Control of compartment size by an EGF ligand from neighboring cells.
Insect bodies are subdivided into anterior (A) and posterior (P) compartments: cohesive fields of distinct cell lineage and cell affinity . Like organs in many animal species, compartments can develop to normal sizes despite considerable variation in cell division . This implies that overall compartment dimensions are subject to genetic control, but the mechanisms are unknown. Here, studying Drosophila's embryonic segments, I show that P compartment dimensions depend on epidermal growth factor receptor (EGFR) signaling. I suggest the primary activating ligand is Spitz, emanating from neighboring A compartment cells. Spi/EGFR activity stimulates P compartment cell enlargement and survival, but evidence is presented that Spitz is secreted in limited amounts, so that increasing the number of cells within the P compartment causes the per-cell Spitz level to drop. This leads to compensatory apoptosis and cell-size reductions that preserve compartment dimensions. Conversely, I propose that lowering P compartment cell numbers enhances per-cell Spitz availability; this increases cell survival and cell size, again safeguarding compartment size. The results argue that the gauging of P compartment size is due, at least in part, to cells surviving and growing according to Spi availability. These data offer mechanistic insight into how diffusible molecules control organ size.
Parker
Joseph
J
Division of Cell Biology, Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom. jp2488@columbia.edu
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D019521:Body Patterning / Q000502:physiology*; D001837:Body Weights and Measures; D004330:Drosophila / Q000196:embryology*; D029721:Drosophila Proteins / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000502:physiology; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism*; D005434:Flow Cytometry; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D008024:Ligands; D008565:Membrane Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
D029721:Drosophila Proteins; D008024:Ligands; D008565:Membrane Proteins; C076026:spi protein, Drosophila; D004815:Epidermal Growth Factor; D066246:ErbB Receptors