A more efficient and specific strategy in the ablation of mRNA in Xenopus laevis using mixtures of antisense oligos

Selective requirement for Cdc25C protein synthesis during meiotic progression in porcine oocytes

Fundamental differences between meiosis and mitosis suggest that the shared central cell cycle machinery may be regulated differently during the two division cycles. This paper focuses on unique features of Cdc25C protein function during meiotic progression. We report on the existence of oocyte-specific CDC25C transcripts that differ from their somatic counterparts in the 3' untranslated region. While CDC25C mRNA levels remain constant in fully-grown oocytes, corresponding protein levels increase progressively during maturation to a maximum at metaphase II. Elevation of Cdc25C protein levels in G2-oocytes by mRNA injection failed to increase MPF-kinase levels or to induce premature entry into M-phase. Likewise, antisense-induced arrest of translation (translational arrest) had no effect on chromosome condensation, nucleolar disassembly, or nuclear membrane contraction. By contrast, translational arrest inhibited subsequent events including membrane disassembly and spindle formation. Neither up- nor down-regulation of Cdc25C synthesis after metaphase I plate formation influenced progression to metaphase II. However, translational arrest during metaphase resulted in incomplete chromosome decondensation and abnormal pronuclear membrane assembly after activation. We conclude that Cdc25 protein, translated from unique transcripts, is preferentially located in the oocyte nucleus and is essential for progress through late diakinesis. Subsequently, new synthesis of Cdc25C protein is required for the orderly transition from meiotic to mitotic cell division.

Antisense therapeutics in chronic myeloid leukaemia: the promise, the progress and the problems

DNA sequences which are complementary or 'antisense' to a target mRNA can inhibit expression of that mRNA's protein product. Antisense therapeutics has therefore received attention for inhibiting oncogenes in haematological malignancy, in particular in chronic myeloid leukaemia. However, it is now becoming clear that antisense therapeutics is considerably more problematic than was naively initially assumed. In this article, some of these difficulties are discussed, together with the achievements in CML so far. Considerable further research is required in order to define an optimal antisense therapeutics strategy for clinical use.

Mmu and D2 receptor antisense oligonucleotides injected in nucleus accumbens suppress high alcohol intake in genetic drinking HEP rats

Numerous pharmacological and other studies have implicated both Mmu and dopamine receptor subtypes in alcohol consumption. In the genetic drinking rat as well as those chemically induced to drink, evidence has accrued that the abnormal intake of alcohol is underpined by these receptors in the brain. The purpose of this investigation was to demonstrate unequivocally that a biological impairment by antisense oligodeoxynucleotide (ODN) targeted specifically to these two receptor subtypes would disrupt ongoing alcohol drinking. In this project, a new strain of female and male high-ethanol preferring (HEP) rats was used that had free access to preferred concentrations of alcohol over water in a two choice paradigm. A guide cannula for a microinjection needle was first implanted bilaterally above the nucleus accumbens (NAC) of each rat. Following recovery, a dose of either 250 or 500 ng of the Mmu ODN or 500 ng D2ODN was microinjected into the NAC of the rat in a volume of 0.8-1.0 microl. A standard temporal sequence was used in which microinjections were given four times at successive 12-h intervals over a 2-day interval. The control mismatch ODNs corresponding to both the Mmu or D2 receptor antisense were microinjected identically at homologous sites in the NAC. Following the experiments, the brain of each rat was removed and sectioned in the coronal plane for histological analysis so that each microinjection site was identified. The results showed that the Mmu receptor antisense caused a significant dose dependent fall in free access alcohol drinking within 12 to 24 h following the initial microinjection. This decline often persisted for 1 to 2 days in terms of both g/kg intake and proportion of alcohol to water consumed. Similarly, the D2 receptor ODN likewise induced an intense and significant decline in both g/kg and proportion measures of alcohol intake. Since the corresponding mismatch ODN for both Mmu and D2 receptors exerted no effect on either of these measures of alcohol consumption, the specificity of molecular action of the respective antisense molecules on drinking behavior of the HEP rats was confirmed. Thus, these results provide the first unequivocal evidence that the genes for D2 and Mmu receptors are fundamentally involved in abnormal alcohol drinking in the genetically predisposed individual. Finally, important new anatomical evidence is introduced for the critical role of the NAC in the genetic basis of aberrant drinking of alcohol.

Introducing antisense oligodeoxynucleotides into Paramecium via electroporation

A method utilizing electroporation to deliver antisense oligodeoxynucleotides into Paramecium tetraurelia has been developed. For these studies antisense oligonucleotides directed to different regions of the calmodulin mRNA were used. It was found that a pulse delivered at 150-250 V (375-625 V/cm field strength) for 3.9-4.2 ms using a 275 microF capacitor with resistance set at 13 Ohms was sufficient to achieve measurable incorporation of fluorescently-labeled oligodeoxynucleotides in up to 95% of the cells treated. Optimal parameters included using oligodeoxynucleotides of at least 12 bases in length with a 3' blocking group at a dose of around 10 microM. In addition, multiple oligodeoxynucleotides directed to the same target mRNA resulted in at least a 10-fold reduction in the dose of oligodeoxynucleotide required to achieve the desired effects. Taken together, these results indicate that the use of antisense oligodeoxynucleotides can be an easy and useful method for linking genes to specific functions in Paramecium tetraurelia. Finally, this report discusses how different 3' blocking groups and the use of combinations of oligodeoxynucleotides directed to different regions of the same target mRNA can help address concerns about specificity.

In vivo antisense oligodeoxynucleotide mapping reveals masked regulatory elements in an mRNA dormant in mouse oocytes

In mouse oocytes, tissue-type plasminogen activator (tPA) mRNA is under translational control. The newly transcribed mRNA undergoes deadenylation and translational silencing in growing oocytes, while readenylation and translation occur during meiotic maturation. To localize regulatory elements controlling tPA mRNA expression, we identified regions of the endogenous transcript protected from hybridization with injected antisense oligodeoxynucleotides. Most of the targeted sequences in either the 5' untranslated region (5'UTR), coding region, or 3'UTR were accessible to hybridization, as revealed by inhibition of tPA synthesis and by RNase protection. Two protected regions were identified in the 3'UTR of tPA mRNA in primary oocytes: the adenylation control element (ACE) and the AAUAAA polyadenylation signal. These sequences were previously shown to be involved in the translational control of injected reporter transcripts. During the first hour of meiotic maturation, part of the ACE and the AAUAAA hexanucleotide became accessible to hybridization, suggesting a partial unmasking of the 3'UTR of this mRNA before it becomes translationally competent. Our results demonstrate that in vivo antisense oligodeoxynucleotide mapping can reveal the dynamics of regulatory features of a native mRNA in the context of the intact cell. They suggest that specific regions in the 3'UTR of tPA mRNA function as cis-acting masking determinants involved in the silencing of tPA mRNA in primary oocytes.

Potent and selective inhibition of gene expression by an antisense heptanucleotide

Factors that govern the specificity of an antisense oligonucleotide (ON) for its target RNA include accessibility of the targeted RNA to ON binding, stability of ON/RNA complexes in cells, and susceptibility of the ON/RNA complex to RNase H cleavage. ON specificity is generally proposed to be dependent on its length. To date, virtually all previous antisense experiments have used 12-25 nt-long ONs. We explored the antisense activity and specificity of short (7 and 8 nt) ONs modified with C-5 propyne pyrimidines and phosphorothioate internucleotide linkages. Gene-selective, mismatch sensitive, and RNase H-dependent inhibition was observed for a heptanucleotide ON. We demonstrated that the flanking sequences of the target RNA are a major determinant of specificity. The use of shorter ONs as antisense agents has the distinct advantage of simplified synthesis. These results may lead to a general, cost-effective solution to the development of antisense ONs as therapeutic agents.

Antisense therapy for angioplasty restenosis. Some critical considerations

The high affinity of even relatively short sequences of DNA for their target mRNA suggests that antisense agents represent an ideal method of suppressing specific gene products both in vitro and in vivo. In experiments performed thus far, an effect on the target mRNA in cultured vascular cells and in the vessel wall can be documented. The in vitro activity, toxicity, and pharmacokinetic data of antisense oligonucleotides are encouraging, and the in vivo animal experiments demonstrating suppression of neointimal formation are very promising. If animals trials presently under way show continued suppression not only of intimal formation but also of loss of lumen caliber after a single application, then effective delivery of antisense oligonucleotides is a realistic possibility. Nevertheless, some words of caution regarding the use of antisense oligonucleotides are warranted. Potential nonspecific effects of antisense oligonucleotides should be carefully considered in studies in which antisense agents are used to define biological functions of specific genes. In particular, demonstration that the target mRNA has been suppressed does not prove that other sequences within the mRNA pool have not also been suppressed. Critical control measures include adding back the target mRNA or protein and demonstrating similar biological effects with antisense sequences, which also suppress target gene expression directed at different regions of the target mRNA. At the clinical level, the systemic effects of antisense oligonucleotides, the dosage required, the timing of administration compared with mechanical intervention, and the toxicity of breakdown products all need to be established. In addition, the most appropriate targets for antisense use in restenosis remain largely obscure. Indiscriminate suppression of cell-cycle genes or proto-oncogenes may be as acutely toxic as current anticancer chemotherapy if the site delivery is not completely localized. Furthermore, much of the clinical evidence suggests that restenosis is a chronic process, continuing to develop weeks to months after the procedure. If this is the case, then the current approaches that rely on a transient, local application of an antisense agent may fail. If, however, a target gene is identified that is specific to vascular tissue, then repeated administration of an antisense agent may be tolerated via a systemic route. This approach has proved successful in targeting mutated genes with little suppression of closely related genes and with minimal systemic toxicity. An alternative approach is to transfect the target tissue with a gene that makes it susceptible to systemic delivery of a drug that is not normally toxic to mammalian cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Xenopus oocytes as a heterologous expression system for plant proteins

The Xenopus oocyte is a robust and convenient system for the transient expression of many different animal proteins and it has recently been demonstrated that oocytes can also translate, process, and target plant proteins. This expression system can also be used to clone genes, characterize function, and study posttranslational processing of proteins. Here we describe the methodology for the expression of plant proteins, in particular membrane proteins, in Xenopus oocytes.

Delocalization of Vg1 mRNA from the vegetal cortex in Xenopus oocytes after destruction of Xlsirt RNA

The Xlsirts are a family of transcribed repeat sequence genes that do not code for protein. Xlsirt RNAs become localized to the vegetal cortex of Xenopus oocytes early in oogenesis, before the localization of the messenger RNA Vg1, which encodes a transforming growth factor-beta-like molecule involved in mesoderm formation, and coincident with the localization of Xcat2 transcripts, which encode a nanos-like molecule. Destruction of the localized Xlsirts by injection of antisense oligodeoxynucleotides into stage 4 oocytes resulted in the release of Vg1 transcripts but not Xcat2 transcripts from the vegetal cortex. Xlsirt RNAs, which may be a structural component of the vegetal cortex, are a crucial part of a genetic pathway necessary for the proper localization of Vg1 that leads to subsequent normal pattern formation.