( led cells is pocked with epidermal grow...)Study finds how organs monitor themselves during early development

led cells is pocked with epidermal growth factor (EGF) receptors, docking ports for signaling molecules. Dr. Gilboa found that primordial germ cells produce a protein called Spitz. This protein is shuttled out of the germ cells and binds to the EGF receptors on the intermingled cells. That docking activates the intermingled cells and is important for their survival.

Spitz acts a bit like a volume control dial. Once it docks onto the EGF receptors, the intermingled cells send a signal to the primordial germ cells to stop growing. Increased EGF signaling in intermingled cells leads to reduced numbers of germ cells. "But if there is very little Spitz, that reduces the number of intermingled cells and thus the number of germ cells will rise," Dr. Gilboa says.

This feedback loop acts as a sensor that ensures there are sufficient primordial germ cells in the ovary at the end of larval development. The level of EGF signaling is used to keep the amount of germ cells just right, so that there are not too few and not too many of them.

The scientists had a hunch that PGCs and the somatic cells communicate. "Dr. Gilboa's experiments clearly show there is a feedback mechanism, whereby the PGCs send a signal to the somatic cells to keep them alive and the somatic cells send a signal back to the germ cells, keeping them in check," says Dr. Lehmann.

The experiments

Using a tool called the Gal4/UAS system, the researchers overexpressed genes of interest. They honed in on a set of signaling molecules in order to interfere or augment particular signaling pathways. They looked at how the interaction between the two types of cells in the ovary plays out. "Somatic cells and primordial germ cells develop in close contact with each other," says Dr. Gilboa. "Different cell types speak to each other, control each other and function together when an organ grows," she says. In the human ovary for example, a follicle ripens every month. Wi
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Source:New York University Medical Center and School of Medicine

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