Three electron beams from a laser-plasma wakefield accelerator and the energy apportioning question

Laser-wakefield accelerators are compact devices capable of delivering ultra-short electron bunches with pC-level charge and MeV-GeV energy by exploiting the ultra-high electric fields arising from the interaction of intense laser pulses with plasma. We show experimentally and through numerical simulations that a high-energy electron beam is produced simultaneously with two stable lower-energy beams that are ejected in oblique and counter-propagating directions, typically carrying off 5–10% of the initial laser energy. A MeV, 10s nC oblique beam is ejected in a 30°–60° hollow cone, which is filled with more energetic electrons determined by the injection dynamics. A nC-level, 100s keV backward-directed beam is mainly produced at the leading edge of the plasma column. We discuss the apportioning of absorbed laser energy amongst the three beams. Knowledge of the distribution of laser energy and electron beam charge, which determine the overall efficiency, is important for various applications of laser-wakefield accelerators, including the development of staged high-energy accelerators.

139. PLACENTAL EXPRESSION OF microRNAs ALTERS WITH GESTATION IN THE GUINEA PIG

Functional development of the placenta ensures an adequate supply of nutrients for fetal growth throughout gestation. Placental nutrient transport capacity increases during gestation, through alterations in structure and abundance of its molecular determinants, including expression of Slc2a1 (glucose transporter type-1) and Slc38a2 (system A amino acid transporter), as well as Igf1and Igf2. Each of these genes are predicted targets of microRNAs. Non-coding RNAs can down-regulate, as well as activate translation, by interacting with complementary regions in the promoter, coding, or 3’UTR of target mRNAs.(1) MicroRNAs are present in the mammalian placenta,(2) but little is known about developmental changes in their expression and actions. We hypothesised that placental expression of microRNAs which target molecular mediators of nutrient transport changes during gestation. Expression of microRNAs in the guinea pig placenta was examined at D30 (n = 7) and D60 (n = 7) of gestation (term = D70) by Exiqon microarray. Gene expression was measured by real-time PCR. Predicted gene targets were identified using miRecords and networks and pathways by Ingenuity Pathway Analysis. Placental expression of 119 microRNAs was upregulated (P < 0.05), and that of 40 was down-regulated (P < 0.05), at late compared to early gestation. Of the 20 most abundant differentially up- or down-regulated microRNAs, 11 are predicted to target members of solute carrier families. This includes has-miR-26a (↑2X), which is predicted to target Slc38a2 mRNA and expression of has-miR-26a and Slc38a2 was positively correlated (P < 0.02). Alternate predicted targets of has-miR-26a include networks involving amino acid metabolism, molecular transport and small molecular biochemistry. These findings support the hypotheses that gestational changes in microRNA expression act to regulate functional development of the placenta, including expression of genes that mediate nutrient transport. (1) Breving K, Esquela-Kerscher A. Int J Biochem Cell Biol 2009.(2) Barad O, et al. Genome Res 2004 14: 2486–2494.

159. MATERNAL NUTRITION AND GESTATIONAL AGE AFFECT PLACENTAL microRNA EXPRESSION IN THE GUINEA PIG

Maternal undernutrition restricts placental growth and nutrient supply to the fetus, but induces compensatory alterations in structure and function of the placenta. Maternal undernutrition in guinea pigs also restricts placental growth and alters structure, and changes expression of Igf1, Igf2, Slc2a1, Slc38a2 mRNA in mid and late gestation, consistent with nutritionally induced changes in nutrient transport across the placenta. MicroRNAs are non-coding RNAs that regulate expression of target genes by translational inhibition and mRNA degradation and are present in the mammalian placenta. Effects of maternal undernutrition on their expression are unknown. We hypothesised that altered expression of key functional genes in the placenta in maternal undernutrition are in part due to altered expression of regulatory microRNAs. The effect of maternal food restriction on the expression of microRNAs in the guinea pig placenta was examined at D30 and D60 of gestation (term = D70). Guinea pigs were fed either ad libitum (AL) or restricted (R). MicroRNA expression was determined by Exiqon microarray v.8.1. In AL placentas, 119 microRNAs were upregulated (p<0.05), whilst 40 were down-regulated (p<0.05) at late compared to early gestation. In R placentas, 163 microRNAs were upregulated (p<0.05), whilst 123 were down-regulated (p<0.05) at late compared to early gestation. Of the 20 most abundant up-regulated microRNAs miR-Plus (ID 17871) and hsa-miR-411 were altered only in AL and hsa-miR-376a and -376b were altered only in R placenta. Of the 20 most abundant down-regulated microRNAs, 13 were altered only in AL and 14 only in R placentas. Placental expression of microRNAs changed with gestation, and maternal undernutrition modified this pattern and altered expression of many additional microRNAs in the guinea pig placenta. This suggests that miRNAs and factors that influence their expression may play a role in the structural and/or functional development of the placenta and hence fetal growth.

162. THE EFFECT OF MATERNAL FOLIC ACID SUPPLEMENTATION THROUGHOUT PREGNANCY ON NEURODEVELOPMENT, MOTOR FUNCTION AND BEHAVIOUR OF PROGENY IN THE RAT

Background: Maternal folic acid supplementation (mFAS) during early pregnancy is recommended to reduce the incidence of neural tube defects and has recently been associated with improved neurodevelopment in children. However, the effect on neurodevelopment of mFAS from before conception and throughout pregnancy is unknown. We examined the effect of mFAS throughout the gestational period on postnatal growth, neurodevelopment and early adult motor function and behaviour in rat offspring. Methods: Female Wistar Rats were fed either a control (folic acid 2mg/kg, n=6) or moderate mFAS diet (folic acid 6mg/kg, n=6) from two weeks before mating with Lewis males, until birth of progeny. Male and female progeny (Control=36, mFAS=36) were weighed on postnatal day (PD) 3, 7, 14, 21, 40 and 90, and underwent various tests between PD4 and 14: righting reflex, palm-grasp reflex, negative geotaxis, forelimb hanging, ascent test and eye opening. Locomotor/ exploratory behaviour, motor coordination and anxiety were assessed using an open field test (PD52), rotarod (PD55) and elevated plus maze (PD58) (Control=24, mFAS=24). Results: mFAS did not alter maternal weight gain, litter-size at birth or progeny growth between PD3-90. mFAS tended to increase righting reflex time (p=0.057) and impair ascent ability (p=0.085). Negative geotaxis time was reduced at PD7 but not later (Diet x Age p=0.051). mFAS increased the proportion of progeny with eyes open at PD14 (p=0.008) and tended to increase forelimb hanging time(p=0.097). mFAS did not alter motor learning/function (rotarod), but increased ambulatory and exploratory behaviour (open field test; p=0.027). Conclusions: mFAS delays some early aspects of neurodevelopment including neonatal postural reflex maturation and proprioceptive/vestibular function, but accelerates others such as eye opening. However, the open field test indicated that mFAS improved the offspring's locomotion and exploratory behaviours in adulthood. Further studies will differentiate the neurodevelopmental effects of mFAS around conception from gestation-long mFAS.

Kinetic and chemical properties of ATP sulphurylase from Penicillin chrysogenum

Adenosine triphosphate sulphurylase (ATP: sulfate adenylyltransferase, EC 2.7.7.4.) has been purified from the filamentous fungus. Penicillium chrysogenum, and characterized physically, kinetically, and chemically. The P. Chrysogenum enzyme is an octomer (mol. wt. 440 000) composed of eight identical subunits (mol. wt. 55 000). Some physical constants are S20,w = 13.0 X 10(-13)s, D20,w = 2.94 X 10(-7) cm2 X s-1, v = 0.733 cm3 X g-1, A1%1cm = 8.71 at 278 nm. The enzyme catalyses (a) the synthesis of adenosine 5'-phosphosulphate (APS) and MgPPi from MgATP and SO2-4, (b) the hydrolysis of MgATP to AMP and MgPPi in the absence of SO2-4, (c) Mg32PPi-MgATP exchange in the absence of SO2-4, (d) molybdolysis of MgATP to AMP and MgPPi, (e) synthesis of MgATP and SO2-4 from APS and MgPPi, and (f) Mg32PPi-MgATP exchange in the presence of SO2-4. The Vmax values of reactions (a)-(c) are about 0.10-0.35 mumole X min-1 X mg enzyme-1. The Vmax values of reactions (d)-(f) are about 12-19 mumole X min-1 X mg enzyme-1. The catalytic activity of the enzyme in the direction of APS synthesis is rather low (0.13 unit X mg protein-1, corresponding to an active site turnover number of 7.15 min-1). However, the ATP sulphurylase content of mycelium growing on excess SO2-4 is 0.22 unit X g dry wt.-1, which is sufficient to account for the maximum in vivo rate of SO2-4 assimilation. The normal catalytic reaction is Ordered Bi Bi with A = MgATP, B = SO2-4, P = MgPPi, and Q = APS. Several lines of kinetic evidence suggest that the E.MgATP and E.APS complexes isomerize (to E approximately AMP.MgPPi and E approximately AMP.SO4, respectively) before the second substrate binds. Chemical modification studies have disclosed the presence of essential arginine, histidine, carboxyl, and tryosine residues. The latter is rather acidic (pKa = 7 or less). Nitration of the tyrosine increases the Km for MgATP without significantly affecting Kia for MgATP or Vmaxf. This result, and the fact that MgATP plus nitrate protects the enzyme against inactivation by tetranitromethane while MgATP alone does not, suggests that the essential tyrosine plays a role in nucleotide isomerization (perhaps as an adenylyl acceptor).

The SAGA continues: expanding the cellular role of a transcriptional co-activator complex

Throughout the last decade, great advances have been made in our understanding of how DNA-templated cellular processes occur in the native chromatin environment. Proteins that regulate transcription, replication, DNA repair, mitosis and other processes must be targeted to specific regions of the genome and granted access to DNA, which is normally tightly packaged in the higher-order chromatin structure of eukaryotic nuclei. Massive multiprotein complexes have been discovered, which facilitate access to DNA and recruitment of downstream effectors through three distinct mechanisms: chemical modification of histone amino-acid residues, ATP-dependent chromatin remodeling and histone exchange. The yeast Spt-Ada-Gcn5-Acetyl transferase (SAGA) transcriptional co-activator complex regulates numerous cellular processes through coordination of multiple histone post-translational modifications. SAGA is known to generate and interact with a number of histone modifications, including acetylation, methylation, ubiquitylation and phosphorylation. Although best characterized for its role in regulating transcriptional activation, SAGA is also required for optimal transcription elongation, mRNA export and perhaps nucleotide excision repair. Here, we discuss findings from recent years that have elucidated the function of this 1.8-MDa complex in multiple cellular processes, and how misregulation of the homologous complexes in humans may ultimately play a role in development of disease.

Insulin-like growth factor binding proteins in follicular fluid from morphologically distinct healthy and atretic bovine antral follicles

In bovine follicles 2-5 mm in diameter, two morphologically distinct types of healthy follicles and two types of atretic follicles have been described recently. Healthy follicles either have columnar basal granulosa cells with follicular basal lamina composed of many layers or 'loops' or they have rounded basal cells with a conventional single-layered, aligned follicular basal lamina. In atretic follicles, cell death either commences at the basal layer and progresses to the antrum (basal atresia) with macrophage penetration of the membrana granulosa or death progresses from the antrum in a basal direction (antral atresia). Little is known about how these different phenotypes develop. To determine whether insulin-like growth factor binding protein (IGFBP) levels in follicular fluid differ between these different types of follicles, we measured IGFBP levels in fluids from these follicles. A total of 61 follicles were assessed by light microscopy and characterized by morphological analysis as either healthy, with columnar or rounded basal granulosa cells, or as undergoing antral or basal atresia. The IGFBP concentration in the follicular fluid of individual follicles from the four groups (n = 12-20 per group) was identified by Western ligand blots using (125)I-insulin-like growth factor (IGF)-II as a probe. Insulin-like growth factor binding proteins 2, 3 (44 and 40 kDa), 4 (glycosylated and non-glycosylated) and 5 were observed. The levels (per volume of fluid) of IGFBPs 2, 4 and 5 were greater in atretic follicles than in healthy follicles. However, there were no statistical differences in levels of each IGFBP between either the two types of healthy follicle or between the two types of atretic follicles. Thus, IGFBP levels are not related to the different types of healthy or atretic follicles.

Late pregnancy increases hepatic expression of insulin-like growth factor-I in well nourished guinea pigs

Blood IGF-I concentrations are persistently elevated throughout pregnancy in humans and guinea pigs and may regulate substrate partitioning between mother and conceptus. In the guinea pig, liver and adipose tissue have recently been suggested to contribute to the increased levels of circulating IGF-I in mid-pregnancy, but whether this persists in late pregnancy in undernutrition is not known. Therefore the effect of pregnancy and undernutrition on circulating IGF-I and hepatic expression of IGF-I in late gestation in the guinea pig was examined. Female guinea pigs (Cavia porcellus) were fed ad libitum throughout pregnancy or 70% of ad libitum intake for 28 days prior to and throughout pregnancy (term is 69 d). Non-pregnant animals were maintained for 88 days on the same diets. Plasma IGF-I was measured by RIA after molecular sieving chromatography at low pH. Abundances of IGF-I and beta-actin mRNA in maternal liver were quantified by digoxigenin-ELISA after RT PCR. Late pregnancy increased both the concentration of IGF-I protein (p<0.001) in plasma and the relative abundance of liver IGF-I mRNA (p<0.001) in ad libitum fed, but not in feed restricted pregnant guinea pigs. The concentration of IGF-I protein in plasma correlated positively with the relative abundance of IGF-I mRNA in liver overall (p<0.002), suggesting the liver as a major source of endocrine IGF-I in late pregnant guinea pigs. This study demonstrates that hepatic expression of IGF-I remains elevated during late pregnancy in the well fed guinea pig, which is in contrast to that observed in other non-human species.

Circulating insulin-like growth factor (IGF)-I and IGF binding proteins -1 and -3 and placental development in the guinea-pig

Restricting maternal nutrition before and throughout pregnancy in the guinea-pig restricts foetal growth in part by altering placental structural determinants of substrate transfer function. The insulin-like growth factors have been implicated in mediating these changes. To assess the role of IGF-I in placental adaptation to maternal undernutrition, we examined the associations of circulating IGF-I and IGF binding proteins -1, -3 and -4 in the mother with placental structural development. In both mid- and late pregnancy, maternal food restriction reduced maternal plasma IGF-I by 56 per cent (P<0.0005) and 50 per cent (P<0.0005) respectively, and plasma IGFBP-3 by 47 per cent (P=0.03) and 55 per cent (P=0.002), respectively. Maternal plasma IGFBP-4 was reduced by 45 per cent (P=0.041) in food restricted guinea-pigs in mid-pregnancy but not late in pregnancy, while IGFBP-1 was unaltered at both stages. Late in pregnancy, food restriction reduced the ratio of maternal circulating IGF-I to IGFBP-1 by 52 per cent (P=0.011) and increased the ratio of IGF-I to IGFBP-3 in maternal plasma by 10 per cent (P=0.011). The relationships between the maternal IGF axis and structural correlates of placental function were assessed using pooled data from both ad libitum fed and food restricted animals. In mid-pregnancy, the volume density of the maternal blood space in the placental labyrinth correlated positively with both maternal plasma IGF-I and IGFBP-3, while maternal blood space volume correlated negatively with maternal plasma IGFBP-1. In late pregnancy, placental weight correlated positively with both maternal plasma IGF-I and IGFBP-4, while the surface area of syncytiotrophoblast and weight of trophoblast correlated positively, and mean syncytiotrophoblast thickness negatively, with maternal plasma IGF-I. Late in pregnancy, the volume density and weight of syncytiotrophoblast, the surface density and total surface area of trophoblast and the volume of the maternal blood space each correlated positively, and syncytiotrophoblast thickness correlated negatively with maternal plasma IGFBP-3. Concomitantly, placental weight, placental diameter, placental volume, volume density and weight of syncytiotrophoblast, weight of foetal capillaries, syncytiotrophoblast surface density and total syncytiotrophoblast surface area in the placental labyrinth, each correlated positively with the ratio of IGF-I to IGFBP-1 in maternal plasma, while syncytiotrophoblast thickness correlated negatively with this ratio. In late pregnancy therefore, increased trophoblast abundance and placental vascularity, and a reduced barrier to diffusion between maternal and foetal blood, occurs in association with increased abundance of IGF-I and its major carrier, IGFBP-3, and a reduction in that of IGFBP-1 in maternal blood in the guinea-pig. This suggests that systemic IGF-I and modulation of its bioavailability by IGFBPs -1 and -3 within the mother may influence placental growth and differentiation in an endocrine fashion, particularly when nutrition is limited.

Altered placental structure induced by maternal food restriction in guinea pigs: a role for circulating IGF-II and IGFBP-2 in the mother?

Maternal feed restriction may restrict fetal growth in part indirectly by impairing placental functional development. Such actions could be mediated by the insulin-like growth factors (IGF), which are important modulators of placental growth and differentiation and more generally, are influenced by nutrient availability. While a role for the fetal IGF axis has been demonstrated, less is known of the influence, if any, of that in the mother. This study aimed to determine whether alterations in the maternal IGF axis and placental functional and structural development due to maternal food restriction are related. We therefore examined the associations between placental structural parameters, the ratios of maternal to fetal plasma glucose and fetal to maternal plasma urea concentration, and maternal circulating IGF-I, IGF-II and IGFBP-2 in ad libitum fed and food restricted (70-90 per cent of the ad libitum intake) pregnant guinea pigs. In mid-gestation, fetal weight (r = 0.65, P = 0.008, n = 17), volume of the maternal blood space (r = 0.58, P = 0.048, n = 17), and surface density of syncytiotrophoblast (r = 0.65, P = 0.023, n = 17), were positively correlated, and syncytiotrophoblast thickness was negatively correlated, with maternal plasma IGF-II concentration (r = -0.69, P = 0.014, n = 17). Late in gestation, fetal weight, placental weight and total exchange surface area in the placenta were each negatively correlated with maternal plasma IGFBP-2 concentration (all P < 0.01), while the arithmetic mean thickness of syncytiotrophoblast was positively correlated with maternal plasma IGFBP-2 concentration. Late in gestation, the ratio of maternal to fetal plasma glucose was positively correlated with fetal weight (r = 0.54, P = 0.038, n = 15) and the ratio of fetal to maternal plasma urea concentration was positively correlated with placental weight (r = 0.52, P=0.046, n=15). Maternal feed restriction reduced the ratio of maternal plasma IGF-II to IGFBP-2 in late gestation by 75 per cent (P = 0.001) and this ratio was positively correlated with fetal weight (r = 0.56, P = 0.01, n = 20), placental weight (r = 0.59, P = 0.006), placental diameter (r = 0.621, P = 0.003), placental volume (r = 0.57, P=0.009), weight of trophoblast (r = 0.51, P=0.037), weight of fetal capillaries (r = 0.49, P = 0.046), syncytiotrophoblast surface density (r = 0.611, P = 0.009) and negatively correlated with syncytiotrophoblast thickness (r = -0.55, P = 0.021). Our results suggest that in mid-pregnancy, maternal circulating IGF-II promotes placental structural development, while later in pregnancy, IGFBP-2 inhibits it, and their relative abundance and interaction strongly influences placental structure and function near term.

A tale of histone modifications

The modification of chromatin structure is important for a number of nuclear functions, exemplified by the regulation of transcription. This review discusses recent studies of covalent histone modifications and the enzymatic machines that generate them.

Sds3 (suppressor of defective silencing 3) is an integral component of the yeast Sin3[middle dot]Rpd3 histone deacetylase complex and is required for histone deacetylase activity

SDS3 (suppressor of defective silencing 3) was originally identified in a screen for mutations that cause increased silencing of a crippled HMR silencer in a rap1 mutant background. In addition, sds3 mutants have phenotypes very similar to those seen in sin3 and rpd3 mutants, suggesting that it functions in the same genetic pathway. In this manuscript we demonstrate that Sds3p is an integral subunit of a previously identified high molecular weight Rpd3p.Sin3p containing yeast histone deacetylase complex. By analyzing an sds3Delta strain we show that, in the absence of Sds3p, Sin3p can be chromatographically separated from Rpd3p, indicating that Sds3p promotes the integrity of the complex. Moreover, the remaining Rpd3p complex in the sds3Delta strain had little or no histone deacetylase activity. Thus, Sds3p plays important roles in the integrity and catalytic activity of the Rpd3p.Sin3p complex.

A mathematical model for assessing changes in neurofilament protein levels in neurites and cell bodies of differentiating neuroblastoma cells

A mathematical model which allows the calculation of the level of neurofilament protein in the cell body (x) and in the neurites (y) of differentiating SK-N-SH cells is presented. The model considers the changes in cell number (proliferating cells) and the number of cells with neurites (differentiating cells). It takes into account the fact that (i) when cells are cultured in differentiating conditions, an increase in cell number is initially observed and (ii) in a non-synchronized population of differentiating cells, the length of neurite extended by individual cells varies within the population. Total neurofilament protein levels in a population of cells were measured by enzyme-linked immunoabsorbant assay and application of the model to the data allowed values for x and y to be calculated. The validity of the model is supported by the fact that the predicted total neurofilament protein levels are highly correlated with the experimentally derived neurofilament protein levels. The model should be of use in temporal studies of cytoskeletal proteins involved in neuronal growth/differentiation and also in studies in which the system is a target of toxic insult.

Treatment of underfed pigs with GH throughout the second quarter of pregnancy increases fetal growth

Circulating growth hormone (GH) concentrations increase in pregnancy and administration of GH during early-mid pregnancy increases fetal growth in well-fed pigs. To determine whether increased maternal GH could promote fetal growth when feed availability is restricted, fifteen cross-bred primiparous sows (gilts) were fed at approximately 30% of ad libitum intake, from mating onwards and were injected daily i.m. with recombinant porcine GH (pGH) at doses of 0, 13.4+/-0.3 and 25.6+/-0.5 microg/kg live weight from day 25 to day 51 of pregnancy (term approximately 115 days). Treatment with pGH increased maternal backfat loss between day 25 and day 51 of pregnancy, and increased maternal plasma IGF-I concentrations measured at day 51 of pregnancy. Fetal body weight, length and skull width at day 51 of pregnancy were increased by maternal treatment with pGH. Fetal plasma glucose concentrations were increased and maternal/fetal plasma glucose concentration gradients were decreased by maternal pGH treatment at 13.4, but not 25.6 microg/kg.day. Fetal plasma concentrations of urea were decreased by both levels of pGH treatment. Overall, fetal weight was negatively correlated with fetal plasma concentrations of urea, positively correlated with maternal plasma alpha-amino nitrogen concentrations and unrelated to glucose concentrations in either maternal or fetal plasma. This suggests that the availability of amino acids, not glucose, limits fetal growth in the first half of pregnancy in underfed gilts, and that maternal GH treatment may improve amino acid delivery to the fetus.

The something about silencing protein, Sas3, is the catalytic subunit of NuA3, a yTAF(II)30-containing HAT complex that interacts with the Spt16 subunit of the yeast CP (Cdc68/Pob3)-FACT complex

We have purified and characterized a Gcn5-independent nucleosomal histone H3 HAT complex, NuA3 (Nucleosomal Acetyltransferase of histone H3). Peptide sequencing of proteins from the purified NuA3 complex identified Sas3 as the catalytic HAT subunit of the complex. Sas3 is the yeast homolog of the human MOZ oncogene. Sas3 is required for both the HAT activity and the integrity of the NuA3 complex. In addition, NuA3 contains the TBP- associated factor, yTAF(II)30, which is also a component of the TFIID, TFIIF, and SWI/SNF complexes. Sas3 mediates interaction of the NuA3 complex with Spt16 both in vivo and in vitro. Spt16 functions as a component of the yeast CP (Cdc68/Pob3) and mammalian FACT (facilitates chromatin transcription) complexes, which are involved in transcription elongation and DNA replication. This interaction suggests that the NuA3 complex might function in concert with FACT-CP to stimulate transcription or replication elongation through nucleosomes by providing a coupled acetyltransferase activity.

Histone acetyltransferase complexes can mediate transcriptional activation by the major glucocorticoid receptor activation domain

Previous studies have shown that the Ada adapter proteins are important for glucocorticoid receptor (GR)-mediated gene activation in yeast. The N-terminal transactivation domain of GR, tau1, is dependent upon Ada2, Ada3, and Gcn5 for transactivation in vitro and in vivo. Using in vitro techniques, we demonstrate that the GR-tau1 interacts directly with the native Ada containing histone acetyltransferase (HAT) complex SAGA but not the related Ada complex. Mutations in tau1 that reduce tau1 transactivation activity in vivo lead to a reduced binding of tau1 to the SAGA complex and conversely, mutations increasing the transactivation activity of tau1 lead to an increased binding of tau1 to SAGA. In addition, the Ada-independent NuA4 HAT complex also interacts with tau1. GAL4-tau1-driven transcription from chromatin templates is stimulated by SAGA and NuA4 in an acetyl coenzyme A-dependent manner. Low-activity tau1 mutants reduce SAGA- and NuA4-stimulated transcription while high-activity tau1 mutants increase transcriptional activation, specifically from chromatin templates. Our results demonstrate that the targeting of native HAT complexes by the GR-tau1 activation domain mediates transcriptional stimulation from chromatin templates.

A conserved motif present in a class of helix-loop-helix proteins activates transcription by direct recruitment of the SAGA complex

The class I helix-loop-helix (HLH) proteins, which include E2A, HEB, and E2-2, have been shown to be required for lineage-specific gene expression during T and B lymphocyte development. Additionally, the E2A proteins function to regulate V(D)J recombination, possibly by allowing access of variable region segments to the recombination machinery. The mechanisms by which E2A regulates transcription and recombination, however, are largely unknown. Here, we identify a novel motif, LDFS, present in the vertebrate class I HLH proteins as well as in a yeast HLH protein that is essential for transactivation. We provide both genetic and biochemical evidence that the highly conserved LDFS motif stimulates transcription by direct recruitment of the SAGA histone acetyltransferase complex.

Histone acetyltransferase complexes

Modification of histone amino terminal tails by acetylation has long been linked to the transcriptional capacity of genes in chromatin and to various aspects of chromatin dynamics. Over the last few years a flurry of reports have described the purification and identification of a large number of histone acetyltransferases. Many of these enzymes had previously been described as transcriptional regulators and have frequently been isolated as part of larger multisubunit protein complexes. This review describes the association of acetyltransferases with partner proteins and the additional functional attributes of such complexes beyond catalytic function.

Expanded lysine acetylation specificity of Gcn5 in native complexes

The coactivator/adaptor protein Gcn5 is a conserved histone acetyltransferase, which functions as the catalytic subunit in multiple yeast transcriptional regulatory complexes. The ability of Gcn5 to acetylate nucleosomal histones is significantly reduced relative to its activity on free histones, where it predominantly modifies histone H3 at lysine 14. However, the association of Gcn5 in multisubunit complexes potentiates its nucleosomal histone acetyltransferase activity. Here, we show that the association of Gcn5 with other proteins in two native yeast complexes, Ada and SAGA (Spt-Ada-Gcn5-acetyltransferase), directly confers upon Gcn5 the ability to acetylate an expanded set of lysines on H3. Furthermore Ada and SAGA have overlapping, yet distinct, patterns of acetylation, suggesting that the association of specific subunits determines site specificity.

Functional organization of the yeast SAGA complex: distinct components involved in structural integrity, nucleosome acetylation, and TATA-binding protein interaction

SAGA, a recently described protein complex in Saccharomyces cerevisiae, is important for transcription in vivo and possesses histone acetylation function. Here we report both biochemical and genetic analyses of members of three classes of transcription regulatory factors contained within the SAGA complex. We demonstrate a correlation between the phenotypic severity of SAGA mutants and SAGA structural integrity. Specifically, null mutations in the Gcn5/Ada2/Ada3 or Spt3/Spt8 classes cause moderate phenotypes and subtle structural alterations, while mutations in a third subgroup, Spt7/Spt20, as well as Ada1, disrupt the complex and cause severe phenotypes. Interestingly, double mutants (gcn5Delta spt3Delta and gcn5Delta spt8Delta) causing loss of a member of each of the moderate classes have severe phenotypes, similar to spt7Delta, spt20Delta, or ada1Delta mutants. In addition, we have investigated biochemical functions suggested by the moderate phenotypic classes and find that first, normal nucleosomal acetylation by SAGA requires a specific domain of Gcn5, termed the bromodomain. Deletion of this domain also causes specific transcriptional defects at the HIS3 promoter in vivo. Second, SAGA interacts with TBP, the TATA-binding protein, and this interaction requires Spt8 in vitro. Overall, our data demonstrate that SAGA harbors multiple, distinct transcription-related functions, including direct TBP interaction and nucleosomal histone acetylation. Loss of either of these causes slight impairment in vivo, but loss of both is highly detrimental to growth and transcription.

The ATM-related cofactor Tra1 is a component of the purified SAGA complex

The SAGA histone acetyltransferase/transcriptional adaptor complex is composed of multiple transcriptional regulators including Ada, Spt, and TAFII proteins. Here we identify an additional novel subunit of the complex, Tra1, an ATM/PI-3-kinase-related homolog of the human TRRAP cofactor, which is essential for c-Myc and E2F-mediated oncogenic transformation. Mass spectrometry, immunoblotting, and immunoprecipitation experiments confirm the stable association of this protein within SAGA. In addition, the Tra1 protein is a component of at least two other histone acetyltransferase protein complexes. These results indicate a role for Tra1 in the regulation of transcriptional activation through the recruitment of HAT activity to an activator-bound promoter.

Purified histone acetyltransferase complexes stimulate HIV-1 transcription from preassembled nucleosomal arrays

Protein acetylation has been implicated in the regulation of HIV-1 gene transcription. Here, we have exploited the activities of four native histone acetyltransferase (HAT) complexes from yeast to directly test whether acetylation regulates HIV-1 transcription in vitro. HAT activities acetylating either histone H3 (SAGA, Ada, and NuA3) or H4 (NuA4) stimulate HIV-1 transcription from preassembled nucleosomal templates in an acetyl CoA-dependent manner. HIV-1 transcription from histone-free DNA is not affected by the HATs, indicating that these activities function in a chromatin-specific fashion. For Ada and NuA4, we demonstrate that acetylation of only histone proteins mediates enhanced transcription, suggesting that these complexes facilitate transcription at least in part by modifying histones. To address a potential mechanism by which HAT complexes stimulate transcription, we performed a restriction enzyme accessibility analysis. Each of the HATs increases the cutting efficiencies of restriction endonucleases targeting the HIV-1 chromatin templates in a manner not requiring transcription, suggesting that histone acetylation leads to nucleosome remodeling.

Identification and analysis of yeast nucleosomal histone acetyltransferase complexes

Many studies have linked acetylation of lysine residues on the amino-terminal tails of the core histones to transcriptional activity of cellular chromatin. New insights into this field were gained on the identification of the first nuclear, type A histone acetyltransferase (HAT). The yeast transcriptional adaptor protein Gcn5 was identified as a nuclear HAT and thus provided a direct link between pathways of transcriptional activation and histone acetylation. However, while recombinant Gcn5 can efficiently acetylate free histone H3 and, to a lesser extent, H4 it is unable to acetylate nucleosomal histones. It is therefore very likely that additional proteins are required for Gcn5-mediated acetylation of chromosomal histones. We have recently shown that Gcn5 is the catalytic subunit of two high-molecular-weight histone acetyltransferase complexes in yeast. In addition to the Gcn5-containing ADA and SAGA HAT complexes we have identified two other HAT complexes in yeast. These are called NuA3 and NuA4 for their predominant specificity to acetylate histones H3 and H4, respectively. Here we describe the identification and characterization of four native nuclear high-molecular-weight HAT complexes in Saccharomyces cerevisiae. These purified HATs can be used in a variety of functional assays to further address questions of how acetylation has an impact on transcriptional regulation.

Transcriptional activators direct histone acetyltransferase complexes to nucleosomes

Transcriptional co-activators were originally identified as proteins that act as intermediaries between upstream activators and the basal transcription machinery. The discovery that co-activators such as Tetrahymena and yeast Gcn5, as well as human p300/CBP, pCAF, Src-1, ACTR and TAFII250, can acetylate histones suggests that activators may be involved in targeting acetylation activity to promoters. Several histone deacetylases have been linked to transcriptional co-repressor proteins, suggesting that the action of both acetylases and deacetylases is important in the regulation of many genes. Here we demonstrate the binding of two native yeast histone acetyltransferase (HAT) complexes to the herpesvirus VP16 activation domain and the yeast transcriptional activator Gcn4, and show that it is their interaction with the VP16 activation domain that targets Gal4-VP16-bound nucleosomes for acetylation. We find that Gal4-VP16-driven transcription from chromatin templates is stimulated by both HAT complexes in an acetyl CoA-dependent reaction. Our results demonstrate the targeting of native HAT complexes by a transcription-activation domain to nucleosomes in order to activate transcription.

A subset of TAF(II)s are integral components of the SAGA complex required for nucleosome acetylation and transcriptional stimulation

A number of transcriptional coactivator proteins have been identified as histone acetyltransferase (HAT) proteins, providing a direct molecular basis for the coupling of histone acetylation and transcriptional activation. The yeast Spt-Ada-Gcn5-acetyltransferase (SAGA) complex requires the coactivator protein Gcn5 for HAT activity. Identification of protein subunits by mass spectrometry and immunoblotting revealed that the TATA binding protein-associated factors (TAF(II)s) TAF(II)90, -68/61, -60, -25/23, and -20/17 are integral components of this complex. In addition, TAF(II)68 was required for both SAGA-dependent nucleosomal HAT activity and transcriptional activation from chromatin templates in vitro. These results illustrate a role for certain TAF(II) proteins in the regulation of gene expression at the level of chromatin modification that is distinct from the TFIID complex and TAF(II)145.

The SAGA unfolds: convergence of transcription regulators in chromatin-modifying complexes

Several previously characterized transcriptional adaptors and coactivators are now known to be histone acetyltransferases (HATs). Recent studies in Saccharomyces cerevisiae indicate that the Gcn5p HAT exists in large complexes containing several phenotypic classes of transcription factors. Genetic and biochemical studies of these transcription factors and their functions within HAT complexes suggest that acetylation of histones is one function of an integrated system of modular activities. These activities include interaction with activators, histone acetylation and interaction with basal factors. Coordination of these functions may well be an important component of gene activation in vivo.

Effects of acute and chronic food restriction on the insulin-like growth factor axis in the guinea pig

The effect of fasting (17-18 h) versus food restriction (70% for 80 +/- 13 days) on the IGF-IGF binding protein (BP) axis in female guinea pigs was studied and related to body weight, weight gain and food conversion efficiency. Circulating IGF-I was reduced in the fasted (13%) and food-restricted (50%) animals. IGF-II was only decreased (61%) in the food-restricted group. There was no effect of fasting on IGFBP-1 to -4 while IGFBP-1, -3 and -4 were reduced by 56%, 60% and 44% respectively, and IGFBP-2 increased by 72%, in the food-restricted group. Food restriction reduced the relative sizes of fat depots, spleen, liver, thymus and heart, increased those of adrenals, kidneys, pancreas, gastrointestinal tract, M. Biceps, M. Soleus and brain while those of uterus, lungs, thyroids and M. Gastrocnemius were unchanged. IGFBP-1 and -2 were negatively correlated to weight gain and food conversion efficiency in the ad libitum-fed group, while IGF-I, -II, IGFBP-1, -3 and -4 were positively correlated to body weight, weight gain and food conversion efficiency in the food-restricted group. The results show that acute and chronic food restriction have different consequences for the IGF-IGFBP axis. Furthermore, IGF-II as well as IGF-I are implicated in the control of body weight, weight gain and food conversion efficiency under conditions of restricted nutrition. Finally, IGFBP-1 and -2 may have different roles during chronic undernutrition compared with unrestrained nutrition in adult life.

Measurement of an analog of insulin-like growth factor-I in blood plasma using a novel enzyme-linked immunosorbent assay

Long-Arg3-IGF-I (LR3IGF-I) is a synthetic analog of IGF-I that has much lower affinity for IGF-binding proteins than do native IGFs-I and -II. Comparisons of the effects of LR3IGF-I with those of IGFs-I and-II in in vitro and in vivo studies have proved useful in defining the functions of IGF-binding proteins. We have developed a sensitive noncompetitive nonisotopic assay of LR3IGF-I. Mouse IgG 1A7-F5-E5 binds an epitope that contains the substituted arginine3 in LR3IGF-I and was used as the solid phase antibody. The solution phase antibody was a rabbit immunoglobulin Nelson which binds to an epitope that is common to IGF-I and LR3IGF-I. The ELISA system was able to detect as little as 50 pg LR3IGF-I in 100 microliters and the native peptides IGFs-I and -II have less than 0.01% activity. Blood plasma from animals treated with pharmacologically active doses of this growth factor analog could be diluted 33.3-fold before assay, at which concentrations plasma had no significant effect on the assay. The ELISA response to LR3IGF-I was unaffected by the presence of IGF-binding proteins. The intra-assay and interassay coefficients of variation are 2.8 and 7.3% respectively. Recovery of LR3IGF-I added to blood plasma was approximately 90%. The ELISA was used to measure LR3IGF-I concentrations in plasma of cows treated with a pharmacologically active dose of this peptide and the results were compared with those obtained by a previously established LR3IGF-I RIA that requires size exclusion chromatography of plasma under acidic conditions to eliminate IGF-binding protein artefacts from the RIA. There was a positive correlation between results obtained by the two assays. The LR3IGF-I ELISA permits discrimination between the exogenous synthetic IGF-I analog and the endogenous native IGFs-I and -II in animals treated with this growth factor without the need for radioiodination of LR3IGF-I and elimination of the requirement for extraction of plasma before assay.

Electrodiagnostic medical consultation in lumbar spine problems

This advanced analysis describes how lumbosacral radiculopathy, lumbosacral spinal stenosis, and other diagnoses featuring low back pain may be determined using electrodiagnostic procedures. The chapter concludes with a list of indications that can help determine when these procedures may be useful, as well as some suggestions for when they may be unnecessary.

Ontogenic and nutritional changes in circulating insulin-like growth factor (IGF)-I, IGF-II and IGF-binding proteins in growing ewe and ram lambs

The ontogeny of the IGF endocrine system was investigated in 15 young lambs before and after weaning at 62 days of age. Before weaning, plasma IGF-I concentrations were higher in rams than ewes, and plasma concentrations of IGF-II and IGF-binding protein-3 (IGFBP-3) also tended to be higher in rams than in ewes. Feed intake of ewes and rams was restricted after weaning to remove sex differences in feed intake. Plasma concentrations of IGF-I and IGFBP-3 did not differ between rams and ewes at 100 days of age, but plasma IGF-II was higher in rams than in ewes at this time. Since circulating concentrations of GH were higher in rams than in ewes at 100 days of age, this implies that the restricted feed intake blocked the IGF-I and IGFBP-3 responses to GH. We conclude that sex differences in circulating IGF-I and IGFBP-3 concentrations in the growing lamb alter with age, and are not present when nutrition is restricted.

Yeast Gcn5 functions in two multisubunit complexes to acetylate nucleosomal histones: characterization of an Ada complex and the SAGA (Spt/Ada) complex

The transcriptional adaptor protein Gcn5 has been identified as a nuclear histone acetyltransferase (HAT). Although recombinant yeast Gcn5 efficiently acetylates free histones, it fails to acetylate histones contained in nucleosomes, indicating that additional components are required for acetylation of chromosomal histones. We report here that Gcn5 functions as a catalytic subunit in two high-molecular-mass native HAT complexes, with apparent molecular masses of 0.8 and 1.8 megadalton (MD), respectively, which acetylate nucleosomal histones. Both the 0.8- and 1.8-MD Gcn5-containing complexes cofractionate with Ada2 and are lost in gcn5delta, ada2delta, or ada3delta yeast strains, illustrating that these HAT complexes are bona fide native Ada-transcriptional adaptor complexes. Importantly, the 1.8-MD adaptor/HAT complex also contains Spt gene products that are linked to TATA-binding protein (TBP) function. This complex is lost in spt20/ada5delta and spt7delta strains and Spt3, Spt7, Spt20/Ada5, Ada2, and Gcn5 all copurify with this nucleosomal HAT complex. Therefore, the 1.8-MD adaptor/HAT complex illustrates an interaction between Ada and Spt gene products and confirms the existence of a complex containing the TBP group of Spt proteins as demonstrated by genetic and biochemical studies. We have named this novel transcription regulatory complex SAGA (Spt-Ada-Gcn5-Acetyltransferase). The function of Gcn5 as a histone acetyltransferase within the Ada and SAGA adaptor complexes indicates the importance of histone acetylation during steps in transcription activation mediated by interactions with transcription activators and general transcription factors (i.e., TBP).

A T cell controlled molecular pathway regulating the IgH locus: CD40-mediated activation of the IgH 3' enhancer

Immunoglobulin heavy chain (IgH) class switch recombination and regulation of IgH expression levels are processes suggested to be controlled by the IgH 3' enhancer. Here we demonstrate that CD40 or IgM receptor stimulation of primary B cells results in transactivation of this enhancer. 4-Hydroxy-3-nitrophenylacetyl (NIP)-BSA induction of a K46 B cell line expressing a chimeric NIP-specific CD40 single chain receptor results in a ligand receptor-dependent response of a 3' enhancer ETS/AP-1 minimal promoter construct. Gel retardation analysis and genomic footprinting experiments reveal that CD40 or IgM induction recruits NFAB (nuclear factors of activated B cells) to the ETS/AP-1 motif. While IgM signalling recruits c-Fos, JunB and Elf-1 (NFAB-I), only JunB and Elf-1 were observed following CD40 signalling (NFAB-II). CD40 signalling, however, induces a Fos family-related partner for JunB, which may account for the transcriptional activity observed by NFAB-II in K46 cells. We propose a model whereby CD40 and IgM receptor-mediated signalling converge in the process of 3' enhancer activation in B lymphocytes. Our data provide a putative molecular explanation as to why CD40L-deficient mice, and possibly patients with hyper-IgM syndrome, are unable to undergo T cell-dependent class switch recombination but respond properly upon lipopolysaccharide-induced switch recombination.

Physiological activation of the IgH 3' enhancer in B lineage cells is not blocked by Pax-5

The mouse 3' enhancer contains a high-affinity binding site for the paired box protein Pax-5. Here, we demonstrate by genomic footprinting that the rat 3' enhancer contains a low-affinity binding site for Pax-5, which is occupied in activated splenic B cells. Thus, binding of Pax-5 to the IgH 3' enhancer appears to be evolutionarily conserved in rodents. Analysis of Pax-5 expression in primary B cells demonstrates that Pax-5 remains expressed after 4 days of lipopolysaccharide (LPS) induction, but is down-regulated in 5-day stimulated cells. Similarly, the expression of Pax-5 is down-regulated in vivo in activated large splenocytes, in contrast to small resting cells. Multimerization of the high-affinity Pax-5 binding site linked to a heterologous reporter gene demonstrates that Pax-5 can function as a transcriptional activator. In contrast, Pax-5 overexpressed in cell lines represses both the mouse and the rat 3' enhancer. Surprinsingly, cross-linking of the IgM receptor in BAL-17 cells containing a stably integrated 3' enhancer-dependent beta globin reporter gene demonstrates that induction of 3' enhancer activity is not blocked by Pax-5. Moreover, stimulation of 3' enhancer beta globin-transgenic splenocytes demonstrate that Pax-5 cannot repress-activation of the 3' enhancer upon LPS induction or CD40 receptor stimulation. Hence, activation of the IgH 3' enhancer occurs independently of changes in Pax-5 gene expression. This indicates that previous studies conducted in vitro may be an oversimplification of the function of Pax-5 and 3' enhancer activity.

Sexual dimorphism of circulating somatotropin, insulin-like growth factor I and II, insulin-like growth factor binding proteins, and insulin: relationships to growth rate and carcass characteristics in growing lambs

The effects of sex and age on patterns of circulating somatotropin (ST) concentration and plasma IGF-I, IGF-II, insulin, and IGF binding protein-3 (IGFBP-3) were studied in ram, wether, and ewe lambs (n = 7 or 8) sampled at mean ages of 81 (I1) and 158 d (I2). Between 81 and 158 d of age, rams grew more rapidly than wethers (P < .01), and wethers grew more rapidly than ewes (P < .01). The sex differences in growth were reflected in empty body weight at slaughter: rams > wethers > ewes (P < .05). Mean plasma ST concentrations, ST pulse amplitude, and integrated plasma ST concentrations were greater (P < .05) in rams than in ewes at I1 and I2. Characteristics of the ST plasma profile in wethers were generally intermediate between those of rams and ewes. The interpulse interval was greater in ewes than in wethers at I2. The IGF-I and IGFBP-3 concentrations were greater in rams than in ewes at both sampling times. Plasma IGF-II was greater in ewes than in rams at I2. Mean plasma ST was approximately two thirds less at I2 than at I1 regardless of sex. Mean plasma ST and IGF-I at both ages were positively correlated with growth. Mean plasma ST at I2 was negatively correlated with fatness at slaughter. Sex and age significantly affected patterns of circulating ST and concentrations of IGF-I and IGFBP-3 in prepubertal growing lambs, under conditions for which growth rates and composition were also sexually dimorphic.

Acetylation of histone H4 plays a primary role in enhancing transcription factor binding to nucleosomal DNA in vitro

Core histones isolated from normal and butyrate-treated HeLa cells have been reconstituted into nucleosome cores in order to analyze the role of histone acetylation in enhancing transcription factor binding to recognition sites in nucleosomal DNA. Moderate stimulation of nucleosome binding was observed for the basic helix-loop-helix factor USF and the Zn cluster DNA binding domain factor GAL4-AH using heterogeneously acetylated histones. However, by coupling novel immunoblotting techniques to a gel retardation assay, we observed that nucleosome cores containing the most highly acetylated forms of histone H4 have the highest affinity for these two transcription factors. Western analysis of gel-purified USF-nucleosome and GAL4-AH-nucleosome complexes demonstrated the predominant presence of acetylated histone H4 relative to acetylated histone H3. Immunoprecipitation of USF-nucleosome complexes with anti-USF antibodies also demonstrated that these complexes were enriched preferentially in acetylated histone H4. These data show that USF and GAL4-AH preferentially interact with nucleosome cores containing highly acetylated histone H4. Acetylation of histone H4 thus appears to play a primary role in the structural changes that mediate enhanced binding of transcription factors to their recognition sites within nucleosomes.

Pretreatment with bovine growth hormone is as effective as treatment during metabolic stress to reduce catabolism in fasted lambs

The effects of recombinant bovine GH (rbGH) treatment on the insulin-like growth factor (IGF) axis and protein metabolism during fasting induced metabolic stress were evaluated in young lambs. To explore whether rbGH pretreatment alone might offer a degree of protection against nutritional stress, we compared the effects of rbGH given only before or during the fasting-induced metabolic stress with that given over the whole period. The animals were fed ad libitum for 5 days (well fed phase) and then fasted for 70 h (fasted phase). The rbGH was administered during either the well fed and the fasted phase (G-G), only during the well fed phase (G-S), or only during the fasted phase (S-G), and the effects were compared with those of saline treatment throughout both phases (S-S; n = 7/group). The rate of net protein catabolism, analyzed on the final day of the study, was reduced (P < 0.001) to a similar degree in all rbGH-treated groups compared with that in the S-S group. rbGH pretreatment was as effective as rbGH administered during the catabolic phase. Plasma IGF-I was increased (P < 0.001) in the well fed phase by rbGH treatment and decreased in the fasted phase in all groups. The rbGH treatment during the fasted phase resulted in a smaller fall in plasma IGF-I levels than saline treatment (P < 0.05, G-G vs G-S and S-G vs. S-S), but no difference was observed in the specific binding of [125I]ovine GH to the hepatic membranes from animals of the different groups. There was a negative correlation between net protein catabolism and plasma IGF-I levels (r = -0.48; P < 0.01) and specific binding of [125I]ovine GH to hepatic membranes (r = -0.56; P < 0.001). Plasma IGF-II levels were decreased by rbGH treatment during the well fed phase, but the responses to treatment during the fasted phase were variable, suggesting that plasma IGF-II is regulated in a different manner than plasma IGF-I. The fasting-induced fall (P < 0.05) in plasma concentrations of IGF-binding protein (IGFBP)-3 was reduced with rbGH treatment, and plasma concentrations IGFBP-2 were altered in an inverse manner. This study suggests that fasting-induced GH resistance can be alleviated by rbGH treatment independent of whether treatment is commenced before or after the onset of catabolic stress. Our observation of prolonged anticatabolic action of prophylactic rbGH treatment supports the proposal that prophylactic use of GH may reduce the degree of catabolism associated with subsequent interventions and, thus, improve clinical outcome.

IgM receptor-mediated transactivation of the IgH 3′ enhancer couples a novel Elf-1-AP-1 protein complex to the developmental control of enhancer function

The function of the temporally regulated B lymphocyte-specific immunoglobulin heavy chain (IgH) 3' enhancer has been linked to the IgH class switch machinery, but the physiological mechanism(s) of activation has not been discerned. Following crosslinking of the IgM receptor, we demonstrate that the enhancer is transactivated in the B lymphoma cell line BAL-17. In both induced primary B lymphocytes and BAL-17 cells, the enhancer activation is concomitant with the recruitment of a novel DNA binding complex, nuclear factor of activated B cells (NFAB). NFAB contains the tissue-restricted Ets protein Elf-1 and the AP-1 factors Jun-B and c-Fos, which bind to a novel 3' enhancer ETS-AP-1 motif. IgM receptor-mediated activation or stimulation by phorbol-ester in BAL-17 cells demonstrates that the ETS-AP-1 motif, when linked to a heterologous gene, can confer a ligand/receptor-dependent response. In NIH 3T3 cells, Elf-1 expression is required for efficient ETS-AP-1 promoter activity in response to stimulation by 12-O-tetradecanylphorbol 13-acetate. Our results suggest a biological role for Elf-1 in the regulation of IgH gene expression, attribute a functional role for receptor-induced AP-1 proteins in B lymphocytes and provide evidence for a direct link between IgM receptor-mediated signalling and 3' enhancer activation.

Effect of restriction of placental growth on expression of IGFs in fetal sheep: relationship to fetal growth, circulating IGFs and binding proteins

To determine whether tissue production of the IGFs is altered when fetal growth is retarded, IGF-I and -II mRNAs were measured in tissues of fetal sheep subjected to placental restriction and the relationships between IGF gene expression, circulating IGF protein and fetal growth were examined. The majority of potential placental attachment sites were surgically removed from the uterus of 12 non-pregnant ewes to restrict placental size in a subsequent pregnancy. Blood and tissues were collected at 121 days of gestation (term = 150) in 12 fetuses with restricted placental size and eight normal fetuses. IGF-I and IGF-II mRNA was detected by solution hybridization/ribonuclease protection assay in placenta and all fetal tissues studied. IGF-I mRNA was most abundant in skeletal muscle and liver and IGF-II mRNA was highest in kidney and lung. Restriction of placental size reduced fetal weight by 17% and reduced the pO2 (18%) and glucose concentration (23%) of fetal blood. Placental restriction also reduced IGF-I mRNA in fetal muscle (P < 0.002), lung (P < 0.05) and kidney (P < 0.01) but had no significant effect on IGF-II mRNA in any tissue. IGF-I mRNA in fetal liver, kidney and skeletal muscle correlated positively with the concentration of IGF-I protein in fetal blood (P < 0.01). There was no relationship between the concentration of IGF-II protein in fetal blood and IGF-II mRNA in any fetal tissue examined. The concentration of IGF-binding protein-3 (IGFBP-3) in fetal arterial blood plasma measured by RIA correlated positively with fetal weight and with plasma IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)

Circulating insulin-like growth factors (IGFs), IGF-binding proteins (IGFBPs) and tissue mRNA levels of IGFBP-2 and IGFBP-4 in the ovine fetus

The IGF-binding proteins (IGFBPs) are a family of at least six structurally related proteins, which bind the IGFs and modulate their actions, including the regulation of pre- and postnatal growth. In this study we have examined the relationship between circulating and tissue mRNA levels of IGFBPs and related this to circulating IGFs in the fetal sheep over the gestational period when rapid growth and development occurs. Circulating IGFBP-2, as measured by Western ligand blot (WLB), increases between early and mid gestation, remains high, then declines throughout late gestation (P = 0.0002). Circulating IGFBP-3 increases throughout gestation, as measured by WLB or RIA (P = 0.04 and P = 0.0001 respectively), as does circulating IGFBP-4 (P = 0.004). These ontogenic changes in circulating IGFBPs-2 and -4 are paralleled by changes in liver mRNA for these proteins and, for IGFBP-2, by those in kidney IGFBP-2 mRNA also. This suggests that liver and kidney may be the primary contributors to circulating IGFBP-2 and the liver to circulating IGFBP-4, IGFBP-2 mRNA is present in the heart and lung in early gestation but barely detectable in these tissues after approximately 60 days gestation. IGFBP-4 mRNA is also present in the heart in early but not late gestation, but is abundant in the lung throughout gestation. These results demonstrate tissue specific and developmental regulation of IGFBPs-2 and -4 at the mRNA level. To assess any role the circulating IGFs may play in mediating these changes in IGFBPs, or vice versa, both plasma IGF-I and IGF-II were measured by RIA. Circulating IGF-I increases as gestation progresses (P = 0.0001), while circulating IGF-II increases between early and mid gestation, remains high (P = 0.01), then declines. Circulating IGF-I is positively correlated with fetal weight (r = 0.66, P = 0.03), circulating IGFBP-3 (r = 0.54, P = 0.01) and IGFBP-4 (r = 0.52, P = 0.01). Circulating IGF-II positively correlates with circulating IGFBP-2 (r = 0.48, P = 0.02) throughout gestation and at 1 day postnatally. These relationships are consistent with circulating IGF-I influencing IGFBPs-3 and -4, and similarly, IGF-II determining IGFBP-2, or vice versa. Alternatively, these correlations may reflect coordinate regulation of IGF and IGFBP by a common factor.

Isolation and characterization of ovine IGFBP-4: protein purification and cDNA sequence

Three different molecular mass forms of IGF-binding proteins (IGFBPs) were purified from ovine plasma by IGF-I affinity chromatography and reverse-phase HPLC: a 46 kDa doublet and 29 kDa and 24 kDa forms. Amino-terminal sequence analysis confirmed that these proteins were ovine (o)IGFBP-3 (46 kDa) and two molecular size variants of oIGFBP-4. oIGFBP-3 and the 29 kDa form of oIGFBP-4 were shown to be N-glycosylated. Isoelectric points were determined to be at approximately pH 6 for oIGFBP-3 and at pH 7 and pH 7.5 for the 29 and 24 kDa forms of oIGFBP-4 respectively. The two different molecular mass variants of oIGFBP-4 had similar IGF-binding properties. Compared with human IGFBP-3 and oIGFBP-3, the two variants of oIGFBP-4 exhibited lower relative binding to amino-terminally modified IGF-I analogues in a competitive IGF-binding assay. The full protein sequence of oIGFBP-4, as deduced from the cDNA sequence, showed a high degree of identity with rat (90%), human (96%) and bovine (98%) IGFBP-4. The cDNA sequence also showed homology over regions of the 3' non-coding sequence, particularly in comparison with bovine IGFBP-4 (96%). Northern analysis of mRNA for oIGFBP-4 indicated a 2.6 kb major transcript and two minor transcripts of approximately 2.1 and 1.8 kb. oIGFBP-4 mRNA transcripts were detected in adult ewe liver > kidney > lung >> heart and also in several fetal tissues, thus suggesting tissue-specific and developmental regulation. The availability of purified oIGFBP-4 and oIGFBP-3 as well as DNA probes for oIGFBP-4 will enable further study of the properties and functions of these proteins, as well as the establishment of specific assays for these IGFBPs.

Lipopolysaccharide-dependent transactivation of the temporally regulated immunoglobulin heavy chain 3' enhancer

To execute different biological functions, the expression pattern of immunoglobulin heavy chain genes (IgH) is altered during B lymphocyte differentiation. Early in B cell differentiation, it is assumed that the heavy chain promoter and the intragenic enhancer (E mu) ensure VDJ recombination. This leads to the expression of the immunoglobulin receptor on the cell surface. An additional strong enhancer in the far 3' end of the IgH locus has, however, prompted a re-evaluation of the regulation of immunoglobulin gene expression. To define the temporal and spatial regulation of the IgH 3' enhancer, transgenic mice harboring an enhancer-dependent reporter gene construct were generated. Here we demonstrate that IgH 3' enhancer activity is largely restricted to activated immunocompetent B cells. Furthermore, the enhancer can be transactivated following mitogen stimulation with lipopolysaccharide and 12-O-tetradecanoylphorbol 13-acetate. We propose a model whereby 3' enhancer activation is linked to the activation of resting immunocompetent B cells. The implications of the enhancer being active in late B lymphocyte differentiation, when heavy chain class switching occurs, are discussed.

Identification of Ets-like lymphoid specific elements within the immunoglobulin heavy chain 3' enhancer

Recently we identified an additional enhancer in the 3' end of the immunoglobulin heavy chain (IgH) locus. To identify individual regulatory elements within the rat IgH 3' enhancer, deletion analysis was performed. Transfection experiments using reporter constructs suggest that the enhancer contains three functionally distinct domains, two of which are lymphoid specific and one domain is active in both lymphoid and in nonlymphoid cells. The three domains together contribute to enhancer function and act synergistically. Further analyses suggest that a putative mu E1 site, octanucleotide motif, mu E3 site, and mu B/Ets-like motif are important for the overall transcriptional activity of the IgH 3' enhancer. Moreover, we provide evidence that an additional Ets-like element, micro A, is involved in the tissue specific regulation of enhancer activity and that binding of a protein to this element correlates with the transcriptional activity of one of the lymphoid restricted domains.

The Martin Titanline arterial clamp. A new lightweight alternative

When haemostatic clamps are applied, evidence of injury at the site of clamp application may be seen when the clamp is removed. Rarely, the intima may be disrupted. When a new arterial clamp became available, a study was designed to compare the Martin Titanline arterial clamp (13-143-35, curved arterial clamp) with several other arterial clamps already in use. The Martin clamp is a modified pivot-point, preset-tension, spring-controlled arterial clamp. The closing pressures of several clamps were measured objectively. The injury produced when the clamps were applied to occlude the blood flow on the carotid artery of a dog was assessed by histological study of the excised segments of the arterial wall. Histological cross-sections were prepared from canine carotid artery which had been perfused for 1 h after the clamp had been applied for 1 h. Histological evidence of injury was limited to disruption of the intimal layer and compression of the medial layer. No significant difference between the amount of damage caused by the DeBakey, Satinsky or Martin clamp was identified. When compared to the other varieties of clamp listed above, the Martin clamp had a significantly lower closing pressure (304 g) compared with 580g (Bulldog), 580 g (Satinsky), and 686 g (DeBakey). The Martin clamp was easier to apply, did not obstruct the operative field as readily and had good clamp-retention characteristics throughout the procedure.