Pierre Tardent

REGENERATION IN THE HYDROZOA

1. This article reviews the present state of knowledge on regeneration in the Hydrozoa and some of the problems related to it. The available data derived from descriptive and experimental studies are confined to only a few genera (Hydra, Tubularia, Cordylophora, Corymorpha, Campanularia, Pennaria). Without enumerating all possible types of regeneration, a number of the most significant cases are examined from various points of view.

Ultrastructure of mechanoreceptors of the polyp Coryne pintneri (hydrozoa, athecata)☆

Abstract 1. 1. The ectoderm of the athecate hydroid polyps of Cladonema, Sarsia and Coryne contains long stereocilia, which act as mechanoreceptors. 2. 2. These stereocilia which are abundant on the filiform tentacles originate from an elongated ciliary cell which is situated within an accessory cell. 3. 3. The present paper describes the ultrastructure of this two-cell system, focusing on the architecture of the ciliary apparatus. 4. 4. The close resemblance between the structures of this ciliary apparatus and that of the nematocytes cnidocil is emphasized and discussed.

Morphology and morphodynamics of the stenotele nematocyst of Hydra attenuata Pall. (Hydrozoa, Cnidaria)

SummaryThis light- and electron-microscopic study has investigated the structure, the morphodynamics of discharge, and the impact of the stenotele cyst of Hydra attenuata (Hydrozoa, Cnidaria) on the preys integument. The triggered capsule, which is ejected from the cell, discharges its tubular content (shaft, stylets and tubule) by a process of evagination. In doing so the three joined stylets punch a hole into the cuticle of the prey through which the long evaginating tubule penetrates into the interior of the target. The behaviour of the tubule is described in detail and the functional significances of the various parts of the capsule are discussed.

Oogenesis in Hydra carnea: A new model based on light and electron microscopic analyses of oocyte and nurse cell differentiation

Oogenesis in Hydra carnea starts with an accumulation of a great number of I-cells in the interstitial spaces of the ectoderm of the body column. One centrally located I-cell becomes the future oocyte, the others differentiate into nurse cells. Presumptive oocyte and nurse cells are not easily distinguishable at that time. The earliest stage of an oocyte we could identify on ultrastructural criteria was in prophase of its first meiotic division. Only at this stage autosynthesis of nutritive substances predominates, the following rapid increase of the oocyte volume relies on the successive adoption of cytoplasmic fragments from nurse cells. Extending fingerlike processes between the epitheliomuscular cells, the oocyte then starts to phagocytose apoptotic nurse cells. Nurse cell differentiation is indicated by the appearance of lipid vesicles in I-cells. As differentiation proceeds glycogen, rEr and Golgi complexes appear and the cells increase due to a continuous production and accumulation of lipid, glycogen and yolk-like electron dense material. Then the loss of cytoplasmic fragments and degenerative changes typical of apoptosis, a morphologically defined form of cell death, converts the nurse cells into apoptotic bodies. The bulk of nurse cells becomes phagocytosed by the oocyte at late stages of their transformation into apoptotic bodies. At the end of oogenesis which in Hydra carnea takes about 4 days, the egg consists for the largest part of apoptotic nurse cells which persist in the developing embryo until hatching.

Hemolytic and toxic properties of Hydra attenuata nematocysts

Crude extract prepared from isolated and purified nematocysts (stenoteles, desmonemes, isorhizas) of Hydra attenuata Pall. (Cnidaria, Hydrozoa) contains two main toxic proteins. The first is a hemolysin (100-200,000 mol.wt) which also causes initial spasmodic contractions in larval and adult specimens of Drosophila. Both, hemolytic and neurotoxic activities are inhibited by low concentrations of Triton X-100. The second protein (30-100,000 mol.wt), which is not susceptible to Triton causes long lasting paralysis leading to death of the test animals (LD50 approximately 5 mg crude nematocyst extract per kg). Neither of the toxins is identical with the previously described phospholipase.

Some physical and chemical properties of purified nematocysts of Hydra attenuata pall. (Hydrozoa, cnidaria)

Abstract 1. 1. A method for purifying undischarged nematocysts from Hydra and other cnidarians is described. 2. 2. Isolated cysts (relative densities 1.22–1.24) evaginate their tubular content even after previous dehydration. 3. 3. The cyst wall is permeable to dyes of mol. wts up to 600,000. 4. 4. Approximately two-thirds of the cysts dry wt are soluble proteins. Eighty per cent of them are of low mol. wt and highly anionic, presumably serving as binding sites for Ca2+ and Mg2+. 5. 5. The other 20% includes 30 different proteins amongst them toxins and enzymes (phospholipase and little proteases but no collagenase, chitinase or hyaluronidase).

A Qualitative and Quantitative Inventory of Nervous Cells in Hydra Attenuata Pall

The nervous system of Hydra (Athecatae, Hydridae) is, as has been shown by Hadza (1909), an elementary network of loosely interconnected neurons and other cells believed to be of sensory nature (Burnett and Diehl, 1964; Davis, Burnett and Haynes, 1968; Haynes, Burnett and Davis, 1968; Lentz, 1966; Lentz and Barrnett, 1965 et al.). In spite of the absence of a morphologically definable center of coordination it endows the polyp with a surprisingly rich behavioural pattern (Haug, 1933; Haase-Eichler, 1931; Passano and McCullough, 1962, 1963, 1964; Rushforth, 1971, 1973; Tardent and Frei, 1969; et al.). This behaviour is motivated by 2 fundamentally different components: One is the “spontaneous contraction-extension activity” which is controlled by 2 pace-maker centers, one of which is situated in the hypostome, the other in the stalk of the polyp (McCullough, 1962, 1965; Passano, 1962; Passano and McCullough, 1963, 1964, 1965). The other component consists of dynamic reactions to external stimuli such as light, chemicals or mechanical stimuli (Haug, 1933; Feldman and Lenhoff, 1960; Passano and McCullough, 1962; Rushforth, Burnett and Maynard, 1963; Singer, 1963; Tardent and Frei, 1969; Frei, 1973 et al.).

Experiments about sex determination inHydra attenuata Pall.

Summary In the labile gonochoristic Hydra attenuaea Pall., spontaneous inversions of the sexual status from male to female and vice versa are relatively frequent whereas cases of true hermaphrodism are extremely rare. Male and female polyps have been cut in 3 axial fragments. After having regenerated their missing parts, the reconstituted animals maintained with few exceptions the sex of the individual from which they had arisen; thus amputation and regeneration in this case do not influence sex determination. Hetcrosexual chimera composed of complementary halves of males and females become males regardless of whether the male portion is in a distal or proximal position. Male “heads” (hypostome and tentacles) and male stalks alone are capable in parabiosis of masculinizing complementary female bodies. In order to obtain complete masculinization, parabiosis between complementary male and female components must last at least 72 hours. When the male component of a heterosexual chimera is exposed to X-radiation (6000 r) before transplantation, it fails to exert its masculinizing action. Seventy percent of normal male polyps exposed to a sublethal X-ray dose (2400 r) undergo sex inversion. This inversion leads to a stable female status. These findings are discussed in the light of the possible mechanisms of sex determination in Hydra attenuata Pall.

Synthesis of the mesoglea by ectoderm and endoderm in reassembled hydra

The structure and synthesis of the mesoglea was investigated in “reassembled” hydra—hydra regenerating from ectoderm and endoderm previously isolated from each other and then recombined. During tissue isolation and reassembly the mesoglea remains attached to the endoderm. It is observed to be quite elastic and resilient. The mesoglea disappears by 6–8 hr after reassembly, having apparently been digested by endoderm. “New” mesoglea is undergoing synthesis by 12 hr after reassembly. It trilaminar appearance at this time suggests an origin from both epithelia. Interepithelial contact, by cell processes of epithelial cells, is reestablished within the mesoglea between 24 and 48 hr after reassembly. Mesoglea appears normal 48 hr after reassembly. Autoradiographic experiments, performed during the reassembly manipulations, conclusively demonstrate that the mesoglea originates from both epithelia. Mesoglea precursors, amino acids, are incorporated within the mesoglea about 5–6 hr after initial acquisition by epithelia, but subsequent turnover of these amino acids is slow.

Heat dissociation and maceration of marine Cnidaria

SummaryThe effect of increased temperature on the tissue integrity of polyps and medusae ofPodocoryne carnea is described. Animals exposed for 10 to 20 min to a temperature of 35°C are easily dissociated into single cells. These dissociated cells round up, form reaggregates and, depending on their origin, regenerate polyp or medusa structures. However, as the exposure time is increased, the dissociated cells gradually lose the ability to reaggregate or to regenerate defined structures. At incubation times exceeding 50 min, the tissue separates into single cells which retain their normalin vivo shapes but which do not form reaggregates. These are termed macerated cells. The ultrastructure and protein profile of macerated cells demonstrate no major changes from those of untreated cells. Both the dissociation and maceration methods are applicable to other cnidarian species for developmental, histological and biochemical studies.