My host's enemy is my enemy: plasmids carrying CRISPR-Cas as a defence against phages

Bacteria are infected by mobile genetic elements like plasmids and virulent phages, and those infections significantly impact bacterial ecology and evolution. Recent discoveries reveal that some plasmids carry anti-phage immune systems like CRISPR-Cas, suggesting that plasmids may participate in the coevolutionary arms race between virulent phages and bacteria. Intuitively, this seems reasonable as virulent phages kill the plasmid's obligate host. However, the efficiency of CRISPR-Cas systems carried by plasmids can be expected to be lower than those carried by the chromosome due to continuous segregation loss, creating susceptible cells for phage amplification. To evaluate the anti-phage protection efficiency of CRISPR-Cas on plasmids, we develop a stochastic model describing the dynamics of a virulent phage infection against which a conjugative plasmid defends using CRISPR-Cas. We show that CRISPR-Cas on plasmids provides robust protection, except in limited parameter sets. In these cases, high segregation loss favours phage outbreaks by generating a population of defenceless cells on which the phage can evolve and escape CRISPR-Cas immunity. We show that the phage's ability to exploit segregation loss depends strongly on the evolvability of both CRISPR-Cas and the phage itself.

New [99mTc]bombesin analogues with improved biodistribution for targeting gastrin releasing-peptide receptor-positive tumors

AIM

Bombesin (BBS) receptors are potential targets for diagnosis and therapy of breast and prostate tumors. To overcome the rapid degradation of natural BBS some modifications were introduced at positions 13 and 14. Additionally, a spacer was inserted between the chelator and the binding sequence in order to further improve the in vivo uptake. The analogues were labeled with the [(99m)Tc(CO)(3)]-core and tested.

METHODS

Stability was analyzed in vitro in human plasma. Binding affinity and internalization were determined in vitro in prostate carcinoma PC-3 cells. Biodistribution studies and single photon emission computed tomography/X-ray computed tomography (SPECT/CT) imaging were performed in nude mice with PC-3 tumor xenografts.

RESULTS

The changes introduced in the BBS(7-14) sequence substantially increased plasma stability. Affinity for gastrin releasing-peptide (GRP) receptors on PC-3 cells was comparable to that of the unmodified analogue with Kd<1 nM. The presence of a spacer in the molecule induced an increment in the in vivo uptake in pancreas and PC-3 xenografts (GRP receptor-positive tissues). The increase in pancreas and tumor uptake was higher when both spacer and stabilization are present in the same molecule. Moreover, in vivo uptake was highly specific. The tumor was clearly visualized by SPECT/CT.

CONCLUSIONS

The modifications in the BBS(7-14) sequence led to a higher plasma stability while binding affinity remained unaffected. Stabilization resulted in improved biodistribution with better tumor to non-tumor ratios. However, the insertion of a spacer had a greater influence on the biodistribution. Analogues with both spacer and stabilization are the most promising radiopharmaceuticals for targeting GRP receptor-positive tumors.

Developmental changes of agonist affinity at GABABR1 receptor variants in rat brain

Recently, two N-terminal splice variants of the metabotropic receptor for GABA (gamma-amino-butyric acid) were cloned. Here, we describe an antiserum that recognizes the two receptor variants. We demonstrate that these proteins are identical with GABAB receptors that are photoaffinity labeled with [125I]CGP71872 in rat brain. The C-terminal epitopes recognized by the antiserum are conserved in several vertebrate species but not in chicken. No hints for the existence of additional closely related receptor subtypes or variants are found in double-labeling experiments with antibody and photoaffinity ligand. Western blot analysis reveals widespread expression of the GABABR1 receptor proteins in rat brain with the highest level of expression at early postnatal stages. The binding affinity of the GABAB receptor agonist L-baclofen at native R1a and R1b variants is similar. In early postnatal development the affinity at R1a and R1b is 10-fold lower than in adult brain and gradually increases with aging.

A novel splice variant of a metabotropic glutamate receptor, human mGluR7b

Two splice variants of the human metabotropic glutamate receptor 7, named hmGluR7a and hmGluR7b, were isolated from a human brain cDNA library. The isoforms differ by an out-of-frame insertion of 92 nucleotides close to the C-terminus of the hmGluR7 coding region, hmGluR7a has a length of 915 amino acids and represents the human homolog of the recently cloned rat mGluR7. hmGluR7b is seven amino acids longer and exhibits a novel C-terminus of 23 amino acids in length. RT-PCR analysis demonstrated the existence of mGluR7b transcripts in wild-type mouse brain and its absence in mGluR7 knockout mice. Northern blot analysis indicate that mGluR7 expression is developmentally regulated. It is expressed at high levels in human fetal brain and at a lower level in many regions of adult human brain. Stimulation of hmGluR7b with L-2-amino-4-phosphonobutyrate (L-AP4), L-serine-O-phosphate (L-SOP) or L-glutamate in stably transfected Chinese hamster ovary (CHO) cells depressed forskolin-induced cAMP accumulation, whereas (1S,3R)-1-aminocyclopentane-1,3,-dicarboxylic acid ((1S,3R)-ACPD) and quisqualate (both at 1mM) had no significant effects. As described for rat mGluR7, the rank order of agonist potencies is: L-SOP, L-AP4 > L-glutamate > (1S,3R)-ACPD, quisqualate.

Molecular cloning, functional expression and pharmacological characterization of the human metabotropic glutamate receptor type 2

A cDNA encoding the human metabotropic glutamate receptor type 2 (hmGluR2) was isolated from human brain cDNA libraries by cross-hybridization with rat mGluR2 probes. The deduced amino acid sequence of the human mGluR2 receptor consists of 872 residues and shows a sequence identity of 97% to the amino acid sequence of rat mGluR2. Northern blot analyses showed that hmGluR2 is widely expressed in different regions of the adult brain as well as in fetal human brain. Genomic Southern blotting localized the mGluR2 gene to human chromosome 3. Chinese hamster ovary (CHO) cells stably transfected with the cloned hmGluR2 cDNA exhibit agonist induced depression of forskolin-stimulated cAMP accumulation. A direct comparison of CHO cells stably expressing human and rat mGluR2 with five agonists revealed the same rank order of potency [(2S,3S,4S)-alpha-(carboxycyclopropyl)-glycine >> (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid = L-glutamate >> quisqualate = L-2-amino-4-phosphonobutyric acid] and similar EC50 values for both homologous receptors. (R,S)-alpha-methyl-4-carboxyphenylglycine, a reported antagonist at some mGluR subtypes, reduced the depression of forskolin-induced cAMP accumulation by (1S,3R)-ACPD in both human and rat mGluR2.

Molecular cloning, functional expression and pharmacological characterization of the human metabotropic glutamate receptor type 4

A cDNA encoding the human metabotropic glutamate receptor type 4 (hmGluR4) was isolated from human brain cDNA libraries by cross-hybridization with rat mGluR4 probes. The deduced amino acid sequence of human mGluR4 consists of 912 residues and shows a sequence identity of 96% to the amino acid sequence of rat mGluR4. Northern blot analyses indicate that hmGluR4 is strongly expressed in the cerebellum of the adult human brain but also at low levels in hippocampus, hypothalamus and thalamus. Stimulation of hmGluR4 with L-2-amino-4-phosphonobutyrate (L-AP4), L-serine-O-phosphate (L-SOP), L-glutamate or (1S,3R)-1-aminocyclo-pentane-1,3-dicarboxylic acid ((1S,3R)-ACPD) in stably transfected Chinese hamster ovary (CHO) cells depressed forskolin-induced cAMP accumulation, whereas quisqualate (0.5 mM) was ineffective. The rank order of agonist potencies is: L-AP4 > L-SOP > L-glutamate > (1S,3R)-ACPD >> quisqualate. (R,S)-alpha-methyl-4-carboxyphenylglycine (1 mM), a reported antagonist at some mGluR subtypes, did not reduce the depression of forskolin-induced cAMP accumulation by L-AP4.

Cellular and subcellular localization of the mGluR5a metabotropic glutamate receptor in rat spinal cord

The cellular and subcellular distribution of the mGluR5a metabotropic glutamate receptor was studied in the spinal cord of the rat using an antibody raised against a mGluR5a-specific carboxy-terminal peptide. Strong mGluR5a-immunoreactivity (mGluR5a-ir) was found in the laminae I-II of the dorsal horn, which gradually decreased towards the deeper layers. At the electron microscopical level, mGluR5a-ir was present exclusively in neuronal somata and dendrites. Immunometal labelling revealed that mGluR5a-ir is concentrated at the periphery of postsynaptic densities of asymmetrical synapses or localized extrasynaptically at dendritic and somatic membranes. The mGluR5a-immunoreactive dendritic profiles were often targeted by synaptic boutons with the morphological characteristics of C-fibre terminals. These observations provide evidence for mGluR5a being involved in the nociceptive transmission at the dorsal horn.

Differential cellular localization of three splice variants of the mGluR1 metabotropic glutamate receptor in rat cerebellum

Antibodies were raised against C-terminal peptides of the splice variants a, b and c of the rat mGluR1 metabotropic glutamate receptor. Affinity purified antibodies each specifically reacting with mGluR1a, mGluR1b and mGluR1c were used to study the cellular localization of these receptors in rat cerebellum. The mGluR1a antibody strongly labelled Purkinje cells at their cells bodies, portions of their dendritic trees and numerous small punctate elements reminiscent of dendritic spines. Also labelled were some stellate, basket, Golgi and Lugaro cells. Granule cells were devoid of staining. The mGluR1b antibody strongly labelled Purkinje cell bodies and their dendrites at levels which varied within the same lobule of the vermis or the hemispheres. No significant labelling was observed at stellate, basket, Golgi and granule cells, while occasionally a fraction of basket cells and cerebellar glomeruli was moderately immunoreactive. The mGluR1c antibody strongly labelled cell bodies and thick principal dendrites of Purkinje cells but not dendritic spines. Immunonegative Purkinje cells were intermingled with strongly labelled ones in lobules 4-10, while in lobules 1, 2 and 3, no stained Purkinje cells were detected. The mGluR1c antibody also labelled stellate, basket, some Golgi and some Lugaro cells as well as granule cells.

Autoaggressive myocytotoxic T lymphocytes expressing an unusual gamma/delta T cell receptor

Polymyositis mediated by gamma/delta T cells is a unique disease in which autoaggressive T lymphocytes surround, invade, and destroy muscle fibers. Histochemically, the vast majority of muscle-infiltrating T cells in a patient with polymyositis were reactive with a pan-gamma/delta T cell receptor (TCR)-specific monoclonal antibody (TCR-delta 1+), but unlike > 90% of peripheral blood gamma/delta T cells, these lymphocytes did not react with V delta 1- or V gamma 9-specific antibodies (A13- and Ti gamma A-, respectively). Differential reactivity with two different V delta 2-specific monoclonal antibodies (BB3-/TiV-delta 2+) indicated that the infiltrating T cells express a V delta 2-containing TCR with unusual additional structural features. Using conventional and anchored polymerase chain reaction for the analysis of TCR transcripts, we found a striking predominance of one unusual V delta 2-J delta 3 recombination and one V gamma 3-J gamma 1 recombination. Both the unusual phenotype (TCR-delta 1+/A13-/Ti gamma A-/BB3-/TiV-delta 2+) and the dominance of distinct TCR transcripts are compatible with the assumption that one T cell clone, which expresses a V gamma 3-J gamma 1-C gamma 2/V delta 2-J delta 3-C delta disulfide-linked TCR, dominates among the infiltrating T cells of the polymyositis muscle specimen analyzed.

Immunoglobulin E-binding site in Fc epsilon receptor (Fc epsilon RII/CD23) identified by homolog-scanning mutagenesis

The IgE-binding site of the human low-affinity receptor for IgE (Fc epsilon RII/CD23) has previously been mapped to the extracellular domain between amino acid residues 160 and 287. We now have investigated which conformational epitope within this domain specifies the receptor-ligand interaction. The analysis of homolog-scanning mutants expressed in mammalian cells demonstrates that amino acid side chains that affect IgE binding are located in two discontinuous segments, between residues 165-190 and 224-256. The overall structure of the chimeric binding domains, as probed with 11 conformation-sensitive monoclonal antibodies, is generally not distorted, except by replacement of residues 165-183. In this region, disruption of binding function appears to be caused by global conformational constraints on the binding site. Substitution and deletion mutants demonstrate that six out of eight extracellular cysteines, Cys163, Cys174, Cys191, Cys259, Cys273, and Cys282, are necessary for IgE binding and are most likely involved in intramolecular disulfide bridges. We show that the Fc epsilon RII domain delineated by Cys163 and Cys282 encodes all the structural information required to form the IgE-binding site.

Binding site for IgE of the human lymphocyte low-affinity Fc epsilon receptor (Fc epsilon RII/CD23) is confined to the domain homologous with animal lectins

The lymphocyte low-affinity receptor for IgE (Fc epsilon RII) is involved in two seemingly unrelated processes: (i) promotion of general B-cell growth and (ii) isotype-specific IgE synthesis. To characterize domains of Fc epsilon RII important for effector function, we have expressed Fc epsilon RII mutants in mammalian cells. The results show that the IgE-binding region of Fc epsilon RII corresponds almost exactly to a domain of 123 amino acid residues homologous with the carbohydrate-binding domain of C-type animal lectins. With the recent demonstration that Fc epsilon RII binds to IgE independently of any lectin-like activity [Vercelli, D., Helm, B., Marsh, P., Padlan, E., Geha, R.S. & Gould, H. (1989) Nature (London) 338, 649-651], it is now clear that, in this case, the lectin module has evolved to interact with a protein rather than a carbohydrate moiety. The epitopes of several independent monoclonal antibodies that inhibit the binding of IgE to Fc epsilon RII are clustered within the lectin-like domain. Some of these antibodies are also known to suppress, isotype-specifically, the interleukin 4-promoted IgE synthesis from peripheral blood mononuclear cells or the spontaneous synthesis of IgE by B cells isolated from atopic donors. The epitope of MHM6, an anti-F epsilon RII monoclonal antibody delivering an epitope-restricted growth-promoting effect on B cells, is also located within the lectin-like domain. Thus, the lectin module of Fc epsilon RII not only acts as a carbohydrate-independent, isotype-specific Fc receptor but may also participate in the general regulation of B-cell growth.

Splicing of an intervening sequence from hybrid cauliflower mosaic viral RNA

A DNA sequence encompassing intervening sequence 2 of the soybean leghemoglobin gene was inserted into the cauliflower mosaic virus (CaMV) genome. Upon passage through host plants progeny virus slowly accumulated that had lost the intron, apparently by exact splicing of the RNA form of the genome at the exon/intron borders. These findings suggest that reverse transcription from (spliced) RNA to DNA is a normal step in CaMV replication. S1 nuclease mapping revealed a mixed population of unspliced and spliced viral RNAs. The inefficiency of the splicing process is discussed.

Corticofugal effects from sensorimotor area I and somatosensory area II on neurones of the pontine nuclei in the cat

1. The objective of the present experiments was to study the cortical influence from sensorimotor area I (SM I) and from somatosensory area II (S II) on single neurones of the pontine nuclei (PN) in cats under N2--thiamylal anaesthesia. 2. Extracellular single unit recordings revealed a considerable convergence from S II and SM I. Out of ninety-one PN neurones (identified as ponto-cerebellas neurones by antidromic stimulation of the contralateral brachium pontis), fifty-seven neurones were influenced by stimulation of at least one cortical site. Slightly less than half of these neurones (twenty-five) had a convergent input from SM I and S II; twenty-three PN neurones were excited by SM I only and nine PN neurones by S II only. The proportion of PN neurones excited via collaterals of cortico-spinal neurones was small and restricted to those neurones which had an input from SM I. 3. Sixty per cent of the ponto-cerebellar neurones were reliably activated by natural stimulation such as tapping or passive manipulations of limbs of various joints. The vast majority (thirty-three out of thirty-six PN neurones) which had receptive fields were also influenced by electrical stimulation of one or both cortical areas. The long latency and low probability of discharge to peripheral nerve stimulation suggest a complex, probably transcortical, pathway from the periphery to the PN. 4. The distribution of latencies to both cortical and brachium pontis stimulation indicates that the PN are a relay for fast and slow cerebro-cerebellar connexions. 5. The convergence from cortical areas on PN indicates that the neurones influenced from somatic areas SM I and S II transmit integrated patterns of activity to the cerebellum.