RESUMO
The regulation of protein expression and activity has been for long time considered only in terms of transcription/translation efficiency. In the last years, the discovery of post-transcriptional and post-translational regulation mechanisms pointed out that the key factor in determining transcript/protein amount is the synthesis/degradation ratio, together with post-translational modifications of proteins. Polyubiquitinaytion marks target proteins directed to degradation mediated by 26S-proteasome. Recent functional genomics studies pointed out that about 5% of Arabidopsis genome codes for proteins of ubiquitination pathway. The most of them (more than one thousand genes) correspond to E3 ubiquitin ligases that specifically recognise target proteins. The huge size of this gene family, whose members are involved in regulation of a number of biological processes including hormonal control of vegetative growth, plant reproduction, light response, biotic and abiotic stress tolerance and DNA repair, indicates a major role for protein degradation in control of plant life.
RESUMO
PURPOSE: We describe a modified surgical technique for the treatment of patients in the early stage of keratoconus, when it is still possible to correct the astigmatic ametropia with contact lenses. METHODS: Excimer laser lamellar keratoplasty of augmented thickness (ELLKAT) is a procedure in which a deep plano excimer laser ablation is done on the host cornea and a donor lamellar button--with or without an excimer laser refractive ablation on the posterior surface--is sutured into the recipient bed. In 12 of 20 eyes, the homoplastic button, which had parallel faces and was devoid of any dioptric power, was treated refractively on its stromal face with a Chiron Keracor 116 excimer laser to correct the axial and/or induced myopia present due to the weakened cornea. RESULTS: The 8 eyes that received donor buttons without excimer laser ablation had improved spectacle-corrected visual acuity from a mean preoperative value of 20/100 (no eye saw 20/40 or better before surgery) to a mean postoperative value of 20/30 after 18 months. Mean refractive astigmatism was reduced from 4.84 +/- 2.34 D to 1.00 +/- 0.46 D. Mean keratometric power was reduced from 56.75 +/- 8.01 D to 44.21 +/- 2.12 D. The associated mean spherical equivalent refraction was reduced from -4.75 to -3.00 D. Mean corneal thickness increased from 422.25 +/- 83 microns preoperatively to 562.87 +/- 57.81 microns postoperatively. The 12 eyes that received donor lamellar buttons treated with excimer laser also had improved spectacle-corrected visual acuity from a mean preoperative value of 20/100 to a mean postoperative value of 20/30 after 18 months. Astigmatism was reduced from a mean 4.84 +/- 2.77 D to 1.66 +/- 1.30 D; mean keratometric power was reduced from 56.08 +/- 7.00 D to 45.31 +/- 2.08 D; and the associated mean spherical equivalent refraction was reduced from -8.75 to -1.75 D. Corneal thickness increased from a mean 414.25 +/- 64.75 microns preoperatively to 576.75 +/- 28.23 microns postoperatively. CONCLUSION: Compared to penetrating keratoplasty, excimer laser lamellar keratoplasty of augmented thickness for keratoconus has the advantage of preserving the host endothelium and of reducing the refractive error in keratoconus.