Barbara A. Vaupel

Protection of Nonobese Diabetic Mice from Diabetes by Gene(s) Closely Linked to IFN-γ Receptor Loci

Nonobese diabetic (NOD) mice carrying a segment of chromosome flanking the disrupted IFN-γ receptor gene from original 129 ES cells are resistant to development of diabetes. However, extended backcrossing of this mouse line to the NOD mouse resulted in a segregation of the IFN-γR-deficient genotype from the diabetes-resistant phenotype. These results indicate that the protection of NOD mice from the development of diabetes is not directly linked to the defective IFN-γ receptor gene but, rather, is influenced by the presence of a diabetes-resistant gene(s) closely linked to the IFN-γR loci derived from the 129 mouse strain.

A calpain unique to alveolates is essential in Plasmodium falciparum and its knockdown reveals an involvement in pre-S-phase development.

Plasmodium falciparum encodes a single calpain that has a distinct domain composition restricted to alveolates. To evaluate the potential of this protein as a drug target, we assessed its essentiality. Both gene disruption by double cross-over and gene truncation by single cross-over recombination failed. We were also unable to achieve allelic replacement by using a missense mutation at the catalytic cysteine codon, although we could obtain synonymous allelic replacement parasites. These results suggested that the calpain gene and its proteolytic activity are important for optimal parasite growth. To gain further insight into its biological role, we used the FKBP degradation domain system to generate a fusion protein whose stability in transfected parasites could be modulated by a small FKBP ligand, Shield1 (Shld1). We made a calpain-GFP-FKBP fusion through single cross-over integration at the endogenous calpain locus. Calpain levels were knocked down and parasite growth was greatly impaired in the absence of Shld1. Parasites were delayed in their ability to transition out of the ring stage and in their ability to progress to the S phase. Calpain is required for cell cycle progression in Plasmodium parasites and appears to be an attractive drug target. We have shown that regulated knockdowns are possible in P. falciparum and can be useful for evaluating essentiality and function.

Thymic and postthymic regulation of diabetogenic CD8 T cell development in TCR transgenic nonobese diabetic (NOD) mice.

Natural development of diabetes in nonobese diabetic (NOD) mice requires both CD4 and CD8 T cells. Transgenic NOD mice carrying αβ TCR genes from a class I MHC (Kd)-restricted, pancreatic β cell Ag-specific T cell clone develop diabetes significantly faster than nontransgenic NOD mice. In these TCR transgenic mice, a large fraction of T cells express both transgene derived and endogenous TCR β chains. Only T cells expressing two TCR showed reactivity to the islet Ag. Development of diabetogenic T cells is inhibited in mice with no endogenous TCR expression due to the SCID mutation. These results demonstrate that the expression of two TCRs is necessary for the autoreactive diabetogenic T cells to escape thymic negative selection in the NOD mouse. Further analysis with MHC congenic NOD mice revealed that diabetes development in the class I MHC-restricted islet Ag-specific TCR transgenic mice is still dependent on the presence of the homozygosity of the NOD MHC class II I-Ag7.

Kinase-associated Endopeptidase 1 (Kae1) Participates in an Atypical Ribosome-associated Complex in the Apicoplast of Plasmodium falciparum

Background: Kae1 proteins are universally conserved and are regulated by a variety of protein-protein interactions. Results: P. falciparum expresses two Kae1 proteins with distinct localizations and atypical binding partners. Conclusion: Kae1api is essential and a potential regulator of ribosome activity. Significance: The Kae1 protein family likely has an expanded role outside of its known tRNA-modifying activity. The universally conserved kinase-associated endopeptidase 1 (Kae1) protein family has established roles in N6-threonylcarbamoyl adenosine tRNA modification, transcriptional regulation, and telomere homeostasis. These functions are performed in complex with a conserved core of protein binding partners. Herein we describe the localization, essentiality, and protein-protein interactions for Kae1 in the human malaria parasite Plasmodium falciparum. We found that the parasite expresses one Kae1 protein in the cytoplasm and a second protein in the apicoplast, a chloroplast remnant organelle involved in fatty acid, heme, and isoprenoid biosynthesis. To analyze the protein interaction networks for both Kae1 pathways, we developed a new proteomic cross-validation approach. This strategy compares immunoprecipitation-MS data sets across different cellular compartments to enrich for biologically relevant protein interactions. Our results show that cytoplasmic Kae1 forms a complex with Bud32 and Cgi121 as in other organisms, whereas apicoplast Kae1 makes novel interactions with multiple proteins in the apicoplast. Quantitative RT-PCR and immunoprecipitation studies indicate that apicoplast Kae1 and its partners interact specifically with the apicoplast ribosomes and with proteins involved in ribosome function. Together, these data indicate an expanded, apicoplast-specific role for Kae1 in the parasite.