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For the cell biologist, identifying changes in gene expression using DNA microarrays is just the start of a long journey from tissue to cell. We discuss how chip users can first filter noise (false-positives) from daunting microarray datasets. Combining laser capture microdissection with real-time polymerase chain reaction and reverse transcription is a helpful follow-up step that allows expression of selected genes to be quantified in populations of recovered cells. The voyage from chip to single cell can be completed using sensitive new in situ hybridization and immunohistochemical methods based on tyramide signal amplification.
Phosphoinositides recruit proteins to distinct intracellular membranes. Now, the Phox homology (PX) domain, an evolutionarily conserved protein domain whose function has so far been elusive, has been demonstrated to bind phosphoinositides. The interactions of PX-domain-containing proteins with specific phosphoinositides are critical for cellular activities such as microbial killing and membrane trafficking.
Cip/Kip proteins that inhibit cyclin-dependent kinase 2 (Cdk2) restrain the initiation of DNA replication. Degradation of a Xenopus Kip1 orthologue, Xic1, is dependent on its recruitment to replication origins. This ensures that activation of Cdk2 and subsequent initiation of replication is co-ordinately regulated at, and localized to, replication origins.
How are Wnt signals made effective in only the right times and places? New studies of the asymmetrical influences of Wnt signals originating from a source show the importance of differential signal degradation and regulated endocytosis.
