A comparison of apparent mRNA half-life using kinetic labeling techniques vs decay following administration of transcriptional inhibitors.

Several different techniques were used to determine the apparent half-lives of immunoglobulin gamma 2b heavy chain and kappa light chain mRNA's in mouse myeloma 4T001 and a mutant derived from 4T001, i.e., mutant I17. The mutant I17 Ig heavy chain mRNA lacks CH1 and has fused CH2 and CH3 domains resulting in a truncated protein. By all four techniques the Ig heavy chain mRNA from mutant I17 displays a half-life that is approximately 70% the half-life of Ig mRNA in 4T001 cells. However, the absolute values of apparent half-life varied by greater than twofold for both lines among several of the techniques employed. The half-life of Ig gamma 2b mRNA in 4T001 cells was found to be 6.4 h by measuring decay following administration of the adenosine analog DRB to block new mRNA synthesis and 5.7 hr by measuring accumulation in an approach to steady-state labeling protocol. In contrast, the observed Ig mRNA half-lives determined by measuring decay following administration of actinomycin D to block new mRNA synthesis, or in a pulse-chase analysis were 2.9 and 3.8 h, respectively. The apparent half-life for Ig kappa light chain mRNA was the same in the 4T001 and I17 lines using any one technique but the value varied depending on the technique from a high value of 5.9 h following DRB to a low value of 2.4 h with actinomycin decay. Approach to steady-state is theoretically the most accurate method to measure mRNA half-life when that value is less than the doubling time of the cells. Pulse-chase analyses are accurate for measuring mRNA half-life when that value is longer than the effective chase period. Measuring preformed message decay following administration of drugs to block new mRNA synthesis is adaptable over a range of half-lives, but the cells must be shown to retain correct RNA metabolism over the time frame of the experiment. Determining a correct half-life for a particular mRNA may not be feasible using only one method and may, in fact, require several different approaches until a consensus value emerges.     

Radio-tracking rafts of giant kelp: local production and regional transport

Forests of giant kelp Macrocystis pyrifera (L.) C.A. Agardh are among the most productive communities on earth. Much of the annual production of kelp in central California is exported from the forests as large floating rafts. Since these rafts may float for days and perhaps weeks, they are capable of being transported long distances but the fate of this material remains largely unknown. Naturally occurring and artificially created M. pyrifera rafts were tagged with radiotransmitters near their point of origin along the shores of the Monterey Peninsula in Monterey County, California, on each of four seasonal tracking experiments. Their movements were followed by aircraft for 5–7 days and the transmitters were then recovered. 39 tagged kelp rafts were recovered within Monterey Bay and one transmitter was lost at sea. Most were recovered ashore. While surface currents in Monterey Bay flow to the north much of the year, the kelp rafts drifted before the prevailing northwest winds (i.e., to the southeast) in the spring, summer and autumn. Rafts tagged during the winter moved primarily toward the north. The regional deposition pattern of locally produced kelp rafts suggests that this material may be delivered to offshore benthic communities as large parcels which may play an important role as food and/or habitat.