How They Lose Their Nuclei

Photo: Red Blood Cells

Illustration of red blood
cells © NCI Visuals Online

Losing the nucleus enables the red blood cell to contain more oxygen-carrying hemoglobin, thus enabling more oxygen to be transported in the blood and boosting our metabolism. It was known that as a mammalian red blood cell nears maturity, a ring of actin filaments contracts and pinches off a segment of the cell that contains the nucleus, a type of “cell division.” The nucleus is then swallowed by macrophages.

“We discovered that the proteins Rac 1, Rac 2 and mDia2 are involved in building the ring of actin filaments”, says Harvey Lodish, professor of biology at Massachusetts Institute of Technology. “These proteins are known for their role in creating actin fibers in many body cells, and a necessary component of many important cellular functions including cell division that support cell growth”, says Peng Ji, lead author and postdoctoral researcher in the Lodish lab.

His cell-culture system began with red blood cell precursors drawn from an embryonic mouse liver. The cultured cells, synchronized to develop together, divided four or five times before losing their nuclei and becoming immature red blood cells. The researchers used simple fluorescence-based assays that enabled them to probe the changes in the red blood cells through the different stages leading up to the loss of the nucleus.

The researchers plan to further investigate the entire process of red blood cell formation, which may lead to insights about genetic alterations that underlie certain red blood cell disorders. “During normal cell division, each daughter cell receives half the DNA,” comments Lodish. “In this case, when the red blood cell divides, one daughter cell gets all the DNA.; Source: Whitehead Institute for Biomedical Research