Cortical contraction drives the 3D patterning of epithelial cell surfaces.

Cellular protrusions create complex cell surface topographies, but biomechanical mechanisms regulating their formation and arrangement are largely unknown. To study how protrusions form, we focused on the morphogenesis of microridges, elongated actin-based structures that are arranged in maze-like patterns on the apical surfaces of zebrafish skin cells. Microridges form by accreting simple finger-like precursors. Live imaging demonstrated that microridge morphogenesis is linked to apical constriction. A nonmuscle myosin II (NMII) reporter revealed pulsatile contractions of the actomyosin cortex, and inhibiting NMII blocked apical constriction and microridge formation. A biomechanical model suggested that contraction reduces surface tension to permit the fusion of precursors into microridges. Indeed, reducing surface tension with hyperosmolar media promoted microridge formation. In anisotropically stretched cells, microridges formed by precursor fusion along the stretch axis, which computational modeling explained as a consequence of stretch-induced cortical flow. Collectively, our results demonstrate how contraction within the 2D plane of the cortex can pattern 3D cell surfaces.

Lux-operon of the marine psychrophilic bacterium Aliivibrio logei: a comparative analysis of the LuxR1/LuxR2 regulatory activity in Escherichia coli cells.

The lux-operon of the psychrophilic bioluminescent bacterium Aliivibrio logei is regulated by quorum sensing (QS). The key components of this system are LuxI, which catalyses synthesis of the autoinducer (AI), and LuxR, which activates transcription of the entire lux-operon. The lux-operon of A. logei contains two copies of the luxR gene: luxR1 and luxR2. In the present study, lux-operon sequence analysis from 16 strains of A. logei, isolated from cold habitats of the White, Baltic, Okhotsk and Bering seas, was carried out. Phylogenetic analysis showed that all isolated strains of A. logei have both copies of luxR genes which are homologous to luxR genes of the related Aliivibrio salmonicida. Evaluation of LuxR1 and LuxR2 activity showed that LuxR2 remains active at significantly lower concentrations of AI (10- 9 M) than LuxR1, which is active only at high AI concentrations (10- 6 M). As the QS response is already prominent at AI concentrations as low as 10- 8 to 10- 9 M, we conclude that LuxR2 is the main activator of the lux-operon of A. logei. The thermolabilities of LuxR1 and LuxR2 are similar and exceed that of LuxR of the mesophilic bacterium Aliivibrio fischeri. In contrast to LuxR2, LuxR1 is not a substrate of Lon protease and does not require the chaperonin GroEL/ES for its folding. This study expands our current understanding of QS regulation in A. logei as it implies differential regulation by LuxR1 and LuxR2 proteins.