Prions

Species-barrier-independent prion replication in apparently resistant species. Hill, A. F. et al. Proc. Natl Acad. Sci. USA 97 , 10248?10253 (2000). [ PubMed]

Until now, it was believed that a species barrier limits infection by prions from different species. For example, mice cannot be infected with hamster prions but humans can be infected with cow prions. Hill et al. now show that hamster prions can replicate in mice ? they just do not cause prion disease. But if either mice or hamsters are inoculated with brain extracts from these sub-clinically infected mice, they do develop the disease.

Cell adhesion

Two cell adhesion molecules, nectin and cadherin, interact through their cytoplasmic domain-associated proteins. Tachibana, K. et al. J. Cell Biol. 150 , 1161?1175 (2000). [ PubMed]

Nectin is a calcium-independent immunoglobulin-like adhesion molecule that can trans-interact with itself to form a cell?cell adhesion system, similar to the well-known cadherin system. The nectin and cadherin adhesion complexes interact with each other through their cytoplasmic domain-associated proteins l-afadin and catenins, respectively. Although the two systems cooperate in organizing adherens junctions, their hierarchy is not known.

Alzheimer's disease

Nicastrin modulates presenilin-mediated notch/glp -1 signal transduction and βAPP processing. Yu, G. et al. Nature 407, 48? 54 (2000).

Processing of the β-amyloid precursor protein (βAPP) to the amyloid-β peptide is a central part of the path to Alzheimer's disease, and this paper reports the identification of a new player in the process. Called nicastrin, this protein interacts with βAPP, and also with presenilins (PS) 1 and 2. The authors believe it to be a functional component of the PS1 and PS2 complexes, and show that, like them, nicastrin is involved in processing both βAPP and Notch.

Cell division

Analysis of mid1p, a protein required for placement of the cell division site, reveals a link between the nucleus and the cell surface in fission yeast  Paoletti, A. & Chang, F. Mol. Biol. Cell 11 , 2757?2771 (2000). [ PubMed]

In fission yeast, a contractile ring forms in the middle of the cell in early mitosis, and its position depends on the position of the nucleus. The position of the plane of cell division with respect to the nucleus is probably defined by mid1p. This protein shuttles between the nucleus and a broad band at the medial cell surface, but how exactly does it convey the positional information?