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Chromosomes: Molecular cytogenetics Radioactive ISH y ( Taylor, 1957 ) Nick translation DNA probe pApGpCpTpApCpGpTpApT pTpCpGpApTpGpCpApTpA DNasi I pApGpCpT…ApCpGpTpApT pTpCpGpApTpGpCpA…TpA DNApolymerase I + dATP,dCTP,dGTP,dTTP + Biotine-16-dUTP pApGpCpT ApCpGpTpApT pTpCpGpApTpGpCpA TpA ) ) A A FISH fluorescent in situ hybridization: (FISH) A technique used to identify the presence of specific chromosomes or chromosomal regions through hybridization (attachment) of fluorescently-labeled DNA probes to denatured chromosomal DNA. Step 1. Preparation of probe. A probe is a fluorescently-labeled segment of DNA complementary to a chromosomal region of interest. Step 2. Hybridization. Denatured chromosomes fixed on a microscope slide are exposed to the fluorescently-labeled probe. Hybridization (attachment) occurs between the probe and complementary (i.e., matching) chromosomal DNA. Fluorescent in situ Hybridization (FISH) Hybridization of complementary gene‐ or region‐ specific fluorescent probes to chromosomes. Interphase or metaphase cells on slide (in situ) Probe Microscopic signal (interphase) Probes wcp whole chromosome painting pcp partial chromosome paonting band specific band-specific pcp alphoid sequences centromere-specific YAC (yeast art. chrom) 600Kb-2Mb BAC (bacterial art. chrom) 150-180 Kb telomeres repeats subtelomeric specific sequences plasmid 100Kb cosmid 40Kb FISH Probes • Chromosome‐specific centromere probes (CEP®) – Hybridize to centromere region – Detect aneuploidy in interphase and metaphase • Chromosome painting probes (WCP) – Hybridize to whole chromosomes or regions – Characterize chromosomal structural changes in metaphase cells • Unique DNA sequence probes (LSI®) – Hybridize to unique DNA sequences – Detect gene rearrangements, deletions, and amplifications Uses of Fluorescent in situ Hybridization (FISH) • Identification and characterization of numerical and structural chromosome abnormalities. • Detection of microscopically invisible deletions. • Detection of sub‐telomeric aberrations. • Prenatal diagnosis of the common aneuploidies (interphase FISH). FISH Step 3. Visualization. Following hybridization, the slide is examined under a microscope using fluorescent lighting. Fluorescent signals indicate the presence of complementary chromosomal DNA; absence of fluorescent signals indicate absence of complementary chromosomal DNA. Green signal = Normal control Pink signal = Chromosome region of interest Normal control: Two green signals Two pink signals Patient with deletion: Two green signals One pink signal Painting 8 Painting 17 iso (17q) Translocation by Metaphase FISH WCP Probe (Whole‐Chromosome Painting) t(7;10;11) Genetic Abnormalities by Interphase FISH LSI® Probe • Greater or less than two signals per nucleus is considered abnormal. Cell nucleus Normal diploid signal Trisomy or insertion Monosomy or deletion Structural Abnormality by Interphase FISH LSI® Probe (Fusion Probe) Structural Abnormality by Interphase FISH LSI® Probe (Break Apart Probe) t(5;17) LSI CSF1R(5q)/D5S721(5p) Alfoide 8 r(20) BAC CTD-3248C18 t(12;15) FISH Probes • Telomere‐specific probes (TEL) – Hybridize to subtelomeric regions – Detect subtelomeric deletions and Probe binding site Unique sequences rearrangements Telomere 100–200 kb 3–20 kb Telomere associated repeats (TTAGGG)n Multipainting FISH on DNA fibers Comparative Genome Hybridization CGH Melanoma Spotter Scanner • 244,000 probes • source NCBI genome (Build 34; July, 2003) • genome-wide survey • coding and noncoding sequences with an average spatial resolution of ~8kB Next future: 488,000 probes Male, Microcephaly , Malformaions. Female, 20 monts, Developmental delay, Dysmorphic features 1 st allele: deletion 2 nd allele: mutation >> recessive disorder Next, Test parents to verify if the anomalies are inherited or de novo