The Use of an Automated Platform to Assemble Multigenic Constructs for Plant Transformation

Compared to traditional means, modern DNA assembly methods allow cloning of large, multigenic vectors for plant transformation in rapid fashion. These methods are often robust and efficient and can assemble multiple DNA fragments into a single vector in one reaction. Here we describe the use of an automated DNA assembly platform for the generation of complex, multigenic T-DNA binary vectors using a hierarchical Golden Gate cloning strategy. These DNA constructs contained diverse DNA elements for the expression of multiple genes for trait stacking in the crop of interest. This platform streamlines the DNA assembly and validation process through high-efficiency cloning methods, integrated automation equipment, and increased throughput. The implementation of this platform removes bottlenecks for routine molecular biology and opens new possibilities for downstream experimental idea testing.

GC-rich coding sequences reduce transposon-like, small RNA-mediated transgene silencing

The molecular basis of transgene susceptibility to silencing is poorly characterized in plants; thus, we evaluated several transgene design parameters as means to reduce heritable transgene silencing. Analyses of Arabidopsis plants with transgenes encoding a microalgal polyunsaturated fatty acid (PUFA) synthase revealed that small RNA (sRNA)-mediated silencing, combined with the use of repetitive regulatory elements, led to aggressive transposon-like silencing of canola-biased PUFA synthase transgenes. Diversifying regulatory sequences and using native microalgal coding sequences (CDSs) with higher GC content improved transgene expression and resulted in a remarkable trans-generational stability via reduced accumulation of sRNAs and DNA methylation. Further experiments in maize with transgenes individually expressing three crystal (Cry) proteins from Bacillus thuringiensis (Bt) tested the impact of CDS recoding using different codon bias tables. Transgenes with higher GC content exhibited increased transcript and protein accumulation. These results demonstrate that the sequence composition of transgene CDSs can directly impact silencing, providing design strategies for increasing transgene expression levels and reducing risks of heritable loss of transgene expression.

Metabolic engineering of seeds can achieve levels of omega-7 fatty acids comparable with the highest levels found in natural plant sources

Plant oils containing ω-7 fatty acids (FAs; palmitoleic 16:1Δ(9) and cis-vaccenic 18:1Δ(11)) have potential as sustainable feedstocks for producing industrially important octene via metathesis chemistry. Engineering plants to produce seeds that accumulate high levels of any unusual FA has been an elusive goal. We achieved high levels of ω-7 FA accumulation by systematic metabolic engineering of Arabidopsis (Arabidopsis thaliana). A plastidial 16:0-ACP desaturase has been engineered to convert 16:0 to 16:1Δ(9) with specificity >100-fold than that of naturally occurring paralogs, such as that from cat's claw vine (Doxantha unguis-cati). Expressing this engineered enzyme (Com25) in seeds increased ω-7 FA accumulation from <2% to 14%. Reducing competition for 16:0-ACP by down-regulating the β-ketoacyl-ACP synthase II 16:0 elongase further increased accumulation of ω-7 FA to 56%. The level of 16:0 exiting the plastid without desaturation also increased to 21%. Coexpression of a pair of fungal 16:0 desaturases in the cytosol reduced the 16:0 level to 11% and increased ω-7 FA to as much as 71%, equivalent to levels found in Doxantha seeds.

Potency estimation of recombinant factor VIII: effect of assay method and standard

Large potency discrepancies between the chromogenic and one-stage clotting methods have been reported for patients' plasma samples following the infusion of recombinant factor VIII (rFVIII) concentrates. We have investigated the potency estimation of two different full-length rFVIII concentrates using both assay methods relative to both plasma and concentrate standards. Potencies by the chromogenic method were significantly higher (53% and 45%) than potencies by the one-stage clotting method when a plasma standard was used. In contrast, there was no significant potency difference between methods when a concentrate standard was used. Time-course studies into thrombin and activated factor X (FXa) generation, in modified clotting and chromogenic methods, respectively, revealed that the two rFVIII concentrates behaved very similarly to the concentrate standard, whereas the plasma standard showed slightly more rapid thrombin generation and markedly slower FXa generation. The different behaviour of rFVIII and plasma FVIII in the chromogenic method is proposed as the main cause of the methods-based potency discrepancy. The results support the use of a concentrate standard to measure rFVIII in post-infusion plasma.

Modification of factor VIII in therapeutic concentrates after virus inactivation by solvent-detergent and pasteurisation

The addition of a pasteurisation step to a solvent/detergent (SD) treated FVIII concentrate has recently resulted in enhanced inhibitor incidence in patients in Germany and Belgium. We have investigated the effect of virus inactivation procedures on FVIII function by preparing experimental concentrates from the same starting cryoprecipitate with the following procedures: none (N); dry heat (DH); pasteurisation (P); solvent/detergent (SD); solvent detergent + dry heat (SDDH); solvent detergent + pasteurisation (SDP). In addition, several clinical SD concentrates with and without pasteurisation were studied. There were no significant differences in fibrinogen and vWF content and in the ratio of one-stage/chromogenic FVIII activity among any of the samples studied. In thrombin proteolysis and FXa generation experiments, there were no differences in results on samples N, DH, P, and SDDH from those on sample SD. However sample SDP gave markedly different results from sample SD in the following respects: slower thrombin proteolysis (t(1/2) = 12.0 min vs 1.9 min); more rapid FXa generation (rate 2.5 times that of SD); enhanced phospholipid binding (K(D) = 3.89 x 10(-11) M vs 5.53 x 10(-10) M). Similar differences between SDP and SD were seen in the clinical samples. The observed changes in the FVIII activity occurred in combination with SD and pasteurisation, but not with either treatment alone. These results suggest that SDP treatment may enhance exposure of the phospholipid binding site in the C2 domain of FVIII, and since inhibitors to the SDP product are predominantly against C2, these findings could be relevant to the enhanced immunogenicity of the SDP product.

In vivo studies of activated porcine factor VIII

The haemostatic effectiveness of activated FVIII was compared to that of non-activated FVIII in a cross-over study in a canine model of haemophilia. Activation of FVIII in porcine concentrate was achieved by the addition of 3 x 10(-5) IU thrombin per ml of concentrate, which gave consistent increases in 1-stage FVIII activity of 13- to 14-fold and slow decay. The haemostatic effect was monitored by measurements of the cuticle bleeding time 10 and 45 min after infusion and there were no consistent differences between the activated and non-activated concentrates. One-stage factor VIII assays on plasmas 5 min after infusion showed identical mean values for activated and non-activated concentrates, indicating that most of the higher activity observed in vitro had disappeared rapidly from the circulation. These results suggest that controlled activation of FVIII by thrombin, which increases its activity in 1-stage assays, is unlikely to be of therapeutic benefit. For therapeutic concentrates which may contain small amounts of activated FVIII, the 1-stage assay may be an unreliable guide to their therapeutic effect.

Variable inactivation of human factor VIII from different sources by human factor VIII inhibitors

The source of human factor VIIII (FVIII) had a marked effect on the inhibitory activity of a panel of eight human FVIII inhibitors. Use of conventional FVIII concentrates gave lower inhibitor titres whereas a monoclonal antibody purified FVIII concentrate gave titres similar to or greater than those with plasma. Addition of phospholipid (PL) protected highly purified FVIII against inhibition. The content of PL-bound FVIII in concentrates may account for the observed differences.

Factor VIII heavy chain polypeptides in plasma and concentrates

Factor VIII polypeptides in plasma and FVIII concentrates have been analysed by an electrophoretic technique based on that of Weinstein et al (1981). Samples were complexed with radiolabelled anti-FVIII Fab', and the immunocomplexes visualized by SDS-polyacrylamide electrophoresis. The technique visualized FVIII heavy chain polypeptides in all types of samples, including plasma, without further purification. Fresh or frozen normal plasma (collected into protease inhibitors) contained a range of polypeptides with the largest dominant band at an apparent Mr of 250-300 kDa, and the smallest at 80-90 kDa: no bands were produced from samples of severe haemophilic plasma. Cryoprecipitate had a similar polypeptide distribution to normal plasma, but intermediate purity FVIII concentrates showed more degraded patterns which varied between products: the 250-300 kDa bands were reduced or absent, the 80-90 kDa bands were more pronounced than in plasma, and in one product a polypeptide was seen at approximately 40-50 kDa. In some products heat treatment for viral inactivation increased the proportion of smaller FVIII polypeptides. Highly-purified FVIII concentrate derived from plasma was also degraded relative to plasma FVIII, and two products obtained by recombinant DNA technology both showed degraded, though slightly different, profiles. The native structure of FVIII in fresh plasma appears heterogeneous with a predominance of higher Mr forms: these are degraded to a greater or lesser extent during concentrate production, dependent on the manufacturing processes used.