Understanding the dynamic cellular behaviours driving morphogenesis and regeneration is a long-standing challenge in biology. Live imaging, together with genetically encoded reporters, may provide the necessary tool to address this issue, permitting the in vivo monitoring of the spatial and temporal expression dynamics of a gene of interest during a variety of developmental processes. Canonical Wnt/β-catenin signalling controls a plethora of cellular activities during development, regeneration and adulthood throughout the animal kingdom. Several reporters have been produced in animal models to reveal sites of active Wnt signalling. In order to monitor in vivo Wnt/β-catenin signalling activity in the freshwater polyp Hydra vulgaris, we generated a β-cat-eGFP transgenic Hydra, in which eGFP is driven by the Hydra β-catenin promoter. We characterized the expression dynamics during budding, regeneration and chemical activation of the Wnt/β-cat signalling pathway using light sheet fluorescence microscopy. Live imaging of the β-cat-eGFP lines recapitulated the previously reported endogenous expression pattern of β-catenin and revealed the dynamic appearance of novel sites of Wnt/β-catenin signalling, that earlier evaded detection by mean of in situ hybridization. By combining the Wnt activity read-out efficiency of the β-catenin promoter with advanced imaging, we have created a novel model system to monitor in real time the activity of Hydra β-cat regulatory sequences in vivo, and open the path to reveal β-catenin modulation in many other physiological contexts
The small, freshwater hydrozoan animal Hydra appears to be truly immortal.
In ancient Greek myth, the Hydra was a multi-headed monster that grew two more heads for every one that it lost. As it turns out, the real-life animal named after this mythical beast may be even more tenacious.
A new study finds that hydra — spindly, freshwater polyps — can live seemingly forever, without aging.
Unlike most multicellular species, hydra don't show any signs of deteriorating with age, according to the new research, published Dec. 7 in the journal Proceedings of the National Academy of Sciences
Over eight years, the researchers found no evidence of senescence in their coddled hydra. Death rates held constant at one per 167 hydras per year, no matter their age. (The "oldest" animals studied were clones of hydras that had been around for 41 years — though individuals were only studied for eight years, some were biologically older because they were genetic clones.) Likewise, fertility remained constant for 80 percent of the individual hydras over time. The other 20 percent fluctuated up and down, likely because of laboratory conditions.
"I do believe that an individual hydra can live forever under the right circumstances," Martinez said.
In the wild, disease, predators and water contamination kill off hydras before they can achieve immortality. But the findings fly in the face of old models that assumed that all animals must decline with age, Martinez said. And that means that studying hydra could help scientists unravel the mystery of why most animals do age.
"I’m hoping this work helps sparks another scientist to take a deeper look at immortality," Martinez said, "perhaps in some other organism that helps bring more light to the mysteries of aging.”
The actual paper is here.
Senescence, the increase in mortality and decline in fertility with age after maturity, was thought to be inevitable for all multicellular species capable of repeated breeding. Recent theoretical advances and compilations of data suggest that mortality and fertility trajectories can go up or down, or remain constant with age, but the data are scanty and problematic. Here, we present compelling evidence for constant age-specific death and reproduction rates in Hydra, a basal metazoan, in a set of experiments comprising more than 3.9 million days of observations of individual Hydra. Our data show that 2,256 Hydra from two closely related species in two laboratories in 12 cohorts, with cohort age ranging from 0 to more than 41 y, have extremely low, constant rates of mortality. Fertility rates for Hydra did not systematically decline with advancing age. This falsifies the universality of the theories of the evolution of aging that posit that all species deteriorate with age after maturity. The nonsenescent life history of Hydra implies levels of maintenance and repair that are sufficient to prevent the accumulation of damage for at least decades after maturity, far longer than the short life expectancy of Hydra in the wild. A high proportion of stem cells, constant and rapid cell turnover, few cell types, a simple body plan, and the fact that the germ line is not segregated from the soma are characteristics of Hydra that may make nonsenescence feasible. Nonsenescence may be optimal because lifetime reproduction may be enhanced more by extending adult life spans than by increasing daily fertility.
Obviously, the mechanisms of immortality (or as scientists would call it “nonsenescence”) for Hydra are not directly applicable to interventions designed to retard the human aging process. However, the benefit of basic science research such as this is that it can lead to novel, sometimes, unexpected, directions, can promote work in other species, and can lead to innovative discovered that may, eventually, directly or indirectly affect human health. So, no, humans cannot have “a high proportion of stem cells, constant and rapid cell turnover, few cell types, a simple body plan, and…[a] germ line is not segregated from the soma;” nevertheless, further investigation into the Hydra and other relevant mechanism may someday help unlock the key to inhibition of senescence in humans, leading to longer and healthier lives.
