Giardia is a single-celled parasite causing significant diarrheal disease in several hundred million people worldwide. Due to limited access to the site of infection in the gastrointestinal tract, our understanding of the dynamics of Giardia infections in the host has remained limited and largely inferred from laboratory culture. To better understand Giardia physiology and colonization in the host, we developed imaging methods to quantify Giardia expressing bioluminescent physiological reporters in two relevant animal models. We discovered that parasites primarily colonize and encyst in the proximal small intestine in discrete, high-density foci. We also show that high parasite density contributes to encystation initiation.

Giardia is a highly prevalent, yet understudied protistan parasite causing diarrheal disease worldwide. Hosts ingest Giardia cysts from contaminated sources. In the gastrointestinal tract, cysts excyst to become motile trophozoites, colonizing and attaching to the gut epithelium. Trophozoites later differentiate into infectious cysts that are excreted and contaminate the environment. Due to the limited accessibility of the gut, the temporospatial dynamics of giardiasis in the host is largely inferred from laboratory culture and thus may not mirror Giardia physiology in the host. Here we have developed bioluminescent imaging (BLI) to directly interrogate and quantify the in vivo temporospatial dynamics of giardiasis, thereby providing an improved murine model to evaluate anti-Giardia drugs. Using BLI, we determined that parasites primarily colonize the proximal small intestine non-uniformly in high-density foci. By imaging encystation-specific bioreporters, we show that encystation initiates shortly after inoculation and continues throughout the entire duration of infection. Encystation also initiates in high-density foci in the proximal small intestine, and high-density laboratory cultures of parasites are also stimulated to encyst. This work overturns the assumption that parasites encyst later during infection as they are dislodged and travel through the colon. We suggest that these high-density regions of parasite colonization likely result in localized pathology to the epithelium, and encystation occurs when trophozoites reach a threshold density due to local nutrient depletion. This more accurate visualization of giardiasis redefines the dynamics of in vivo Giardia life cycle, paving the way for future mechanistic studies of density-dependent parasitic processes in the host.SignificanceGiardia is a single-celled parasite causing both acute and chronic diarrheal disease in over one billion people worldwide. Due to limited access to the site of infection in the gastrointestinal tract, our understanding of the dynamics of Giardia infections in the host has remained limited, and largely inferred from laboratory culture. To better understand giardiasis in the host, we developed imaging methods to quantify Giardia expressing bioluminescent physiological reporters in live mice. We discovered that parasites primarily colonize and encyst in the proximal small intestine in discrete, high-density foci. Furthermore, this work provides evidence of a parasite density-based threshold for the differentiation of Giardia into cysts in the host. These findings overturn existing paradigms of giardiasis infection dynamics in the host.

High plant lignan intake is associated with a number of health benefits, possibly induced by the lignan metabolite enterolactone (ENL). The gut microbiota plays a crucial role in converting dietary lignans into ENL, and epidemiological studies have shown that use of antibiotics is associated with lower levels of ENL. Here we investigate the link between antibiotic use and lignan metabolism in pigs using LC-MS/MS. The effect of lignan intake and antibiotic use on the gut microbial community and the pig metabolome is studied by 16S rRNA sequencing and nontargeted LC-MS. Treatment with antibiotics resulted in substantially lower concentrations of ENL compared with concentrations detected in untreated animals, whereas the plasma concentrations of plant lignans were unchanged. Both diet and antibiotic treatment affected the clustering of urinary metabolites and significantly altered the proportions of taxa in the gut microbiota. Diet, but not antibiotic treatment, affected the plasma lipid profile, and a lower concentration of LDL cholesterol was observed in the pigs fed a high lignan diet. This study provides solid support for the associations between ENL concentrations and use of antibiotics found in humans and indicates that the lower ENL concentration may be a consequence of the ecological changes in the microbiota.

20Adult neural stem cells are largely quiescent, and require transcriptional reprogramming 21 to reenter the cell cycle and undergo neurogenesis. However, the precise mechanisms 22 that underlie the rapid transcriptional overhaul during NSC activation remain undefined. 23Here, we identify the genome-wide chromatin accessibility differences between primary 24 neural stem and progenitor cells in quiescent and activated states. We show that these 25 distinct cellular states exhibit both shared and unique chromatin profiles, which are both 26 associated with gene regulation. Interestingly, we find that accessible chromatin states 27 specific to quiescent or activated cells are active enhancers bound by pro-neurogenic 28 and quiescence factors, ASCL1 and NFI. In contrast, shared sites are gene promoters 29 harboring constitutively accessible chromatin enriched for particular core promoter 30 elements that are functionally associated with translation and metabolic functions. 31Together, our findings reveal how accessible chromatin states regulate a transcriptional 32 overhaul and drive the switch between quiescence and proliferation in NSC activation. 33 34 46In vivo, the majority of NSCs reside in a state of quiescence 10 . Quiescent NSCs (qNSCs) 47 have exited the cell cycle but can be prompted by intrinsic or extrinsic cues to "activate" 48 and re-enter the cell cycle (we refer to these cells as activated NSCs, or aNSCs). Once 49 activated, aNSCs proliferate and may return to quiescence and self-renew, or 50 differentiate into neurons or glia. Activation of qNSCs is the first critical step in 51 neurogenesis in the adult brain, and is enhanced in response to damage (e.g. stroke) or 52 environmental stimuli such as parabiosis [11][12][13] . Evidence shows that decreased 53 neurogenesis with age occurs due to reduced activation of qNSCs, senescence of the 54 NSC niche, and exhaustion of the qNSC pool [14][15][16][17] . Accumulation of qNSCs has also been 55 observed in a rodent model for neurodevelopmental disorders, suggesting that a careful 56 balance of NSC quiescence and activation is necessary for healthy cognitive function 18 . 57However, the precise mechanisms that regulate this balance and prompt qNSCs to re-58 enter the cell cycle in the healthy mammalian brain are mostly unknown. 59 60 Recent studies reported that quiescent and activated NSCs employ cell type-specific 61 mechanisms to support their functionality, including distinct metabolic states and 62 differences in proteostasis [19][20][21] . Transcriptional profiling of qNSCs and aNSCs revealed 63 both shared and distinct transcriptional signatures in the two cell types, indicating that a 64 transcriptional overhaul occurs at a subset of genes during the process of NSC 65 activation 10,19,22,23 . For example, genes involved in cell proliferation, lipid metabolism, and 66 protein homeostasis were differentially expressed in quiescent and activated NSCs. 67 Similar changes have also been observed using in vitro models of NSC quiescence and 68 activation...

The effects of arabinoxylan (AX)-rich rye bran based diet (RB) and antibiotics on digestion, fermentation and short-chain fatty acids (SCFA) absorption were studied compared with an iso-dietary fibre (DF) cellulose...