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UGA study reveals new role for germ cells

By Cat Holmes
University of Georgia

Anyone who's ever watched an ant farm or beehive knows that some insects are social creatures.

In fact, “a lot of insects are social,” said University of Georgia entomologist Michael Strand. “They've evolved societies in which different individuals have different functions. They've also evolved completely different body shapes and behaviors.”

That means that, despite the fact that they begin with essentially the same genetic material, some individuals develop into queens that reproduce while others develop into soldiers or workers that defend and maintain the colony.

This ability for something with the same genetic material to look and behave differently is called phenotypic plasticity. Examples of phenotypic plasticity are also known to occur in many other animals, yet scientists do not understand very well how this occurs at a cellular or molecular level.

However, recent UGA studies have shed new light on this question by finding that caste formation in a unique type of wasp is strongly influenced by whether individuals possess a specialized type of cells called germ cells.

The study, published in the July 6 issue of the Proceedings of the National Academy of Sciences, also reveals a previously unknown role for germ cells in development according to Strand, one of the authors of the study.

Doubl[ing] agents

The wasp used in the study is “a particularly elegant model [for this research] because its eggs develop clonally to produce genetically identical offspring,” Strand said.

So, in much the same way human identical twins are formed from one egg, each egg laid by this wasp produces roughly 2,000 identical sibling wasps.

Yet despite each wasp in a colony being genetically identical, individuals develop into two distinctly different castes: soldiers and queens.

The question addressed in the UGA study was what determines at a cellular and molecular level whether a given offspring develops into a queen or soldier. The answer is germ cells.

Germ cells

Germs cells are determined very early in the development of mammals as well as insects.

“Germs cells are formed very early in the embryogenesis of wasps, long before any individuals develop into a soldier or queen,” Strand said.

In humans as well as insects, the main function of germ cells is to give rise to reproductive cells (sperm and eggs) that will produce offspring in the next generation. Germ cells usually remain dormant in humans and other animals until they reach maturity and are able to reproduce.

In the wasps used in this study, however, germ cells were parceled out to some embryos and not others. The embryos that inherited germ cells went on to develop into queens, while embryos without germ cells developed into soldiers.

“These results indicate that germ cells are not only important for gamete formation but also influence how individuals look and behave,” Strand said.

The next step for the UGA research team will be to uncover how germ cells modulate the activity of other cells and genes that regulate growth, development and behavior.

The full text of this study can be found at the PNAS Web site: www.pnas.org/cgi/content/abract/101/27/10095

(Cat Holmes is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)

(Cat Holmes was a science writer with the University of Georgia College of Agricultural and Environmental Sciences.)

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