A modified n-3 fatty acid desaturase gene from Caenorhabditis briggsae produced high proportion of DHA and DPA in transgenic mice.

The functions of polyunsaturated fatty acids (PUFAs) have been widely investigated. In mammals, levels of n-3 PUFAs are relatively low compared to those of n-6 PUFAs. Either a lack of n-3 PUFAs or an excess of n-6 PUFAs could potentially cause health problems in humans. Hence, methods to increase the amount of n-3 PUFAs in diet have been intensely sought. In this study, we demonstrated that the n-3 fatty acid desaturase gene (sFat-1) synthesized from revised and optimized codons based on roundworm Caenorhabditis briggsae genomic gene for enhanced expression in mammals was successfully expressed in Chinese hamster ovary (CHO) cells and significantly elevated cellular n-3 PUFA contents. We generated sFat-1 transgenic mice by introducing mammal expression vector DNAs containing the sFat-1 gene into regular mice through the method of microinjection. Fatty acid compositions were then altered and the levels of docosahexaenoic acid (DHA, 22:6n-3) and docosapentaenoic acid (DPA, 22:5n-3) were greatly increased in these transgenic mice. Various types of tissues in the transgenic mice produced many types of n-3 PUFAs, such as alpha-linolenic acid (ALA; 18:3n-3), eicosapentaenoic acid (EPA, 20:5n-3), DPA, and DHA, for example, muscle tissues of the transgenic mice contained 12.2% DHA, 2.0% DPA, and 23.1% total n-3 PUFAs. These research results demonstrated that the synthesized sFat-1 gene with modified and optimized codons from C. briggsae possess functional activity and greater capability of producing n-3 PUFAs, especially DHA and DPA, in transgenic mice.

[The synthesis and function analysis of omega-3 fatty acid desaturase gene from Caenorhabditis briggssae].

Omega-3 polyunsaturated fatty acids (PUFAs) have been broadly investigated and shown to exert many preventive and therapeutic actions besides their important role in maintenances human health and normal development. In mammals, the level of omega-3 PUFAs is relatively too low compared with omega-6 PUFAs, which metabolically and functionally distinct from omega-3 PUFAs and often have important opposing physiological functions. Either the inefficiency of omega-3 PUFAs or the excess of omega-6 PUFAs will cause many healthy problems. So methods have been sought to increase the amount of omega-3 PUFAs and to improve the omega-6/omega-3 ratio in body. In this study, the sFat-1 gene, which putatively encodes a omega-3 fatty acid desaturase, was chemically synthesized according to the sequence from Caenorhabditis briggssae (with codon usage modified), and constructed into a mammal expression vector pcDNA3. 1-sFat1-EGFP. This vector was introduced into CHO cells by lipid-mediated transfection, and it's expression quickly and effectively elevated the cellular omega-3 PUFAs (from 18-carbon to 22-carbon) contents and dramatically improved the ratio of omega-6/omega-3 PUFAs. Cellular lipids extracts from stably selected cells were analyzed with GC-MS and the results showed that amount of total omega-6 PUFAs dropped from 48.97% (in GFP cells)to 35.29% (in sFat-1 cells), whereas the amount of total omega-3 PUFAs increased from 7.86% to 24.02%, respectively. The omega-6/omega-3 ratio also dropped from 6.23 to 1.47. These data demonstrates the Caenorhabditis briggssae omega-3 Fatty Acid Desaturase gene, sFat-1, was synthesized successfully and can produce omega-3 PUFAs by using the corresponding omega-6 PUFAs as substrates, which shows its potential for use in the production of omega-3 PUFAs in transgenic animals.

[Synthesis of total sFat-1 gene by PCR-restrict enzyme ligation method].

Gene synthesis is very important in life science research, and it becomes a technique in common use. It is difficult for long gene synthesis, because the mismatches and mutations of DNA sequence in nucleotide fragments assembling. This study established a new method for long gene synthesis, which was referred to as PCR-restrict enzyme ligation method. With this method, a omega-3 fatty acid desaturase gene, sFat-1, from Caenorhabditis briggssae, was successfully assembled from 27 synthesized nucleotide fragments (60 ~ 68 bp for each fragment ) following 3 rounds of PCR (7 reactions) and 2 rounds of restrict enzyme ligation (3 reactions). This shows that the PCR-restrict enzyme ligation method is an effective method for long gene synthesis.

[The construction and characterization of human pro-urokinase mutant].

It is very easy for the pro-UK to lose it's biological activity because of the digestion of pro-UK by the thrombin or the inhibition of pro-UK by the PAI-I. So three pro-UK mutant (pro-UK) genes were constructed in this experiment with the PCR point-mutant method. The thrombin cleavage site Arg156 in pro-UK was mutated into His156, and named as pro-UKM1; PAI binding sites Arg178, Arg179, Arg181 were mutated into Lys178, Lys179, His181, named as pro-UKM2; The mutant containing His156, Lys178, Lys179, His181 as pro-UKM3. Three mutants were expressed in CHO cells respectively and analyzed with SDS-PAGE fibrin plate assay and western blot. The results showed that the three mutants and the native pro-UK have the same single electrophoresis band indicating most of the pro-UK was single chain. In vitro plasma clot lysis assays indicated that the pro-UKM1 have the ability to resistant against thrombin digestion; pro-UK2 could resist against PAI inhibition; while pro-UK3 improved resistances against both thrombin and PAI. It looks very promising that the pro-UK3 can be a new medicine of dissolving thrombus.