Sequences and expression patterns of alkaline phosphatase isozymes in preattachment bovine embryos and the adult bovine

Mechanical loading down-regulates peroxisome proliferator-activated receptor gamma in bone marrow stromal cells and favors osteoblastogenesis at the expense of adipogenesis

Because a lack of mechanical information favors the development of adipocytes at the expense of osteoblasts, we hypothesized that the peroxisome proliferator-activated receptor gamma (PPARgamma)-dependent balance between osteoblasts and adipocytes is affected by mechanical stimuli. We tested the robustness of this hypothesis in in vivo rodent osteogenic exercise, in vitro cyclic loading of cancellous haversian bone samples, and cyclic stretching of primary stromal and C3H10T1/2 cells. We found that running rats exhibit a decreased marrow fat volume associated with an increased bone formation, presumably through recruitment of osteoprogenitors. In the tissue culture model and primary stromal cells, cyclic loading induced higher Runx2 and lower PPARgamma2 protein levels. Given the proadipocytic and antiosteoblastic activities of PPARgamma, we studied the effects of cyclic stretching in C3H10T1/2 cells, treated either with the PPARgamma activator, Rosiglitazone, or with GW9662, a potent antagonist of PPARgamma. We found, through both cytochemistry and analysis of lineage marker expression, that under Roziglitazone cyclic stretch partially overcomes the induction of adipogenesis and is still able to favor osteoblast differentiation. Conversely, cyclic stretch has additive effects with GW9662 in inducing osteoblastogenesis. In conclusion, we provide evidence that mechanical stimuli are potential PPARgamma modulators counteracting adipocyte differentiation and inhibition of osteoblastogenesis.

Maturation medium supplements affect transcript level of apoptosis and cell survival related genes in bovine blastocysts produced in vitro

The aim of the present study was to investigate whether protein or macromolecule supplements to in vitro maturation media affect transcript abundance of seven genes (Bax, Bcl2, Hsp70, IGF1, IGF1R, IGF2, and IGF2R) in oocytes and blastocysts. Cumulus-oocyte complexes aspirated from slaughterhouse ovaries were matured in TCM199 medium supplemented either with 10% FBS, 6% fatty acid free BSA (fafBSA) or 4% PVP40, then inseminated and cultured in vitro for 9 days. Transcript abundance analysis was carried out on immature and in vitro matured oocytes, as well as on blastocysts. Total RNA was isolated from pools of oocytes and embryos, reverse transcribed into cDNA and subjected to transcript analysis by real-time PCR. No transcript of IGF1 gene was detected either in oocytes or in blastocysts. Maturation conditions significantly affected transcript levels of investigated loci in blastocysts but not in matured oocytes, with one exception. Only relative abundance (RA) of IGF2 gene was higher in oocytes matured with fafBSA. Moreover, oocyte maturation with fafBSA elevated transcript abundance of IGF1R, IGF2, and IGF2R genes in resulting blastocysts, whereas Hsp70 transcription was stimulated by FBS supplementation. Thus, under described conditions, fafBSA may be the optimal supplement to IVM medium due to higher transcript level of growth factor coding genes accompanied by a lower transcript level of Hsp70.

Alkaline phosphatase is involved in the control of adipogenesis in the murine preadipocyte cell line, 3T3-L1

OBJECTIVE

As alkaline phosphatase may play a role in cell differentiation, our aim was to study the possible role of this enzyme in the differentiation of preadipocytes (3T3-L1 cells) into adipocytes.

RESEARCH METHODS AND PROCEDURES

3T3-L1 cells were grown in medium containing insulin, dexamethasone and IBMX to induce adipogenesis. Adipogenesis was measured using the triglyceride-specific dye, oil red O at 0, 3, 7 and 11 days after initiation of adipogenesis in the presence or absence of the alkaline phosphatase inhibitors, levamisole, histidine and Phe-Gly-Gly. Intracellular localisation of the enzyme was detected using ELF-phosphatase, a fluorescent substrate and alkaline phosphatase gene expression was assessed using RT-PCR.

RESULTS

Alkaline phosphatase activity was detected in untransformed cells (1.91+/-0.62 mU/mg protein) and activity increased 11.5+/-1.4-fold after 11 days treatment with transformation medium and 5.3+/-0.3-fold in transformation medium containing levamisole (p<0.05). Triglyceride content of cells increased 3.1+/-0.2-fold after 11 days treatment with transformation medium and 2.1+/-0.3-fold in the presence of levamisole (p<0.005). Histidine inhibited adipogenesis and alkaline phosphatase to a greater extent than did levamisole, but Phe-Gly-Gly had no effect on these variables. Alkaline phosphatase was localised around the lipid droplets of the cells. Gene expression of alkaline phosphatase increased during adipogenesis.

DISCUSSION

This study demonstrates that tissue-nonspecific alkaline phosphatase is present in 3T3-L1 cells and that it may play a role in the control of adipogenesis.

Gene expression and in vitro development of inter-species nuclear transfer embryos

This study examined the chromatin morphology, in vitro development, and expression of selected genes in cloned embryos produced by transfer of mouse embryonic fibroblasts (MEF) into the bovine ooplasm. After 6 hr of activation, inter-species nuclear transfer (NT) embryos (MEF-NT) had one (70%) or two pronuclei (20%), respectively. After 72 hr of culture in vitro, 62.6% of the MEF-NTs were arrested at the 8-cell stage, 31.2% reached the 2- to 4-cell stage, and only 6.2% had more than eight blastomeres, but none of these developed to the blastocyst stage. Whereas, 20% of NT embryos derived from bovine embryonic fibroblast fused with bovine ooplasm (BEF-NT) reached the blastocyst stage. Donor MEF nuclei expressing an Enhanced Green Fluorescent Protein (EGFP) transgene resulted in 1- to 8-cell stage MEF-NT that expressed EGFP. The expression of selected genes was examined in 8-cell MEF-NTs, 8-cell mouse embryos, enucleated bovine oocytes, and MEFs using RT-PCR. The mRNA for heat shock protein 70.1 (Hsp 70.1) gene was detected in MEF-NTs and MEF, but not in mouse embryos. The hydroxy-phosphoribosyl transferase (HPRT) mRNA was found in normal mouse embryos and MEF but not in MEF-NTs. Expression of Oct-4 and embryonic alkaline phospatase (eAP) genes was only detected in normal mouse embryos and not in the inter-species NT embryos. Abnormal gene expression profiles were associated with an arrest in the development at the 8-cell stage, but MEF-NT embryos appeared to have progressed through gross chromatin remodeling, typical of intra-species NT embryos. Therefore, molecular reprogramming rather than chromatin remodeling may be a better indicator of nuclear reprogramming in inter-species NT embryos.

Expression of growth hormone and its transcription factor, Pit-1, in early bovine development

During bovine embryogenesis, bovine growth hormone (bGH) contributes to proliferation, differentiation, and modulation of embryo metabolism. Pituitary-specific transcription factor-1 (Pit-1) is a transcription factor that binds to promoters of GH, prolactin (PRL), and thyroid-stimulating hormone-beta (TSHbeta) encoding genes. A polymorphism in the fifth exon of the bGH gene resulting in a leucine (Leu) to valine (Val) substitution provides an Alu I restriction site when the Leu allele is present. To determine the onset of embryonic expression of the bGH gene, oocytes derived from ovaries homozygous for Leu alleles were fertilized in vitro with spermatozoa obtained from a Val homozygote. For each developmental stage examined, three separate pools of embryos composed of approximately 100 cell samples underwent RNA isolation, reverse transcription to cDNA, and amplification by nested PCR (nPCR). Bovine GH gene transcripts were identified at 2- to 4-cell (n = 162), 8- to 16-cell (n = 73), morulae (n = 51), and blastocyst (n = 15) stages. Likewise, transcripts for Pit-1 were detected at 2-cell (n = 125), 4-cell (n = 114), 8-cell (n = 56), 12-to-32-cell (n = 32), morulae (n = 68), and blastocyst (n = 14) stages. After digestion with Alu1, bGH cDNA was genotyped by restriction fragment length polymorphism (RFLP) analysis. Bovine GH mRNA was present in all pools of stages examined. Both Leu and Val alleles (maternal and paternal) were only detected in pools of embryos that had reached 8- to 16-cell stage. Results suggest that transcription of the bGH gene begins at the 8- to 16-cell stage in bovine embryos, possibly under control of the transcription factor, Pit-1, and that RFLP analysis of the bGH gene can be used to determine parental origin of transcripts in early embryonic development.

Inhibitor profiles of alkaline phosphatases in bovine preattachment embryos and adult tissues

The alkaline phosphatases are a small family of isozymes. Bovine preattachment embryos transcribe mRNA for two tissue-specific alkaline phosphatases (TSAP2 and TSAP3) beginning at the 4- and 8-cell stages. Whereas no mRNA has been detected in oocytes, there is maternally inherited alkaline phosphatase activity. It is not known which isozyme(s) is responsible for the maternal activity or when TSAP2 and TSAP3 form functional protein. No antibodies are available that recognize the relevant bovine alkaline phosphatases. Therefore, sensitivity to heat and chemical inhibition was used to separate the different isozymes. By screening tissues, it was determined that the bovine tissue-nonspecific alkaline phosphatase (TNAP) is inactivated by low temperatures (65C) and low concentrations of levamisole (<1 mM), whereas bovine tissue-specific isozymes require higher temperatures (90C) and levamisole concentrations (>5 mM). Inhibition by L-homoarginine and L-phenylalanine was less informative. Cumulus cells transcribe two isozymes and the pattern of inhibition suggested heterodimer formation. Inhibition of alkaline phosphatase in bovine embryos before the 8-cell stage indicated the presence of only TNAP. At the 16-cell stage the pattern was consistent with TNAP plus TSAP2 or -3 activity, and in morulae and blastocysts the pattern indicated that the maternal TNAP is fully supplanted by TSAP2 or TSAP3.

Alterations of expression of developmentally important genes in preimplantation bovine embryos by in vitro culture conditions: implications for subsequent development

Recent advances in molecular technology and in vitro production of bovine embryos have enabled studies of gene transcription in preimplantation embryos. On the basis of knowledge of the sequence of the selected gene, various modifications of Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) technology have been employed. Several lines of evidence in mouse and cattle indicate that expression patterns of genes from in vitro-produced embryos are not necessarily representative of those of in vivo embryos. An important gene that has been found to be expressed by in vivo-derived bovine blastocysts, but not in their in vitro-produced counterparts, is the Connexin43 gene that is crucial for maintenance of compaction. The bovine leukemia inhibitory factor (bLIF) and LIF-receptor-beta (LR-beta) genes were expressed by in vitro-produced embryos, but not in their in vivo counterparts. The heat shock protein gene 70.1 (Hsp 70.1) was upregulated by blastocysts produced in vitro compared to in vivo embryos, while the glucose transporter-1 mRNA (Glut-1) was downregulated by morulae produced in vitro as compared to in vivo-derived morulae. Furthermore, mRNA expression levels of a set of "marker genes" were shown to be affected by the presence or absence of serum in the culture medium. Most embryos grown under serum-free conditions had higher mRNA abundances than those cultured in serum-enriched medium. It is hypothesized that persistent alterations of the normal gene expression patterns may be responsible for the large offspring syndrome that is observed in approximately one third of the calves resulting from the transfer of in vitro-produced embryos. A primary candidate for such deviations may be an altered methylation pattern that can either lead to silencing or induction of a specific gene. Messenger RNA phenotyping of genes essential in early development provides a useful tool to assess the normality of the produced embryos and a tool to optimize in vitro culture conditions for bovine embryos.

X inactive-specific transcript (Xist) expression and X chromosome inactivation in the preattachment bovine embryo

Expression of the X inactive-specific transcript (Xist) is thought to be essential for the initiation of X chromosome inactivation and dosage compensation during female embryo development. In the present study, we analyzed the patterns of Xist transcription and the onset of X chromosome inactivation in bovine preattachment embryos. Reverse transcription-polymerase chain reaction (RT-PCR) revealed the presence of Xist transcripts in all adult female somatic tissues evaluated. In contrast, among the male tissues examined, Xist expression was detected only in testis. No evidence for Xist transcription was observed after a single round of RT-PCR from pools of in vitro-derived embryos at the 2- to 4-cell stage. Xist transcripts were detected as a faint amplicon at the 8-cell stage initially, and consistently thereafter in all stages examined up to and including the expanded blastocyst stage. Xist transcripts, however, were subsequently detected from the 2-cell stage onward after nested RT-PCR. Preferential [3H]thymidine labeling indicative of late replication of one of the X chromosomes was noted in female embryos of different developmental ages as follows: 2 of 7 (28.5%) early blastocysts, 6 of 13 (46.1%) blastocysts, 8 of 11 (72.1%) expanded blastocysts, and 14 of 17 (77.7%) hatched blastocysts. These results suggest that Xist expression precedes the onset of late replication in the bovine embryo, in a pattern compatible with a possible role of bovine Xist in the initiation of X chromosome inactivation.

Genetic complexity, structure, and characterization of highly active bovine intestinal alkaline phosphatases

Mammalian alkaline phosphatases (APs) display 10-100-fold higher kcat values than do bacterial APs. To begin uncovering the critical residues that determine the catalytic efficiency of mammalian APs, we have compared the sequence of two bovine intestinal APs, i.e. a moderately active isozyme (bovine intestinal alkaline phosphatase, bIAP I, approximately 3,000 units/mg) previously cloned in our laboratory, and a highly active isozyme (bIAP II, approximately 8, 000 units/mg) of hitherto unknown sequence. An unprecedented level of complexity was revealed for the bovine AP family of genes during our attempts to clone the bIAP II cDNA from cow intestinal RNAs. We cloned and characterized two novel full-length IAP cDNAs (bIAP III and bIAP IV) and obtained partial sequences for three other IAP cDNAs (bIAP V, VI, and VII). Moreover, we identified and partially cloned a gene coding for a second tissue nonspecific AP (TNAP-2). However, the cDNA for bIAP II, appeared unclonable. The sequence of the entire bIAP II isozyme was determined instead by a classical protein sequencing strategy using trypsin, carboxypeptidase, and endoproteinase Lys-C, Asp-N, and Glu-C digestions, as well as cyanogen bromide cleavage and NH2-terminal sequencing. A chimeric bIAP II cDNA was then constructed by ligating wild-type and mutagenized fragments of bIAP I, III, and IV to build a cDNA encoding the identified bIAP II sequence. Expression and enzymatic characterization of the recombinant bIAP I, II, III, and IV isozymes revealed average kcat values of 1800, 5900, 4200, and 6100 s-1, respectively. Comparison of the bIAP I and bIAP II sequences identified 24 amino acid positions as likely candidates to explain differences in kcat. Site-directed mutagenesis and kinetic studies revealed that a G322D mutation in bIAP II reduced its kcat to 1300 s-1, while the converse mutation, i.e. D322G, in bIAP I increased its kcat to 5800 s-1. Other mutations in bIAP II had no effect on its kinetic properties. Our data clearly indicate that residue 322 is the major determinant of the high catalytic turnover in bovine IAPs. This residue is not directly involved in the mechanism of catalysis but is spatially sufficiently close to the active site to influence substrate positioning and hydrolysis of the phosphoenzyme complex.