The PAX3 Assignment
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The PAX3 Assignment
Describe the identification of PAX3 as the gene causing Waardenburg syndrome type 1?Waardenburg syndrome type 1 (WS1) occurs when PAX3 gene undergoes mutations. It is located on the chromosome band 2q35. This condition causes hypopigmentation of the hair, skin and eyes. It also results in deafness in humans. PAX3 belongs to the human PAX coding for DNA-binding. It is the gene that is mutated in Sp mice and WS individuals causing Splotch phenotype in mice and WS1 disorder in humans. In order to determine the gene, PAX3-FKHR is introduced into the human RD ERMS cells in an inducible form. Whole blood of humans is then obtained from both patients with the syndrome, and normal individuals. Genomic DNA was then extracted from the blood. Exons of the PAX3 gene were then analyzed by use of quantitative Polymerase Chain Reaction using primers. The multiplex ligation-dependent probe amplification (MLPA) and sequence analysis can also be performed in order to identify the PAX3 gene. The nucleotide probe sequence is determined to identify a segment of DNA that contains the gene. Shifted bands were an indicator of mutations which were analyzed by sequencing the PCR products directly. In order to verify the mutations, the PCR products were cloned. Three different, independent clones were then sequenced. The microarray analysis revealed a number of genes including MYCN gene that encodes for the transcriptional factor and it is regulated by PAX3-FKHR. If this gene is amplified, it causes tumors, especially neuroblastomas.
Point mutations of the PAX3 gene are identified. The first was a missense mutation which was found within the paired domain region of exon 2. Methionine is substituted by valine at codon 62. The role of methionine is to ensure the proper functioning of the PAX3 transcriptional factor. Its exchange or removal leads to WS1 disorder. The other nonsense mutation occurs at exon 6 which changes the codon for glutamine into a premature stop codon. This also leads to WS1 disorder (Hol et al. 1995).
Reference
Hol et al., (1995) ‘Identification of two PAX3 mutations causing Waardenburg syndrome, one within the paired domain (M62V) and the other downstream of the Homeodomain (Q282X)’. Human Mutation Volume 11, (Issue supplement S1). Retrieved from >http://onlinelibrary.wiley.com/doi/10.1002/humu.1380110149/pdf< [25th October 2011].
