The length of things

摘要

It is important to know when to stop. A cell has to know when to stop expanding. A flower's pistil and its stamen when to stop elongating. And a flagellum to stop extending. Because there is a fair chance that without this knowledge, it would be difficult to keep organisms alive. But how do all these various parts of living matter know when the time has come to stop growing? There must be a mechanism of some kind. A sort of molecular device which holds up a STOP sign, or acts as a means of measure when something has reached the required shape or length. Recently, such a scheme was discovered in the flagella of the alga Chlamydomonas reinhardtii ; a ruler of sorts that defines not only the length of the units which make up the axoneme but also the nature of the flagellum's structure. This molecular yardstick is a protein known as coiled-coil domain-containing protein 40 - or CCDC40.