Lay Summary Chromo.docx

Joseph Humphries

Chromothripsis From DNA Damage in Micronuclei Recent cancer studies and research through genome sequencing has discovered a newer process labeled as chromothripsis. It is described as an excess of genomic rearrangements with fluctuating DNA copy number levels. These characteristics are also only observed a small number of chromosomes at a time; usually one or a few. Micronuclei have been previously tested for their response to damage that occurs. Connecting these two ideas, several experiments were conducted to find a relationship between micronuclei and the unknown mechanism that chromothripsis follows. To reach the conclusions and either support or denounce the hypothesis required the extensive use of several different methods and cell cultures. As the methods section of the original journal is quite overwhelming, they will be discussed more in depth when presenting the actual material. However, it would be in good practice to list the more mentionable and appropriate methods such as live cell imaging, immunofluorescence, detection of loss of heterozygosity and look sequencing strategy. Testing the micronuclei for how chromosomal rearrangements occur and their relatedness to chromothripsis required several different experiments and tests. The basis for most of the treatments and observations required cells to be synchronized to maintain cell cycle similarities. This and micronuclei induction in general were accomplished by using nocodazole which blocked mitotic activity by preventing microtubule assembly. Release from nocodazole-induced microtubule depolymerization caused merotelic kinetochore attachment. Two types of micronucleated cells were discussed as a reasoning for the rearrangement differences; disomic and trisomic daughter cells. Disomic cells will produce one daughter that is

Joseph Humphries

underreplicated and a normal daughter cell. Trisomic produces one near trisomic daughter and one disomic daughter. This enables a disproportionate DNA copy number in the daughter cells. As there is a difference in copy number, the cells are divided once more into plus and minus copies; with the higher DNA copy number being the ‘plus’. The experiments conducted helped provide evidence that supports the hypothesis that the rearranging of chromosomes that are seen in micronuclei are a possible explanation for chromothripsis. Disomic micronuclei and trisomic micronuclei describe the lagging chromosome and where it ended up after replication. Disomic MN contained a lagging chromosome that was correctly segregated into the daughter cells whereas trisomic meant that it was missegregated. These cells were then tested for the levels of rearrangements that occurred in either one. Micronuclei are a key source in discovering the way we as a society diagnose, understand and treat cancer. The amount of rearrangements they undergo with the variability they provide are unparalleled when observing cells. Overall however, there was not enough evidence to conclusively state the strength that micronuclei may or may not play in the mechanism for chromothripsis. While providing lots of new and useful information that may be helpful in the future tests on this matter, chromothripsis’ mechanism still remains mostly a mystery.