Multiple stressor responses are regulated by sirtuins in Mytilus congeners.

Understanding physiological tolerances of marine organisms to environmental stress is key to predicting species susceptability under climate change. Along the Pacific Coast of the U.S.A. intertidal mussel congeners (genus Mytilis) vary in their physiological stress tolerances, with the invasive M. galloprovincialis being heat tolerant but vulnerable to hyposalinity while the native M. trossulus is vulnerable to heat stress and tolerant of hyposalinity. Sirtuins, a family of NAD+-dependent deacylases, may influence the environmental stressor tolerances in these mussel congeners. The purpose of our study was to determine the mechanism by which sirtuins may confer differential stress responses in the two mussel congeners. Mussels (N = 6 per species) were acclimated to laboratory conditions in tidal simulators and exposed to sirtuin inhibitors (suramin and nicotinamide). Following inhibition, mussels were exposed to hyposalinity stress (29 ppt) for 6 h followed by aerial heat stress (32 °C) for 6 h after which mussel gill was dissected for proteomic analysis. During sirtuin inhibition we found a reduction of cellular stress response (CSR) proteins (molecular chaperones, antioxidants), which are key to maintaining cellular homeostasis. Moreover, we found differential stress responses between the two species under aerial heat combined with hyposalinity exposure. Three-way interactions (aerial heat, hyposalinity and sirtuin inhibition combined) showed complex interactive effects with sirtuins as potential modulators. Thus, our study suggests that sirtuins are contributing to the species-specific CSR in Mytilus and our multiple-stressor approach provides information used to make predictions regarding climate change effects on these competing species.

Signals from the caudal diencephalon are required for the projection of the Interstitial Nuclei of Cajal.

Axonal projection is controlled by discrete regions localized at the neuroepithelium, guiding the neurite growth during embryonic development. These regions exert their effect through the expression of a family of chemotropic molecules, which actively participate in the formation of neuronal connections of the central nervous system in vertebrates. Previous studies describe prosomere 1 (P1) as a possible organizer of axonal growth of the rostral rhombencephalon, contributing to the caudal projection of reticulospinal rhombencephalic neurons. This work studies the contribution of chemotropic signals from P1 or pretectal medial longitudinal fascicle (MLF) neurons upon the caudal projection of the interstitial nuclei of Cajal (INC). By using in ovo surgeries, retrograde axonal labeling, and immunohistochemical techniques, we were able to determine that the absence of P1 generates a failure in the INC caudal projection, while drastically diminishing the reticulospinal rhombencephalic neurons projections. The lack of INC projection significantly decreases the number of reticulospinal neurons projecting to the MLF. We found a 48.6% decrease in the projections to the MLF from the rostral and bulbar areas. Similarly, the observed decrease at prosomere 2 was 51.5%, with 61.8% and 32.4% for prosomeres 3 and 4, respectively; thus, constituting the most affected rostral regions. These results suggest the following possibilities: i, that the axons of the reticulospinal neurons employ the INC projection as a scaffold, fasciculating with this pioneer projection; and ii, that the P1 region, including pretectal MLF neurons, exerts a chemotropic effect upon the INC caudal projection. Nonetheless the identification of these chemotropic signals is still a pending task.

The improvement of lipase secretion and stability by addition of inert compounds into Acinetobacter calcoaceticus cultures.

Acinetobacter calcoaceticus BD413 produces variable amounts of an exocellular lipase that becomes rapidly inactivated upon secretion. To achieve high yield and protect the enzyme, we assayed the addition of several inert compounds to cell-free supernatants, cell fractions, and whole cultures. Glass beads, poly(ethylene glycol) 600, Triton X-100, saccharose, gum arabic, and beta-cyclodextrin were among the compounds tested. beta-Cyclodextrin and gum arabic (and saccharose to a lesser extent) were effective enzyme stabilizers in cell-free supernatants, while gum arabic, glass beads, and Triton X-100 improved lipase secretion from cells, and, therefore, total lipase yield (30-50%, according to the additive). In whole cultures, beta-cyclodextrin was the most effective additive, particularly in combination with glass beads or gum arabic. Indeed, cultures containing beta-cyclodextrin plus gum arabic were able to maintain 95% (+/- 1.5%) of the initial lipase activity for more than 16 h, while control cultures with no additives maintained only 10% (+/- 4%) of the enzyme activity after the same period. In conclusion, the addition of inert compounds in cultures may be considered a useful approach for achieving increased yield and lipase stabilization, amenable for downstream processing.