In today’s new issue of JCB, Burkart et al. explain how a secreted protease helps egg cells avoid being fertilized by more than one sperm. Initial fertilization leads to the exocytosis of cortical granules containing the protease ovastacin, which cleaves ZP2, a component of the egg’s outer layer, the zona pellucida. ZP2 cleavage prevents additional sperm from binding to the oocyte, ensuring that the fertilized egg can undergo normal embryonic development. You can read more in this summary.
Rullo et al. describe how actin polymerization helps leukocytes stay attached to blood vessel walls instead of being swept away by the flow of blood. The force of fluid flow stimulates leukocytes to form actin-rich structures (that the researchers term anchors), which reinforce the cells’ integrin-based adhesions to the underlying surface. (You can see a great example of a leukocyte anchor in the scanning electron micrograph on this week’s cover). Anchor formation depends on a signaling pathway involving PI-3-kinase and the small GTPases Rap1 and Rac. More here.
Anastasia et al. reveal that mitotic entry is linked to membrane transport, potentially explaining how cells coordinate growth and division. The researchers uncover a signaling pathway that leads from the GTPase Rho1 to the checkpoint proteins Wee1 and Cdc25, which prevents budding yeast from entering mitosis when vesicle transport to the plasma membrane is inhibited. Senior author Doug Kellogg explains in this week’s In Focus how the pathway might let cells know when they’ve grown big enough to divide in two.
Erlemann et al. use quantitative fluorescence microscopy to count how many gamma-tubulin small complexes (gamma-TuSCs) nucleate microtubules at budding yeast spindle bodies. The answer – summarized here – is 7 gamma-TuSCs (each containing two gamma-tubulin subunits) plus a few additional gamma-tubulin and Spc98 molecules. Senior author Elmar Schiebel also provides a review of centrosome biology in this issue, discussing recent developments in our understanding of the centrosome duplication cycle.
Meanwhile, Stavoe and Colon-Ramos describe how a Netrin signaling pathway (best known for its role in axonal guidance) also controls synapse formation by clustering synaptic vesicles at pre-synaptic terminals. Senior author Daniel Colon-Ramos discusses why and how this pathway multitasks in this week’s biobytes podcast, where you can also hear Chris Kaiser explain his lab’s recent work (Kim et al.) on the regulation of a key enzyme involved in protein folding in the ER. You can listen below or subscribe in iTunes.
Lots of other interesting papers in this week’s issue as well. You can find them all listed on our table of contents by clicking here…
Cover image courtesy of Jacob Rullo and Henry Hong.