Cell fate

Blimp1 is a critical determinant of the germ cell lineage in mice. Ohinata, Y. et al. Nature 5 June 2005

Primordial germ cells (PGCs), the precursors of germ cells, are formed by inductive signals from extra-embryonic tissues, and must then segregate from their somatic neighbours. Ohinata et al. showed that proximal posterior epiblast cells expressing the transcriptional repressor Blimp1 are lineage-restricted so that they only produce PGCs. Without Blimp1, fewer PGCs — which do not migrate, proliferate or undergo homeobox gene repression (as normally occurs) — were formed.

Translation

A newly discovered function for RNase L in regulating translation termination. Le Roy, F. et al. Nature Struct. Mol. Biol. 12, 505–512 (2005)

The endoribonuclease RNase L participates in inhibiting protein synthesis during interferon-mediated anti-viral and anti-proliferative effects. Le Roy et al. report a new function for RNase L — it regulates translation termination. The authors characterized RNA-binding protein (RNABP), a known partner of RNase L, and showed that it was human eRF3/GSPT1, a component of the translation termination complex. The RNase-L–eRF3/GSPT1 interaction increased ribosomal readthrough and increased the +1 frameshift efficiency.

Signalling

Mechanism of divergent growth factor effects in mesenchymal stem cell differentiation. Kratchmarova, I. et al. Science 308, 1472–1477 (2005)

Why can epidermal growth factor (EGF), but not platelet-derived growth factor (PDGF), induce human mesenchymal stem cells (MSCs) to differentiate into osteoblasts? Both growth factors induce the phosphorylation of common protein subsets, but these authors used a mass-spectrometry-based proteomics approach to identify some differences in the response to EGF and PDGF. The accumulation of phosphorylated components of the phosphatidylinositol 3-kinase pathway in response to PDGF, but not EGF, accounts for the divergence of the differentiation response of MSCs.

Cytoskeleton

Microtubule-induced focal adhesion disassembly is mediated by dynamin and focal adhesion kinase. Ezratty, E. J., Partridge, M. A. & Gunderson, G. G. Nature Cell Biol. 15 May 2005

Rho-family GTPases are involved in focal adhesion assembly, but what mediates disassembly? These authors developed an assay in which they observed microtubule-regrowth-induced focal adhesion dissassembly after nocodazole washout (nocodazole depolymerizes microtubules). They showed that Rho or Rac weren't required for disassembly, but that focal adhesion kinase (FAK) and dynamin were — FAK localizes dynamin around focal adhesions, where it might endocytose focal adhesion components.