FAUSTA: Scaling Dynamic Analysis with Traffic Generation at WhatsApp

We introduce Fausta, an algorithmic traffic gener-ation platform that enables analysis and testing at scale. Fausta has been deployed at Meta to analyze and test the WhatsApp plat-form infrastructure since September 2020, enabling WhatsApp developers to deploy reliable code changes to a code base of millions of lines of code, supporting over 2 billion users who rely on WhatsApp for their daily communications. Fausta covers expected and unexpected program behaviors in a privacy-safe controlled environment to support multiple use cases such as reliability testing, privacy analysis and performance regression detection. It currently supports three different algorithmic input generation strategies, each of which construct realistic backend server traffic that closely simulates production data, without replaying any real user data. Fausta has been deployed and closely integrated into the WhatsApp continuous integration process, catching bugs in development before they hit production. We report on the development and deployment of Fausta's reliability use case between September 2020 and August 2021. During this period it has found 1,876 unique reliability issues, with a fix rate of 74%, indicating a high degree of true positive fault revelation. We also report on the distribution of fault types revealed by Fausta, and the correlation between coverage and faults found. Overall, we do find evidence that higher coverage is correlated with fault revelation

A Voltage-Gated H+ Channel Underlying pH Homeostasis in Calcifying Coccolithophores

Marine coccolithophorid phytoplankton are major producers of biogenic calcite, playing a significant role in the global carbon cycle. Predicting the impacts of ocean acidification on coccolithophore calcification has received much recent attention and requires improved knowledge of cellular calcification mechanisms. Uniquely amongst calcifying organisms, coccolithophores produce calcified scales (coccoliths) in an intracellular compartment and secrete them to the cell surface, requiring large transcellular ionic fluxes to support calcification. In particular, intracellular calcite precipitation using HCO3− as the substrate generates equimolar quantities of H+ that must be rapidly removed to prevent cytoplasmic acidification. We have used electrophysiological approaches to identify a plasma membrane voltage-gated H+ conductance in Coccolithus pelagicus ssp braarudii with remarkably similar biophysical and functional properties to those found in metazoans. We show that both C. pelagicus and Emiliania huxleyi possess homologues of metazoan Hv1 H+ channels, which function as voltage-gated H+ channels when expressed in heterologous systems. Homologues of the coccolithophore H+ channels were also identified in a diversity of eukaryotes, suggesting a wide range of cellular roles for the Hv1 class of proteins. Using single cell imaging, we demonstrate that the coccolithophore H+ conductance mediates rapid H+ efflux and plays an important role in pH homeostasis in calcifying cells. The results demonstrate a novel cellular role for voltage gated H+ channels and provide mechanistic insight into biomineralisation by establishing a direct link between pH homeostasis and calcification. As the coccolithophore H+ conductance is dependent on the trans-membrane H+ electrochemical gradient, this mechanism will be directly impacted by, and may underlie adaptation to, ocean acidification. The presence of this H+ efflux pathway suggests that there is no obligate use of H+ derived from calcification for intracellular CO2 generation. Furthermore, the presence of Hv1 class ion channels in a wide range of extant eukaryote groups indicates they evolved in an early common ancestor

Expression profile of genes regulated by activity of the Na-H exchanger NHE1

BACKGROUND: In mammalian cells changes in intracellular pH (pH(i)), which are predominantly controlled by activity of plasma membrane ion exchangers, regulate a diverse range of normal and pathological cellular processes. How changes in pH(i )affect distinct cellular processes has primarily been determined by evaluating protein activities and we know little about how pH(i )regulates gene expression. RESULTS: A global profile of genes regulated in mammalian fibroblasts by decreased pH(i )induced by impaired activity of the plasma membrane Na-H exchanger NHE1 was characterized by using cDNA microarrays. Analysis of selected genes by quantitative RT-PCR, TaqMan, and immunoblot analyses confirmed results obtained from cDNA arrays. Consistent with established roles of pH(i )and NHE1 activity in cell proliferation and oncogenic transformation, grouping regulated genes into functional categories and biological pathways indicated a predominant number of genes with altered expression were associated with growth factor signaling, oncogenesis, and cell cycle progression. CONCLUSION: A comprehensive analysis of genes selectively regulated by pH(i )provides insight on candidate targets that might mediate established effects of pH(i )on a number of normal and pathological cell functions