Na/K-ATPase-mediated 86Rb+ uptake and asymmetrical trophectoderm localization of alpha1 and alpha3 Na/K-ATPase isoforms during bovine preattachment development

This study evaluated Na/K-ATPase alpha 1- and alpha 3-subunit isoform polypeptide expression and localization during bovine preattachment development. Na/K-ATPase cation transport activity from the one-cell to blastocyst stage was also determined by measuring ouabain-sensitive 86Rb+ uptake. Both alpha1- and alpha 3-subunit polypeptides were detected by immunofluorescence to encircle the entire cell margins of each blastomere of inseminated zygotes, cleavage stage embryos, and morulae. Immunofluorescent localization of alpha1-subunit polypeptide in bovine blastocysts revealed an alpha1 immunofluorescence signal confined to the basolateral membrane margins of the trophectoderm and encircling the cell periphery of each inner cell mass (ICM) cell. In contrast, alpha 3-subunit polypeptide immunofluorescence was localized primarily to the apical cell surfaces of the trophectoderm with a reduced signal present in basolateral trophectoderm regions. There was no apparent alpha 3-subunit signal in the ICM. Analysis of 86Rb+ transport in vitro demonstrated ouabain-sensitive activity throughout development from the one-cell to the six- to eight-cell stage of bovine development. 86Rb+ uptake by morulae (day 6 postinsemination) did not vary significantly from uptake detected in cleavage stage embryos; however, a significant increase was measured at the blastocyst stage (P < 0.05). Treatment of embryos with cytochalasin D (5 micrograms/ml) did not influence 86Rb+ uptake in cleavage stage embryos. Cytochalasin D treatment however was associated with a significant rise in ion transport in morulae and blastocysts (13.49 and 61.57 fmol/embryo/min, respectively) compared to untreated controls (2.65 and 22.83 fmol/embryo/min, respectively). Our results, for the first time, demonstrate that multiple Na/K-ATPase alpha-subunit isoforms are distributed throughout the first week of mammalian development and raise the possibility that multiple isozymes of the Na/K-ATPase contribute to blastocyst formation.

Comparative effects of Bcl-2 over-expression and ZVAD.FMK treatment on dexamethasone and VP16-induced apoptosis in CEM cells

It is becoming apparent that caspases are essential mediators of the execution phase of apoptosis. A decrease in mitochondrial membrane potential (PsiM) is also thought to be an early event in apoptosis. In this study, we compare the effects of Bcl-2 over-expression against N-benzyloxycabonyl-Val-Ala-Asp-fluoromethylketone (ZVAD. FMK)-sensitive caspase blockade on dexamethasone (DEX) and etoposide (VP16)-induced apoptosis in CEM T lymphoid cells. We assessed changes in nuclear chromatin, cell size, fragmentation, cell membrane permeability and PsiM. We found Bcl-2 over-expression and ZVAD.FMK-sensitive caspase inhibition were able to prevent chromatin condensation and cellular fragmentation. However, ZVAD.FMK was neither able to prevent loss of plasma membrane integrity nor PsiM depolarization which occur in both VP16 and DEX-induced apoptosis. In VP16-induced apoptosis, the increase in cell membrane permeability was actually potentiated by caspase inhibition. Interestingly, ZVAD.FMK did prevent VP16-induced but not DEX-induced cell shrinkage. These results suggest that not all the actions of Bcl-2 can be explained by its ability to prevent caspase activation. Rather Bcl-2 must have other targets of action which include functions associated with mitochondria.

Chemopreventive effects of NSAIDs against colorectal cancer: regulation of apoptosis and mitosis by COX-1 and COX-2

There is a wealth of evidence that nonsteroidal anti-inflammatory drugs (NSAIDs) can prevent colorectal cancer. In this article the role of cyclooxygenase 1 and 2, the principle target of NSAIDs, in the development of colorectal cancer is reviewed. Cyclooxygenase is constitutively expressed in normal colonic epithelium and surrounding stroma and could catalyse the generation of malondialdehyde which is a known mutagen and could initiate colorectal carcinogenesis. Mutation of APC which is an early genetic event leads to the expression of cyclooxygenase 2 which may prevents the appropriate apoptosis of mutant adenoma cells. Other proneoplastic effects of cyclooxygenase include changing the action of Transforming Growth Factor beta from anti-proliferative to pro-proliferative, reducing adherence to extracellular matrix, promotes metastasis and angiogenesis. These properties of cyclooxygenases suggest that inhibition of both isoforms may have important protective effects against colorectal cancer.

Activity of fotemustine in medulloblastoma and malignant glioma xenografts in relation to O6-alkylguanine-DNA alkyltransferase and alkylpurine-DNA N-glycosylase activity

Fotemustine is a chloroethylnitrosourea with antitumor activity in disseminated melanoma and adult primary brain tumors. Because new drugs are required for the treatment of medulloblastoma in children, we evaluated the preclinical antitumor activity of fotemustine in four s.c. medulloblastoma xenografts, in comparison with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). Both drugs were administered as a single i.p. injection to nude mice bearing advanced-stage tumor. Fotemustine displayed significant antitumor activity in three of four medulloblastoma xenografts; two, IGRM34 and IGRM57, were highly sensitive, with 37 and 100% tumor-free survivors, respectively, more than 120 days after treatment at the highest nontoxic dose (50 mg/kg). Fotemustine was also highly active in a malignant glioma xenograft (IGRG88; five of six tumor-free survivors on day 177). Fotemustine proved to be significantly more active than BCNU in IGRM34 and the glioma xenograft IGRG88. The DNA repair protein O6-alkylguanine-DNA alkyltransferase (ATase) was detected in all tumor xenografts, ranging in activity from 6 to 892 fmol/mg protein. The high in vivo sensitivity to fotemustine and BCNU observed in three xenografts was clearly associated with a low ATase activity (> 20 fmol/mg), whereas the two poorly sensitive or refractory medulloblastoma xenografts showed high ATase activity (> 500 fmol/mg). Alkylpurine-DNA N-glycosylase activity was detected in all tumor xenografts but at levels ranging only from 513 to 1105 fmol/mg/h; no consistent relationship was found between alkylpurine-DNA N-glycosylase activity and the in vivo sensitivity to the two chloroethylnitrosoureas. The improved activity and tolerance of fotemustine in comparison with BCNU in pediatric medulloblastoma xenografts strongly support the clinical development of this agent in children with brain tumors, in which ATase should be examined as a potential prognostic indicator.

Analysis of variation in relative mRNA abundance for specific gene transcripts in single bovine oocytes and early embryos

Variation in the abundance of a specific gene transcript was assessed in single bovine oocytes and in vitro-derived blastocysts. Transcripts encoding the Na+,K(+)-ATPase alpha 1 subunit were detected by reverse-transcription polymerase chain reaction (RT-PCR) and quantified relative to an exogenously supplied rabbit alpha-globin mRNA using laser-induced fluorescence capillary electrophoresis (LIF-CE). The precision of this relative abundance (RA) calculation was predicted and shown to resolve 2-fold differences in transcript abundance between individual blastocysts and predicted in oocytes to resolve 3-fold differences. The RA of the alpha 1 subunit transcript differed by 2- to 3-fold among blastocysts, and 3- to 6-fold among oocytes. Comparison of a general population of oocytes with blastocysts revealed little overlap in RA values between the two groups, with a 8- to 14-fold increase in the mean RA for each group with development observed in two successive experiments (P < or = 0.05). In contrast, oocytes selected for their developmental competence on the basis of morphologic criteria exhibited only a 1.6- to 1.7-fold developmental increase when the assay was performed on cDNA generated from either embryo pools (n = 6 versus 6) or individuals (n = 7 versus 7), respectively. These results provide the first characterization of the degree of heterogeneity in the abundance of a specific mRNA transcript among individual mammalian oocytes and preimplantation embryos and demonstrate that transcript relative abundance can be correlated with bovine oocyte morphology.

Temporal patterns of embryonic gene expression and their dependence on oogenetic factors

Successful development of a fertilized egg beyond early cleavage divisions requires the de novo initiation and subsequent regulation of embryonic transcription. The egg provides the specialized environment within which the newly formed zygotic nucleus initiates its developmental program and as a result plays an obligatory role in its regulation. Although the precise timing of the onset of embryonic transcription in mammals varies during early cleavage divisions, several common elements exist. In the present essay we review the current literature on the timing and control of embryonic gene expression in mammals, and discuss recent findings from our laboratory on gene expression patterns in bovine embryos and their relation to other species, and zygotic gene activation (ZGA). Lastly, we discuss the putative role of maternally inherited factors in conferring developmental competence to the blastocyst stage, and a method to identify such factors present in oocytes as mRNA.

Commitment to cell death measured by loss of clonogenicity is separable from the appearance of apoptotic markers

Kinetic analysis of dexamethasone-induced apoptosis in the human lymphoblastoid cell line CCRF CEM C7A has revealed a point when cells, morphologically indistinguishable from untreated cells, have irreversibly engaged a program leading to death, measured by a loss of clonogenicity. Since all cells that fail to clone eventually died through apoptosis, measurements of clonogenicity in this system provide an accurate measure of commitment to apoptotic death. Inhibition of caspases by peptide inhibitors blocked proteolysis of endogenous substrates and reduced nuclear condensation yet did not alter either dexamethasone-induced changes in clonogenicity or mitochondrial membrane potential. In contrast to the results with caspase inhibitors, expression of BCL-2 in CCRF CEM C7A cells proved sufficient to block all changes associated with apoptosis, including loss of both clonogenicity and changes in mitochondrial membrane potential. These results demonstrate that commitment to cell death can precede the key biochemical or morphological features of apoptosis by several hours and indicate that separate regulators govern cellular commitment to clonogenic death and the subsequent execution phase characterised as apoptosis.

Melatonin modulates vascular smooth muscle tone

The molecular cloning of a family of melatonin receptors has created a renewed interest in the diverse actions of the hormone melatonin. The radioligand 2-[125I]iodomelatonin has identified potential sites of action for melatonin throughout the central nervous system and periphery of numerous species. Interestingly, in addition to the suprachiasmatic nucleus (the "biological clock"), 2-[125I]iodomelatonin binding sites have been localized to the rat caudal and cerebral arteries. Furthermore, in vitro, melatonin has been shown to induce a concentration-dependent vasoconstriction of rat caudal and cerebral arteries, and pig and human coronary arteries. The lack of melatonin receptor subtype-selective agonists and antagonists prevents the full pharmacological characterization of these responses. The physiological significance of the in vitro vasoconstrictive properties is far from clear, however; in rats, melatonin has been shown to reduce cerebral blood flow. The widespread use of melatonin warrants appropriately designed studies to probe the role of melatonin and its receptors in the modulation of in vitro vascular tone.

v-Abl protein tyrosine kinase (PTK) mediated suppression of apoptosis is associated with the up-regulation of Bcl-XL

We demonstrated previously that the activation of v-Abl protein tyrosine kinase (PTK) in IC.DP murine pre-mast cells resulted in suppression of apoptosis after withdrawal of interleukin 3 (IL-3), that protein kinase C (PKC) translocated to the nucleus 6 h after v-Abl PTK activation and that inhibition of PKC restored apoptosis after IL-3 deprivation in the presence of v-Abl PTK activity. Here we demonstrate that v-Abl PTK activation is followed by an approximately twofold increase in mRNA level of Bcl-XL by 6 h and a corresponding increase in Bcl-XL protein level by 24 h. Bcl-xL RNA and protein decreased in IL-3 deprived cells in the absence of v-Abl PTK activity. Exposure of cells with v-Abl PTK active to the PKC inhbitor calphostin C (125 ng/ml) prevented the increase in Bcl-xL protein and resulted in apoptosis. No changes in Bax or Bcl-2 protein level were noted after IL-3 withdrawal and/or activation of v-Abl PTK. Bak was barely detectable and Bad protein level decreased in cells undergoing apoptosis. The data suggest that suppression of apoptosis by v-Abl PTK in the absence of IL-3 is associated with PKC signalling and the upregulation of Bcl-xL in IC.DP cells.

Bovine oviductal and embryonic insulin-like growth factor binding proteins: possible regulators of "embryotrophic" insulin-like growth factor circuits

Bovine oviductal monolayer and vesicle primary cultures express insulin-like growth factor (IGF)-I and -II mRNAs and polypeptides. Early bovine embryos also express IGF-I, IGF-II, IGF-I receptor, IGF-II receptor, and insulin receptor mRNAs. This study reports the expression of IGF binding protein (IGFBP) mRNAs and polypeptides in bovine oviduct primary cultures and IGFBP mRNAs in preattachment embryos. Release of immunoreactive IGF-I and IGF-II by oviduct cultures and bovine blastocysts was also determined. IGFBP-2, -3, -4, and -5 transcripts were observed in oviduct primary cultures throughout an 8-day interval. IGFBP-1 and -6 mRNAs were consistently not detected in the oviduct. Messenger RNAs encoding IGFBPs -2, -3, and -4 were detected throughout bovine preattachment development, while transcripts encoding IGFBP-5 were detected only in blastocysts. IGFBP-1 and -6 transcripts were not detected in early embryos. Ligand blot analysis with 125I-labeled IGF-II revealed the presence of four prominent polypeptide bands of approximate molecular masses 24, 31, and 36 kDa, and a broad band extending from 46 to 53 kDa, in conditioned media samples prepared from oviduct primary cultures. Western immunoblot analysis confirmed the identity of the 24-kDa, 31-kDa, and 36-kDa species as IGFBP-4, -5, and -2, respectively. Levels of the release of IGF-II from oviductal vesicle cultures were significantly greater than levels observed for monolayer cultures (p < 0.005). No significant difference in the levels of IGF-I release between monolayer and vesicle cultures was observed. Pools of 10 blastocysts released on average 36.2 +/- 3.9 pg of IGF-II per embryo, while the release of embryonic IGF-I was below the levels of detection for our assay. The results suggest that maternally derived IGF may be regulated by IGFBPs to support bovine preattachment development.

Inhibition by uridine but not thymidine of p53-dependent intestinal apoptosis initiated by 5-fluorouracil: evidence for the involvement of RNA perturbation

The epithelia from the crypts of the intestine are exquisitely sensitive to metabolic perturbation and undergo cell death with the classical morphology of apoptosis. Administration of 40 mg/kg 5-fluorouracil (5-FU) to BDF-1 p53+/+ mice resulted in an increase in p53 protein at cell positions in the crypts that were also those subjected to an apoptotic cell death. In p53-/- mice apoptosis was almost completely absent, even after 24 hr. 5-FU is a pyrimidine antimetabolite cytotoxin with multiple mechanisms of action, including inhibition of thymidylate synthase (TS), which gives rise to DNA damage, and incorporation into RNA. The inhibition of TS can be increased by coadministration of folinic acid and can be abrogated by administration of thymidine. The incorporation of 5-FU into RNA is inhibited by administration of uridine. p53-Dependent cell death induced by 5-FU was only inhibited by administration of uridine. Uridine had no effect on the apoptosis initiated by 1 Gy of gamma-radiation. Although thymidine abrogated apoptosis induced by the pure TS inhibitor Tomudex, it had no effect on 5-FU-induced apoptosis, and coadministration of folinic acid did not increase apoptosis. The data show that 5-FU-induced cell death of intestinal epithelial cells is p53-dependent and suggests that changes in RNA metabolism initiate events culminating in the expression of p53.

Role of acid/base homeostasis in the suppression of apoptosis in haemopoietic cells by v-Abl protein tyrosine kinase

Removal of interleukin-3 from murine IC.DP pre-mast cells results in irreversible commitment to apoptosis within 18 hours. To identify early events necessary for the engagement of apoptosis we examined the regulation of intracellular pH (pH(i)). IC.DP cells acidified 2 hours after removal of interleukin-3 (before discernible signs of apoptosis) and by 18 hours pH(i) had decreased by 0.15 units. The acidification was due to both an increase in an acid-loading process which only occurs when intracellular pH is above 6.8 and a slight reduction in H+ efflux via NA+/H+ exchange. Activation of a temperature sensitive mutant of v-Abl protein tyrosine kinase suppressed apoptosis of IC.DP cells in the absence of interleukin-3 but did not stimulate proliferation, and moreover prevented cellular acidification. Acidification of the cells by 0.2 units to pH 6.86 by complete inhibition of Na+/H+ exchange by 10 microM 5′-(N-methyl-N-isobutyl)-amiloride prevented the suppression of apoptosis by v-abl protein tyrosine kinase following IL 3 withdrawal. However in the presence of interleukin-3, addition of 10 microM 5′-(N-methyl-N-isobutyl)-amiloride only resulted in a fall of pH(i) to 7.17. Apoptosis did not occur and the cells continued to proliferate. Thus, in this model intracellular pH must fall below a critical value for apoptosis to occur. Together these data point to a step in cytokine deprivation induced apoptosis (at least in some haemopoietic cell types) which is either enhanced by or dependent upon an acidic intracellular environment which is the result of an increase in acid loading and inhibition of Na+/H+ exchange activity. One of the mechanisms by which activation of v-Abl protein tyrosine kinase suppresses apoptosis is by prevention of intracellular acidification.

Ouabain sensitivity and expression of Na/K-ATPase alpha- and beta-subunit isoform genes during bovine early development

The fluid movements that arise during blastocyst formation (cavitation) are, at least in part, driven by the Na/K-ATPase. In this study, the reverse transcriptase-polymerase chain reaction (RT-PCR) was used to survey bovine pre-attachment embryos for transcripts encoding known isoforms of the Na/K-ATPase alpha- and beta-subunits, including isoforms not previously detected during the first week of mammalian development. Transcripts encoding the Na-K-ATPase alpha 1, alpha 2, alpha 3 and beta 2 isoforms were detected throughout bovine preattachment development. This is the first indication that alpha 2, alpha 3 and beta 2 mRNAs are expressed during this early developmental interval. As in the mouse, beta 1-subunit transcripts were not detected until the morula stage and were also present in blastocysts. Thus, in two mammalian species an increase in abundance of beta 1 isoform transcripts in the morula stage is coincident with the onset of cavitation. Transcripts encoding the recently characterized alpha 4 isoform were not detected. The sensitivity of bovine blastocysts to ouabain (a potent inhibitor of Na/K-ATPase) was determined by assessing the ability of bovine blastocysts to recover in ouabain supplemental culture medium following cytochalasin-induced blastocyst collapse. Re-expansion of bovine blastocysts was inhibited in all ouabain concentrations down to 10(-9) M. Mouse blastocysts, in contrast, were sensitive to ouabain at or above 10(-3)M. These results have established that transcripts encoding multiple isoforms of both the alpha and beta subunits of the Na/K-ATPase are expressed throughout early bovine development and that bovine blastocysts display a greater sensitivity to ouabain than murine blastocysts. Future analysis will determine the possible individual and collective roles of these isoforms during blastocyst formation.

A new linear V1A vasopressin antagonist and its use in characterizing receptor/G protein interactions

We characterized a new iodinated, high affinity, linear V1a vasopressin antagonist, phenylacetylD-Tyr(Et)Phe-Gln-Asn-Lys-Pro-Arg-Tyr-NH2. The antagonist bound specifically to the V1a vasopressin receptor in crude rat liver membranes with an apparent Kd value of 0.168 nM. This affinity is approximately 1 order of magnitude greater than that of the natural agonist, vasopressin. The inhibitory activity of the antagonist can be demonstrated by its inability to elicit activation and uncoupling of G proteins from the receptor. Thus, after occupancy of receptor sites in rat liver membranes with labeled antagonist and detergent solubilization, the labeled receptor (approximately 60 kDa) was eluted as a stable 400-kDa complex on size-exclusion chromatography. In contrast, when the receptor sites were occupied by the agonist [3H]vasopressin, the receptor eluted as a 60-kDa peak. Coincubation of membranes with iodinated antagonist and an excess of unlabeled vasopressin caused both reduced antagonist binding and a complete shift from the 400-kDa to the 60-kDa peak. The addition of vasopressin to unliganded 400-kDa fractions resulted in a 75% increase in [35S]guanosine-5'-O-(3-thio)triphosphate binding activity, indicating that the 400-kDa fraction contains complexes between the V1a receptor and G proteins. The vasopressin-elicited increase was inhibited by antagonist. Using specific antibodies and immunoadsorption to protein A/Sepharose columns, we found that G protein isotypes G(alpha q/11), G(alpha i3), and G(alpha s), and effector enzymes PLC-beta1, PLC-gamma2 and PLA-2 were associated with the antagonist-labeled receptor in the 400-kDa fraction. Because the 400-kDa complex was found in the absence of ligand, the V1a receptor and the appropriate G proteins and effector enzymes are likely preassociated with each other and do not aggregate after antagonist addition. The association of V1a receptor with the different specific G proteins and effector enzymes is consistent with the multiple actions of vasopressin on liver cells. Antibodies directed against a portion of the carboxyl-terminal domain of the V1a receptor interacted with 60-kDa antagonist-occupied receptor but not with receptor in the 400-kDa complex. These results suggest that the carboxyl-terminal region of the receptor is sterically hindered when coupled to G proteins. The iodinated linear vasopressin antagonist therefore allows stable receptor/G protein complexes and can be an important tool (along with the antisera) for use in the study of factors that control V1a receptor/G protein coupling.

Effect of estrogen-treated porcine ampulla oviductal epithelial cells on early embryonic development in vitro and characterization of their protein synthetic activity

Recent studies by Buhi et al. have demonstrated that estrogen (E2) is responsible for the induction of de novo synthesis and secretion of certain oviductal secretory proteins (OSP) and inhibition of other OSP in porcine oviductal explant cultures. The present work was undertaken to evaluate the effect of E2-treated oviductal epithelial cell coculture on the development of early porcine embryos derived from in vitro matured and fertilized oocytes. In vitro synthesis of secretory proteins by E2-treated oviductal cells used for coculture was also investigated by one-dimensional (1D) and two-dimensional (2D) sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE). The results showed that the cleavage rate was significantly enhanced by coculturing fertilized eggs with E2-treated oviductal epithelial cells. The in vitro protein synthetic pattern of oviductal secretory proteins was influenced by E2 treatment. These variations included the disappearance of one protein (82,000 M(r)) and the appearance of another (33,000 M(r)) in the E2-treated group as assessed by 1D-SDS-PAGE. Additional proteins of M(r) 97,000 and an M(r) 36,000-45,000 complex were increased in abundance by the E2 treatment. Analyses by 2D-SDS-PAGE revealed three major E2-dependent proteins, of M(r) 45,000 (pI 5.5), 43,000 (pI 5.5) and a 36,000-45,000 M(r) (pI 4.8) protein complex, whereas polypeptides of M(r) 97,000 (pI 5.1), 36,000 (pI 8.0) and 25,000 (pI 6.8) were inhibited by E2 treatment. The results demonstrated that porcine epithelial cell protein synthetic patterns are influenced by E2 treatment and that estradiol treatment of oviductal cells may increase the rate of zygote cleavage during early development in vitro in pigs.

Basis for the loss of aryl hydrocarbon receptor gene expression in clones of a mouse hepatoma cell line

Rare benzo[a]pyrene-resistant clones were previously isolated from the mouse hepatoma cell line, Hepa-1 (Hepa1c1c7), and shown to be deficient in induction of CYP1A1 mRNA by ligands for the aryl hydrocarbon receptor (AHR). Clones belonging to complementation group B were shown to have reduced levels of ligand binding to AHR. It is shown here that all 15 independently derived B clones analyzed had much reduced levels of AHR mRNA, but in each case, the mRNA was normal in size. Infection of B clones with a retroviral expression vector for AHR restores CYP1A1 inducibility (although viral AHR expression is progressively silenced and CYP1A1 expression progressively diminishes as the cells are maintained in culture). Treatment of the B clones with the histone deacetylase inhibitors sodium butyrate or trichostatin A restores AHR expression and also restores CYP1A1 inducibility to nearly 100% of the cells in the treated cultures. Fusion of a representative B clone with a rat hepatoma cell line restores expression to the mouse AHR gene encoded by the B clone's genome. These results demonstrate that the loss of CYP1A1 inducibility in B clones is probably totally ascribable to their reduced levels of AHR and that the clones are most probably not mutated in the AHR gene but are deficient in its expression. The evidence suggests that the reduction in expression of mRNA encoded by the endogenous AHR gene in the B clones is not due to an epigenetic alteration in chromatin structure but that the clones are probably defective either in a transcription factor for the AHR gene or in a protein required for generating an open chromatin configuration over the gene.

A novel form of the G protein beta subunit Gbeta5 is specifically expressed in the vertebrate retina

The G protein beta subunit, Gbeta5, is predominantly expressed in the central nervous system. In rodent brain, Gbeta5 is expressed as a protein with an apparent molecular mass of 39,000 daltons (39 kDa). We have identified an additional Gbeta5 immunoreactive protein of apparent size 44 kDa in the vertebrate retina. Molecular cloning and sequencing of polymerase chain reaction products revealed that the cDNA encoding the larger species of Gbeta5 (Gbeta5L) was identical to the shorter form with the addition of 126 base pairs of 5' DNA sequence potentially encoding an in-frame 42-amino acid extension. Sequencing of mouse Gbeta5 genomic clones demonstrated that the 126-base pair of retinal-specific coding material is derived from a hitherto undetected 5' exon. During sucrose density gradient fractionation of bovine retinas, the 44-kDa Gbeta5L protein co-purified with rod outer segment membranes. Incubation of rod outer segment membranes with the nonhydrolyzable guanine nucleotide, GTPgammaS (guanosine 5'-3-O-(thio)triphosphate), which released the Gbeta subunit of transducin (Gbeta1), failed to remove Gbeta5L. The 39-kDa Gbeta5 protein displayed differential association with retinal and brain membranes. In the retina, Gbeta5 was present as a soluble protein and was undetectable in the membrane fraction, whereas in the brain approximately 70% of Gbeta5 was associated with cellular membranes. In transient COS-7 cell expression experiments, Gbeta5L formed functional Gbetagamma dimers and Galphabetagamma heterotrimers, and activated phosphoinositide-specific phospholipase Cbeta2 in a manner indistinguishable from the 39-kDa Gbeta5 protein. The cloning of the retinal-specific Gbeta5L cDNA suggests the existence of potentially novel G protein-mediated signaling cascades in photoreception.

Combined systemic and intra-amniotic treatment of cervical pregnancy by methotrexate. A report of two cases

Two cervical pregnancies were treated with systemic and local methotrexate. Neither involuted significantly but one was successfully removed vaginally after 17 days of treatment. The other required hysterectomy.

Expression of growth factor ligand and receptor genes in rat cancellous bone trabeculae and marrow

The technique of reverse transcription-PCR for mRNA phenotyping was applied to total RNA isolated from the two compartments of cancellous bone, namely trabecular bone and hematopoitic tissue or marrow. The pattern of gene expression for ten different growth factor ligands and five growth factor receptors was examined in total RNA isolated from the two compartments of cancellous bone of the female rat distal femur. Our results show that transcripts encoding IGF-I, IGF-II, transforming growth factor-beta 1 (TGF-beta 1), TGF-alpha, basic fibroblast growth factor, platelet-derived growth factor A and osteocalcin are detectable in samples from both trabeculae and marrow. Expression of epidermal growth factor (EGF) was confined to samples from trabeculae while nerve growth factor expression was only detected in marrow. Transcipts encoding insulin were not detected in any of the bone-derived samples in this study. Samples from cancellous bone trabeculae and marrow both showed evidence of expression of the genes encoding receptors for IGF-I, parathyroid hormone (PTH)/PTH-related protein and insulin. Neither compartment of cancellous bone contained transcripts encoding the receptor for IGF-II. Transcripts encoding the EGF receptor were detected in samples from cancellous bone marrow and not trabeculae as has been previously reported. These patterns of growth factor ligand and receptor gene expression suggest that it is likely that both autocrine and paracrine regulatory circuits are established in cancellous bone. This study also demonstrated the feasibility of assessing the expression of multiple genes from the small samples of total RNA obtained from separated tissues of cancellous bone. This is the first time that growth factor gene expression has been examined in separated trabeculae and marrow from cancellous bone and this approach will allow a more detailed analysis of molecular events in cancellous bone as opposed to whole bone or extracts of isolated and cultured bone cells.