Transcriptomic Profiling of High-Density Giardia Foci Encysting in the Murine Proximal Intestine

Giardia is a highly prevalent, understudied protistan parasite causing significant diarrheal disease worldwide. Its life cycle consists of two stages: infectious cysts ingested from contaminated food or water sources, and motile trophozoites that colonize and attach to the gut epithelium, later encysting to form new cysts that are excreted into the environment. Current understanding of parasite physiology in the host is largely inferred from transcriptomic studies using Giardia grown axenically or in co-culture with mammalian cell lines. The dearth of information about the diversity of host-parasite interactions occurring within distinct regions of the gastrointestinal tract has been exacerbated by a lack of methods to directly and non-invasively interrogate disease progression and parasite physiology in live animal hosts. By visualizing Giardia infections in the mouse gastrointestinal tract using bioluminescent imaging (BLI) of tagged parasites, we recently showed that parasites colonize the gut in high-density foci. Encystation is initiated in these foci throughout the entire course of infection, yet how the physiology of parasites within high-density foci in the host gut differs from that of cells in laboratory culture is unclear. Here we use BLI to precisely select parasite samples from high-density foci in the proximal intestine to interrogate in vivo Giardia gene expression in the host. Relative to axenic culture, we noted significantly higher expression (>10-fold) of oxidative stress, membrane transporter, and metabolic and structural genes associated with encystation in the high-density foci. These differences in gene expression within parasite foci in the host may reflect physiological changes associated with high-density growth in localized regions of the gut. We also identified and verified six novel cyst-specific proteins, including new components of the cyst wall that were highly expressed in these foci. Our in vivo transcriptome data support an emerging view that parasites encyst early in localized regions in the gut, possibly as a consequence of nutrient limitation, and also impact local metabolism and physiology.

High-resolution crystal structure and in vivo function of a kinesin-2 homologue in Giardia intestinalis

A critical component of flagellar assembly, the kinesin-2 heterotrimeric complex powers the anterograde movement of proteinaceous rafts along the outer doublet of axonemes in intraflagellar transport (IFT). We present the first high-resolution structures of a kinesin-2 motor domain and an ATP hydrolysis-deficient motor domain mutant from the parasitic protist Giardia intestinalis. The high-resolution crystal structures of G. intestinalis wild-type kinesin-2 (GiKIN2a) motor domain, with its docked neck linker and the hydrolysis-deficient mutant GiKIN2aT104N were solved in a complex with ADP and Mg(2+) at 1.6 and 1.8 A resolutions, respectively. These high-resolution structures provide unique insight into the nucleotide coordination within the active site. G. intestinalis has eight flagella, and we demonstrate that both kinesin-2 homologues and IFT proteins localize to both cytoplasmic and membrane-bound regions of axonemes, with foci at cell body exit points and the distal flagellar tips. We demonstrate that the T104N mutation causes GiKIN2a to act as a rigor mutant in vitro. Overexpression of GiKIN2aT104N results in significant inhibition of flagellar assembly in the caudal, ventral, and posterolateral flagellar pairs. Thus we confirm the conserved evolutionary structure and functional role of kinesin-2 as the anterograde IFT motor in G. intestinalis.

Stable transformation of an episomal protein-tagging shuttle vector in the piscine diplomonad Spironucleus vortens

Background

Diplomonads are common free-living inhabitants of anoxic aquatic environments and are also found as intestinal commensals or parasites of a wide variety of animals. Spironucleus vortens is a putatively commensal diplomonad of angelfish that grows to high cell densities in axenic culture. Genomic sequencing of S. vortens is in progress, yet little information is available regarding molecular and cellular aspects of S. vortens biology beyond descriptive ultrastructural studies. To facilitate the development of S. vortens as an additional diplomonad experimental model, we have constructed and stably transformed an episomal plasmid containing an enhanced green fluorescent protein (GFP) tag, an AU1 epitope tag, and a tandem affinity purification (TAP) tag. This construct also contains selectable antibiotic resistance markers for both S. vortens and E. coli.

Results

Stable transformants of S. vortens grew relatively rapidly (within 7 days) after electroporation and were maintained under puromycin selection for over 6 months. We expressed the enhanced GFP variant, eGFP, under transcriptional control of the S. vortens histone H3 promoter, and visually confirmed diffuse GFP expression in over 50% of transformants. Next, we generated a histone H3::GFP fusion using the S. vortens conventional histone H3 gene and its native promoter. This construct was also highly expressed in the majority of S. vortens transformants, in which the H3::GFP fusion localized to the chromatin in both nuclei. Finally, we used fluorescence in situ hybridization (FISH) of the episomal plasmid to show that the transformed plasmid localized to only one nucleus/cell and was present at roughly 10–20 copies per nucleus. Because S. vortens grows to high densities in laboratory culture, it is a feasible diplomonad from which to purify native protein complexes. Thus, we also included a TAP tag in the plasmid constructs to permit future tagging and subsequent purification of protein complexes by affinity chromatography via a two-step purification procedure.

Conclusion

Currently, progress in protistan functional and comparative genomics is hampered by the lack of free-living or commensal protists in axenic culture, as well as a lack of molecular genetic tools with which to study protein function in these organisms. This stable transformation protocol combined with the forthcoming genome sequence allows Spironucleus vortens to serve as a new experimental model for cell biological studies and for comparatively assessing protein functions in related diplomonads such as the human intestinal parasite, Giardia intestinalis.

Pluripotent marker expression and differentiation of human second trimester Mesenchymal Stem Cells

Mesenchymal stem cells are an easily obtainable stem cell source from bone marrow. Presently, they are the most widely used cell type for cellular replacement strategies in humans as a result of extensive research that has demonstrated that these cells are capable of self-renewal, able to undergo multi-lineage differentiation, engraft, and ameliorate symptoms in numerous animal models. In this study, we comprehensively characterize human second trimester mesenchymal stem cells (STMSCs). We demonstrate that STMSCs are easily expandable to clinical relevance and express pluripotent markers such as Oct-4, Nanog, Sox-2, and SSEA-4 at the cellular and molecular level. Moreover, we directionally differentiate STMSCs into osteogenic, chondrogenic, adipogenic, neurogenic, and cardiogenic cell lineages. These studies demonstrate the plasticity of STMSCs and the potential for their use in cellular replacement therapy.