User:Bioclocks2021/Christine Merlin

Christine Merlin is a French chronobiologist and Associate Professor of Biology at Texas A&M University. Merlin investigates the intricacies and underlying genetics of the monarch butterfly circadian clock, and explores how these circadian rhythms modulate monarch behavior and navigation.

Christine Merlin
Born	September 24, 1980
Nationality	French
Alma mater	Pierre and Marie Curie University
Occupation	Associate Professor of Biology at Texas A&M University
Website	https://www.merlinlab.org/

Background

Christine Merlin was born on September 24, 1980 in Soues, Hautes-Pyrénées, France. In high school, she became interested in circadian biology while studying moth pheromone release timing. 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. She studied circadian rhythms in moths in Versailles while she studied for her doctorate. In 2007, she began working in the lab of Steven Reppert at the University of Massachusetts. There, she studied the migration of monarch butterflies, and collaborated on a paper outlining the monarch genome. In 2013, she became an assistant professor of biology at Texas A&M University, where she works now.

Scientific contributions

Merlin has helped to publish over 20 papers during the course of her career and has garnered over 2000 citations for her work.

Insect olfactory receptors and chemosensory

Olfactory receptors (Ors) can help to provide information on the molecular basis of chemical signal recognition in insects.  Merlin and colleagues reviewed data on Drosophila melanogaster Ors to understand the olfactory mechanism of insects in relation to vertebrates.  It was found that subtypes of olfactory receptor neurons express one Or type, olfactory neurons express a single type of Or, and all olfactory neurons converge at the glomerulus in the antennal lobe.  Merlin and colleagues concluded that insects and vertebrates have a conserved olfactory mechanism and that insects such as Drosophila melanogaster can act as model organisms to better understand chemical communication mechanisms.  In a subsequent paper, Merlin and coworkers analyzed the signal termination step of the olfactory process which uses a variety of odorant-degrading enzymes.  The team isolated an aldehyde oxidase partial cDNA from the cabbage armyworm Mamestra brassicae and looked at which part of the chemosensory organs had expression.  The results showed expression in the antennae, particularly the olfactory sensilla, suggesting that aldehyde odorant compounds (pheromones or plant's volatiles) could be degraded by specific enzymes.

The migration of monarch butterflies

Merlin determined that circadian clocks located in the antennae play a significant role in navigation in migratory monarch butterflies. Using tests of necessity, she analyzed butterfly orientation with and without antennae and concluded that butterflies without antennae were unable to orient themselves relative to the sun.

In 2011, Merlin authored (along with Steven Reppert, Shuai Zhan, and Jeffrey Boore) a groundbreaking paper in Cell that outlined the genome of the migratory monarch butterfly. The paper described the  operation of circadian clocks as a method of regulating migration. The monarch clock is a Transcription-Translation Feedback Loop (TTFL) and contains many of the same genetic components as the clocks of other arthropods, such as drosophila. One notable difference between the monarch clock and the drosophila clock is the appearance of both CRY1 and CRY2 in the monarch clock, while drosophila 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.” There are two main uses for the clock highlighted in the paper. One is the sun compass, 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 the initiation of migration by detecting decreasing day length in the autumn.

Monarch butterflies use a time-compensated sun compass that is a part of the insect’s light-entrained circadian clocks located in the antennae.  This sun compass allows the butterfly to accurately navigate across long distances in times of migration.  Merlin and colleagues conducted a test of sufficiency to determine if one or both antennae are needed to properly orient.  They found that either antenna can be sufficient for time compensation, but surprisingly that butterflies with one of their antennae painted black and the other painted clear had disoriented flight.  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.  The team also observed that period and timeless gene expression was highly rhythmic in the clear-painted antennae, but disrupted in the black-painted antennae.  Merlin and coworkers concluded that each antenna has its own clock outputs that are then processed together in the sun compass to direct the orientation of flight.

Ongoing research

The Merlin lab is currently focused on further unraveling the specifics of monarch circadian genetics, utilizing reverse genetic tools to determine how previously identified candidate genes contribute to butterfly migration and the larger circadian cycle of the monarch. The lab is currently working with known clock genes in vivo to attempt to understand circadian repressive mechanisms within the monarch and also gain further knowledge regarding how insect clocks have evolved over the ages. Merlin is also exploring means to modify selected genes via genetic knock-out and knock-in methods. Utilizing CRISPR/Cas9 and other genetic editing machinery, Merlin aims to improve the efficiency of NHEJ mediated targeting, and furthermore develop a reliable knock-in approach to introduce reporter tags into loci of interest within the Monarch genome.

Collaborators

Throughout her career, Merlin has worked with several other chronobiologists. She performed her graduate research in Emmanuelle Jacquin-Joly and Martine Maibeche-Coisne’s lab in Versailles. She carried out her post-doctoral training in Steven Reppert’s lab at the University of Massachusetts Medical School. Other notable co-authors include Marie-Christine François, Robert J. Gegear, Sébastien Malpel, Scot A. Wolfe, Patrick Porcheron, and Patrick A. Guerra.

Honors and awards

Christine Merlin became a Presidential Impact Fellow at Texas A&M University in 2020. She was awarded the 2018 Junior Faculty Research Award from the International Society for Research on Biological Rhythms and the 2017 Klingenstein-Simons Fellowship Award in Neuroscience. Her lab receives funding from the National Science Foundation, the National Institutes of Health, and the Esther A. & Joseph Klingenstein Fund.