The reorganization of cells in response to mechanical forces converts simple epithelial sheets into complex tissues of various shapes and dimensions. Epithelial integrity is maintained throughout tissue remodeling, but the mechanisms that regulate dynamic changes in cell adhesion under tension are not well understood. In , planar polarized actomyosin forces direct spatially organized cell rearrangements that elongate the body axis. We show that the LIM-domain protein Ajuba is recruited to adherens junctions in a tension-dependent fashion during axis elongation. Ajuba localizes to sites of myosin accumulation at adherens junctions within seconds, and the force-sensitive localization of Ajuba requires its N-terminal domain and two of its three LIM domains. We demonstrate that Ajuba stabilizes adherens junctions in regions of high tension during axis elongation, and that Ajuba activity is required to maintain cell adhesion during cell rearrangement and epithelial closure. These results demonstrate that Ajuba plays an essential role in regulating cell adhesion in response to mechanical forces generated by epithelial morphogenesis.

Antimicrobial peptides continue to garner attention as potential alternatives to conventional antibiotics. Hipposin is a histone-derived antimicrobial peptide (HDAP) that was previously isolated from Atlantic halibut. Though its potency against several bacterial strains has been documented, its antibacterial mechanism had not been characterized. The mechanism of this peptide is particularly interesting to consider since the full hipposin sequence contains the sequences of parasin and buforin II (BF2), two other known antimicrobial peptides that act via different antibacterial mechanisms. While parasin kills bacteria by inducing membrane permeabilization, buforin II enters cells without causing significant membrane disruption, harming bacteria through interactions with intracellular nucleic acids. In this study, we used a modular approach to characterize hipposin and determine the role of the parasin and buforin II fragments in the overall hipposin mechanism. Our results show that hipposin kills bacteria by inducing membrane permeabilization, and this membrane permeabilization is promoted by the presence of the N-terminal parasin domain. Portions of hipposin lacking the parasin sequence do not cause membrane permeabilization and function more similarly to buforin II. We also determined that the C-terminal portion of hipposin, HipC, is a cell-penetrating peptide that readily enters bacterial cells but has no measurable antimicrobial activity. HipC is the first membrane active histone fragment identified that does not kill bacterial or eukaryotic cells. Together, these results not only characterize hipposin but also provide a useful starting point for considering the activity of chimeric peptides made by combining peptides that operate via differing mechanisms.

We have investigated the bactericidal activity, specificity, and mechanism of a several antimicrobial peptides (AMPs) derived from histone H2A alone and combined into chimeric peptides. Relative antibacterial efficacy of these AMPs was determined using radial diffusion assays, and eukaryotic cytotoxicity assays indicate that these peptides demonstrate bacterial specificity. Confocal microscopy was used to determine the mechanism of action of the peptides. Parasin, buforin II, and buforin I are segments of the larger hipposin AMP. Buforin II can translocate membranes while parasin is a permeabilizing peptide. Buforin I and hipposin are larger peptides containing both parasin and buforin II segments, and both are permeabilizing peptides relatively unable to translocate the membrane. These findings suggest that the addition of a lytic fragment to an otherwise‐translocating peptide confers a lytic property. We further explored this hypothesis by studying a chimeric peptide of parasin and DesHDAP1, another peptide known to translocate effectively. This chimera was found to be more strongly bactericidal than either parasin or DesHDAP1 alone.

Hipposin and buforin II (BF2) are naturally occurring antimicrobial peptides (AMPs). Although BF2 is essentially identical to the middle section of hipposin, BF2 is a membrane translocating peptide and hipposin is a membrane permeabilizing peptide. To investigate this difference, we compared the structure, antimicrobial activity, translocating ability, and membrane permeabilizing ability of hipposin, BF2, parasin (analogous to the N‐terminal section of hipposin), and buforin I (essentially parasin plus BF2). Hipposin and BF2 had the highest activities against bacteria, followed by buforin I then parasin. Cellular permeabilization assays demonstrated that hipposin, buforin I, and parasin all display membrane permeabilizing ability, while translocation assays showed that only BF2 was membrane translocating. These observations imply that the addition of the parasin fragment to BF2 alters its antibacterial mechanism. Ongoing studies are examining the activity and mechanisms of other portions of the hipposin peptide.