Nitric oxide-induced suspended animation promotes survival during hypoxia

Oxygen plays a key role in energy metabolism. However, there are organisms that survive severe shortfalls in oxygen. Drosophila embryos rapidly arrest development upon severe hypoxia and recover upon restoration of oxygen, even days later. Stabilization of the normally unstable engrailed RNA and protein preserved the localized striped pattern of this embryonic patterning gene during 3 days in hypoxia. Severe hypoxia blocked expression of a heat-shock-inducible lacZ transgene. Cyanide, a metabolic poison, did not immediately block gene expression or turnover, arguing against a passive response to energy limitation. In contrast, nitric oxide, a putative hypoxia signal, induced a reversible arrest of development, gene expression and turnover. Reciprocally, a nitric oxide scavenger allowed continued gene expression and turnover during hypoxia, but it reduced hypoxia tolerance. We suggest that hypoxia-induced stasis preserves the status quo of embryonic processes and promotes survival. Our data implicate nitric oxide as a mediator of this response and provide a system in which to investigate its action.     

Dephosphorylation of cell cycle-regulated proteins correlates with anoxia-induced suspended animation in Caenorhabditis elegans

Some metazoans have evolved the capacity to survive severe oxygen deprivation. The nematode, Caenorhabditis elegans, exposed to anoxia (0 kPa, 0% O(2)) enters into a recoverable state of suspended animation during all stages of the life cycle. That is, all microscopically observable movement ceases including cell division, developmental progression, feeding, and motility. To understand suspended animation, we compared oxygen-deprived embryos to nontreated embryos in both wild-type and hif-1 mutants. We found that hif-1 mutants survive anoxia, suggesting that the mechanisms for anoxia survival are different from those required for hypoxia. Examination of wild-type embryos exposed to anoxia show that blastomeres arrest in interphase, prophase, metaphase, and telophase but not anaphase. Analysis of the energetic state of anoxic embryos indicated a reversible depression in the ATP to ADP ratio. Given that a decrease in ATP concentrations likely affects a variety of cellular processes, including signal transduction, we compared the phosphorylation state of several proteins in anoxic embryos and normoxic embryos. We found that the phosphorylation state of histone H3 and cell cycle-regulated proteins recognized by the MPM-2 antibody were not detectable in anoxic embryos. Thus, dephosphorylation of specific proteins correlate with the establishment and/or maintenance of a state of anoxia-induced suspended animation.     

Type 2 diabetic mice enter a state of spontaneous hibernation-like suspended animation following accumulation of uric acid

Hibernation is an example of extreme hypometabolic behavior. How mammals achieve such a state of suspended animation remains unclear. Here we show that several strains of type 2 diabetic mice spontaneously enter into hibernation-like suspended animation (HLSA) in cold temperatures. Nondiabetic mice injected with ATP mimic the severe hypothermia analogous to that observed in diabetic mice. We identified that uric acid, an ATP metabolite, is a key molecular in the entry of HLSA. Uric acid binds to the Na⁺ binding pocket of the Na⁺/H⁺ exchanger protein and inhibits its activity, acidifying the cytoplasm and triggering a drop in metabolic rate. The suppression of uric acid biosynthesis blocks the occurrence of HLSA, and hyperuricemic mice induced by treatment with an uricase inhibitor can spontaneously enter into HLSA similar to that observed in type 2 diabetic mice. In rats and dogs, injection of ATP induces a reversible state of HLSA similar to that seen in mice. However, ATP injection fails to induce HLSA in pigs due to the lack of their ability to accumulate uric acid. Our results raise the possibility that nonhibernating mammals could spontaneously undergo HLSA upon accumulation of ATP metabolite, uric acid.     

Renin disappearance rate in puppies

The disappearance rate of endogenous renin from the circulating blood after bilateral nephrectomy was studied in 4 puppies aged 16-21 days. Mean half-times of the fast and slow component of the disappearance curves of renin were 9.15 min +/- 0.87 (SD) and 84.0 min +/- 16.8 (SD), respectively. These values are not different from the values reported for adult dogs in the literature. The metabolic degradation of renin is not different between young and adult dogs and does not contribute to the elevated plasma renin activity in the puppy.     

Growth in revascularized bone grafts in young puppies.

The results of microvascular transfers of growing ulnas in puppy forelegs have been studied. These transfers were carried out both heterotopically and orthotopically. The growth in the revascularized bone grafts has been compared to that in heterotopic, nonvascularized ulna transfers and to normal ulnar growth. The growth in the vascularized bone grafts was significantly greater than in the nonvascularized grafts, but significantly less than in normal ulnar growth. A metaphyseal contribution to the blood supply of the growing portion of long bones is suggested.     

Workshop on molecular animation

From February 25 to 26, 2010, in San Francisco, the Resource for Biocomputing, Visualization, and Informatics (RBVI) and the National Center for Macromolecular Imaging (NCMI) hosted a molecular animation workshop for 21 structural biologists, molecular animators, and creators of molecular visualization software. Molecular animation aims to visualize scientific understanding of biomolecular processes and structures. The primary goal of the workshop was to identify the necessary tools for producing high-quality molecular animations, understanding complex molecular and cellular structures, creating publication supplementary materials and conference presentations, and teaching science to students and the public. Another use of molecular animation emerged in the workshop: helping to focus scientific inquiry about the motions of molecules and enhancing informal communication within and between laboratories.     

Crafting a career in molecular animation

When I first set out on a path to becoming a cell biologist, I would have never imagined that it would lead to a career in molecular animation. I had always thought I would follow a more traditional route. What happened? In this essay, I will describe the experiences that led to my decision to forge a career as an academic molecular animator, and how my work has evolved over the years. I will also provide some resources and advice for those who may be considering following a similar route.