What Hydra can teach us about chemical ecology how a simple, soft organism survives in a hostile aqueous environment

As scientists it is our duty to fight against obscurantism and loss of rational thinking if we want politicians and citizens to freely make the most intelligent choices for the future generations. With that aim, the scientific education and training of young students is an obvious and urgent necessity. We claim here that Hydra provides a highly versatile but cheap model organism to study biology at any age. Teachers of biology have the unenviable task of motivating young people, who with many other motivations that are quite valid, nevertheless must be guided along a path congruent with a 'syllabus' or a 'curriculum' . The biology of Hydra spans the history of biology as an experimental science from Trembley's first manipulations designed to determine if the green polyp he found was plant or animal to the dissection of the molecular cascades underpinning, regeneration, wound healing, stemness, aging and cancer. It is described here in terms designed to elicit its wider use in classrooms. Simple lessons are outlined in sufficient detail for beginners to enter the world of 'Hydra biology' . Protocols start with the simplest observations to experiments that have been pretested with students in the USA and in Europe. The lessons are practical and can be used to bring 'life' , but also rational thinking into the study of life for the teachers of students from elementary school through early university. KEY WORDS: ecology, evolution and developmental biology education, science policy, authentic assessment, inquiry-based learning, student portfolio How the authors met the Hydra model systemIn the USA, Patricia Bossert taught Biology on Long Island for 35 years, making Hydra her accomplice for many of those years. Initially trained as a classroom teacher, she decided to go back to academic studies after 15 years of teaching and, with the support of her family (husband, mother and two young sons), she performed a PhD in Ecology and Evolution in the laboratory of Lawrence B. Slobodkin at Stony Brook University. During this period she gained a deeper appreciation of the amazing potential of Hydra to address ecological and evolutionary issues experimentally (Bossert and Dunn, 1986;Slobodkin and Bossert, 1991) as well as its outstanding value for stimulating the curiosity of even the youngest students while also providing a challenging model for older students to perform authentic investigations. Thanks to her original approach that combined ecology and evolution with molecular strategies, several of them obtained prizes in national and international scientific competitions. This led her to be recruited by Stony Brook University as an expert for mentoring teachers to do research using Hydra; focusing on students from families of lower socio-economic Int. J. Dev. Biol. 56: 637-652 (2012) doi: 10.1387/ijdb.123523pb www.intjdevbiol.com *Address correspondence to: Brigitte Galliot. Department of Genetics and Evolution, University of Geneva, Switzerland. e-mail: brigitte.galliot@unige.ch Abbreviations used in this pa...

Section: Ecology and Evolutionmentioning

confidence: 99%

How to use Hydra as a model system to teach biology in the classroom

Bossert¹,

Galliot²

2012

“…This process is accompanied by the release of soluble neurotoxins into the tissue of a prey organism (Ozbek et al, 2009). The secretion of molecules with toxic function might therefore have been at the base of nematocyst evolution (see in this issue Rachamim and Sher, 2012). …”

Section: Introductionmentioning

confidence: 99%

The Nematocyst: a molecular map of the Cnidarian stinging organelle

Beckmann¹,

Özbek²

2012

108

Nematocysts or cnidocysts represent the common feature of all cnidarians. They are large organelles produced from the Golgi apparatus as a secretory product within a specialized cell, the nematocyte or cnidocyte. Nematocysts are predominantly used for prey capture and defense, but also for locomotion. In spite of large variations in size and morphology, nematocysts share a common build comprising a cylindrical capsule to which a long hollow thread is attached. The thread is inverted and coiled within the capsule and may be armed with spines in some nematocyst types. During the discharge of nematocysts following a chemical or mechanical stimulus, the thread is expelled from within the capsule matrix in a harpoon-like fashion. This process constitutes one of the fastest in biology and is accompanied by a release of toxins that are potentially harmful also for humans. The long history of research on Hydra as a model organism has been accompanied by the cellular, mechanistic and morphological analysis of its nematocyst repertoire. Although representing one of the most complex organelles of the animal kingdom, the evolutionary origin and molecular map of the nematocyst has remained largely unknown. Recent efforts in unraveling the molecular content of this fascinating organelle have revealed intriguing parallels to the extracellular matrix.

“…Firstly, and despite its apparent (Palm, 1996;Tannreuther, 1908;Hyman, 1928;Otto and Campbell, 1977a;Bottger and Hassel, 2012); the discovery of Hydra regeneration and its scientific impact (Trembley, 1744;Lenhoff and Lenhoff, 1986;Gierer, 2012;Ratcliff, 2012); digestion (Greenwood, 1888;Chera et al, 2006;Sher et al, 2008;Rachamim and Sher, 2012); sex determination, sex reversal and embryogenesis (Kleinenberg, 1872;Brauer, 1891;Hertwig, 1906;Tannreuther, 1908;Goetsch, 1922;Hyman, 1928;Loomis, 1954;Zihler, 1972;Sugiyama and Fugisawa, 1977a;Martin et al, 1997;Nishimiya-Fujisawa and Kobayashi, 2012); tissue induction and organizing activity (Browne, 1909;Yao, 1945;MacWilliams, 1983a,b;Lenhoff, 1991;Broun and Bode, 2002;Bode, 2012); regeneration from reaggregated cells (Child, 1928;Noda, 1971;Murate et al, 1997;Technau et al, 2000); the paradigmatic value of i-cell free (i.e. epithelial) Hydra Campbell, 1976;Sugiyama and Fujisawa, 1978a); genetic analyses of developmental mechanisms (Sugiyama and Fujisawa, 1977a, b;Marcum and Campbell, 1978;Sugiyama and Fujisawa, 1978a, b;Shimizu, 2012); modeling of patterning (Turing, 1952;...…”

Section: Setting Up the Boundaries In Adult And Developing Hydramentioning

confidence: 99%

“…In this issue Tamar Rachamim and Daniel Sher discuss the impact of Hydra on its environment, first considering the venom they produce in their nematocysts, but also taking into account all the bioactive compounds they release (Rachamim and Sher, 2012). The venom is supposed to be a complex mix up of toxic as well as non-toxic molecules that all together are responsible for the toxicity of a given venom.…”

Section: The Chemical Arsenal and The Chemical Landscape Of Hydramentioning

confidence: 99%

Hydra, a fruitful model system for 270 years

Galliot¹

2012

152

113

The discovery of Hydra regeneration by Abraham Trembley in 1744 promoted much scientific curiosity thanks to his clever design of experimental strategies away from the natural environment. Since then, this little freshwater cnidarian polyp flourished as a potent and fruitful model system. Here, we review some general biological questions that benefitted from Hydra research, such as the nature of embryogenesis, neurogenesis, induction by organizers, sex reversal, symbiosis, aging, feeding behavior, light regulation, multipotency of somatic stem cells, temperature-induced cell death, neuronal transdifferentiation, to cite only a few. To understand how phenotypes arise, theoricists also chose Hydra to model patterning and morphogenetic events, providing helpful concepts such as reaction-diffusion, positional information, and autocatalysis combined with lateral inhibition. Indeed, throughout these past 270 years, scientists used transplantation and grafting experiments, together with tissue, cell and molecular labelings, as well as biochemical procedures, in order to establish the solid foundations of cell and developmental biology. Nowadays, thanks to transgenic, genomic and proteomic tools, Hydra remains a promising model for these fields, but also for addressing novel questions such as evolutionary mechanisms, maintenance of dynamic homeostasis, regulation of stemness, functions of autophagy, cell death, stress response, innate immunity, bioactive compounds in ecosystems, ecotoxicant sensing and science communication. KEY WORDS: historical perspective, transplantation, modeling, developmental reactivation, Hydra regeneration, multipotency, stemness, symbiosis, environmentThe heuristic value of the Hydra model systemIn the early 18th century the word biology was not yet in use but the nature of living organisms and their evolutionary relationships was the focus of interest for philosophers and naturalists, as evidenced by their pioneering efforts to develop new tools such as microscopes that would allow finer observation (Palm, 1996). The microscopic observation of organisms taken in the field undoubtedly helped develop morphological keys to sort between the animal and vegetal kingdoms and to group them into phyla (Linnaeus, 1758). Among the ambiguous species that could not be easily classified were the seawater corals that looked like flowers (Watson, 1753;McConnell, 1990) and the freshwater Hydra polyp that was considered to exhibit both animal and vegetal features. For example, Hydra easily reproduces asexually through budding, a trait frequently assigned to plants or fungi.Having observed some Hydra polyps in a pond, Abraham Trembley (1710-1784) (who had received a PhD in mathematics from the University of Geneva (Switzerland) and was now educating the children of the Count of Bentick in the Netherlands) decided Int. J. Dev. Biol. 56: 411-423 (2012) to solve that problem by testing their capacity to regenerate, assuming that if Hydra regenerates, then it should be considered a plant, but if it does...