The transcription activator-like effectors (TALEs) are a family of proteins, first discovered in the plant pathogen Xanthomonas sp., which contain a conserved central domain for specific DNA binding [1, 2]. The molecular and structural characteristics of the DNA-binding domain of TALE proteins have made them applicable for generation of designable DNA-binding proteins that can modify organisms at the genetic level by coupling with various effector domains [3, 4]. For example, TALEs fused with nucleases (TALENs) were used to modify DNA sequence for gene silencing or introducing exogenous DNA sequence at a specific locus [5]. In addition, TALEs fused with transcription activators were used to induce the expression of a target gene [6]. In the past two years, TALE-based technologies have been applied in many organisms including human cells, rats, zebrafish, worms and plants.
Although TALENs are similar in function to zinc-finger nucleases (ZFNs), they have advantages of greater flexibility in selecting target sequences, fewer constraints in engineering novel specificities, and no apparent toxicity thus far [7]. Also, TALENs are better than RNAi since the off-targeting effects is little.
The first three reports about the applications of TALENs in insects were published in this year. In Drosophila melanogaster, the yellow gene (on the sex chromosome) and a novel autosomal gene were modified [8]. TALENs were designed using“unit assembly” strategy and the mRNAs of TALENs were subsequently injected into the embryos. Inheritable modification was detected from 31.2% of the injected F0 fertile flies involving the yellow gene. In the hemimetabolous insect Gryllus bimaculatus, TALENs were used to generate homozygous mutant crickets, which exhibit the knock-out phenotype of the target gene, Gb’lac2. After microinjection of TALENs, 17% of founder animals transmit disrupted gene alleles [9]. In Bombyx mori, after injected with two pairs of TALENs which designed for BmBlos2 gene, germline mutations were resulted in a percentage of 31% and 15% of injected individuals, respectively. Furthermore, the simultaneous injection of these two pairs of TALENs generates inheritable large chromosomal deletion, which resulted in 14% germline mutations in the G1 broods [10].
TALE proteins have potential to be widely used in biological studies because of their effectiveness. It have been confirmed that TALE-based technologies are also applicable to insect research, although only gene silencing has been tried so far. It is expected that other TALE-based technologies will be also used in insects in near future.
References:
[1] S. Schornack et al. (2006) Gene-for-gene-mediated recognition of nuclear-targeted AvrBs3-like bacterial effector proteins. Journal of Plant Physiology163: 256 ? 272
[2] J. Boch et al. (2009) Breaking the code of DNA binding specificity of TAL-type III effectors. Science. DOI: 10.1126/science.1178811
[3] JC Miller et al. (2011) A TALE nuclease architecture for efficient genome editing. Nature Biotechnology. doi:10.1038/nbt.1755
[4] Bogdanove et al. (2011) TAL Effectors: Customizable Proteins for DNA Targeting. Science. DOI: 10.1126/science.1204094
[5] Bedell et al. (2012) In vivo genome editing using a high-efficiency TALEN system. Nature. DOI: doi: 10.1038/nature11537
[6] JP. Tremblay et al. (2012) Transcription activator-like effector proteins induce the expression of the frataxin gene. HUMAN GENE THERAPY 23:883?890
[7] T. Cermak et al. (2011) Efficient design and assembly of custom TALEN and other TAL effector-based constructs for DNA targeting. Nucleic Acids Research. DOI:10.1093/nar/gkr218
[8] Liu Jiyong et al. (2012) Efficient and Specific Modifications of the Drosophila Genome by Means of an Easy TALEN Strategy. JOURNAL OF GENETICS AND GENOMICS. 39(5): 209-215
[9] Takahito Watanabe et al. (2012) Non-transgenic genome modifications in a hemimetabolous insect using zinc-finger and TAL effector nucleases. Nature Communication. DoI: 10.1038/ncomms2020
[10] Ma et al. (2012) Highly Efficient and Specific Genome Editing in Silkworm Using Custom TALENs. PLoS ONE. DOI: doi:10.1371/journal.pone.0045035