HAND, S.C.: Induction of Quiescence and Diapause During Life Cycles of Aquatic Invertebrates: Mechanisms and Implications.

With one exception, all major animal phyla contain species that display dormancy at certain points in their life cycles, a feature that affords tolerance to harsh or ephemeral habitats. Diapause is an obligate, developmentally-programmed form of dormancy that precedes the onset of environmental insult. Under conditions that normally promote activity and development, calorimetric/respirometric studies have revealed that major metabolic depressions accompany entry into diapause in aquatic invertebrates like sponge gemmules and brine shrimp embryos. This depression occurs rather slowly over a period of several days. Release from diapause can be promoted by various environmental ques and artificial chemical factors. Metabolism increases 500-fold or more. In contrast to diapause, quiescence is a type of dormancy directly induced by an environmental stress like oxygen deprivation. Data from many aquatic species show that survivorship under anoxia is proportional to the degree of metabolic depression. There is a suite of molecular mechanisms underlying these metabolic and developmental patterns. In the nucleo-cytoplasmic and mitochondrial compartments, gene expression is severely depressed at transcriptional and translational levels, as assessed by nuclear run-on and cell-free translation assays. Direct measurements of protein and mRNA half-lives indicate that macromolecular turnover is greatly reduced. Stress proteins of low molecular mass undergo intracellular translocation to the nucleus. These and other molecular changes associated with natural states that border on suspended animation provide clues as to how other cells might be placed into stasis. (NSF Grant IBN-9723746)