Module 3: Viral vectors

Lecture 22: Transposons

·        

22.3 Sleeping beauty (SB) transposon :

The genome of salmonid fish was reconstructed to make sleeping beauty (SB) transposon with the help of molecular phylogenetic data. SB transposon belongs to Tc1/mariner superfamily of transposons. Both the sides of sleeping beauty transposon are flanked by 230bp of inverted terminal repeat sequences (IRs) which have non direct repeats (DRs) in between them. It is one of the leading non-viral vectors for gene therapy. SB consists of two components: (i) a gene-expression cassette present in a transposon & (ii) a source for transposase enzyme. Sustained transgene can be achieved by transposing the expression of cassette from a plasmid into the genome. Treatment of epidermolysis bullosa, glioblastoma multiforme, sickle cell anemia and B-cell lymphoma have been done by using SB transposon. In rats, pulmonary hypertension and jaundice have been treated with the help of SB transposon. Various improvements that have been done for the use of SB transposon in clinics are:

  1. i.  Efficacy: to achieve appropriate expression of therapeutic or reporter genes and SB transposase more significance is given to efficiency of transposition and engineered cassettes.

    3. ii.  Delivery: the method and routes that are being used for plasmid delivery as well as for cell culture conditions in which gene transfer is done ex vivo in cells which are therapeutic.

    iii.  Safety: the time period of the transposition reaction and insertion preferences of SB transposes in cells which are transduced.

22.4 piggyBac transposon :

It was isolated from cabbage looper moth Trichoplusia ni . The significant feature of this transposon is the precise excision of the transposon from the donor site without any footprints leaving behind. This feature of piggyBac transposon makes it more attractive feature for cellular reprogramming. When the transposon is excised from the donor site, there is a creation of complimentary TTAA overhangs which can undergo simple ligation thereby regenerating the donor site without involving the process of DNA synthesis during transposition.