The objective of the BRIC payload is to investigate the effects of space flight on small arthropod animal and plant specimens. The BRIC hardware has a variety of configurations, depending on the scientific requirements of each flight. The canisters contain two aluminum chambers that hold the specimen support hardware. The canisters and freezer are stowed in a standard middeck locker with at least one-half inch of Pyrell foam on each side. No orbiter power is required for any experiment configuration.

STS-93 will use the Block II configuration, which consists of two BRIC-60 (82-mm diameter) canisters, one pair of cryogenic gloves, and one gaseous nitrogen freezer (GN2) in a single middeck locker. The flight crew will be available at regular intervals to monitor and control payload/experiment operations. The Block II configuration also requires a crew member to don a pair of insulating gloves, remove a canister from the locker, and replace it in the GN2 freezer. There will be two experiments on STS-93, BRIC-11 and BRIC-12.

BRIC-11: Investigations of Global Changes in Gene Expression in Response to Gravity

Growth of plants in space is essential for long-term presence of humans in space. Plants, in addition to producing food, can replenish oxygen and remove carbon dioxide and other nitrogenous wastes. Hence, plants play a critical role in developing a self-sustained, regenerative life support system in space. Plants on Earth are constantly influenced by gravity, which controls several aspects of their growth and development. For example, the roots grow toward gravity (positive gravitropism) and the shoots grow away from gravity (negative gravitropism). The effect of reduced gravity on plants is poorly understood. Furthermore, the mechanisms by which plants sense and respond to gravity remain largely unknown. In order to grow plants in space, it is essential to understand the effects of microgravity on growth and development, especially at the molecular and cell biological level. Recent genetic studies of mutants with no response or an altered response to gravity indicate that the perception and transduction of gravity signals involve specific gene products.

The objective of BRIC-11 is to investigate gravity-regulated gene expression by using Earth- and space-grown seedlings. These studies represent a first step toward understanding the effects of gravity on gene regulation. Arabidopsis was chosen because it offers a number of advantages for molecular genetic studies. It also allows the investigator to analyze the expression of thousands of genes simultaneously by using a DNA "chip" technology.

The experiment involves growing seedlings in microgravity on the space shuttle middeck and on Earth, and then analyzing them to determine the effects of gravity on gene expression. BRIC hardware will be used to germinate Arabidopsis seeds in the dark under sterile conditions. Each BRIC module will accommodate twelve 65-mm Petri dishes, each with about 10,000 seeds. Four such canisters will be used for germinating the seeds in the flight, and four canisters will be used as ground controls in the orbiter environment simulator at Kennedy Space Center. About four days into germination, a crew member will freeze two of the flight canisters in the gaseous nitrogen freezer and the ground crew will also freeze two of the ground canisters.

The Earth- and space-grown seedlings will be then analyzed through microarray-based monitoring for global changes in the expression of thousands of Arabidopsis genes. The RNA from the Earth- and space-grown samples will be used to synthesize fluorescent-labeled cDNAs and hybridize them to a bank of about 10,000 Arabidopsis cDNAs on DNA "chips." These chips will then be scanned to determine qualitative and quantitative changes in gene expression in response to microgravity. The microarray analysis will be performed in collaboration with the Monsanto Company, St. Louis, Mo.

The genes whose expression is affected by gravity and/or microgravity will be identified and characterized to understand their role in gravity signal transduction. In the long run, it may be possible to engineer such genes for regulation by controllable factors other than gravity.

BRIC-12: Early Development of Fern Gametophytes in
Microgravity

The physiological responses of animals and plants to gravity are complex, involving the interaction of many different cell types. In order to simplify their study of the cellular basis of gravity sensing and response, biologists have recently begun studying gravity effects in single cells, where all the actions and reactions occur in one place.

One such model system for gravitational biology studies is the germinating spore cell of the fern Ceratopteris richardii. These spore cells appear to be insensitive to gravity as long as they are kept in darkness; but once induced to germinate by light, they show a characteristic gravity response. Each single-celled spore has a nucleus in the center. During the first 30 hours or so after light activation, the nucleus moves along a kind of random path restricted to a region near the cell center. Then, under the influence of 1 g on Earth, the nucleus abruptly migrates downward along a relatively straight path to the lower part of the cell. There, about 18 hours later, it divides, producing two cells--a smaller one that develops into a rootlike rhizoid and a larger one that develops into the leafy part of the plant, the prothallus. The gravity-directed migration of the nucleus exactly predicts the direction in which the rhizoid will emerge and grow after the spore germinates. In addition, the unequal cell division that results from the asymmetric positioning of the nucleus after its downward migration may be a prerequisite for the two different cell types to form (rhizoid and prothallus). Thus, within a limited period following light activation of the spores, gravity determines the polarity of each spore cell--which end will have the rhizoid and which end will have the prothallus.

On STS-93, scientists will take advantage of this simple system to study gravity effects at the most basic level. The shuttle facilities, which include the Space Tissue Loss (STL) B hardware developed at the Walter Reed Army Institute of Research, will allow them to investigate two sets of questions. One set of experiments will use the STL-B on-board video microscopy system to find out whether, in the absence of a strong gravity signal, the nucleus will migrate randomly or not at all and, if not, whether the failure to migrate will prevent normal development of the rhizoid and prothallus. Another question to be answered concerns the "random walk" of the nucleus about the center of the cell during the first 30 hours after the spore cell is activated. This movement (as well as the later downward movement of the nucleus) is driven by molecular motors, which may be "turned on" by the tension and compression forces created in the cell by gravity. Scientists want to see whether the molecular motors will operate normally in microgravity or will fail to turn on, leaving the nucleus motionless in the center of the cell. This information would give us an insight into how these molecular motors, which are common to all plant and animal cells, can be controlled.

A second set of BRIC-12 experiments will investigate whether gravity is turning on or off any specific genes during the period in which it is setting the polarity of the cell. Scientists already know that hundreds of genes are turned on (transcribed into messenger RNA) or turned off during this period, and they believe that most are programmed do so at this time whether gravity is present or not. It is possible, though, that the expression of some of these genes may require the tension and compression forces caused by gravity in the cell. To help scientists find the answer, astronauts on the STS-93 mission will freeze light-activated spores at four different time points--three during the period when gravity fixes the cell polarity on Earth and one after this period should be over (45 hours after the spores are light-activated in orbit). After the shuttle lands, the pattern of gene expression in these space-flown spores at the selected four time points will be compared to the pattern at the same four time points in spores on Earth.

The germinating spores represent a relatively uniform population of cells that have all been induced to start their development at the same time (by a light signal). Because of the cells' uniformity and the relative synchrony of their development, there is a unique opportunity to resolve subtle differences in the pattern of gene expression between cells growing in microgravity and cells on Earth. If the experiment demonstrates that any genes are regulated by gravity, it is reasonable to postulate are they are instrumental to the cells' ability to sense or respond to gravity.