Elimination by Hydra interstitial and nerve cells by means of colchicine

Hydra treated with colchicine or Colcemid become depleted of 95–99% of their interstitial cells and derivatives of this stem cell: nematoblasts, nematocytes and nerve cells. A second treatment removes most or all remaining interstitial cells. The most effective treatment is an 8-h immersion of whole Hydra attenuata in 0.04% Colcemid or 0.4% colchicine. Interstitial cells are eliminated through phagocytosis by both ectodermal and endodermal epithelial cells. The endodermal digestive cells send processes through the mesoglea which engulf interstitial cells and retract them into the endoderm. The resultant hydra, though devoid of nematocysts, can be artificially fed: these animals grow and bud and can be used to study the behaviour and development of tissue lacking nerve and interstitial cells.

Distribution and dynamics of nematocyte populations in Hydra attenuata

The distribution and dynamics of the 4 nematocyte populations of Hydra attenuata were investigated. Ninety-seven per cent of all nematocytes, including all 4 types, are mounted in the battery cells of the tentacles. The remaining 3%, including 2 types (stenoteles and holotrichous isorhizas) are mounted in the ectoderm of the body column. Eight-two per cent of all nematocytes are desmonemes; 11%, atrichous isorhizas; 5%, stenoteles; and 2%, holotrichous isorhizas. The density of each nematocyte population increases along the length of the tentacle towards the tip. The percentages of the total nematocytes per quarter of tentacle for each of the 4 quarters starting at the base is 15, 18, 25 and 42% respectively. The turnover time of the nematocyte populations in the tentacles was measured with 2 methods. First, the transit time for a carbon-marked battery cell from the base to the tip of the tentacle was measured. Secondly, the time required to replace the unlabelled nematocytes in the tentacles with [3H]proline-labelled nematocytes was measured. In both cases the time was 7–9 days. Based on these data (distribution and turnover time) a model was constructed for the dynamics of the nematocyte populations in the tentacles. The numbers of nematocytes produced dialy in the body column as predicted by the model are in reasonable agreement with the measured values.

The morphology of green hydra endosymbionts as influenced by host strain and host environment

The ultrastructure of Chlorella-like algal endosymbionts from the Florida and English strains of green hydra was compared under different host feeding and photoperiodic regimes. Under standard conditions (host fed daily, 12-h photoperiod) the algae from the 2 strains exhibited considerable differences. The English symbionts had a pyrenoid, compact chloroplast membranes and vesiculated polyphosphate bodies. By comparison, Florida symbionts lacked a pyrenoid, had chloroplasts with less compact membranes and exhibited spherical polyphosphate bodies. When maintained in the dark, algae from English hydra lost their pyrenoids, showed great compaction of the chloroplast and developed large, shield-shaped, electron-dense bodies. In contrast, algae from Florida hosts did not exhibit gross ultrastructural modification. Reciprocal cross-transfers of symbionts were made by placing Florida algae in English aposymbiotic (algal-free) hosts and vice versa. After residence in Florida hosts, English symbionts appeared to undergo ultrastructural modifications resulting in a morphology indistinguishable from the native Florida symbionts. Florida algae showed no modifications resulting from residence in English hosts. It thus appears that the English symbiont has great morphological plasticity, as its structure is greatly modified depending upon the host in which it resides and the conditions under which the host is maintained. The results of these studies are discussed and compared with published accounts of free-living Chlorella and with reports dealing with other Chlorella symbionts.

Polarity reversal in hydra by oligomycin

Intact hydra treated for 24 h with oligomycin gradually lose their head structures and the distal ends form feet. Grafting experiments show that the distal ends of treated animals induce proximal structures.

Modulation of Hydra attenuata rhythmic activity. Photic stimulation

We investigated in Hydra attenuata the possibility of altering more or less permanently and in different environmental conditions, the frequency of Contraction Pulse Trains (CPT's) associated with the rhythmic spontaneous contraction activity, by repetitive light stimuli of variable duration, frequency and amplitude. The CPT's activity of various pieces of Hydra has been also investigated in indisturbed conditions and under stimulation. The following observations have been performed. 1. A transient effect, consisting of an increase or a decrease of CPT's frequency, occurs respectively after an abrupt decrease or increase of the light level. 2. If Hydra is stimulated by repetitive light pulses of 0.5-10 sec duration, at a frequency different from the CPT's average one, the CPT's frequency modifies; if the stimulation frequency is included in a range not too much up or below that of CPT's the new CPT's frequency equals exactly that of stimulation; close to this range the CPT's frequency is a multiple or submultiple of that of stimulation. 3. No habituation to such repetitive stimulation was found. 4. The phase relation between CPT's at the new frequency and light stimuli is a function of the difference between CPT's and stimulation frequencies. 5. Stimulation with repetition of light and darkness periods of some minutes duration induces activity only or mainly during darkness. 6. Modification of CPT's frequency by means of repetitive light stimulation [of the type mentioned either in 2) or 5)] has been observed also with hypostomal preparations. 7. With cessation of the light stimulation, the new CPT's frequency of the whole animal lasts in darkness for a time (10-85 min) that is about 5-10 times longer than that necessary to obtain CPT's syncronization with stimulation. 8. The influence of the light intensity level on transient CPT's frequency variation (see 1), CPT's inhibition and stimulation, promptness of entrainment, range of entrainability, phase relation between entrained CPT's and stimuli, retention time of entrained rhythm has been examined, together with the influence of the reversal of polarity of light transitions on CPT's inhibition and entrainment.

Morphogenetic gradients in moltiple-graft Hydra viridis. I. The effects of colcemid and colchicine

The morphogenesis of so-called secondary (2 degree) heads, budding regions and feet, and separations at graft borders, is studied in multiple-graft animals containing three gastric regions (3g animals) treated with Colcemid or colchicine. Control animals consist of three non-treated pieces. Animals consisting of two non-treated and one treated piece are also employed. The main effects of Colcemid are the promotion of graft healing at the distal graft border, and of 2 degree head formation on the proximal gastric region (g-1). Colchicine also promotes graft healing at the distal graft border, but in contrast to the effect of Colcemid, promotes the formation of ectopic feet (tertiary feet) and inhibits head regeneration at the distal end of the middle gastric region (g-2). Colchicine also accelerates an inversion of polarity in 2 degree budding regions on the g-2 pieces of animals with 2 degree heads on their g-1 pieces. Treatment of a distal graft piece with Colcemid promotes 2 degree head formation on the nearest proximal piece which is not treated, but the inhibition of 2 degree head formation by colchicine occurs only on colchicine treated pieces. The morphogenetic effects of the drugs are interpreted as consequences of their actions on nerve differentiation and cell division. The paper argues that homeostatic control of a hydra's cell population depends on dividing cells influencing cell loss, and that similar mechanisms are involved in the rejection of a graft and the separation of a bud.

Abnormal regeneration of hydra induced with vinblastine sulfate

The effect of vinblastine sulfate on the regeneration of hydra was examined. When the three segments of hydra (fore, mid, and hind segments) were treated with 0.01% vinblastine sulfate immediately after separation, transferred to normal culture medium, and observed for 7 days, various types of abnormal regeneration were observed, especially in the regenerates from the mid segments. Other segments of hydra did not reveal any abnormal pattern of regeneration, although incomplete regeneration or no regeneration of the segments was seen in the advanced period of the treatment. In the case of treatment of the three segments with 0.01% vincristine sulfate, no abnormal regeneration was seen, in spite of marked inhibition of regeneration which was observed in the advanced period of the treatment.

Investigation of oogenesis in hydra. Communication I. Ultrastructure of interstitial cells at early stages of their transformation into oocytes

We studied ultrastructure of the interstitial cells (i-cells) at successive stages of their transformation into oocytes. The i-cells that form the epidermal thickening in the genital zone of the animal start to proliferate in hydras approaching sexual reproduction. Undifferentiated i-cells are characterized by a high density of diffusely disposed ribosomes and almost total absence of membranous structures. Femal sex cells starting to undergo differentiation are characterized by the appearance of aggregations of finely filamentous material in the cytoplasm. This material is of nuclear origin and is often surrounded by mitochondria. Dimensions of the i-cells increase rapidly, and single elongated cisterns of the granular endoplasmic reticulum appear in them. These cisterns run parallel to the cell surface and give rise to minute smooth-surfaced vesicles, whose membranes fuse wtih the cytoplasmic membrane in such a way that their contents are emptied into the intercellular space. Different sectors of the cell are marked by the appearance of grouped cisterns of the granular endoplasmic reticulum. Such cisterns give rise to smooth-surfaced vesicles, which form numerous Golgi complexes. The number of mitochondria increases simultaneously; aggregations of lipid drops with glycogen granules among them start to appear; and escape of nuclear material into the cytplasm intensifies. Such cells at the stage of cytoplasmic growth and accumulation of organelles and yolk inclusions. In connection with this, it is suggested that the term "oogonium" (which is used to designate such cells in the literature) be retained only for proliferating i-cells containing finely filamentous nuclear material in the cytoplasm in the genital zone of the hydra.