In her postdoctoral work in the Alon lab, Lahav investigated the response of
p53 to DNA damage. p53 is highly studied due to its role as "guardian of the genome"; in response to DNA damage, p53 activation may lead to a delay in the
cell cycle to allow
DNA repair, or may cause the cell to undergo
senescence or
apoptosis. Previous work had shown that the
feedback loop between p53 and its regulator
Mdm2 could theoretically cause oscillations in the level of p53. Oscillations were in fact observed in cells exposed to radiation, using a
Western blot technique that measures the average p53 level in a population of cells. This finding suggests that p53 may measure the intensity of some signals in a digital manner (number of pulses), not in an analog manner (higher concentrations of p53). Lahav then discovered that DNA damage caused by
UV-irradiation results in a different p53 behavior, leading to a single pulse that increases in size and duration with increasing damage. This led her to hypothesize that the dynamic behavior of p53 contained information on the nature of the damage to DNA and determined the nature of the response by the damaged cell. She developed a method for forcing a cell damaged by gamma irradiation to adopt the p53 dynamics seen in UV irradiation, based on precisely timed additions of the Mdm2 inhibitor
Nutlin-3. Cells damaged using gamma irradiation without drug treatment showed cell cycle arrest and then recovered, while the same cells treated with drug to simulate UV-type p53 dynamics entered senescence and failed to divide. There is growing consensus that dynamics are important for signaling in multiple biological pathways. Lahav has measured the cell-to-cell variation in p53 response in colon cancer cells responding to damage by the
chemotherapeutic drug
cisplatin and has argued that this variation may underlie the phenomenon of
fractional kill, in which a fraction of cancer cells survive chemotherapeutic treatment and subsequently grow, causing a recurrence of the cancer. Lahav joined the Department of Systems Biology at
Harvard Medical School in 2004. In 2017 she was appointed Deputy Chair, and in 2018 Dean
George Q. Daley appointed her as Chair of the Department. In the announcement of her appointment, Daley highlighted "her pioneering role in developing computational and quantitative experimental approaches to studying the fate and behavior of human cells in disease and health at the single-cell level."
Contributions to mentoring Lahav is an advocate for improved mentoring in science. As an assistant professor, she initiated a peer-to-peer mentoring group at Harvard Medical School. She has written on the challenges of combining the role of a mother with the demands of a research career. She served as Junior Faculty Liaison for Faculty Development at Harvard Medical School from 2013 to 2018. == Awards and honors==