Christine Merlin

Christine Merlin is a French chronobiologist and an associate professor of biology at Texas A&M University.

Background Merlin was born on 24 September 1980, in southwestern France. She attended Pierre and Marie Curie University in Paris, where she received a BS in animal biology, an MS in invertebrate physiology, and finally her PhD in insect physiology in 2006.

In 2013, she became an assistant professor of biology at Texas A&M University, where she works now. She joined the Center of Biological Clocks Research as a faculty member studying biology, specifically the circadian clock regulation of monarch butterfly migration. She also became a faculty member of Texas A&M's Genetics and Neuroscience interdisciplinary program in 2014, as well as their Ecology and Evolutionary Biology interdisciplinary program in 2015.

The migration of monarch butterflies and its control by circadian clocks Monarch butterflies use the sun as a compass to precisely orient themselves across long distances during migration. Merlin and colleagues determined that circadian clocks located in the antennae play a significant role in navigation in migratory monarch butterflies. Using tests of necessity, Merlin and colleagues analyzed migratory butterfly orientation with intact antennae, without antennae, or with antennae coated with black paint, and concluded that butterflies without antennae or with antennae harboring desynchronized antennal clocks (coated black) were unable to orient relative to the sun. She isolated butterfly antennae in vitro and discovered that they sustained 24-hour rhythms in constant conditions after entrainment to light-dark cycles. By measuring the expression of clock genes Per, Tim, and Cry2, Merlin determined that a circadian clock exists in the monarch antennae, functioning independently of the brain clock. In this experimental condition, the antenna painted black would block entrainment from light cues while the antenna painted clear would allow entrainment from light cues. When the black-painted antenna from this experimental condition was ablated, the butterfly would then be able to properly orient by using just the single clear-painted antenna to entrain. One notable difference between the monarch clock and the Drosophila melanogaster clock is the appearance of both a light-sensitive CRY1 and a transcriptionally repressive CRY2 in the monarch clock, while Drosophila melanogaster only contains CRY1. As most arthropods have both CRY types, this result provided additional evidence that both CRY were at "the base of arthropod evolution." They highlighted two main uses for the clock. One use is for sun compass orientation, which allows the monarch to navigate towards its destination by detecting the horizontal position of the sun and the polarized skylight patterns produced. The other use is for the initiation of migration by detecting decreasing day length in the autumn. Merlin and her team were able to generate genetic knockouts of the Cry2 and Clk genes within the monarch genome, two notable clock genes responsible in part for the regulation and modulation of the monarch circadian clock. These knockouts were shown to be heritable, with the injection of fewer than 100 eggs being sufficient to recover mutant progeny, enabling the generation of mutant knockout lines in around 3 months. Monarchs who migrate in the fall experience a reproductive diapause response to prepare for their migration, which is triggered by the shortened days and colder temperatures of autumn. While the molecular and cellular mechanisms underlying magnetic sensing has not yet been discovered, the connection to the photoexcitation of CRY proteins has been linked to both CRY1 in Drosophila and CRY2 in monarchs and humans. Merlin C, Gegear RJ and Reppert SM (2009) Antennal circadian clocks coordinate sun compass orientation in migratory monarch butterflies. Science 325: 1700–1704. Lugena AB, Zhang Y, Menet JS, and Merlin C (2019). Genome-wide discovery of the daily transcriptome, DNA regulatory elements and transcription factor occupancy in the monarch butterfly brain. PLOS Genetics, 15(7). doi:10.1371/journal.pgen.1008265 Wan G, Hayden AN, Liams SE, Merlin C (2021) Cryptochrome 1 mediates light-dependent inclination magnetosensing in monarch butterflies. Nat Commun. 12(1):771. Junior Faculty Research Award from the International Society for Research on Biological Rhythms (2018) Presidential Impact Fellowship at Texas A&M University (2020)