Calcineurin is responsible for mediating a wide variety of cellular processes in response to dynamic calcium (Ca2+) signals, yet the precise mechanisms involved in the spatiotemporal control of calcineurin signaling are poorly understood. Here, we use genetically encoded fluorescent biosensors to directly probe the role of cytosolic Ca2+ oscillations in modulating calcineurin activity dynamics in insulin-secreting MIN6 β-cells. We show that Ca2+ oscillations induce distinct temporal patterns of calcineurin activity in the cytosol and plasma membrane vs at the ER and mitochondria in these cells. Furthermore, we found that these differential calcineurin activity patterns are determined by variations in the subcellular distribution of calmodulin (CaM), indicating that CaM plays an active role in shaping both the spatial and temporal aspects of calcineurin signaling. Together, our findings provide new insights into the mechanisms by which oscillatory signals are decoded to generate specific functional outputs within different cellular compartments.DOI: http://dx.doi.org/10.7554/eLife.03765.001

Fluorescence-based, genetically encodable biosensors are widely used tools for real-time analysis of different biological process. Over the last few decades the number of available genetically encodable biosensors and the types of processes they can monitor has increased rapidly. In this review we aim to introduce the reader to general principles and best practices in biosensor development and highlight some of the ways in which biosensors can be used to illuminate outstanding questions of biological function. Specifically, we will focus on sensors developed for monitoring kinase activity and use them to illustrate some common considerations for biosensor design. We will describe several uses to which kinase and second-messenger biosensors have been put, and conclude with considerations for the use of biosensors once they are developed. Overall, as fluorescence-based biosensors continue to diversify and improve we expect them to continue to be widely used as reliable and fruitful tools for gaining deeper insights into cellular and organismal function.

Neisseria gonorrhoeae is the second most common sexually transmitted bacterial pathogen worldwide. Diseases associated with N. gonorrhoeae cause localized inflammation of the urethra and cervix. Despite this inflammatory response, infected individuals do not develop protective adaptive immune responses to N. gonorrhoeae . N. gonorrhoeae is a highly adapted pathogen that has acquired multiple mechanisms to evade its host's immune system, including the ability to manipulate multiple immune signaling pathways. N. gonorrhoeae has previously been shown to engage immunosuppressive signaling pathways in B and T lymphocytes. We have now found that N. gonorrhoeae also suppresses adaptive immune responses through effects on antigen presenting cells. Using primary, murine bone marrow-derived dendritic cells and lymphocytes, we show that N. gonorrhoeae -exposed dendritic cells fail to elicit antigen-induced CD4+ T lymphocyte proliferation. N. gonorrhoeae exposure leads to upregulation of a number of secreted and dendritic cell surface proteins with immunosuppressive properties, particularly Interleukin 10 (IL-10) and Programmed Death Ligand 1 (PD-L1). We also show that N. gonorrhoeae is able to inhibit dendritic cell- induced proliferation of human T-cells and that human dendritic cells upregulate similar immunosuppressive molecules. Our data suggest that, in addition to being able to directly influence host lymphocytes, N. gonorrhoeae also suppresses development of adaptive immune responses through interactions with host antigen presenting cells. These findings suggest that gonococcal factors involved in host immune suppression may be useful targets in developing vaccines that induce protective adaptive immune responses to this pathogen.