MTV proteins unveil ER- and microtubule-associated compartments in the plant vacuolar trafficking pathway.

The factors and mechanisms involved in vacuolar transport in plants, and in particular those directing vesicles to their target endomembrane compartment, remain largely unknown. To identify components of the vacuolar trafficking machinery, we searched for Arabidopsis modified transport to the vacuole (mtv) mutants that abnormally secrete the synthetic vacuolar cargo VAC2. We report here on the identification of 17 mtv mutations, corresponding to mutant alleles of MTV2/VSR4, MTV3/PTEN2A MTV7/EREL1, MTV8/ARFC1, MTV9/PUF2, MTV10/VPS3, MTV11/VPS15, MTV12/GRV2, MTV14/GFS10, MTV15/BET11, MTV16/VPS51, MTV17/VPS54, and MTV18/VSR1 Eight of the MTV proteins localize at the interface between the trans-Golgi network (TGN) and the multivesicular bodies (MVBs), supporting that the trafficking step between these compartments is essential for segregating vacuolar proteins from those destined for secretion. Importantly, the GARP tethering complex subunits MTV16/VPS51 and MTV17/VPS54 were found at endoplasmic reticulum (ER)- and microtubule-associated compartments (EMACs). Moreover, MTV16/VPS51 interacts with the motor domain of kinesins, suggesting that, in addition to tethering vesicles, the GARP complex may regulate the motors that transport them. Our findings unveil a previously uncharacterized compartment of the plant vacuolar trafficking pathway and support a role for microtubules and kinesins in GARP-dependent transport of soluble vacuolar cargo in plants.

Identification of Domains and Factors Involved in MINIYO Nuclear Import.

The transition of stem cells from self-renewal into differentiation is tightly regulated to assure proper development of the organism. Arabidopsis MINIYO (IYO) and its mammalian orthologue RNA polymerase II associated protein 1 (RPAP1) are essential factors for initiating stem cell differentiation in plants and animals. Moreover, there is evidence suggesting that the translocation of IYO and RPAP1 from the cytosol into the nucleus functions as a molecular switch to initiate this cell fate transition. Identifying the determinants of IYO subcellular localization would allow testing if, indeed, nuclear IYO migration triggers cell differentiation and could provide tools to control this crucial developmental transition. Through transient and stable expression assays in Nicotiana benthamiana and Arabidopsis thaliana, we demonstrate that IYO contains two nuclear localization signals (NLSs), located at the N- and C-terminus of the protein, which mediate the interaction with the NLS-receptor IMPA4 and the import of the protein into the nucleus. Interestingly, IYO also interacts with GPN GTPases, which are involved in selective nuclear import of RNA polymerase II. This interaction is prevented when the G1 motif in GPN1 is mutated, suggesting that IYO binds specifically to the nucleotide-bound form of GPN1. In contrast, deleting the NLSs in IYO does not prevent the interaction with GPN1, but it interferes with import of GPN1 into the nucleus, indicating that IYO and GPN1 are co-transported as a complex that requires the IYO NLSs for import. This work unveils key domains and factors involved in IYO nuclear import, which may prove instrumental to determine how IYO and RPAP1 control stem cell differentiation.

Computed tomography or magnetic resonance imaging - our experiences in determining preoperative TNM staging of bladder cancer.

UNLABELLED: Bladder cancer is the ninth most common cancer diagnosis worldwide. Early detection of bladder cancer is important, since up to 47% of bladder cancer-related deaths might be avoided. AIM: To show our experience in determining the staging of bladder cancer with multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI), making comparison of stage accuracy with contrast enhanced MDCT, conventional MR imaging and dynamic contrast-enhanced MR imaging on the one hand and pathoistological diagnoses after transurethral resection of the non-muscle invasive bladder cancers or radical cystectomy for patients with muscle-invasive bladder cancers. MATERIALS AND METHODS: Ninety patients with histologically proved bladder cancer were prospectively examined with MDCT, conventional and dynamic MR imaging before tumour resection. RESULTS: Staging was correct in 55.6% with CT, 56.7% with conventional MRI and in 86.7% with dynamic MRI, which was highly significant compared with CT and conventional MRI. Overestimation for superficial tumors was high with CT (31.25%) and conventional MR imaging (25%), but was significantly reduced with dynamic MR imaging (8.3%). The percentages of underestimation in surgically proved invasive tumours (pT2- pT4) were lowest with dynamic MR imaging. CONCLUSION: CT and MR imaging are less accurate in the evaluation of the depth of mural invasion and for both techniques overstaging is the most frequent error. Dynamic contrast-enhanced MRI with 87% of accuracy, 8.3% overestimation for superficial tumours and lowest underestimation for invasive tumours, make this imaging considerably more accurate.