ORIGIN OF THE MULTI-HEADED GREEN HYDRA (as told by Howard Lenhoff; Howard may be reached by e-mail at hmlenhof@uci.edu)
STRAIN OF THE GREEN HYDRA AND INDUCING OOGENESIS: When I was at the University of Miami in the 1960s, I found a green hydra in a tropical fish store and brought it to my laboratory, fed it, and grew a clone. It was a very unusual strain of hydra because I could control the onset of oogenesis with precision and predictability by controlling the number of brine shrimp I fed each animal individually. This technique was described in HYDRA: RESEARCH METHODS, pp. 75-76. Unfortunately this strain was lost while I was on an extended trip. Nonetheless, I feel it is a useful technique for inducing egg (and spermary) formation that will work once someone finds a related strain of green hydra. We assume that this strain came along with some tropical fish from South America.
HARVESTING MANY EMBRYOS: Actually, I was trying to get axenic hydra for my studies with reduced glutathione. I reasoned that if I had many thecated embryos, I could sterilize the cysts and then let the embryos "hatch" in a sterile environment. Then my plan was to feed the germ-free hydra on axenic brine shrimp, which were easy to prepare.
Thus, I took about 2,000 of the "Florida" green hydra, fed them on limited food, and soon noticed that I had hundreds of fertilized eggs and cysts. I collected the cysts to prepare them for sterilization, but got too busy and they started to hatch. Many were abnormal and never developed tentacles or buds. My selection technique was to feed the animals that developed tentacles and to observe them. Those that ate and budded normally, I discarded. A few, however captured the shrimp, ate and grew, but did not bud. I saved one of those animals. It had no algae, and would grow, and grow, and grow, but not bud.
I decided that in order to get more of this singular non-budding fat hydra, about 20X the dry weight of a normal budding green hydra, I would cut the animal in half, let the two pieces regenerate, feed the two pieces until they got larger, cut them in half, etc. until I had a large clone of these non-budding "mutant " hydra (LENHOFF, H.M. 1965 CELLULAR SEGREGATION AND HETEROCYTIC DOMINANCE IN HYDRA. SCIENCE 148: 1105-1107).
OBSERVING THE FORMATION OF THE MULTI-HEADED HYDRA: But that is where the fun began, because lo and behold, the top piece of the cut animal regenerated a second head, and eventually both pieces started to develop supernumerary tentacles that arranged themselves into groups with a mouth forming in the middle, and each "mouth" then developed into a long hydranth, and after about six weeks separated from the now branched stalk. A series of good photographs showing and describing all of these steps can be found in: LENHOFF, H.M., CHARLES RUTHERFORD, AND H.D. HEATH. 1969 ANOMALIES OF GROWTH AND FORM IN HYDRA: POLARITY, GRADIENTS, AND A NEOPLASIA ANALOG. NAT. CANCER INST. MONO. 31: 709-737.
I should add that all of my initial observations were made on animals free of algae. However, one day years later we observed a few green patches developing in a number of the animals. The "patches" began to spread, increase in size, and eventually all of the animals became green with the algal endosymbionts.
The rest is history. I understand that the mutant is still around, and I think that it has a lot to tell us yet. You just have to figure out a way to make it reveal its secrets. If you are interested, you should read the thesis work of Tricia Novak:
NOVAK, P. AND H. LENHOFF. 1981 ASEXUAL REPRODUCTION AND REGENERATION PROPERTIES OF A NONBUDDING MUTANT OF H. VIRIDIS. J. EXPTL. ZOOL. 217: 213-224.
NOVAK, P. AND H. LENHOFF. 1981 DEVELOPMENTAL PROPERTIES OF INDUCED BUDS FROM A NONBUDDING MUTANT OF H. VIRIDIS. J. EXPTL. ZOOL. 217: 225-238.
NOVAK, P. AND H. LENHOFF. 1981 INDUCTION OF BUDDING IN A NONBUDDING MUTANT OF H. VIRIDIS AS A RESULT OF GRAFTS USING WILD-TYPE TISSUE WITH VARYING COMPOSITIONS OF INTERSTITIAL AND NERVE CELLS. J. EXPTL. ZOOL. 217: 234-250.
This all seems like yesterday. Hope it is of value. I like this story because it taught me the value of serendipity. Often you can not always find what you are looking for, but with an open mind your experiments may tell you something more interesting. We call that "organismic biology."
Or, as Abraham Trembley said when describing his discovery of regeneration in hydra (see p. 4 of our translation)
"Because of its nature, that finding was to be not the fruit of long patience and great wisdom, but a gift of chance. It is to such a happy chance that I owe this discovery which I made, not only without forethought, but without my ever having had in my entire life any idea even slightly related to it."
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