Early treatment of the pregnant guinea pig with IGFs promotes placental transport and nutrient partitioning near term

Appropriate partitioning of nutrients between the mother and conceptus is a major determinant of pregnancy success, with placental transfer playing a key role. Insulin-like growth factors (IGFs) increase in the maternal circulation during early pregnancy and are predictive of fetal and placental growth. We have previously shown in the guinea pig that increasing maternal IGF abundance in early to midpregnancy enhances fetal growth and viability near term. We now show that this treatment promotes placental transport to the fetus, fetal substrate utilization, and nutrient partitioning near term. Pregnant guinea pigs were infused with IGF-I, IGF-II (both 1 mg.kg-1.day-1) or vehicle subcutaneously from days 20-38 of pregnancy (term=69 days). Tissue uptake and placental transfer of the nonmetabolizable radio analogs [3H]methyl-D-glucose (MG) and [14C]aminoisobutyric acid (AIB) in vivo was measured on day 62. Early pregnancy exposure to elevated maternal IGF-I increased placental MG uptake by>70% (P=0.004), whereas each IGF increased fetal plasma MG concentrations by 40-50% (P<0.012). Both IGFs increased fetal tissue MG uptake (P<0.048), whereas IGF-I also increased AIB uptake by visceral organs (P=0.046). In the mother, earlier exposure to either IGF increased AIB uptake by visceral organs (P<0.014), whereas IGF-I also enhanced uptake of AIB by muscle (P=0.044) and MG uptake by visceral organs (P=0.016) and muscle (P=0.046). In conclusion, exogenous maternal IGFs in early pregnancy sustainedly increase maternal substrate utilization, placental transport of MG to the fetus, and fetal utilization of substrates near term. This was consistent with the previously observed increase in fetal growth and survival following IGF treatment.     

The effects of maternal undernutrition on maternal and fetal serum insulin-like growth factors, thyroid hormones and cortisol in the guinea pig.

The insulin-like growth factors (IGF-I and -II) are potential mediators of the effects of maternal undernutrition on fetal growth and muscle development. The effects of a 40% reduction in maternal feed intake on serum levels of the IGFs, the thyroid hormones and cortisol, were investigated for the last two trimesters (day 25 to birth). This level of undernutrition is known to cause a 35% reduction in fetal and placental weights, and a 20-25% reduction in muscle fibre number. Maternal IGF-I level was greater than non-pregnant levels on day 25 gestation, in both control and restricted dams, and declined with gestational age. The increase in IGF-I level in the 40% restricted group was approximately two-thirds that of control animals. Fetal serum IGF-I was also reduced in undernourished fetuses throughout gestation. Maternal IGF-II did not change with gestational age and was unaffected by undernutrition. Fetal IGF-II reached a peak at day 55 of gestation, this peak was greatly diminished by maternal feed restriction. Both IGF-I and IGF-II tended to be related to fetal, placental and muscle weights at day 65 of gestation. Thyroid hormone concentration declined in maternal serum and increased in fetal serum with increasing gestational age. Levels were not significantly affected by undernutrition. Both triiodothyronine (T3) and thyroxine (T4) were correlated with IGF-I in maternal serum (P < 0.05), but not in fetal serum. Cortisol levels were elevated by undernutrition in both maternal and fetal serum, and increased with gestational age. Cortisol was inversely correlated with serum IGF-I in both maternal and fetal serum. Maternal serum IGF-I may mediate the effects of undernutrition on fetal growth by affecting the growth and establishment of the feto-placental unit in mid-gestation. Fetal IGF-I may mediate the effects on muscle growth, whereas IGF-II seems to be related to hepatic glycogen deposition. Cortisol may play a role via its effect on the IGFs, but the thyroid hormones are unlikely to be important until the late gestation/early postnatal period.     

A novel binding site for the human insulin-like growth factor-II (IGF-II)/mannose 6-phosphate receptor on IGF-II

The mammalian insulin-like growth factor (IGF)-II/cation-independent mannose 6-phosphate receptor (IGF2R) binds IGF-II with high affinity. By targeting IGF-II to lysosomal degradation, it plays a role in the maintenance of correct IGF-II levels in the circulation and in target tissues. Loss of IGF2R function is associated with tumor progression; therefore, the IGF2R is often referred to as a tumor suppressor. The interaction between IGF2R and IGF-II involves domains 11 and 13 of the 15 extracellular domains of the receptor. Recently, a hydrophobic binding region was identified on domain 11 of the IGF2R. In contrast, relatively little is known about the residues of IGF-II that are involved in IGF2R binding and the determinants of IGF2R specificity for IGF-II over the structurally related IGF-I. Using a series of novel IGF-II analogues and surface plasmon resonance assays, this study revealed a novel binding surface on IGF-II critical for IGF2R binding. The hydrophobic residues Phe(19) and Leu(53) are critical for IGF2R binding, as are residues Thr(16) and Asp(52). Furthermore, Thr(16) was identified as playing a major role in determining why IGF-II, but not IGF-I, binds with high affinity to the IGF2R.     

Effect of a high maternal dietary intake during mid-gestation on components of the utero-placental insulin-like growth factor (IGF) system in adolescent sheep with retarded placental development

The aim of the present study was to investigate the effects of administering a high plane diet during early to mid-gestation on the uterine and placental insulin-like growth factor (IGF) system and on systemic IGF-I concentrations in pregnant adolescent ewes with restricted placental growth. Embryos recovered from superovulated ewes inseminated by a single sire were transferred in singleton to the uterus of adolescent recipients. After transfer ewes were offered a high (H) or moderate (M) amount of a complete diet calculated to promote rapid or normal maternal growth rates, respectively. Five ewes from each group were switched from either M to H or H to M diets at day 52 of gestation. Maternal and fetal blood samples and placental tissues were collected from all animals at day 104. Ewes on the high plane diet from mid-gestation (HH, MH groups) had restricted placental mass (P < 0.01) and tended to have smaller fetuses. This was associated with increased maternal plasma IGF-I concentrations (P < 0.001). The pattern of expression of components of the IGF system in the uterus and placenta was studied by in situ hybridization. IGF-I mRNA concentrations were below the limit of detection. IGF-II mRNA expression was high in the fetal mesoderm and present in maternal stroma, but was not influenced by nutritional treatment. In contrast, IGF binding protein 1 (IGFBP-1) mRNA expression was higher (P < 0.05) and IGFBP-3 mRNA expression was lower (P < 0.05) in the endometrial glands of ewes in HH and MH groups. In the fetal trophoblast, IGFBP-3 mRNA expression was higher in the MH group. Type 1 IGF receptor expression was increased (P < 0. 01) in the luminal epithelium of the HM group and IGFBP-2 mRNA expression was highest in the placentome capsule of ewes in the HH group. Together, these results indicate that reprogramming of the uterine and placental IGF axis by maternal nutrition could contribute to placental growth retardation in growing adolescent sheep.     

Placental insulin‐like growth factor II (IGF‐II) and its relation to litter size in the common marmoset monkey (Callithrix jacchus)

The primate placenta produces a wide variety of hormones throughout gestation that regulate placental function and fetal growth. One such hormone is insulin‐like growth factor‐II (IGF‐II), a peptide implicated in cell division, differentiation, and amino acid transport. IGF‐II concentrations were measured in 23 common marmoset (Callithrix jacchus) term placentas from twin and triplet litters in order to determine whether previously described differences in fetoplacental phenotype such as placental and litter mass and placental surface area were related to differences in endocrine function. IGF‐II was extracted from frozen tissue samples and measured using an enzyme‐linked immunosorbent assay kit designed for human tissue, which was validated for marmoset placenta. IGF‐II concentrations were not related to placental or litter mass, and twin and triplet placentas did not differ in total concentration. However, per individual fetus, triplets were associated with a significant 42% reduction in IGF‐II concentration (P=0.03), and IGF‐II concentration per gram of fetal mass was a third lower in triplet litters. The triplet placenta exhibits a global expansion of the surface area which was contrasted by a per unit area reduction in IGF‐II concentration (r=?0.75, P=0.01), a pattern that explains why twin and triplet placentas overall did not differ in concentration. Per fetus, triplet pregnancies are associated with relatively less maternal mass, placental mass and microscopic surface area suggesting that the intrauterine growth of triplets is supported by systems that increase the efficiency of nutrient transfer. The finding that individual triplet fetuses are also associated with significantly lower IGF‐II concentrations is consistent with the view that the marmoset fetoplacental unit exhibits a flexible pattern of placental allocation and metabolism. Plasticity in placental endocrine and metabolic function is likely to play an important role in the ability of the fetus to sense and accommodate the intrauterine environment and, by extension, the external ecology. Am. J. Primatol. 71:969–975, 2009. © 2009 Wiley‐Liss, Inc.     

Acute ethanol exposure in pregnancy alters the insulin-like growth factor axis of fetal and maternal sheep

Maternal ethanol intake during pregnancy impairs fetal growth, but mechanisms are not clearly defined. Reduced IGF abundance or bioavailability in the fetus and/or mother may contribute to this growth restriction. We hypothesized that an episode of acute ethanol exposure, mimicking binge drinking would restrict fetal growth and perturb the maternal and fetal IGF axes. Pregnant sheep were infused intravenously with saline or ethanol (1 g/kg maternal wt) over 1 h, on days 116, 117, and 118 of gestation (start of 1st infusion = time 0, term is 147 days). Maternal and fetal plasma IGF and IGF-binding protein (IGFBP) concentrations were measured before and after each infusion. Compared with controls, ethanol exposure reduced fetal weight at day 120 by 19%, transiently reduced maternal plasma IGF-I (-35%) at 30 h, and decreased fetal plasma IGF-II (-28%) from 24 to 54 h after the first infusion. Ethanol exposure did not alter maternal or fetal plasma concentrations of IGFBP-2 and IGFBP-3, measured by Western ligand blotting. We conclude that suppression of maternal and fetal IGF abundance may contribute to fetal growth restriction induced by acute or binge ethanol exposure.     

Intrauterine growth retardation and consequences for endocrine and cardiovascular diseases in adult life: does insulin-like growth factor-I play a role?

Low birth weight has been associated with an increased incidence of ischaemic heart disease (IHD) and type 2 diabetes. Endocrine regulation of fetal growth by growth hormone (GH) and insulin-like growth factor (IGF)-I is complex. Placental GH is detectable in maternal serum from the 8th to the 12th gestational week, and rises gradually during pregnancy where it replaces pituitary GH in the maternal circulation. The rise in placental GH may explain the pregnancy-induced rise in maternal serum IGF-I levels. In the fetal compartment, IGF-I levels increase significantly in normally growing fetuses from 18 to 40 weeks of gestation, but IGF-I levels are four to five times lower than those in the maternal circulation. Thus IGF-I levels in fetal as well as in maternal circulation are thought to regulate fetal growth. Circulating levels of IGF-I are thought to be genetically controlled and several IGF-I gene polymorphisms have been described. IGF-I gene polymorphisms are associated with birth weight in some studies but not in all. Likewise, IGF-I gene polymorphisms are associated with serum IGF-I in healthy adults in some studies, although some controversy exists. Serum IGF-I decreases with increasing age in healthy adults, and this decline could hypothetically be responsible for the increased risk of IHD with ageing. A recent nested case-control study found that adults without IHD, but with low circulating IGF-I levels and high IGF binding protein-3 levels, had a significantly increased risk of developing IHD during a 15-year follow-up period. In summary, the GH/IGF-I axis is involved in the regulation of fetal growth. Furthermore, it has been suggested that low IGF-I may increase the risk of IHD in otherwise healthy subjects. Hypothetically, intrauterine programming of the GH/IGF axis may influence postnatal growth, insulin resistance and consequently the risk of cardiovascular disease. Thus IGF-I may serve as a link between fetal growth and adult-onset disease.     

The gene structure of the insulin-like growth factor family

The insulin-like growth factors (IGF) constitute a family of proteins with insulin-like and growth-stimulating properties. The best characterized members of this family are IGF-I, a protein of 70 amino acids which plays an important role in post-natal growth, and IGF-II, a 67 amino acid protein which is most likely involved in fetal development.The gene structure of IGF-II has been elucidated for the human and the rat and shows extensive interspecies homologies. The gene structure of IGF-I has only partially been established. A striking feature of the IGF genes is that they are controlled by multiple promoters which are expressed in a tissue-specific and development-dependent way.     

Insulin-like growth factor II binding and action in human fetal fibroblasts

To investigate the role of insulin-like growth factor II (IGF-II) in human prenatal growth, IGF-II binding and biological action were studied in four lines of fetal and three lines of postnatal human fibroblasts. Specific binding of IGF-II was similar in both groups: 15.7% and 14.9% for fetal and postnatal fibroblasts, respectively. This was 5-10 times the amount of IGF-I binding found in these cells. IGF-I and IGF-II caused dose-dependent increases in [14C]aminoisobutyric acid (AIB) uptake. IGF-II was sevenfold less potent than IGF-I in stimulating this metabolic response in both fetal and postnatal fibroblasts. The maximal effect of IGF-II in stimulating [14C]AIB uptake approach that of IGF-I. Similar results were obtained when IGF-I and IGF-II stimulation of [3H]thymidine incorporation was compared in fetal and postnatal fibroblasts. Incubation in the presence of alpha IR-3, a monoclonal antibody to the type I IGF receptor, inhibited the ability of both IGF-I and IGF-II to stimulate [14C]AIB uptake and [3H]thymidine incorporation in fetal and postnatal cells. A monoclonal antibody to the insulin receptor did not affect IGF action. These data indicate that IGF-II is a potent metabolic and mitogenic stimulus for human fetal fibroblasts. However, despite the presence of abundant type II IGF receptors on both fetal and postnatal human fibroblasts, IGF-II stimulation of amino acid transport and DNA synthesis appears to be mediated through the type I rather than through its own type II IGF receptor.     

Repeated betamethasone treatment of pregnant sheep programs persistent reductions in circulating IGF-I and IGF-binding proteins in progeny

Exposure to synthetic glucocorticoids in utero markedly improves survival after preterm birth, but repeated exposures impair fetal and postnatal growth and are associated with evidence of insulin resistance in later life. The insulin-like growth factor (IGF) axis is an important regulator of growth and metabolism before and after birth. We have therefore investigated the effects of repeated maternal betamethasone injections on plasma IGF-I, IGF-II, and IGF-binding proteins (IGFBP) in fetal and postnatal progeny in the sheep. Pregnant sheep carrying male fetuses were injected with saline or betamethasone at 104, 111, and 118 days of gestation (dG, term approximately 150 dG). Plasma samples were collected postmortem from fetuses before (75, 84, 101 dG) or after one (109 dG), two (116 dG), or three (121-122, 132-133, 145-147 dG) doses of saline or betamethasone and from progeny at 42 and 84 days of age. Fetal weight was reduced after two or more maternal betamethasone injections, and this effect persisted to term. Repeated betamethasone exposures reduced plasma IGF-I and total IGFBP in fetuses at 133 dG and progeny at 84 days, and reduced plasma IGFBP-3 at 84 days. Fetal plasma IGF-II tended to increase transiently at 109 dG following the first betamethasone injection. Fetal, placental, and/or postnatal weights correlated positively with concomitant plasma IGF-I, IGF-II, and total IGFBP. We conclude that repeated exposure to synthetic glucocorticoids in utero programs the IGF axis before and after birth, which may contribute to the adverse effects of betamethasone exposure on growth and metabolism.     

Receptors for insulin-like growth factors I and II in developing embryonic mouse limb bud

Insulin-like growth factors (IGF) or somatomedins (SM) have been classically defined as promoting the actions of growth hormone in skeletal growth. IGF is divided into two groups, IGF-I and II, and are presumed to act via IGF type I (higher affinity for IGF-I and II and very low affinity for insulin) and II (higher affinity for IGF-II than I and no affinity for insulin) receptors, respectively. Recently, a switchover role of IGF-II to I during fetal to adult growth has been suggested. We have investigated the possible transitional role of IGF-II to I in a developing mouse embryonic limb bud organ culture model. In this in vitro system, limb bud develops from the blastoma stage to a well-differentiated cartilage tissue. Both IGF type I and II receptors were found to be present in limb buds at all stages of differentiation. Type I receptor decreased with differentiation while Type II receptor increased. The effect of IGF-I on [3H]thymidine and [35S]sulfate uptake by the tissue increased with differentiation while the effect of IGF-II on [3H]thymidine uptake of the undifferentiated tissue was abolished with differentiation of the tissue. The increase of the IGF-I response with decreased type I receptor may reflect an altered receptor sensitivity (occupancy) during differentiation. The decrease of the IGF-II response with increased type II receptor with differentiation may on the other hand suggest that IGF-II in differentiated tissue no longer acts as a classical growth factor. These results tend to support the hypothesis of the switchover role of IGF-I and II during fetal and adult growth, however, confirmation of the precise role of IGF-I and II in biological growth may have to wait until further studies clarifying the significance of the increased IGF type II receptor in differentiated tissue are made.     

A systems biology approach: new insights into fetal growth restriction using Bayesian Networks

IL-6, IGF-II and IGFBP-2 concentrations in placental lysates were previously shown to be associated with foetal growth. This study aimed to apply a Bayesian Network (BN) model in order to investigate complex dependencies among biochemical and clinical factors and fetal growth outcome. Twenty-one Intra-Uterine Growth Restricted (IUGR) and 25 Appropriate for Gestational Age (AGA) pregnancies were followed throughout pregnancy. Information was collected on maternal and gestational age, neonatal gender, previous gynaecological history. Total protein content, IGF-II, IGFBP-1, IGFBP-2, IL-6, and TNF-alpha concentrations in placental lysates were measured, and IGF-I, IGF-II, IGFBP-1, IGFBP-2 and IL-6 relative gene expression in placenta assessed. A BN and a hybrid forecasting system were implemented: BN revealed a key role of maternal age and TNF-alpha on IUGR and confirmed a close relationship among IGF-II, IL-6 and foetal growth. A relationship between duration of gestation, appropriateness for gestational age, and placental IL-6 concentration was also confirmed. Compared with other techniques, BN showed a better accuracy. Findings confirmed a major role of maternal age in addition to IGF-II, IL-6 and TNF-alpha in IUGR. A direct role of IGFBP-2 was not shown. BN confirmed to be useful in understanding the system's biology and graphically representing variable relationships and hierarchy, particularly where, as in IUGR, many interactions among predictors exist.     

Placental efficiency and intrauterine resource allocation strategies in the common marmoset pregnancy

Mothers and fetuses are expected to be in some degree of conflict over the allocation of maternal resources to fetal growth in the intrauterine environment. Variation in placental structure and function may be one way a fetus can communicate need and quality to its mother, potentially manipulating maternal investment in its favor. Whereas common marmosets typically produce twin litters, they regularly give birth to triplet litters in captivity. The addition of another fetus is a potential drain on maternal resource availability and thus a source of elevated conflict over resource allocation. Marmoset littermates share a single placental mass, so that differences in the ratio of fetal to placental weight across litter categories suggest the presence of differential intrauterine strategies of resource allocation. The fetal/placental weight ratio was calculated for 26 marmoset pregnancies, representing both twin and triplet litters, to test the hypothesis that triplet fetuses respond to intrauterine conflict by soliciting placental overgrowth as a means of accessing maternal resources. In fact, relative to fetal mass, the triplet marmoset placenta is significantly undergrown, with individual triplets associated with less placental mass than their twin counterparts, suggesting that the triplet placenta is relatively more efficient in its support of fetal growth. There still may be an important role for maternal-fetal conflict in the programming of placental structure and function. Placental adaptations that solicit potential increases of maternal investment may occur at the microscopic or metabolic level, and thus may not be reflected in the size of the placenta as a whole.     

Presence of insulinlike growth factor receptors and lack of insulin receptors on fetal bovine smooth muscle cells

Summary Previous investigations have demonstrated specific receptors and associated mitogenic actions for insulin and insulinlike growth factors I and II (IGF-I and II) in postnatal bovine aortic smooth muscle. Using fetal tissue we have observed different patterns of binding and action for these peptides. Smooth muscle cells isolated from near-term fetal bovine aortae were studied in early passage. Specific receptors for both IGF-I and IGF-II were identified. Specific binding averaged 5.7%/2.5×10⁵ cells for IGF-I, and 16.2% for IGF-II, and 0.3% for insulin. High affinity K _d for both IGF receptors were nanomolar. IGF-II was fivefold less potent than IGF-I in displacing IGF-I binding. IGF-I showed no affinity for the IGF-II receptor. Insulin, at physiologic concentrations, was incapable of displacing either IGF-I or IGF-II binding. Cellular incorporation of [methyl-³H]thymidine was stimulated at the lowest dose of IGF-I tested, 0.5 ng/ml. IGF-II showed no effect up to 100 ng/ml, after which a sharp increase in incorporation was noted. Insulin had a similar effect only at concentrations &gt;0.5 μg/ml, with a maximal response noted at 5 to 10 μg/ml. Our results indicate that fetal bovine aortic smooth muscle cells have an abundance of IGF receptors but lack specific insulin receptors. In addition, IGF-II binding levels are three times higher than for IGF-I. These results are consistent with observations in other species, in which a predominance of IGF over insulin receptors has been demonstrated in fetal tissue, and provide further evidence for a role for the IGFs in embryonic cellular metabolism. This project was supported by grants AM22190 (R. L. H.), AM28229 (R. G. R.) from the National Institutes of Health, Bethesda, MD, and Research Career Development Award AM01275 from the NIH (R. G. R.). Dr. Lee was the recipient of a fellowship award from the Juvenile Diabetes Foundation International and is currently supported by funds from the American Diabetes Association. Dr. Benitz is the recipient of a Clinician-Scientist Award from the American Heart Association, with funds contributed in part by the California Affiliate.     

IGF-II is up-regulated and myofibres are hypertrophied in regenerating soleus of mice lacking FGF6

Important functions in myogenesis have been proposed for FGF6, a member of the fibroblast growth factor family accumulating almost exclusively in the myogenic lineage. However, the use of FGF6(-/-) mutant mice gave contradictory results and the role of FGF6 during myogenesis remains largely unclear. Using FGF6(-/-) mice, we first analysed the morphology of the regenerated soleus following cardiotoxin injection and showed hypertrophied myofibres in soleus of the mutant mice as compared to wild-type mice. Secondly, to examine the function of the IGF family in the hypertrophy process, we used semiquantitative and real-time RT-PCR assays and Western blots to monitor the expression of the insulin-like growth factors (IGF-I and IGF-II), their receptors [type I IGF receptor (IGF1R) and IGF-II receptor (IGF2R)], and of a binding protein IGFBP-5 in regenerating soleus muscles of FGF6(-/-) knockout mice vs. wild-type mice. In the mutant, both IGF-II and IGF2R, but not IGF-I and IGF1R, were strongly up-regulated, whereas IGFBP5 was down-regulated, strongly suggesting that, in the absence of FGF6, the mechanisms leading to myofibre hypertrophy were mediated specifically by an IGF-II/IGF2R signalling pathway distinct from the classic mechanism involving IGF-I and IGF1R previously described for skeletal muscle hypertrophy. The potential regulating role of IGFBP5 on IGF-II expression is also discussed. This report shows for the first time a specific role for FGF6 in the regulation of myofibre size during a process of in vivo myogenesis.     

Placental regulation of maternal-fetal interactions and brain development

A variety prenatal insults are associated with the incidence of neurodevelopmental disorders such as schizophrenia, autism and cerebral palsy. While the precise mechanisms underlying how transient gestational challenges can lead to later life dysfunctions are largely unknown, the placenta is likely to play a key role. The literal interface between maternal and fetal cells resides in the placenta, and disruptions to the maternal or intrauterine environment are necessarily conveyed to the developing embryo via the placenta. Placental cells bear the responsibility of promoting maternal tolerance of the semiallogeneic fetus and regulating selective permeability of nutrients, gases, and antibodies, while still providing physiological protection of the embryo from adversity. The placenta's critical role in modulating immune protection and the availability of nutrients and endocrine factors to the offspring implicates its involvement in autoimmunity, growth restriction and hypoxia, all factors associated with the development of neurological complications. In this review, we summarize primary maternal-fetal interactions that occur in the placenta and describe pathways by which maternal insults can impair these processes and disrupt fetal brain development. We also review emerging evidence for placental dysfunction in the prenatal programming of neurodevelopmental disorders. ? 2012 Wiley Periodicals, Inc. Develop Neurobiol, 2012.     

The IGF axis and placental function. a mini review

It is well known that the insulin-like growth factor (IGF) axis is an important regulator of foetal growth and in recent years, it has been suggested that the ligands IGF-I and IGF-II may, in part, mediate this effect by promoting proper placental development and function. In other tissues, IGF effects on metabolism, proliferation and differentiation are primarily mediated via IGF binding protein-regulated interaction of IGFs with the type 1 IGF receptor and therefore here, we review the placental expression and postulated role, of each of the IGF axis components and discuss the cellular mechanisms through which these effects are exerted.     

Insulin-like growth factor (IGF) family genes are aberrantly expressed in bovine conceptuses produced in vitro or by nuclear transfer

Embryos produced through somatic cell nuclear transfer (NT) or in vitro production (IVP) are often associated with increased abortion and abnormalities thought to arise from disruptions in normal gene expression. The insulin-like growth factor (IGF) family has a major influence on embryonic, fetal and placental development; differences in IGF expression in NT- and IVP-derived embryos may account for embryonic losses during placental attachment. In the present study, expression of IGF-I, IGF-II, IGF-I receptor (IGF-IR), and IGF-IIR mRNAs was quantitated in Day 7 and 25 bovine embryos produced in vivo, by NT, IVP, or parthenogenesis, to further understand divergent changes occurring during development. Expression of the IGF-I gene was not detected in Day 7 blastocysts for any treatment. However, there were no differences (P>0.10) among Day 7 treatments in the amounts of IGF-IR, IGF-II, and IGF-IIR mRNA. For Day 25 conceptuses, there was higher expression of IGF-I mRNA for NT and IVP embryonic tissues than for in vivo embryonic tissues (P<0.05). Furthermore, embryonic tissues from NT-derived embryos had higher expression of IGF-II mRNA than IVP embryonic tissues (P<0.05). Placental expression of IGF-IIR mRNA was greater for NT-derived than in vivo-derived embryos (P<0.05). There were no differences in IGF-IR mRNA across all treatments and tissues (P>0.10). In conclusion, these differences in growth factor gene expression during early placental attachment and rapid embryonic growth may directly or indirectly contribute to increased losses and abnormalities in IVP- and NT-derived embryos.