SummarySkin sun exposure induces two protection programs: stress responses and pigmentation, the former within minutes and the latter only hours afterward. Although serving the same physiological purpose, it is not known whether and how these programs are coordinated. Here, we report that UVB exposure every other day induces significantly more skin pigmentation than the higher frequency of daily exposure, without an associated increase in stress responses. Using mathematical modeling and empirical studies, we show that the melanocyte master regulator, MITF, serves to synchronize stress responses and pigmentation and, furthermore, functions as a UV-protection timer via damped oscillatory dynamics, thereby conferring a trade-off between the two programs. MITF oscillations are controlled by multiple negative regulatory loops, one at the transcriptional level involving HIF1α and another post-transcriptional loop involving microRNA-148a. These findings support trait linkage between the two skin protection programs, which, we speculate, arose during furless skin evolution to minimize skin damage.

Over the last few years, hydrogels have been proposed for many biomedical applications, including drug delivery systems and scaffolds for tissue engineering.

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Engineering ordered nanostructures through molecular self‐assembly of simple building blocks constitutes the essence of modern nanotechnology to develop functional supramolecular biomaterials. However, the lack of adequate chemical and functional diversity often hinders the utilization of unimolecular self‐assemblies for practical applications. Co‐assembly of two different building blocks can essentially harness both of their attributes and produce nanostructured macro‐scale objects with improved physical properties and desired functional complexity. Herein, the authors report the co‐operative co‐assembly of a modified amino acid, fluorenylmethoxycarbonyl‐pentafluoro‐phenylalanine (Fmoc‐F5‐Phe), and a peptide, Fmoc‐Lys(Fmoc)‐Arg‐Gly‐Asp [Fmoc‐K(Fmoc)‐RGD] into a functional supramolecular hydrogel. A change in the morphology and fluorescence emission, as well as improvement of the mechanical properties in the mixed hydrogels compared to the pristine hydrogels, demonstrate the signature of co‐operative co‐assembly mechanism. Intriguingly, this approach harnesses the advantages of both components in a synergistic way, resulting in a single homogeneous biomaterial possessing the antimicrobial property of Fmoc‐F5‐Phe and the biocompatibility and cell adhesive characteristics of Fmoc‐K(Fmoc)‐RGD. This work exemplifies the importance of the co‐assembly process in nanotechnology and lays the foundation for future developments in supramolecular chemistry by harnessing the advantages of diverse functional building blocks into a mechanically stable functional biomaterial.