Temporal Dynamics in the Mouse Pre-Somitic Mesoderm

Since the first identification of c-hairy1 as the first evidence for the existence of a molecular clock, the field of somitogenesis has advanced greatly. We know that there is a large network of genes that oscillate and that Hes7 is at the core of the mechanism that generates oscillations in the PSM. The oscillations are exhibited as waves of expression that traverse the tissue. This spatiotemporal pattern requires local synchronization between cells that Notch signaling is mediating but the mechanism is elusive. In addition, the period of the oscillations is changing over time and the mechanism through which this is achieved is unclear. My work aimed to address these two unmet challenges in the field.
A system that allows to investigate the synchronization of PSM cells is a randomization ex-vivo assay. Utilizing this together with live imaging, I aimed to understand the nature of Notch signaling response. In that, to try and distinguish between unilateral and bilateral response of cells, an aspect that would help deeming Kuramoto as an appropriate coupling mechanism for the PSM cells. In addition, another aim is to quantify important aspects of Notch signaling such as its duration and how quickly it brings cells to synchrony. Lastly, understanding which phase on the cycle cells synchronize to would be very insightful to unravel the nature of the coupling mechanism.
On the second part of my work, I aimed to unravel the way through which Wnt signaling regulates the period of the oscillations. Past research has shown that alterations on Wnt signaling induce changes in the periodicity of the oscillations. I focused my efforts on a TCF binding site upstream of Hes7 promoter. The aim was to disrupt the site and assess its functionality through biochemistry and microscopy. I planned to test whether its disruption leads to any phenotypical traits that would imply its importance in somitogenesis. Importantly, I set out to investigate whether the TCF site has an activator or inhibitory role in the Hes7 expression and what are the effect of its disruption on the oscillations.