Drosophila as a Model Organism to Understand the Effects during Development of TFIIH-Related Human Diseases

Abstract

Human mutations in the transcription and nucleotide excision repair (NER) factor TFIIH are linked with three human syndromes: xeroderma pigmentosum (XP), trichothiodystrophy (TTD) and Cockayne syndrome (CS). In particular, different mutations in the XPB, XPD and p8 subunits of TFIIH may cause one or a combination of these syndromes, and some of these mutations are also related to cancer. The participation of TFIIH in NER and transcription makes it difficult to interpret the different manifestations observed in patients, particularly since some of these phenotypes may be related to problems during development. TFIIH is present in all eukaryotic cells, and its functions in transcription and DNA repair are conserved. Therefore, Drosophila has been a useful model organism for the interpretation of different phenotypes during development as well as the understanding of the dynamics of this complex. Interestingly, phenotypes similar to those observed in humans caused by mutations in the TFIIH subunits are present in mutant flies, allowing the study of TFIIH in different developmental processes. Furthermore, studies performed in Drosophila of mutations in different subunits of TFIIH that have not been linked to any human diseases, probably because they are more deleterious, have revealed its roles in differentiation and cell death. In this review, different achievements made through studies in the fly to understand the functions of TFIIH during development and its relationship with human diseases are analysed and discussed.

Keywords: Cancer; Drosophila; TFIIH; development; human syndromes.

Figure 1

The TFIIH complex, its subunits and links with human diseases. The TFIIH cartoon model is based in the recently published high-resolution structure of the core subcomplex of TFIIH with the MAT1 subunit [5]. Cdk7 and CycH cartoon is fictitious. The name of each subunit is indicated and the core and cyclin-dependent-activating-kinase (CAK) subcomplexes are delimitated by blue and black dashed circles. The functions of TFIIH are also indicated as cell-cycle control for the CAK, and nucleotide excision repair (NER) for the core and transcription by the 10 subunits TFIIH. Also, the subunits affected in the Xeroderma Pigmentosum (XP), Cockeyne Syndrome (CS) and Ticothiodistrohy (TTD), are indicated with dashed arrows.

Figure 2

Effect of triptolide (Trip) on third instar wing imaginal disc tumours. (A) Shows the generation of apoptosis (TUNEL assay, used to visualize apoptotic cells) by Trip on wing imaginal disc tumours, induced by the knock down (KD) of the disc large 1 (dlg) gene using the MS1096 driver in a Ras85^v125d mutant allele background (MS1096>dgl(II) Ras85^v125d). In green the dlg expression is visualized and in red the apoptotic cells. Note that the number of apoptotic cells is increased in the tumour tissues treated with Trip. (B) TUNEL assay to determine apoptosis in a wild type disc treated with Trip. Note the absence of apoptotic cells. (C) Quantification of apoptotic cells from MS1096>dgl(II) Ras85^v125d treated with DMSO or with Trip. (D) Total area of third instar imaginal discs, wild type (ORR) and MS1096>dgl(II) Ras85^v125d from third instar larvae feed with DMSO or Trip. Note that the total area in tumour discs is higher than in ORR as well as reduction of the total area in tumour wing discs from larvae feed with Trip. (E) Expression pattern (immunostaining) of wingless (wg) in a wild type third instar larvae wing disc. wg is indicated in pink and DNA in blue. (F) Expression of wg (pink) in MS1096>dgl(II) Ras85^v125d tumour wing discs, DNA is in blue, from three instar larvae feed with DMSO. Note that the distribution of wg is heterogeneous. (G) Distribution of wg in MS1096>dgl(II) Ras85^v125d tumour wing discs, from three instar larvae feed with Trip. Note the suppression on wg distribution in the discs as well as the reduction of the tumour size.

Figure 3

Confocal microscopy images (65X) of syncytial blastoderm nuclei from embryos expressing the p52 subunit of TFIIH fused to the yellow florescent protein (p52-YFP). As control to visualize the chromatin the histone 2Av (H2Av) fused to the red fluorescent protein is show in the same nuclei. Note the presence of p52-YPP foci that resemble liquid-liquid phase separation condensates.