Members of the Extavour Lab at Harvard work on embryonic development. This page highlights some of their work, with some amazing images.
The Grownup Bug
Copyright David Govoni
Most people in the northeastern U.S. have seen milkweed bugs. Their bright colors warn would-be predators that they don't taste good. That's because they feed on milkweed, just as do caterpillars of monarch butterflies, which are also distasteful.
During development, each cell in the embryo must adopt its proper fate in order to give rise to all of the structures of the adult. These images, representing 6 hours of development of the milkweed bug (Oncopeltus fasciatus), show the birth of one of the most important types of cells in the body: the germ cells, which will ultimately give rise to sperm or egg. In this species, germ cell formation was first described in 1949 by Ferdinand W. Butt - his original drawings are reproduced along the top row. Recent studies in the Extavour lab have used a molecular marker for these cells (a gene called vasa, shown in purple in the bottom row) to follow this process in more detail. The light blue dots in the bottom row represent the cell nuclei. The numbers along the bottom correspond to hours after egg-laying. [Image and text by Ben Ewen-Campen of the Extavour lab at Harvard.]
These images depict the formation of the germ cells (which ultimately produce sperm and eggs) during the embryonic development of a cricket (Gryllus bimaculatus). The top row of drawings represents progressive stages of development. For each stage, a molecular stain for germ cells (a gene called piwi,indicated with arrowheads) is shown below, revealing the birth of these cells as the embryo develops. At the right, a drawing from the original 1893 description of these cells by William Morton Wheeler is shown next an image of a molecular marker for germ cells, highlighting the incredible accuracy of these original drawings. [Image and text by Ben Ewen-Campen of the Extavour lab at Harvard.]
It Takes Time ...
A newly laid insect egg is simply one large cell. However, this single cell very quickly begins to divide, ultimately giving rise to all of the cells that will eventually form the adult. This image shows, from top to bottom, the earliest stages of development for the milkweed bug Oncopeltus fasciatus. Each white dot represents a single cell nucleus. [Image and text by Ben Ewen-Campen of the Extavour Lab at Harvard.]
This image shows, from left to right, the progression of embryonic development in the milkweed bug Oncopeltus fasciatus. One can easily see the development of the characteristic six legs possessed by all insects ad they begin to protrude from the thorax of the embryo. These embryos were imaged using a dye that labels the DNA of each cell. [Image and text by Ben Ewen-Campen of the Extavour Lab at Harvard.]