Thursday, February 17, 2011

The Cell Biology - One Question Multitudinous Possibilities!

  Telomeres and Targeting Telomerase- A Prelude
                                                                                               By Deepesh Soni
Telomeres are conglomerated of insistent DNA sequences at the end of one-dimensional chromosomes. There are 92 telomeres in human chromosomes at each end because humans have 23 pairs of chromosomes. Telomere, a ribonucleoprotein complex, is present at the end of the chromosomes to defend its haleness and furthermore to give one of the most indispensable things i.e. constancy to the chromosomes. Telomeres are a part of DNA rich in G base (TAAGGG) in almost all craniates. One of the most interesting things about telomeres is that they are bound by a complex called shelterin. Shelterin is composed of 6 complexes namely POT1 and TPP heterodimers, telomeric-repeat binding factors i.e. TRF1 and TRF2, and Rap1 and Tin2. Another interesting realism about telomeres is that they contain epigenetic modifications like DNA hypermethylation and modification of histone which, interestingly, acts as down regulator of telomere length (1). Sex hormones such as androgens and estrogens, on the other end, act as a telomere up regulators and this made me wonder if epigenetic modifications maybe used to target telomeres in neoplastic cells or in normally dissevering cells and decipher the change (if any) in the structure of a cell as a whole or part of it. Any change, however, in the structural integrity of telomeres or the protein complex will have substantial change in the functional property of telomeres. Shortening of telomeres is colligated with cell division over a period of time, telomeres gradually subjugates in size due to ‘end-replication problem’ as DNA polymerase cannot continue replication of the linear ends of the chromosome and this is one of the reasons imputed to senescence in vertebrates. In addition, any change in the chromosome structure will have DNA repair mechanisms activated barricading the crusade of a cell from one stage to the other of the cell cycle. 
Telomerase is a cellular reverse transcription enzyme that takes care of telomeres attrition via addition of TAAGGG from the beginning. Telomerase, not unlike, telomeres consist of complex domains namely a subunit with reverse transcriptase activity (Tert), an RNA component (Terc) and Dyskerin (Dkc1), a stabilizer for Terc. In the absence of telomerase, telomeres will not be able to maintain shelterin integrity. Telomerase is an essential part of almost all tumor cells giving them the immortality however there is an exception to this statement. In some cancers such as Acute Myelocytic Leukemia (AML), it was found that (perhaps) telomerase does not play a role in the malignancy, or there’s an alternate pathway which floods the telomerase in the cells. Also, down regulation of telomerase is associated with aging of cells and cell death via apoptotic pathways.

Materials and Methods:
   There are various methods available to detect the presence of telomeres in a cell. One of the methods is Fluorescent in Situ Hybridization (FISH). FISH is used to detect different types of DNA sequences using fluorescent probes which bind to the sequences corresponding to the probes and can be detected using fluorescence microscope. Other techniques include Southern Blot and Polymerase Chain Reaction are also equally useful. Telomerase, too, can be detected by using techniques such as Enzyme Linked Immunosorbent Assay, using antigen targeting specific epitope on telomerase. Other techniques involve the use of Southern blot, Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis.

 My Research Intent:
     After reading versatile research papers on telomere, I marveled if it would be possible to target one of the complexes of shelterin by modifying epigenetic marks such as histone or DNA methylation and bypassing the telomerase activity in that cell. Secondly, to insulate telomerase from the tumor and normal cells and canvass the structures and the difference, if any, in both types of cell. Thirdly, to confirm the function of sex hormones in the up regulation of telomeres in tumor, as well as normal cells and compare the results.