phenanthrene at concentrations as low as 0.1 μg/L resulted in thyroid disruption and growth inhibition in zebrafish larvae. Therefore, the estimation of phenanthrene levels in the aquatic environment needs to be revisited.

Igf signaling couples retina growth with body growth by modulating progenitor cell division

How the body and organs balance their relative growth is of key importance for coordinating size and function. This is of particular relevance in organisms, which continue to grow over their entire life span. We addressed this issue in the neuroretina of medaka fish (Oryzias latipes), a well-studied system with which to address vertebrate organ growth. We reveal that a central growth regulator, Igf1 receptor (Igf1r), is necessary and sufficient for proliferation control in the postembryonic retinal stem cell niche: the ciliary marginal zone (CMZ). Targeted activation of Igf1r signaling in the CMZ uncouples neuroretina growth from body size control, and we demonstrate that Igf1r operates on progenitor cells, stimulating their proliferation. Activation of Igf1r signaling increases retinal size while preserving its structural integrity, revealing a modular organization in which progenitor differentiation and neurogenesis are self-organized and highly regulated. Our findings position Igf signaling as a key module for controlling retinal size and composition, with important evolutionary implications.

Highlighted Article: Targeted activation of Igf1r signaling in the retinal stem cell niche increases retina size through expanding the progenitor but not stem cell population.

Polymorphisms in genes involved in breast cancer among Iranian patients

This review gives a summary of the important genetic polymorphisms in breast cancer with a focus on people in Iran. Several single nucleotide polymorphisms were considered as breast cancer susceptibility polymorphisms within genes (STK15, ERRs, ESR1, p53, SEP15, AURKA, SHBG, SRC, FAS, VEGF, XRCC1, GST, NFκB1, XPC, XRCC3, sirtuin-3, NKG2D). Cytosine-adenine repeat (IGF-I), rs3877899, G-2548A, GGC (eRF3a/GSPT1), IVS2nt-124A/G have shown an increased risk of breast cancers and a decreased risk has been observed in 4G/5G (PAI-1), rs6505162, tri-nucleotide (GCG TGFBR1). We observed that the signaling pathways and antioxidant related genes are the main molecular processes associated with breast cancer progression. Further studies on types of polymorphisms in breast cancer could validate the prognostic value of biomarkers.

Zebrafish (Danio rerio) as a Model for Understanding the Process of Caudal Fin Regeneration

After its introduction for scientific investigation in the 1950s, the cypriniform zebrafish, Danio rerio, has become a valuable model for the study of regenerative processes and mechanisms. Zebrafish exhibit epimorphic regeneration, in which a nondifferentiated cell mass formed after amputation is able to fully regenerate lost tissue such as limbs, heart muscle, brain, retina, and spinal cord. The process of limb regeneration in zebrafish comprises several stages characterized by the activation of specific signaling pathways and gene expression. We review current research on key factors in limb regeneration using zebrafish as a model.

Expression of acid-labile subunit (ALS) in developing and adult zebrafish and its role in dorso-ventral patterning during development

Mammalian acid-labile subunit (ALS) is a serum protein that binds binary complexes between Insulin-like growth factors (IGFs) and Insulin-like growth factor-binding proteins (IGFBPs) extending their half-life and keeping them in the vasculature. Human ALS deficiency (ACLSD), due to homozygous or compound heterozygous mutations in IGFALS, leads to moderate short stature with reduced levels of IGF-I and IGFBP-3. There is only one corresponding zebrafish ortholog gene and it has not yet been studied. In this study we elucidate the role of igfals during zebrafish development. In zebrafish embryos igfals mRNA is expressed throughout development, mainly in the brain and subsequently also in the gut and swimbladder. To determine its role during development, we knocked down igfals gene product using morpholinos (MOs). Igfals morphant embryos displayed dorsalization in different degrees of severity, including a shortened trunk and loss of tail. Furthermore, co-injection of human IGFALS (hIGFALS) mRNA was able to rescue the MO-induced phenotype. Finally, overexpression of either hIGFALS or zebrafish igfals (zigfals) mRNA leads to ventralization of embryos including a reduced head and enlarged tail. These findings suggest that als plays an important role in dorso-ventral patterning during zebrafish development.

Insulin-like growth factor 1 of wild vertebrates in a life-history context

Broad variation in intra- and interspecific life-history traits is largely shaped by resource limitation and the ensuing allocation trade-offs that animals are forced to make. Insulin-like growth factor 1 (IGF-1), a growth-hormone-dependent peptide, may be a key player in the regulation of allocation processes. In laboratory animals, the effects of IGF-1 on growth- and development (positive), reproduction (positive), and longevity (negative) are well established. We here review the evidence on these effects in wild vertebrates, where animals are more likely to face resource limitation and other challenges. We point out the similarities and dissimilarities in patterns of IGF-1 functions obtained in these two different study settings and discuss the knowledge we need to develop a comprehensive picture of the role of IGF-1 in mediating life-history variation of wild vertebrates.

Limitations and Promise of Retinal Tissue From Human Pluripotent Stem Cells for Developing Therapies of Blindness

The self-formation of retinal tissue from pluripotent stem cells generated a tremendous promise for developing new therapies of retinal degenerative diseases, which previously seemed unattainable. Together with use of induced pluripotent stem cells or/and CRISPR-based recombineering the retinal organoid technology provided an avenue for developing models of human retinal degenerative diseases "in a dish" for studying the pathology, delineating the mechanisms and also establishing a platform for large-scale drug screening. At the same time, retinal organoids, highly resembling developing human fetal retinal tissue, are viewed as source of multipotential retinal progenitors, young photoreceptors and just the whole retinal tissue, which may be transplanted into the subretinal space with a goal of replacing patient's degenerated retina with a new retinal "patch." Both approaches (transplantation and modeling/drug screening) were projected when Yoshiki Sasai demonstrated the feasibility of deriving mammalian retinal tissue from pluripotent stem cells, and generated a lot of excitement. With further work and testing of both approaches in vitro and in vivo, a major implicit limitation has become apparent pretty quickly: the absence of the uniform layer of Retinal Pigment Epithelium (RPE) cells, which is normally present in mammalian retina, surrounds photoreceptor layer and develops and matures first. The RPE layer polarize into apical and basal sides during development and establish microvilli on the apical side, interacting with photoreceptors, nurturing photoreceptor outer segments and participating in the visual cycle by recycling 11-trans retinal (bleached pigment) back to 11-cis retinal. Retinal organoids, however, either do not have RPE layer or carry patches of RPE mostly on one side, thus directly exposing most photoreceptors in the developing organoids to neural medium. Recreation of the critical retinal niche between the apical RPE and photoreceptors, where many retinal disease mechanisms originate, is so far unattainable, imposes clear limitations on both modeling/drug screening and transplantation approaches and is a focus of investigation in many labs. Here we dissect different retinal degenerative diseases and analyze how and where retinal organoid technology can contribute the most to developing therapies even with a current limitation and absence of long and functional outer segments, supported by RPE.

Characterization of Insulin-Like Growth Factor Binding Protein 7 (Igfbp7) and Its Potential Involvement in Shell Formation and Metamorphosis of Pacific Abalone, Haliotis discus hannai

Insulin-like growth factor binding proteins (IGFBPs) are secreted proteins that play an important role in IGF regulation of growth and development of vertebrate and invertebrates. In this study, the IGFBP7 gene was cloned and characterized from mantle tissues of H. discus hannai, and designated as Hdh IGFBP7. The full-length cDNA sequence transcribed from the Hdh IGFBP7 gene was 1519-bp long with an open reading frame of 720-bp corresponding to a putative polypeptide of 239 amino acids. The molecular mass of its mature protein was approximately 23.44 KDa with an estimated isoelectric point (pI) of 5.35, and it shared significant homology with IGFBP7 gene of H. madaka. Hdh IGFBP7 has a characteristic IGFBP N-terminal domain (22–89 aa), a kazal-type serine proteinase inhibitor domain (77–128), and an immunoglobulin-like C2 domain (144–223). Furthermore, twelve cysteine residues and a signature motif of IGFBPs (XCGCCXXC) were found in its N-terminal domain. Phylogenetic analysis revealed that Hdh IGFBP7 was aligned with IGFBP7 of H. madaka. Tissue distribution analysis showed that the mRNA of Hdh IGFBP7 was expressed in all examined tissues, with the highest expression level observed in the mantle and gill tissues. The expression level of Hdh IGFBP7 mRNA was relatively higher at the juvenile stage during its metamorphosis period. In situ hybridization showed that Hdh IGFBP7 transcript was expressed in epithelial cells of the dorsal mantle pallial and mucus cells of the branchial epithelium in gill. These results provide basic information for future studies on the role of IGFBP7 in IGF regulation of shell growth, development and metamorphosis of abalone.

Characterization of Insulin-Like Growth Factor Binding Protein-5 (IGFBP-5) Gene and Its Potential Roles in Ontogenesis in the Pacific Abalone, Haliotis discus hannai

Insulin-like growth factor binding protein family is known to be involved in regulating biological actions of insulin-like growth factors (IGFs). In the present study, a full-length cDNA encoding the IGFBP-5 gene was cloned and characterized from the cerebral ganglion of Haliotis discus hannai. The 921-bp full-length sequence of Hdh IGFBP-5 cDNA transcript had an open reading frame of 411 bp encoding a predicted polypeptide of 136 amino acids, sharing high sequence identities with IGFBP-5 of H. diversicolor. The deduced Hdh IGFBP-5 protein contained a putative transmembrane domain (13-35 aa) in the N-terminal region. It also possessed a signature domain of IGFBP protein family (IB domain, 45-120 aa). Six cysteine residues (Cys-47, Cys-55, Cys-73, Cys-85, Cys-98, and Cys-118) in this cloned sequence could potentially form an intrachain disulfide bond. Phylogenetic analysis indicated that the Hdh IGFBP-5 gene was robustly clustered with IGFBP-5 of H. diversicolor. Tissue distribution analysis based on qPCR assay showed that Hdh IGFBP-5 was widely expressed in all examined tissues, with significantly (p < 0.05) higher expression in the cerebral ganglion. In male and female gametogenetic cycles, Hdh IGFBP-5 mRNA was expressed at all stages, showing significantly higher level at ripening stage. The expression level of Hdh IGFBP-5 mRNA was significantly higher in the polar body stage than in other ontogenic stages. In situ hybridization revealed that Hdh IGFBP-5 mRNA was present in the neurosecretory cells of the cerebral ganglion. This is the first study describing IGFBP-5 in H. discus hannai that might be synthesized in the neural ganglia. Our results demonstrate Hdh IGFBP-5 is involved in regulating ontogenic development and reproductive regulation of H. discus hannai.

Oxygen and embryonic growth: the role of insulin-like growth factor signaling

Oxygen is indispensable for the efficient release of chemical energy from nutrient molecules in cells. Therefore, the local oxygen tension is one of the most critical factors affecting physiological processes. In most viviparous species, many pathological conditions result in abnormal oxygen tension in the uterus, which modifies the growth and development of the fetus. Insulin-like growth factor (IGF/Igf) is one of the most important hormones for the regulation of somatic growth in animals. Changes in oxygen levels modulate the activity of the IGF/Igf signaling system, which in turn regulates the embryonic growth rate. In general, there are serious difficulties associated with monitoring and studying rodent embryos in utero. The zebrafish is a convenient experimental model to study the relationship between embryonic growth and environmental conditions. Most importantly, the fish model makes it possible to rapidly evaluate embryonic growth and development under entirely controlled environments without interfering with the mother organism. In this review, firstly an overview is given of the fluctuation of environmental oxygen, the IGF-system, and the advantages of the zebrafish model for studying embryonic growth. Then, the relationships of dynamic environmental oxygen and embryonic growth rate are outlined with a specific focus on the changes in the IGF/Igf-system in the zebrafish model. This review will shed light on the fine-tuning mechanisms of the embryonic IGF/Igf-system under different oxygen levels, including constant normoxia, hypoxia, and re-oxygenation.

Gonadotropin-releasing hormone neuron development in vertebrates

Gonadotropin-releasing hormone (GnRH) neurons are master regulators of the reproductive axis in vertebrates. During early mammalian embryogenesis, GnRH1 neurons emerge in the nasal/olfactory placode. These neurons undertake a long-distance migration, moving from the nose to the preoptic area and hypothalamus. While significant advances have been made in understanding the functional importance of the GnRH1 neurons in reproduction, where GnRH1 neurons come from and how are they specified during early development is still under debate. In addition to the GnRH1 gene, most vertebrate species including humans have one or two additional GnRH genes. Compared to the GnRH1 neurons, much less is known about the development and regulation of GnRH2 neuron and GnRH3 neurons. The objective of this article is to review what is currently known about GnRH neuron development. We will survey various cell autonomous and non-autonomous factors implicated in the regulation of GnRH neuron development. Finally, we will discuss emerging tools and new approaches to resolve open questions pertaining to GnRH neuron development.

Impact of gadolinium-based contrast agents on the growth of fish cells lines

The present study was the first approach conducted under environmental concentrations of Gd-DOTA and Gd-DTPA-BMA to assess cellular impacts of these compounds. Gd-DOTA (Gadoteric acid) is one of the most stable contrast agent, currently used as Dotarem^® formulation during Magnetic Resonance Imaging exams. The study was mainly performed on a Zebra Fish cell line (ZF4; ATCC CRL-2050). At the concentrations of 0.127 nM and 63.59 nM (respectively 20 ng and 10 μg of Gd/L), we did not observed any toxicity of Dotarem^® but a slowdown of the cell growth was clearly measured. The effect is independent of medium renewing during 6 days of cell culturing. The same effect was observed i-with Gd-DOTA on another fish cell line (RT W1 gills; ATCC CRL-2523) and ii-with another contrast agent (Gd-DTPA-BMA - Omniscan^®) on ZF4 cells. On the ZF4 cell line, the diminution of the cell growth was of the same order during 20 days of exposure to a culture medium spiked with 63.59 nM of Dotarem^® and was reversible within the following 8 days when Dotarem^® was removed from the medium. As shown by using modified DOTA structure (Zn-DOTA), the effect may be due to the chelating structure of the contrast agent rather than to the Gd ion. Until now, the main attention concerning the impact of Gd-CA on living cells concerned the hazard due to Gd release. According to our results, quantifying the presence of Gd-CA chelating structures in aquatic environments must be also monitored.

Zebrafish as a translational regeneration model to study the activation of neural stem cells and role of their environment

The review is an overview of the current knowledge of neuronal regeneration properties in mammals and fish. The ability to regenerate the damaged parts of the nervous tissue has been demonstrated in all vertebrates. Notably, fish and amphibians have the highest capacity for neurogenesis, whereas reptiles and birds are able to only regenerate specific regions of the brain, while mammals have reduced capacity for neurogenesis. Zebrafish (Danio rerio) is a promising model of study because lesions in the brain or complete cross-section of the spinal cord are followed by an effective neuro-regeneration that successfully restores the motor function. In the brain and the spinal cord of zebrafish, stem cell activity is always able to re-activate the molecular programs required for central nervous system regeneration. In mammals, traumatic brain injuries are followed by reduced neurogenesis and poor axonal regeneration, often insufficient to functionally restore the nervous tissue, while spinal injuries are not repaired at all. The environment that surrounds the stem cell niche constituted by connective tissue and stimulating factors, including pro-inflammation molecules, seems to be a determinant in triggering stem cell proliferation and/or the trans-differentiation of connective elements (mainly fibroblasts). Investigating and comparing the neuronal regeneration in zebrafish and mammals may lead to a better understanding of the mechanisms behind neurogenesis, and the failure of the regenerative response in mammals, first of all, the role of inflammation, considered the main inhibitor of the neuronal regeneration.

Parental exposure to tris(1,3-dichloro-2-propyl) phosphate results in thyroid endocrine disruption and inhibition of growth in zebrafish offspring

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) is a re-emerging environmental contaminant used as a suitable substitute for brominated flame retardants. The objective of this study was to evaluate the effects of TDCIPP on thyroid disruption and growth inhibition in zebrafish (Danio rerio) offspring after chronic parental exposure, and to examine the possible molecular mechanisms involved. When adult zebrafish (4 months old) were exposed to 5.66, 25.55, or 92.8 μg TDCIPP/L for 90 days, bioconcentration of TDCIPP and its metabolic product [bis(1,3-dichloro-2-propyl) phosphate, BDCIPP] was observed in 7-day postfertilization (dpf) F1 larvae, which suggests the transfer of this compound from adult fish to their offspring. Our results demonstrated that parental exposure to TDCIPP induced thyroid disruption in the offspring, demonstrated by significantly decreased thyroxine (T4) and increased 3,5,3'-triiodothyronine (T3) levels, and disruption of the transcription of several genes and expression of proteins involved in the hypothalamic-pituitary-thyroid (HPT) axis in F1 larvae. Parental exposure to TDCIPP resulted in developmental abnormalities in offspring; the smaller body length that was recorded might be partly the result of the perturbation of the HPT axis. In addition, the results revealed that growth inhibition also resulted from the downregulation of the transcription of genes and expression of proteins involved in the growth hormone/insulin-like growth factor (GH/IGF) axis. Our study provides a new set of evidence showing that parental exposure to TDCIPP can induce thyroid disruption and inhibition of growth in offspring, and that perturbation of the HPT axis and GH/IGF axis contribute to these adverse effects.

Molecular characterization and expression profiles of insulin-like growth factors in yellowtail kingfish (Seriola lalandi) during embryonic development

In this study, to understand the role of the insulin-like growth factor (IGF) system in the regulation of early development in yellowtail kingfish (YTK, Seriola lalandi), an economically important marine fish species with a high potential for aquaculture, we first cloned the full-length cDNAs for igf1 and igf2 from the liver. YTK igf1 cDNA was 1946 base pairs (bp) in length with an open reading frame (ORF) of 558 bp encoding preproIGF1 of 185 amino acids (aa). The preproIGF1 consisted of 44 aa for the signal peptide, 68 aa for the mature peptide comprising B, C, A, and D domains, and 73 aa for the E domain. YTK igf2 cDNA had an ORF of 648 bp that encoded a total of 215 aa spanning the signal peptide (47 aa), the mature peptide (70 aa), and the E domain (98 aa). At the protein level, both YTK IGF1 and IGF2 exhibited high sequence identities with their corresponding fish counterparts, respectively. Subsequently, quantitative RT-PCR analysis indicated that the highest level of igf1 mRNA expression was recorded in the gonad and liver, while the igf2 mRNA expression was most abundant in the gill and liver. In addition, both igf1 and igf2 were detected in all stages of embryonic development and exhibited different gene expression patterns, supporting that IGF1 and IGF2 could be functional and play important roles during YTK embryogenesis. Overall, this initial study of IGF1 and IGF2 provides an insight into the endocrine mechanism involved in the early development of yellowtail kingfish.

The signaling pathways that mediate the anti-cancer effects of caloric restriction

Caloric restriction (CR) has been shown to promote longevity and ameliorate aging-associated diseases, including cancer. Extensive research over recent decades has revealed that CR reduces IGF-1/PI3K/AKT signaling and increases sirtuin signaling. We recently found that CR also enhances ALDOA/DNA-PK/p53 signaling. In the present review, we summarize the molecular mechanisms underlying the modulation of the IGF-1/PI3K/AKT pathway, sirtuin signaling, and the ALDOA/DNA-PK/p53 pathway by CR. We also summarize the evidence concerning the roles of these signaling pathways in carcinogenesis, and discuss how they are regulated by CR. Finally, we discuss the crosstalk between these signaling pathways.

Insulin-like growth factor 1 receptor signaling regulates embryonic epicardial cell proliferation through focal adhesion kinase pathway

Embryonic epicardial cells (EPCs) can facilitate cardiomyocyte growth through secreting several essential growth factors, and participate in cardiac development through auto-differentiating into many cardiac cell lineages. Proper proliferation of EPCs is the precondition of these functions, so it is quite necessary to explore the mechanisms involving in EPC proliferation. In this study, we aimed to explore whether insulin-like growth factor 1 receptor (IGF1R) signaling participated in regulating the proliferation of EPCs. Our results showed that the expressions of IGF1R and its ligands IGF1 and IGF2 can be clearly spotted on the epicardium layer from E11.5d to E17.5d. Inhibition of IGF1R signaling using picropodophyllin or NVP-AEW541 significantly decreased the proliferation activity and blocked the cell cycle progression of epicardial cells in vitro. On the contrary, activating IGF1R with recombinant IGF1 and IGF2 promoted epicardial cell proliferation and cell cycle. We also found that decreased expression and phosphorylation of FAK in IGF1R inhibitor-treated cells and use of FAK inhibitor Y15 could significantly inhibit the IGFs-induced EPC proliferation. In conclusion, our results suggest that IGF1R signaling plays an important role in regulating EPC proliferation, and this effect may be mediated by FAK pathway.

Evaluation of apoptosis, oxidative stress responses, AChE activity and body malformations in zebrafish (Danio rerio) embryos exposed to deltamethrin

In this study, we observed the zebrafish embryo/larvae (Danio rerio) exposed to Deltamethrin (DM) used as pesticide in agricultural fields. We determined respectively, changes in body morphology, cell apoptosis, antioxidant enzyme (SOD, CAT, GPx) activities, MDA and acetylcholinesterase (AChE) levels after 96h of DM exposure. The embryos were exposed to 2.5 μg/l - 10 μg/l - 25 μg/l - 50 μg/l of DM concentration for 96 h. Survival and hatching rates, and body malformations were determined under a stereo microscope for in 24, 48, 72 and 96th hours. DM caused the cellular apoptosis and an increase in MDA levels while inhibiting SOD, CAT, GPx enzyme activities and AChE level (P < 0.05). In addition, pericardial edema, yolk sac edema, spinal cord curvature and body malformations were determined in the embryo by depending on the dose of pesticide. As conclusion it can be concluded that DM inhibits the antioxidant enzyme mechanism, increases the cellular apoptosis, malformations. This study may provide enable us for understanding toxic mechanisms of DM in zebrafish embryos.

Tissue-Specific Transcriptome for Poeciliopsis prolifica Reveals Evidence for Genetic Adaptation Related to the Evolution of a Placental Fish

The evolution of the placenta is an excellent model to examine the evolutionary processes underlying adaptive complexity due to the recent, independent derivation of placentation in divergent animal lineages. In fishes, the family Poeciliidae offers the opportunity to study placental evolution with respect to variation in degree of post-fertilization maternal provisioning among closely related sister species. In this study, we present a detailed examination of a new reference transcriptome sequence for the live-bearing, matrotrophic fish, Poeciliopsis prolifica, from multiple-tissue RNA-seq data. We describe the genetic components active in liver, brain, late-stage embryo, and the maternal placental/ovarian complex, as well as associated patterns of positive selection in a suite of orthologous genes found in fishes. Results indicate the expression of many signaling transcripts, "non-coding" sequences and repetitive elements in the maternal placental/ovarian complex. Moreover, patterns of positive selection in protein sequence evolution were found associated with live-bearing fishes, generally, and the placental P. prolifica, specifically, that appear independent of the general live-bearer lifestyle. Much of the observed patterns of gene expression and positive selection are congruent with the evolution of placentation in fish functionally converging with mammalian placental evolution and with the patterns of rapid evolution facilitated by the teleost-specific whole genome duplication event.

The Role of Insulin-Like Growth Factor 1 in the Progression of Age-Related Hearing Loss

Aging is associated with impairment of sensorial functions and with the onset of neurodegenerative diseases. As pari passu circulating insulin-like growth factor 1 (IGF-1) bioavailability progressively decreases, we see a direct correlation with sensory impairment and cognitive performance in older humans. Age-related sensory loss is typically caused by the irreversible death of highly differentiated neurons and sensory receptor cells. Among sensory deficits, age-related hearing loss (ARHL), also named presbycusis, affects one third of the population over 65 years of age and is a major factor in the progression of cognitive problems in the elderly. The genetic and molecular bases of ARHL are largely unknown and only a few genes related to susceptibility to oxidative stress, excitotoxicity, and cell death have been identified. IGF-1 is known to be a neuroprotective agent that maintains cellular metabolism, activates growth, proliferation and differentiation, and limits cell death. Inborn IGF-1 deficiency leads to profound sensorineural hearing loss both in humans and mice. IGF-1 haploinsufficiency has also been shown to correlate with ARHL. There is not much information available on the effect of IGF-1 deficiency on other human sensory systems, but experimental models show a long-term impact on the retina. A secondary action of IGF-1 is the control of oxidative stress and inflammation, thus helping to resolve damage situations, acute or made chronic by aging. Here we will review the primary actions of IGF-1 in the auditory system and the underlying molecular mechanisms.

Acute exposure to tris (2-butoxyethyl) phosphate (TBOEP) affects growth and development of embryo-larval zebrafish

Tris (2-butoxyethyl) phosphate (TBOEP), is used as a flame retardant worldwide. It is an additive in materials and can be easily discharged into the surrounding environment. There is evidence linking TBOEP exposure to abnormal development and growth in zebrafish embryos/larvae. Here, using zebrafish embryo as a model, we investigated toxicological effects on developing zebrafish (Danio rerio) caused by TBOEP at concentrations of 0, 20, 200, 1000, 2000μg/L starting from 2h post-fertilization (hpf). Our findings revealed that TBOEP exposure caused developmental toxicity, such as malformation, growth delay and decreased heart rate in zebrafish larvae. Correlation analysis indicated that inhibition of growth was possibly due to down-regulation of expression of genes related to the growth hormone/insulin-like growth factor (GH/IGF) axis. Furthermore, exposure to TBOEP significantly increased thyroxine (T4) and 3,5,3'-triiodothyronine (T3) in whole larvae. In addition, changed expression of genes involved in the hypothalamic-pituitary-thyroid (HPT) axis was observed, indicating that perturbation of HPT axis might be responsible for the developmental damage and growth delay induced by TBOEP. The present study provides a new set of evidence that exposure of embryo-larval zebrafish to TBOEP can cause perturbation of GH/IGF axis and HPT axis, which could result in developmental impairment and growth inhibition.

Molecular identification of an insulin growth factor binding protein (IGFBP) and its potential role in an insulin-like peptide system of the pearl oyster, Pinctada fucata

Insulin-like growth factors (IGFs) play critical roles in regulating metabolism, growth, and reproduction in invertebrates. IGF binding proteins (IGFBPs) serve as major regulators of IGF activity and regulate endocrine system. In the present study, the full-length cDNA of an igfbp was identified from the pearl oyster, Pinctada fucata, using expressed sequence tag (EST) sequence. The 1124bp Pfigfbp cDNA contains a 465bp open reading frame (ORF) encoding a putative protein of 154 amino acids, a 5'-untranslated region (UTR) of 238bp, and a 3'-UTR of 394bp (not including polyA+). Multiple sequence alignment of the deduced IB domain sequences revealed that twelve conserved Cys and ILP binding site in PfIGFBP were well aligned with human IGFBPs1-7, Mizuhopecten yessoensis IGFBP5 and Eriocheir sinensis IGFBP7. Gene expression analysis indicated that Pfigfbp mRNA was expressed in all the tissues and developmental stages examined, with a higher level in the foot than in other tissues and a higher level in the polar body stage and 32-cell stage than in the other stages. Pfigfbp and PfILP (insulin-like peptide) mRNA levels significantly increased in the digestive gland after feeding, while levels were dramatically reduced during a week of food deprivation and increased upon refeeding. In vitro experiments indicated that Pfigfbp mRNA expression in mantle cells was affected by insulin/IGFs (IGF-I, IGF-II). Our data suggests that Pfigfbp may be involved in endocrine signaling in P. fucata via the regulation of insulin-like peptide signaling.

Neuroprotective Role of the PI3 Kinase/Akt Signaling Pathway in Zebrafish

Neuronal survival and growth in the embryo is controlled partly by trophic factors. For most trophic factors (such as Insulin-like growth factor-1), the ability to regulate cell survival has been attributed to the phosphoinositide 3-kinase (PI3K)/Akt kinase cascade. This study presents data illustrating the role of PI3K/Akt in attainment of normal brain size during zebrafish embryogenesis. Blocking PI3K with inhibitor LY294002 caused a significant reduction in brain size (in addition to global growth retardation) during zebrafish embryogenesis. This PI3 Kinase inhibition-induced brain size decrease was recovered by the overexpression of myristoylated Akt (myr-Akt), a constitutive form of Akt. Further analysis reveals that expressing exogenous myr-Akt significantly augmented brain size. Whole mount in situ hybridization analysis of several marker genes showed that myr-Akt overexpression did not alter brain patterning. Furthermore, the expression of myr-Akt was found to protect neuronal cells from apoptosis induced by heat shock and UV light, suggesting that inhibition of neuronal cell death may be part of the underlying cause of the increased brain size. These data provide a foundation for addressing the role of PI3K/Akt in brain growth during zebrafish embryogenesis.

PfIRR Interacts with HrIGF-I and Activates the MAP-kinase and PI3-kinase Signaling Pathways to Regulate Glycogen Metabolism in Pinctada fucata

The insulin-induced mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways are major intracellular signaling modules and conserved among eukaryotes that are known to regulate diverse cellular processes. However, they have not been investigated in the mollusk species Pinctada fucata. Here, we demonstrate that insulin-related peptide receptor of P. fucata (pfIRR) interacts with human recombinant insulin-like growth factor I (hrIGF-I), and stimulates the MAPK and PI3K signaling pathways in P. fucata oocytes. We also show that inhibition of pfIRR by the inhibitor PQ401 significantly attenuates the basal and hrIGF-I-induced phosphorylation of MAPK and PI3K/Akt at amino acid residues threonine 308 and serine 473. Furthermore, our experiments show that there is cross-talk between the MAPK and PI3K/Akt pathways, in which MAPK kinase positively regulates the PI3K pathway, and PI3K positively regulates the MAPK cascade. Intramuscular injection of hrIGF-I stimulates the PI3K and MAPK pathways to increase the expression of pfirr, protein phosphatase 1, glucokinase, and the phosphorylation of glycogen synthase, decreases the mRNA expression of glycogen synthase kinase-3 beta, decreases glucose levels in hemocytes, and increases glycogen levels in digestive glands. These results suggest that the MAPK and PI3K pathways in P. fucata transmit the hrIGF-I signal to regulate glycogen metabolism.

Nedd4-induced monoubiquitination of IRS-2 enhances IGF signalling and mitogenic activity

Insulin-like growth factors (IGFs) induce proliferation of various cell types and play important roles in somatic growth and cancer development. Phosphorylation of insulin receptor substrate (IRS)-1/2 by IGF-I receptor tyrosine kinase is essential for IGF action. Here we identify Nedd4 as an IRS-2 ubiquitin ligase. Nedd4 monoubiquitinates IRS-2, which promotes its association with Epsin1, a ubiquitin-binding protein. Nedd4 recruits IRS-2 to the membrane, probably through promoting Epsin1 binding, and enhances IGF-I receptor-induced IRS-2 tyrosine phosphorylation. In thyroid FRTL-5 cells, activation of the cyclic AMP pathway increases the association of Nedd4 with IRS-2, thereby enhancing IRS-2-mediated signalling and cell proliferation induced by IGF-I. The Nedd4 and IRS-2 association is also required for maximal activation of IGF-I signalling and cell proliferation in prostate cancer PC-3 cells. Nedd4 overexpression accelerates zebrafish embryonic growth through IRS-2 in vivo. We conclude that Nedd4-induced monoubiquitination of IRS-2 enhances IGF signalling and mitogenic activity.

Skeletal muscle insulin resistance in zebrafish induces alterations in β-cell number and glucose tolerance in an age- and diet-dependent manner

Insulin resistance creates an environment that promotes β-cell failure and development of diabetes. Understanding the events that lead from insulin resistance to diabetes is necessary for development of effective preventional and interventional strategies, and model systems that reflect the pathophysiology of disease progression are an important component toward this end. We have confirmed that insulin enhances glucose uptake in zebrafish skeletal muscle and have developed a zebrafish model of skeletal muscle insulin resistance using a dominant-negative IGF-IR. These zebrafish exhibit blunted insulin signaling and glucose uptake in the skeletal muscle, confirming insulin resistance. In young animals, we observed an increase in the number of β-cells and normal glucose tolerance that was indicative of compensation for insulin resistance. In older animals, the β-cell mass was reduced to that of control with the appearance of impaired glucose clearance but no elevation in fasting blood glucose. Combined with overnutrition, the insulin-resistant animals have an increased fasting blood glucose compared with the control animals, demonstrating that the β-cells in the insulin-resistant fish are in a vulnerable state. The relatively slow progression from insulin resistance to glucose intolerance in this model system has the potential in the future to test cooperating genes or metabolic conditions that may accelerate the development of diabetes and provide new therapeutic targets.

Insulin-like growth factors I and II in starry flounder (Platichthys stellatus): molecular cloning and differential expression during embryonic development

In order to elucidate the possible roles of insulin-like growth factors I and II (IGF-I and IGF-II) in the embryonic development of Platichthys stellatus, their cDNAs were isolated and their spatial expression pattern in adult organs and temporal expression pattern throughout embryonic development were examined by quantitative real-time PCR assay. The IGF-I cDNA sequence was 1,268 bp in length and contained an open reading frame (ORF) of 558 bp, which encoded 185 amino acid residues. With respect to IGF-II, the full-length cDNA was 899 bp in length and contained a 648-bp ORF, which encoded 215 amino acid residues. The amino acid sequences of IGF-I and IGF-II exhibited high identities with their fish counterparts. The highest IGF-I mRNA level was found in the liver for both sexes, whereas the IGF-II gene was most abundantly expressed in female liver and male liver, gill, and brain. The sex-specific and spatial expression patterns of IGF-I and IGF-II mRNAs are thought to be related to the sexually dimorphic growth and development of starry flounder. Both IGF-I and IGF-II mRNAs were detected in unfertilized eggs, which indicated that IGF-I and IGF-II were parentally transmitted. Nineteen embryonic development stages were tested. IGF-I mRNA level remained high from unfertilized eggs to low blastula followed by a significant decrease at early gastrula and then maintained a lower level. In contrast, IGF-II mRNA level was low from unfertilized eggs to high blastula and peaked at low blastula followed by a gradual decrease. Moreover, higher levels of IGF-I mRNA than that of IGF-II were found from unfertilized eggs to high blastula, vice versa from low blastula to newly hatched larva, and the different expression pattern verified the differential roles of IGF-I and IGF-II in starry flounder embryonic development. These results could help in understanding the endocrine mechanism involved in the early development and growth of starry flounder.

Differences in IGF axis-related proteins in amniotic fluid of trisomy 21 and trisomy 18 using a multiple reaction monitoring approach

OBJECTIVE

Trisomy 21 and trisomy 18 are the two most common chromosomal anomalies in live births. To find new biomarkers for aneuploidies and pathogenesis of fetal malformations, we measured insulin-like growth factor (IGF) axis-related proteins in amniotic fluid (AF) of pregnant women carrying trisomies 21 or 18 affected fetuses using multiple reaction monitoring (MRM) approach.

METHOD

Eighty-five AF samples from pregnant women carrying either trisomy 21, trisomy 18, or normal fetuses were collected. IGF axis-related proteins in AF after serial treatments were quantitated with MRM method. The differential protein levels were also confirmed by western blot in AF without any treatment.

RESULTS

The IGF type I receptor and pregnancy-associated plasma protein-A in AF of trisomy 21 (1.35 ± 0.32 and 13.36 ± 3.64 µg/mg protein) and trisomy 18 (1.39 ± 0.40 and 12.80 ± 1.84 µg/mg protein) were decreased versus normal controls (2.16 ± 0.59 and 23.77 ± 6.18 µg/mg protein). IGF binding protein 5 was reduced in trisomy 18 (1.47 ± 0.33 vs 2.36 ± 0.77 µg/mg protein). These alterations were confirmed by western blot. The other proteins showed no significant difference between the three groups.

CONCLUSION

Our data suggested that MRM can provide a powerful platform for the identification of biomarkers in AF that have crucial developmental effects in the aneuploid fetus.

Aspp2 negatively regulates body growth but not developmental timing by modulating IRS signaling in zebrafish embryos

The growth and developmental rate of developing embryos and fetus are tightly controlled and coordinated to maintain proper body shape and size. The insulin receptor substrate (IRS) proteins, key intracellular transducers of insulin and insulin-like growth factor signaling, play essential roles in the regulation of growth and development. A short isoform of apoptosis-stimulating protein of p53 2 (ASPP2) was recently identified as a binding partner of IRS-1 and IRS-2 in mammalian cells in vitro. However, it is unclear whether ASPP2 plays any role in vertebrate embryonic growth and development. Here, we show that zebrafish Aspp2a and Aspp2b negatively regulate embryonic growth without affecting developmental rate. Human ASPP2 had similar effects on body growth in zebrafish embryos. Aspp2a and 2b inhibit Akt signaling. This inhibition was reversed by coinjection of myr-Akt1, a constitutively active form of Akt1. Zebrafish Aspp2a and Aspp2b physically bound with Irs-1, and the growth inhibitory effects of ASPP2/Aspp2 depend on the presence of their ankyrin repeats and SH3 domains. These findings uncover a novel role of Aspp2 in regulating vertebrate embryonic growth.

Genome wide expression profiling during spinal cord regeneration identifies comprehensive cellular responses in zebrafish

BACKGROUND

Among the vertebrates, teleost and urodele amphibians are capable of regenerating their central nervous system. We have used zebrafish as a model to study spinal cord injury and regeneration. Relatively little is known about the molecular mechanisms underlying spinal cord regeneration and information based on high density oligonucleotide microarray was not available. We have used a high density microarray to profile the temporal transcriptome dynamics during the entire phenomenon.

RESULTS

A total of 3842 genes expressed differentially with significant fold changes during spinal cord regeneration. Cluster analysis revealed event specific dynamic expression of genes related to inflammation, cell death, cell migration, cell proliferation, neurogenesis, neural patterning and axonal regrowth. Spatio-temporal analysis of stat3 expression suggested its possible function in controlling inflammation and cell proliferation. Genes involved in neurogenesis and their dorso-ventral patterning (sox2 and dbx2) are differentially expressed. Injury induced cell proliferation is controlled by many cell cycle regulators and some are commonly expressed in regenerating fin, heart and retina. Expression pattern of certain pathway genes are identified for the first time during regeneration of spinal cord. Several genes involved in PNS regeneration in mammals like stat3, socs3, atf3, mmp9 and sox11 are upregulated in zebrafish SCI thus creating PNS like environment after injury.

CONCLUSION

Our study provides a comprehensive genetic blue print of diverse cellular response(s) during regeneration of zebrafish spinal cord. The data highlights the importance of different event specific gene expression that could be better understood and manipulated further to induce successful regeneration in mammals.

Calcium deficiency-induced and TRP channel-regulated IGF1R-PI3K-Akt signaling regulates abnormal epithelial cell proliferation

Calcium deficiency causes abnormal colonic growth and increases colon cancer risk with poorly understood mechanisms. Here we elucidate a novel signaling mechanism underlying the Ca(2+) deficiency-induced epithelial proliferation using a unique animal model. The zebrafish larval yolk sac skin contains a group of Ca(2+)-transporting epithelial cells known as ionocytes. Their number and density increases dramatically when acclimated to low [Ca(2+)] environments. BrdU pulse-labeling experiments suggest that low [Ca(2+)] stimulates pre-existing ionocytes to re-enter the cell cycle. Low [Ca(2+)] treatment results in a robust and sustained activation of IGF1R-PI3K-Akt signaling in these cells exclusively. These ionocytes specifically express Igfbp5a, a high-affinity and specific binding protein for insulin-like growth factors (IGFs) and the Ca(2+)-selective channel Trpv5/6. Inhibition or knockdown of Igfbp5a, IGF1 receptor, PI3K, and Akt attenuates low [Ca(2+)]-induced ionocyte proliferation. The role of Trpv5/6 was investigated using a genetic mutant, targeted knockdown, and pharmacological inhibition. Loss-of-Trpv5/6 function or expression results in elevated pAkt levels and increased ionocyte proliferation under normal [Ca(2+)]. These increases are eliminated in the presence of an IGF1R inhibitor, suggesting that Trpv5/6 represses IGF1R-PI3K-Akt signaling under normal [Ca(2+)]. Intriguingly, blockade of Trpv5/6 activity inhibits the low [Ca(2+)]-induced activation of Akt. Mechanistic analyses reveal that the low [Ca(2+)]-induced IGF signaling is mediated through Trpv5/6-associated membrane depolarization. Low extracellular [Ca(2+)] results in a similar amplification of IGF-induced PI3K-PDK1-Akt signaling in human colon cancer cells in a TRPV6-dependent manner. These results uncover a novel and evolutionarily conserved signaling mechanism that contributes to the abnormal epithelial proliferation associated with Ca(2+) deficiency.

Microarray analysis of gene expression alteration in human middle ear epithelial cells induced by micro particle

OBJECTIVES

The primary aim of this study is to reveal the effect of particulate matter (PM) on the human middle ear epithelial cell (HMEEC).

METHODS

The HMEEC was treated with PM (300 μg/ml) for 24 h. Total RNA was extracted and used for microarray analysis. Molecular pathways among differentially expressed genes were further analyzed by using Pathway Studio 9.0 software. For selected genes, the changes in gene expression were confirmed by real-time PCR.

RESULTS

A total of 611 genes were regulated by PM. Among them, 366 genes were up-regulated, whereas 245 genes were down-regulated. Up-regulated genes were mainly involved in cellular processes, including reactive oxygen species generation, cell proliferation, apoptosis, cell differentiation, inflammatory response and immune response. Down-regulated genes affected several cellular processes, including cell differentiation, cell cycle, proliferation, apoptosis and cell migration. A total of 21 genes were discovered as crucial components in potential signaling networks containing 2-fold up regulated genes. Four genes, VEGFA, IL1B, CSF2 and HMOX1 were revealed as key mediator genes among the up-regulated genes. A total of 25 genes were revealed as key modulators in the signaling pathway associated with 2-fold down regulated genes. Four genes, including IGF1R, TIMP1, IL6 and FN1, were identified as the main modulator genes.

CONCLUSIONS

We identified the differentially expressed genes in PM-treated HMEEC, whose expression profile may provide a useful clue for the understanding of environmental pathophysiology of otitis media. Our work indicates that air pollution, like PM, plays an important role in the pathogenesis of otitis media.

Regulation of skeletal muscle growth in fish by the growth hormone--insulin-like growth factor system

The growth hormone (GH)-insulin-like growth factor (IGF) system is the key promoter of growth in vertebrates; however, how this system modulates muscle mass in fish is just recently becoming elucidated. In fish, the GH induces muscle growth by modulating the expression of several genes belonging to the myostatin (MSTN), atrophy, GH, and IGF systems as well as myogenic regulatory factors (MRFs). The GH controls the expression of igf1 via Janus kinase 2 (JAK2)/signal transducers and activators of the transcription 5 (STAT5) signaling pathway, but it seems that it is not the major regulator. These mild effects of the GH on igf1 expression in fish muscle seem to be related with the presence of higher contents of truncated GH receptor1 (tGHR1) than full length GHR (flGHR1). IGFs in fish stimulate myogenic cell proliferation, differentiation, and protein synthesis through the MAPK/ERK and PI3K/AKT/TOR signaling pathways, concomitant with abolishing protein degradation and atrophy via the PI3K/AKT/FOXO signaling pathway. Besides these signaling pathways control the expression of several genes belonging to the atrophy and IGF systems. Particularly, IGFs and amino acid control the expression of igf1, thus, suggesting other of alternative signaling pathways regulating the transcription of this growth factor. The possible role of IGF binding proteins (IGFBPs) and the contribution of muscle-derived versus hepatic-produced IGF1 on fish muscle growth is also addressed. Thus, a comprehensive overview on the GH-IGF system regulating fish skeletal muscle growth is presented, as well as perspectives for future research in this field.

Igf Signaling is Required for Cardiomyocyte Proliferation during Zebrafish Heart Development and Regeneration

Unlike its mammalian counterpart, the adult zebrafish heart is able to fully regenerate after severe injury. One of the most important events during the regeneration process is cardiomyocyte proliferation, which results in the replacement of lost myocardium. Growth factors that induce cardiomyocyte proliferation during zebrafish heart regeneration remain to be identified. Signaling pathways important for heart development might be reutilized during heart regeneration. IGF2 was recently shown to be important for cardiomyocyte proliferation and heart growth during mid-gestation heart development in mice, although its role in heart regeneration is unknown. We found that expression of igf2b was upregulated during zebrafish heart regeneration. Following resection of the ventricle apex, igf2b expression was detected in the wound, endocardium and epicardium at a time that coincides with cardiomyocyte proliferation. Transgenic zebrafish embryos expressing a dominant negative form of Igf1 receptor (dn-Igf1r) had fewer cardiomyocytes and impaired heart development, as did embryos treated with an Igf1r inhibitor. Moreover, inhibition of Igf1r signaling blocked cardiomyocyte proliferation during heart development and regeneration. We found that Igf signaling is required for a subpopulation of cardiomyocytes marked by gata4:EGFP to contribute to the regenerating area. Our findings suggest that Igf signaling is important for heart development and myocardial regeneration in zebrafish.

Pregnancy-associated plasma protein A (PAPP-A) modulates the early developmental rate in zebrafish independently of its proteolytic activity

Pregnancy-associated plasma protein-A (PAPP-A) is a large metalloproteinase specifically cleaving insulin-like growth factor (IGF) binding proteins, causing increased IGF bioavailability and, hence, local regulation of IGF receptor activation. We have identified two highly conserved zebrafish homologs of the human PAPP-A gene. Expression of zebrafish Papp-a, one of the two paralogs, begins during gastrulation and persists throughout the first week of development, and analyses demonstrate highly conserved patterns of expression between adult zebrafish, humans, and mice. We show that the specific knockdown of zebrafish papp-a limits the developmental rate beginning during gastrulation without affecting the normal patterning of the embryo. This phenotype is different from those resulting from deficiency of Igf receptor or ligand in zebrafish, suggesting a function of Papp-a outside of the Igf system. Biochemical analysis of recombinant zebrafish Papp-a demonstrates conservation of proteolytic activity, specificity, and the intrinsic regulatory mechanism. However, in vitro transcribed mRNA, which encodes a proteolytically inactive Papp-a mutant, recues the papp-a knockdown phenotype as efficiently as wild-type Papp-a. Thus, the developmental phenotype of papp-a knockdown is not a consequence of lacking Papp-a proteolytic activity. We conclude that Papp-a possesses biological functions independent of its proteolytic activity. Our data represent the first evidence for a non-proteolytic function of PAPP-A.

Molecular, functional, and gene expression analysis of zebrafish hypoxia-inducible factor-3α

Hypoxia-inducible factors 1-3 (HIF1-3) are transcription factors that regulate gene expression in response to hypoxia. Compared with our extensive understanding of HIF-1 and HIF-2, our knowledge of HIF-3 is limited. In this study, we characterized the zebrafish hif-3α gene and determined its temporal and spatial expression, physiological regulation, and biological activity. We show that the chromosomal location, gene structure, and protein structure of zebrafish hif-3α are similar to its mammalian orthologs. When tagged with enhanced green fluorescent protein and transfected into cultured cells, zebrafish Hif-3α was localized in the nucleus and stimulated reporter gene expression in a hypoxia response element-dependent manner. During early development, hif-3α mRNA was detected in all tissues with higher levels in the head. This expression pattern became more apparent in larvae at the 72, 96, and 120 hours post fertilization stages. In the adult stage, hif-3α mRNA was detected in all examined tissues with the highest levels in the ovary. Hypoxia treatment increased Hif-3α protein levels in both embryos and adults. Hypoxia also increased hif-3α mRNA expression levels, and this regulation was tissue-specific. Expression of a stabilized form of Hif-1α in zebrafish embryos increased the expression of igfbp-1a, a Hif-1 target gene, whereas it did not change hif-3α mRNA levels, suggesting that hif-3α is not a Hif-1α target. These results provide new information about the structural and functional conservation, spatial and temporal expression, and physiological regulation of hif-3α in a teleost model organism.