Generation of T-cell receptor retrogenic mice

T-cell receptor (TCR) transgenic (Tg) mice have revolutionized our understanding of many aspects of T-cell biology. Whereas they provide an almost unlimited source of T cells with a single specificity, breeding them onto different backgrounds and/or new knockout/knock-in mouse models is often time-consuming (6 months to several years), which can make the process costly and can significantly delay research. This protocol describes a new method for expressing defined TCR-alpha and TCR-beta proteins from a single 2A peptide-linked multicistronic retroviral vector in mice, using retrovirus-mediated stem cell gene transfer. We refer to these as 'retrogenic' (Rg) mice ('retro' from retrovirus and 'genic' from Tg) to avoid confusion with traditional transgenic mice. We have successfully used this approach to express over 50 different TCRs on several different mouse backgrounds in as little as 6 weeks.     

Ago-allosteric modulation and other types of allostery in dimeric 7TM receptors

Conventionally, an allosteric modulator is neutral in respect of efficacy and binds to a receptor site distant from the orthosteric site of the endogenous agonist. However, recently compounds being ago-allosteric modulators have been described i.e., compounds acting both as agonists on their own and as enhancers for the endogenous agonists in both increasing agonist potency and providing additive efficacy-superagonism. The additive efficacy can also be observed with agonists, which are neutral or even negative modulators of the potency of the endogenous ligand. Based on the prevailing dimeric concept for 7TM receptors, it is proposed that the ago-allosteric modulators bind in the orthosteric binding site, but-importantly-in the "other" or allosteric protomer of the dimer. Hereby, they can act both as additive co-agonists, and through intermolecular cooperative effects between the protomers, they may influence the potency of the endogenous agonist. It is of interest that at least some endogenous agonists can only occupy one protomer of a dimeric 7TM receptor complex at a time and thereby they leave the orthosteric binding site in the allosteric protomer free, potentially for binding of exogenous, allosteric modulators. If the allosteric modulator is an agonist, it is an ago-allosteric modulator; if it is neutral, it is a classical enhancer. Molecular mapping in hetero-dimeric class-C receptors, where the endogenous agonist clearly binds only in one protomer, supports the notion that allosteric modulators can act through binding in the "other" protomer. It is suggested that for the in vivo, clinical setting a positive ago-allosteric modulator should be the preferred agonist drug.     

Comparison of fertility data from vaginal vs intrauterine insemination of frozen-thawed dog semen: a retrospective study

Fertility data from 327 artificial inseminations (AIs) using frozen-thawed dog semen are presented here. The AIs were performed in 274 bitches using semen from 185 males of 76 breeds. The data cover all AIs conducted during 1983 through 1995 at Cryogenetic Laboratories (CLONE) in the United States with AKC-registered and research bitches, and all AIs carried out at the Department of Obstetrics and Gynecology at the Swedish University of Agricultural Sciences in Uppsala, Sweden, using semen frozen by CLONE, in 0.5-mL straws. Semen was frozen using a standardized, three-step liquid nitrogen vapor freezing method. Whelping rates > 70% were obtained when post-thaw motility was 40% or higher. The inseminations were made either directly into the uterus using transcervical catheterization with the Norwegian catheter (NIU; 167 AIs) or a fiberoptic endoscope (EIU; 19 AIs), or in the cranial vagina (VAG; 141 AIs). Resulting whelping rates were 84.4% (NIU), 58.9% (VAG; P < 0.001), and 57.9% (EIU). Increasing the number of VAG AIs per cycle from 1 to 2 enhanced the whelping rate (P < 0.05). The mean interval from the first AI to whelping was 61.8 +/- 2.4 d, and was longer for VAG AIs (62.7 +/- 2.7 d) than for NIU AIs (61.2 +/- 2.1 d; P < 0.001). The mean interval from the last AI was 60.1 +/- 1.9 d, and did not differ between VAG AIs (60.2 +/- 2.2 d) and NIU AIs (60.0 +/- 1.6 d). Gestation length was not influenced by breed or litter size. A total of 1158 pups resulted from the 327 AIs. Litter size was 5.4 +/- 3.0 (NIU), 4.0 +/- 2.7 (VAG; P < 0.001), and 6.0 +/- 2.1 (EIU). Litter size was also influenced by breed (P = 0.006) and, for VAG AIs, by the number of inseminations performed per cycle (P = 0.009). This study is the largest that has been carried out on frozen-thawed dog semen AI. It shows that using a good method for cryopreservation, together with nonsurgical intrauterine AI employing the Norwegian catheter, can yield whelping rates and litter sizes similar to those reported from well-controlled natural matings. Furthermore, this is the first study to show that intrauterine deposition of frozen-thawed dog semen results in a significantly higher whelping rate and larger litter size than vaginal deposition.     

Genetic and structural characterization of the core region of the lipopolysaccharide from Serratia marcescens N28b (serovar O4)

The gene cluster (waa) involved in Serratia marcescens N28b core lipopolysaccharide (LPS) biosynthesis was identified, cloned, and sequenced. Complementation analysis of known waa mutants from Escherichia coli K-12, Salmonella enterica, and Klebsiella pneumoniae led to the identification of five genes coding for products involved in the biosynthesis of a shared inner core structure: [L,D-HeppIIIalpha(1-->7)-L,D-HeppIIalpha(1-->3)-L,D-HeppIalpha(1-->5)-KdopI(4<--2)alphaKdopII] (L,D-Hepp, L-glycero-D-manno-heptopyranose; Kdo, 3-deoxy-D-manno-oct-2-ulosonic acid). Complementation and/or chemical analysis of several nonpolar mutants within the S. marcescens waa gene cluster suggested that in addition, three waa genes were shared by S. marcescens and K. pneumoniae, indicating that the core region of the LPS of S. marcescens and K. pneumoniae possesses additional common features. Chemical and structural analysis of the major oligosaccharide from the core region of LPS of an O-antigen-deficient mutant of S. marcescens N28b as well as complementation analysis led to the following proposed structure: beta-Glc-(1-->6)-alpha-Glc-(1-->4))-alpha-D-GlcN-(1-->4)-alpha-D-GalA-[(2<--1)-alpha-D,D-Hep-(2<--1)-alpha-Hep]-(1-->3)-alpha-L,D-Hep[(7<--1)-alpha-L,D-Hep]-(1-->3)-alpha-L,D-Hep-[(4<--1)-beta-D-Glc]-(1-->5)-Kdo. The D configuration of the beta-Glc, alpha-GclN, and alpha-GalA residues was deduced from genetic data and thus is tentative. Furthermore, other oligosaccharides were identified by ion cyclotron resonance-Fourier-transformed electrospray ionization mass spectrometry, which presumably contained in addition one residue of D-glycero-D-talo-oct-2-ulosonic acid (Ko) or of a hexuronic acid. Several ions were identified that differed from others by a mass of +80 Da, suggesting a nonstoichiometric substitution by a monophosphate residue. However, none of these molecular species could be isolated in substantial amounts and structurally analyzed. On the basis of the structure shown above and the analysis of nonpolar mutants, functions are suggested for the genes involved in core biosynthesis.     

Structural and serological characterisation of the O-antigenic polysaccharide of the lipopolysaccharide from Acinetobacter baumannii strain 24

Extraction of dry bacteria of Acinetobacter baumannii strain 24 by phenol-water yielded a lipopolysaccharide (LPS) that was studied by serological methods and fatty acid analysis. After immunisation of BALB/c mice with this strain, monoclonal antibody S48-3-13 (IgG(3) isotype) was obtained, which reacted with the LPS in western blot and characterized it as S-form LPS. Degradation of the LPS in aqueous 1% acetic acid followed by GPC gave the O-antigenic polysaccharide, whose structure was determined by compositional analyses and NMR spectroscopy of the polysaccharide and O-deacylated polysaccharide as [carbohydrate structure: see text] where QuiN4N is 2,4-diamino-2,4,6-trideoxyglucose and GalNAcA 2-acetamido-2-deoxygalacturonic acid. The amino group at C-4 of the QuipN4N residues is acetylated in about 2/3 of LPS molecules and (S)-3-hydroxybutyrylated in the rest.     

Overexpression of the waaZ gene leads to modification of the structure of the inner core region of Escherichia coli lipopolysaccharide,truncation of the outer core,and reduction of the amount of O polysaccharide on the cell surface

The waa gene cluster is responsible for the biosynthesis of the lipopolysaccharide (LPS) core region in Escherichia coli and Salmonella: Homologs of the waaZ gene product are encoded by the waa gene clusters of Salmonella enterica and E. coli strains with the K-12 and R2 core types. Overexpression of WaaZ in E. coli and S. enterica led to a modified LPS structure showing core truncations and (where relevant) to a reduction in the amount of O-polysaccharide side chains. Mass spectrometry and nuclear magnetic resonance spectroscopy were used to determine the predominant LPS structures in an E. coli isolate with an R1 core (waaZ is lacking from the type R1 waa gene cluster) with a copy of the waaZ gene added on a plasmid. Novel truncated LPS structures, lacking up to 3 hexoses from the outer core, resulted from WaaZ overexpression. The truncated molecules also contained a KdoIII residue not normally found in the R1 core.     

Differential regional metabolism of glucagon in anesthetized pigs

Glucagon metabolism under basal (endogenous) conditions and during intravenous glucagon infusion was studied in anesthetized pigs by use of midregion (M), COOH-terminal (C), and NH2-terminal (N)-RIAs. Arteriovenous concentration differences revealed a negative extraction of endogenous glucagon immunoreactivity across the portal bed (-35.4 +/- 11.0, -40.3 +/- 9.6, -35.6 +/- 16.9%, M-, C-, N-RIA, respectively), reflecting net secretion of pancreatic glucagon and intestinal glicentin and oxyntomodulin, but under exogenous conditions, a net extraction occurred (11.6 +/- 3.6 and 18.6 +/- 5.7%, C- and N-RIA, respectively). Hindlimb extraction of endogenous (17.4 +/- 3.7%, C-RIA) and exogenous (29.1 +/- 4.8 and 19.8 +/- 5.1%, C- and M-RIA) glucagon was detected, indicating M and C cleavage of the molecule. Renal extraction of glucagon was detected by all assays under endogenous (19.4 +/- 6.7, 33.9 +/- 7.1, 29.5 +/- 6.7%, M-, C-, N-RIA) and exogenous conditions (46.9 +/- 4.8, 46.4 +/- 6.0, 47.0 +/- 7.7%; M-, C-, N-RIA), indicating substantial elimination of the peptide. Hepatic glucagon extraction was undetectable under basal conditions and detected only by M-RIA (10.0 +/- 3.8%) during glucagon infusion, indicating limited midregional cleavage of the molecule. The plasma half-life determined by C- and N-RIAs (2.7 +/- 0.2 and 2.3 +/- 0.2 min) were similar, but both were shorter than when determined by M-RIA (3.2 +/- 0.2 min, P < 0.02). Metabolic clearance rates were similar regardless of assay (14.4 +/- 1.1, 13.6 +/- 1.7, 17.0 +/- 1.7 ml x kg-1 x min-1, M-, C-, N-RIA). Porcine plasma degraded glucagon, but this was not significantly affected by the dipeptidyl peptidase IV (DPP IV) inhibitor valine-pyrrolidide, and in anesthetized pigs, glucagon's metabolic stability was unchanged by DPP IV inhibition. We conclude that tissue-specific metabolism of glucagon occurs, with the kidney being the main site of removal and the liver playing little, if any, role. Furthermore, valine-pyrrolidide has no effect on glucagon stability, suggesting that DPP IV is unimportant in glucagon metabolism in vivo, in contrast to its significant role in the metabolism of the other proglucagon-derived peptides and glucose-dependent insulinotropic polypeptide.     

Enhanced cAMP protein kinase A signaling determines improved insulin secretion in a clonal insulin-producing beta-cell line (INS-1 832/13)

In type 2 diabetes, beta-cells become glucose unresponsive, contributing to hyperglycemia. To address this problem, we recently created clonal insulin-producing cell lines from the INS-1 insulinoma line, which exhibit glucose responsiveness ranging from poor to robust. Here, mechanisms that determine secretory performance were identified by functionally comparing glucose-responsive 832/13 beta-cells with glucose-unresponsive 832/2 beta-cells. Thus, insulin secretion from 832/13 cells maximally rose 8-fold in response to glucose, whereas 832/2 cells responded only 1.5-fold. Insulin content in both lines was similar, indicating that differences in stimulus-secretion coupling account for the differential secretory performance. Forskolin or isobutylmethylxanthine markedly enhanced insulin secretion from 832/13 but not from 832/2 cells, suggesting that cAMP is essential for the enhanced secretory performance of 832/13 cells. Indeed, 8-bromoadenosine-3',5'-cyclic monophosphorothioate, rp-isomer (Rp-8-Br-cAMPS) an inhibitor of protein kinase A (PKA), inhibited insulin secretion in response to glucose with or without forskolin. Interestingly, whereas forskolin markedly increased cAMP in 832/2 cells, 832/13 cells exhibited only a marginal rise in cAMP. This suggests that 832/13 cells are more sensitive to cAMP. Indeed, the cAMP-induced exocytotic response in patch-clamped 832/13 cells was 2-fold greater than in 832/2 cells. Furthermore, immunoblotting revealed that expression of the catalytic subunit of PKA was 2-fold higher in 832/13 cells. Moreover, when the regulatory subunit of PKA was overexpressed in 832/13 cells, to reduce the level of unbound and catalytically active kinase, insulin secretion and PKA activity were blunted. Our findings show that cAMP-PKA signaling correlates with secretory performance in beta-cells.