News archives


OCTOBER - DECEMBER 17

JULY - SEPTEMBER 17

APRIL - JUNE 17

JANUARY - MARCH 17

OCTOBER - DECEMBER 16

JULY - SEPTEMBER 16

APRIL - JUNE 16

JANUARY - MARCH 16

OCTOBER - DECEMBER 15

JULY - SEPTEMBER 15

APRIL - JUNE 15

JANUARY - MARCH 15

OCTOBER - DECEMBER 14

JULY - SEPTEMBER 14

APRIL - JUNE 14

JANUARY - MARCH 14

OCTOBER - DECEMBER 13

JULY - SEPTEMBER 13

APRIL - JUNE 13

JANUARY - MARCH 13

OCTOBER - DECEMBER 12

JULY - SEPTEMBER 12

APRIL - JUNE 12

JANUARY - MARCH 12

OCTOBER - DECEMBER 11

JULY - SEPTEMBER 11

APRIL - JUNE 11

JANUARY - MARCH 11

OCTOBER - DECEMBER 10

JULY - SEPTEMBER 10

APRIL - JUNE 10

JANUARY - MARCH 10

OCTOBER - DECEMBER 09

JULY - SEPTEMBER 09

APRIL - JUNE 09

JANUARY - MARCH 09

OCTOBER - DECEMBER 08

JULY - SEPTEMBER 08

APRIL - JUNE 08

JANUARY - MARCH 08

OCTOBER - DECEMBER 07

JULY - SEPTEMBER 07

APRIL - JUNE 07

JANUARY - MARCH 07

 
  current news   Press   selected story    
     
  24 November 2009  
 

Congratulations to IMCB’s recent PhD graduates

 
 



(To view more about each student's thesis, please click on his/her name in the image above)

PhD Gradute: Tran Thi Ton Hoai
Thesis Title: Interaction of Scribble with Zonula Occludens and Intermediate Filament Proteins.

Abstract
SNAREs (soluble N-ethylamaleimide sensitive factor attachment protein receptor) are key regulators of the last stage of vesicle docking and subsequent fusion in diverse intracellular membrane transport events. Since the function of SNAREs is regulated primarily by their localization, it is important to understand their targeting mechanisms. VAMP4 (vesicle-associated membrane protein 4) is a SNARE located mainly in the trans-Golgi network (TGN). It functions in membrane traffic from the sorting and recycling endosomes to the TGN, but its trafficking itinerary is unknown. The N-terminal domain preceding the SNARE motif of VAMP4 contains an autonomous targeting signal for the TGN, which resides in a region consisting of a double-Leu motif followed by two acidic clusters. For detailed study of the role(s) of this region as the targeting signals of VAMP4, Ala-mutagenesis screening was performed. Immunofluorescence study showed that the double-Leu motif and an acidic cluster play essential roles in mediating efficient TGN targeting.

An antibody internalization assay using C-terminally EGFP-tagged VAMP4 also showed that VAMP4-EGFP cycles between the PM and the TGN and that its N-terminal domain may participate in regulating this recycling. Detailed time-course analysis of anti-GFP antibody transport to the TGN as well as pharmacological and thermal perturbation experiments suggest that VAMP4-EGFP is endocytosed by clathrin-dependent pathways. It is then transported to the TGN via the sorting and recycling endosomes, but not the late endosome. The double-Leu motif of the TGN-targeting signal is important for internalization, whereas the acidic cluster is crucial for endosome-to-TGN transport. Site-directed mutagenesis in VAMP4-EGFP showed that the negative charge and steric size of the phosphorylated Ser-30, which is sandwiched between the two acidic clusters, are important for the TGN-to-PM transport of VAMP4-EGFP. These results suggest that the TGN-targeting signal of VAMP4 mediates the efficient cycling of VAMP4 between the TGN and the PM, thus conferring steady-state enrichment of VAMP4 at the TGN .

 
 


 
 


Figure Legend: A schematic model depicting the recycling pathway of VAMP4.

VAMP4-EGFP internalized from the PM by clathrin-mediated endocytosis is at first delivered to the sorting endosomes (SE) marked by EEA1 and TfR, and then transported to the peri-Golgi RE marked by TfR before being delivered to the TGN. This is revealed by the accumulation of VAMP4-EGFP at the TfR-marked compartments when cells were incubated at 18oC or treated with BFLA1 or ConA. The negative charge at the position of Ser-30 in the TGN-targeting signal of VAMP4 is important for the transport of VAMP4-EGFP from the TGN to the PM. The double-Leu motif is necessary for the internalization from the PM; whereas the distal acidic cluster is involved in efficient delivery from the endosome to the TGN. The strong correlation of signal responsible for TGN targeting and recycling indicates that this recycling pathway contributes to the steady-state enrichment of VAMP4 in the TGN. The elucidation of this recycling pathway is in line with the function of VAMP4 as a v-SNARE participating in traffic from the RE to the TGN.

 

 
 


PhD Gradute: Cai Lei
Thesis Title: SNX27 is important for postnatal development in mice

Abstract
Phox (PX) domain-containing sorting nexins (SNXs) are emerging as important regulators of endocytic trafficking. Sorting nextin 27 (SNX27) is unique as it contains a PDZ (Psd-95/Dlg/ZO1) domain which recognizes PDZ-binding motifs generally present at the C-terminus of proteins. SNX27 is targeted to the early endosome by interaction of its PX domain with endosome-enriched PtdIns(3)P. Targeted ablation of SNX27 gene in mice revealed that SNX27 plays an essential role in postnatal growth and survival. Through yeast two hybrid screening, the N-methyl-D-aspartate (NMDA) receptor 2C (NR2c) was identified as a novel SNX27-interacting protein and this interaction is mediated by the PDZ domain of SNX27 and the C-terminal PDZ-binding motif of NR2c. Consistent with a role of SNX27 shown earlier to mediate endosomal sorting of Kir3, the level of Kir3.2 was increased in SNX27Cai lei mice. Similar to Kir3.2, the level of NR2c was increased to comparable extents in SNX27Cai lei mice, implying that SNX27 may also function to regulate endosomal sorting of NR2c. In view of the regulation of other proteins by SNX27, our results suggest that SNX27 may act as a general regulator for endosomal sorting of membrane proteins containing PDZ-binding motif and its absence may alter the trafficking of these proteins, leading to growth and survival defects.

 
 


 

 
 


Figure Legend: SNX27 deficiency caused severe postnatal growth retardation and lethality of newborn pups.
(A) The body weights during postnatal growth of SNX27-/- and SNX27+/+ pups were plotted as a function of time, showing severe delayed growth in body weight gain of SNX27-/- pups. All SNX27-/- mice died before weaning.

(B) a. The image of a SNX27-/- mouse and a wild-type mouse from the same litter at 10 days after birth. b. The image of a SNX27-/- mouse and a wild-type mouse from the same litter at 20 days after birth, showing the dramatically reduced sizes.Bars:1 cm

(C) The image of some major organs from SNX27-/- and a wild-type mouse at 10 days after birth, showing reduced sizes of multiple organs of SNX27-/- mouse. Bar: 1cm

For more information on Wanjin HONG's Lab, Please Click here.