Campa, V. | bioRxiv Science

bioRxiv2024

Long-term evolution reveals the role of the circadian cycle in the environmental adaptation of cyanobacteria

Circadian clocks synchronize internal cellular states with diurnal rhythms. Widespread in bacteria and eukaryotes, they regulate a variety of physiological processes, from hormone secretion in animals to carbon fixation in photosynthetic organisms. The adaptive role of circadian clocks is assumed to stem from their ability to anticipate environmental change, yet their impact on ecological adaptation remains unclear. Here, we use experimental evolution to study the interplay between fitness and circadian regulation in the model cyanobacterium Synechococcus elongatus PCC 7942. After 1,200 generations under continuous, high-intensity illumination, we obtained a strain that grew six times faster than its ancestral counterpart. Genome sequencing revealed three mutations fixed in the population, two of which replicated the fast-growing phenotype in the wild-type. A deletion in SasA, a key circadian regulator, was essential for fast growth. Transcriptomic and metabolomic analyses revealed that this mutation perturbed the rhythmicity of the cycle, while simultaneously locking the cell in a transcriptomic response to high intensity illumination. A comparison with another fast- growing isolate, UTEX 2973, showed convergent transcriptomic states despite different driving mutations. Our results indicate that the clock acts not only as a timekeeping device, but also as an adaptive mechanism to optimize growth across diverse ecological conditions.

microbiology↗

bioRxiv2020

Sp8 regulatory function in the limb bud ectoderm

Sp8 and Sp6 are two closely related Sp genes expressed in the limb ectoderm, where they regulate proximo-distal and dorso-ventral patterning. Genetic studies in mice have shown that they act in a dose-dependent manner, with Sp8 exerting a substantially stronger effect than Sp6. Here, we integrate ChIPmentation-seq and RNA-seq analyses to elucidate their genome-wide regulatory networks and mechanisms of action. Our results show that Sp8 has a dual mode of action either directly binding GC-rich motifs or indirectly binding AT-rich motifs through Dlx. In contrast, Sp6 primarily acts through AT-rich motifs, via interaction with cofactors such as Dlx5. Both factors regulate key components of the Wnt, FGF, and BMP signaling pathways, central to limb patterning, and display both cooperative and independent roles. We further show that Sp8 and Sp6 can form homo- and heterodimers, as well as interact with Dlx5, revealing a complex regulatory network. Our findings provide molecular insight into limb morphogenesis and have potential implications for understanding congenital limb malformations.

developmental biology↗