Three Brief Papers on the ER

Here are some cool ER papers I've seen recently:

Direct membrane protein-DNA interactions required early in nuclear envelope assembly
Sebastian Ulbert, Melpomeni Platani, Stephanie Boue, and Iain W. Mattaj
JCB (2006) 173:469-476

When the nuclear envelope reforms after mitosis, ER vesicles must bind to the condensed chromatin, but how does this occur? Well about half of the nuclear envelope (NE) proteins have basic luminal domains that mediate electrostatic interactions with the DNA itself. (In comparison about 4% of general ER and Golgi proteins have basic luminal domains.) To prevent ER/DNA association during mitosis, these basic NE proteins are phosphorylated.

ER-bound PTP1B is targeted to newly forming cell-matrix adhesions
Mariana V. Hernández, Maria G. Davies Sala, Janne Balsamo, Jack Lilien and Carlos O. Arregui
JCS (2006) 119:1233-1243

How does the ER remain extended in cells? This becomes a problem once you realize that actin, which is constantly polymerized at the cell's edge, is constantly being pushed towards the nucleus, and taking everything else along with it. Now it seems like the ER can interact with focal adhesions via protein tyrosine phosphatase 1B. This interaction may help anchor the ER at peripheral focal adhesion sites. Whether this is the only ER protein that can interact with focal adhesions remains unclear.

The secretory membrane system in the Drosophila syncytial blastoderm embryo exists as functionally compartmentalized units around individual nuclei
David Frescas, Manos Mavrakis, Holger Lorenz, Robert DeLotto, and Jennifer Lippincott-Schwartz
JCB (2006) 173:219-230

In Drosophila melanogaster embryogenesis, the first 13 nuclear division cycles are not accompanied by any cellularization. What you get is a giant single syncytium with over 6000 nuclei. At a specific time point all the nuclei migrate to the surface of the syncytium and then around each nuclei a cell membrane is constructed. In this paper the authors examined how the ER and Golgi of the syncytium are formed. After nuclear migration, the ER which previously was one giant cortical network, compartmentalizes around each nucleus. This even occurs prior to cellularization and requires a functional microtubule array.


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