ATM

A tissue microarray is a fairly recent high-throughput application that allows researchers to test hundreds of tissue samples with antibodies of their choice at once.  Essentially, a tissue microarray is a paraffin block that is produced by a composition of tissue cores from paraffin donor blocks within defined coordinates to account for a variety of tissue types.

Our genome experiences a moderate amount of DNA damage in our cells on a daily basis.  This DNA damage can be in response to external environmental factors, or be a result of our internal metabolic processes going awry.  While normal rates of DNA damage are not an immense threat to our cell processes, DNA damage in critical genes can lead to a variety of disease, including cancer and tumor formation.   After induction of DNA damage (for example, in the form of double strand breaks), phosphorylation and recruitment of the H2AX protein occurs.  This phosphorylation produces gamma H2AX

The p53-binding protein 1 (53BP1) is a DNA damage response factor, which is recruited to nuclear structures at the site of DNA damage.  DNA double-strand breaks (DSBs) are mutations that are detrimental to cell viability and genome stability, and must be repaired either through homologous recombination (HR) or non-homologous end joining (NHEJ). 53BP1 specifically promotes both NHEJ as well as the inhibition of HR repair, yet the decision making on a molecular level between these two routes not clearly understood.

Telomeres are a region of repeat nucleotide sequences located at the end of chromosomes to protect our DNA from becoming damaged via end-to-end fusion.  TERF2, or telomeric-repeat binding factor 2, is important for telomere integrity and aids in the formation of the telosome, the telomeric loop, and control of the amount of DNA needed for telomere replication.

Ataxia telangiectasia mutated (ATM) is essential for the maintenance of genomic stability. ATM is a 370 kDa serine-threonine kinase that is constitutively expressed in various tissues. Although primarily nuclear, ATM is also found at lower levels associated with cytoplasmic vesicles. As a PI 3-kinase family member, ATM is able to phosphorylate a wide variety of substrates including proteins involved in sensing and repairing DNA damage such as p53 and Brca1 (2). Normally ATM is found as an inactive homodimer.

53BP1 (p53 binding protein 1) was originally thought to be an enhancer for p53 transcriptional, but later studies have demonstrated that it is actually a substrate for ataxia telangiectasia mutated (ATM). 53BP1 is a classic late DNA damage response (DDR) marker that is present during the cell cycle phases of telophase and cytokinesis (within mitotic mammalian cells).

The 53BP1 (p53 binding protein 1) was initially believed to be a p53 transcriptional enhancing partner, but it has now been established as an ataxia telangiectasia mutated (ATM) substrate. As a late DNA damage response (DDR) marker, 53BP1 appears during the telophase and cytokinesis phase of mitotic mammalian cells¹.

Ataxia Telangiectasia Mutated (ATM) is a serine/threonine protein kinase that is the master regulator of the DNA double-strand break (DSB) repair pathway. ATM is a key part of the cell cycle machinery that activates checkpoint signaling in response to DSBs, apoptosis, and genotoxic insults. ATM normally exists in its inactive state as a dimer or tetramer - upon DNA damage, it dissociates into monomers triggered by its own autophosphorylation.