Caption
Macrophages in the peritoneum of mice deficient in the MafB transcription factor, exhibiting significant morphological modifications. These cells were cultivated for five minutes in a medium containing M-CSF (a cytokine), and were fixed and coloured using a phalloidin combined with TRITC (in red) to reveal the actin organisation. The MafB-deficient macrophages have prominent protuberances and are often branched. It was long thought that production of the various specialist cells from stem cells in the blood occurred randomly. However, scientists have discovered that in the case of myeloid cells (stem cells that evolve into leukocytes, of which macrophages are one form), the decisive factor is the combined action of two different proteins, one located inside the cell (a MafB transcription factor), the other outside it (the cytokine M-CSF). Transcription factors activate or inhibit genes, thereby determining a cell's identity.
