
Time
for a quick roundup of today’s new issue of JCB.
Briguglio et al. investigate how different classes of cargo proteins are sorted
into mucocysts, secretory granules found in the ciliate protozoan Tetrahymena thermophila. The researchers find that sortilins, better
known as receptors that transport hydrolase enzymes to lysosomes, also deliver
soluble, non-aggregating cargo proteins to mucocysts. In contrast,
self-aggregating cargo proteins are still sorted to mucocysts in the absence of
sortilins, but, as described in this week’s In Focus, they aren’t processed to
their mature, secretion-ready forms due to the mislocalization of cathepsin
proteases.
Stephens
et al. reveal that the chromatin-organizing proteins condensin and cohesin
crosslink the pericentromeres of budding yeast chromosomes to coordinate their
dynamics during mitosis. In metaphase, the pericentric chromatin surrounding
each centromere forms a spring that resists the microtubule-based forces
pulling chromosomes toward the spindle poles. By crosslinking the
pericentromeres of different chromosomes, condensin and cohesin, along with the
kinesin motor cin8, may help to distribute tension across multiple microtubule
attachment sites. More here.
Hou
et al. describe how neurons activate the protein phosphatase PP1 in response to
synaptic stimulation. By reducing the function of active synapses, PP1 promotes
a type of synaptic plasticity called long-term depression. Hou et al. show that
the neuron-specific cyclin-dependent kinase Cdk5 phosphorylates and inhibits
PP1. But synaptic stimulation triggers the degradation of the Cdk5 activator p35,
so that PP1 can dephosphorylate and activate itself. As discussed here, the
researchers also report a key role for the PP1 regulator Inhibitor-2.
Espenel
et al. describe how a FRET-based biosensor can be used to track the activity of
a kinesin motor protein in living cells. The researchers show that the active
form of kinesin KIF17, which promotes epithelial cell polarization, accumulates
on stable microtubules at the cell periphery through the combined actions of
Protein Kinase C and the microtubule plus-end binding protein EB1. You can
learn more here.
Zhang
et al. demonstrate that the submembranous cytoskeleton formed by βII-spectrin acts
as a barrier to organize axonal membranes. You can learn more in this
commentary by Eshed-Eisenbach and Peles, and you can listen to the study’s
senior author, Matthew Rasband, discuss his lab’s results in this month’s neurobiology-themed
biobytes podcast, where you can also hear Nicolas Morel discuss his lab’s
recent paper describing the function of V-ATPase in regulating neurotransmitter
release.
And,
sticking with the neurobiology theme, this issue sees the last in our series of
“Cell biology in neuroscience” reviews. I’ll let our reviews editor, Priya
Prakash Budde, wrap things up:
We finish
our series on ‘cell biology in neuroscience’ (for an introduction to the
series, see here) with two excellent reviews.
The first, from Dekkers, Nikoletopoulou and Barde, is on cell death in the
brain, which focuses on how components of cell death pathways contribute to
synaptic function, as well as to degeneration in response to injury. We then end the series with a fascinating
review from Megan Corty and Marc Freeman on the role that glia and cell-cell
communication play in shaping the nervous system. In addition to clearing neuronal debris in
the brain, glia play instructive roles in brain development and, as the review
discusses, control neuron number and connectivity.
The
entire collection of reviews is freely available here. But if you are attending the annual ASCB
meeting in New Orleans this December, please stop by the JCB booth and pick up
our ‘Cell Biology in Neuroscience’ special issue, which has all seven reviews in
the series plus highlights of some of the exciting research we have published
this year, both in neuroscience and across the breadth of cell biology.
Cover image of mucocysts (green) in a Tetrahymena cell © 2013 Briguglio et al.