“If a straight line cutting two other straight lines…”The first six books of the elements of Euclid, in which coloured diagrams and symbols are used instead of letters for the greater ease of learners. 1847.
Color used as a teaching tool in the mid-19th century.
Cells are not uniform spheres; they generally come in a variety of
disparate shapes. In the broadest sense, this variation in shapes is
known as cell polarity, and it is an essential property for a variety of
cell functions. Growth in accordance with their polarity allows cells
to shape themselves in forms appropriate to their function. It has been
found that the establishment and maintenance of polarity is governed by
the interdependent relationship between the polarity marker protein on
the plasma membrane (cell membrane), actin, the microtubule
cytoskeleton, and membrane vesicle transport. The polarity marker
determines the polarity site, and with membrane vesicle transport toward
it, site-specific growth (polarity growth) is achieved. However, when
the plasma membrane elongates due to fusion of membrane vesicles, there
have been questions about how polarity markers are maintained without
being scattered over the elongated plasma membrane.
Y. Ishitsuka, N. Savage, Y. Li, A. Bergs, N. Gru n, D. Kohler, R. Donnelly, G. U. Nienhaus, R. Fischer, N. Takeshita. Superresolution microscopy reveals a dynamic picture of cell polarity maintenance during directional growth. Science Advances, 2015; 1 (10): e1500947 DOI: 10.1126/sciadv.1500947
Transient polarity model.
Credit: Image courtesy of University of Tsukuba