Annual Interim Report    August 2004-July 2005

Skin is composed of two tissues namely, epidermis and dermis. The epidermis sticks to the underlying dermis using various adhesive mechanisms. These include button like structures, called hemidesmosomes, tied together with the threads of keratin protein and a cement or glue formed of proteins, called as the basement membrane, which is further anchored on to the dermis by protein cables. In some individuals one of the proteins of these buttons or glue or cables is missing or defective and this leads to the blistering skin disease Epidermolysis Bullosa (EB).
The information to make a protein is stored in a stretch of DNA (Deoxyribonucleic acid) as a text composed of four letters, A, T, G and C. Such a stretch of DNA is called as a `gene´. Sometimes this text in a gene is scrambled or a letter is missing or a wrong letter is added instead of the proper one and hence proteins can not be made or if made, they are defective and can not function properly. Such a modification in the DNA text is called a mutation. Mutations can be caused by some chemicals and certain kinds of radiations. The heritable EB is a result of mutations in the genes, which store the information to make keratin proteins or the protein components of hemidesmosomes or basement membrane. So far mutations in 10 genes are known to cause this disease. However, in many EB patients the mutations in some unknown genes seem to cause this disease. We aim to find additional genes, mutations in which would lead to epidermolysis bullosa.

The adhesive mechanisms used in zebrafish to tether epidermis to the dermis are very similar to those in humans. To find unknown gene mutations causing EB, we are using zebrafish as a model system. To achieve this, we treated adult zebrafish with a chemical, called ethyl-nitroso-urea, which randomly introduces mutations in DNA. We bred these mutagenised fish and raised families from each fish. We then followed an inbreeding scheme for next two generations and then assayed if the progeny of these fish exhibit skin blisters during embryonic or larval development. If progeny indeed shows this blistering, then these fish are called as skin mutants. So far, I have screened 2190 families and have identified 11 mutants exhibiting specific skin defects. I believe that my screen will find mutations in some novel genes, which would lead to EB like disorders. In addition to this screen, we have done detailed analysis of already available skin mutant named penner. We have identified that a gene called lethal giant larvae-2 is mutated in penner and showed for the first time that the function of this gene is essential for hemidesmosome formation. I hope to screen another 2000 mutagenised families within next 6 months so as to identify more genes involved in maintaining integrity of the skin. I feel that knowing additional mutated genes involved in causing EB will help scientists to develop effective tools to diagnose and to treat this disorder.