Studies on the ovotestis of the slug Agriolimax reticulatus (Müller)

Summary The ovarian oocytes of Agriolimax reticulatus (Müller) have been studied by light and electron microscopy and electron cytochemistry. The development of the oocyte in the ovotestis may be divided into three stages.During Stage I the oocyte cytoplasm contains mainly ribosomes and also strands of endoplasmic reticulum, scattered mitochondria and Golgi systems. The nucleus contains both a paranucleolus and an eunucleolus. By Stage II the oocyte has enlarged, especially in a plane parallel to the basement membrane. In addition to the above mentioned organelles, the cytoplasm contains lipid, glycogen and early yolk platelets. During Stage III, the oocyte continues to enlarge, but mainly in a plane perpendicular to the basement membrane. A considerable degree of cytoplasmic differentiation has also taken place. The plasma membrane of the oocyte has become specialized with the appearance of a polysaccharide-rich glycocalyx, microvilli and pinocytotic tubules. Elsewhere, much of the background cytoplasm, containing Golgi-derived, polysaccharide and acid phosphatase-rich multivesiculate bodies, lipid and glycogen, is sequestered by smooth membranes and ultimately fuses with the growing yolk platelets. The nucleus contains an amphinucleolus, characteristic of many gastropods.The findings of this study are discussed in relation to results from other studies on oogenesis.     

Studies on the ovotestis of the slug Agriolimax reticulatus (Müller)

Summary The follicle cells, nurse cells and germinal epithelia, which are closely associated with the oocyte of Agriolimax reticulatus (Müller) during its development in the ovotestis, have been studied using light and electron microscopy. The various secretory, digestive and phagocytic activities of these cells have also been investigated using electron cytochemical tests for oxidisable polysaccharide, acid phosphatase and electron-opaque tracer molecules. The oocyte lies initially between the germinal epithelia and a layer of nurse cells but, as oocyte vitellogenesis proceeds, it becomes encapsulated by a layer of follicle cells. Both the follicle and the nurse cells are active in secretion and digestion and contain Golgi apparatus, granular endoplasmic reticulum and acid phosphatase-rich digestive vacuoles. The significance of these activities is discussed in relation to oocyte vitellogenesis, secondary envelope formation and the digestion and recycling of cellular material.     

Physiological adaptations in the survival of rotifers (Brachionus plicatilis,O. F. Müller) at low temperatures

The biology of the rotifer Brachionus plicatilis has been studied extensively in recent years, due to its importance in aquaculture. Today, the culture of several marine fish species relies completely on the daily production of live rotifers.In the present paper we explore the conditions that facilitate maintaining live rotifers for extensive periods at low temperatures. In addition to its possible contribution in providing reserve stocks for commercial application, these studies may be of ecological importance. They could explain some of the physiological adaptive mechanisms that are involved in the survival of rotifers under adverse environmental conditions.Experimental results showed relatively high survival rates (82–85%) in rotifers that were cultured at 25 °C and exposed later to -1 °C for 12–14 days. During this period, rotifers were kept without food and their media were not changed. The survival was found to depend on the rotifer culture conditions, prior to exposure to -1 °C. These included the type of food fed to rotifers (yeast or algae), the salinity in which they were cultured, and an essential acclimation period of 2–6 day at 4 °C or 10 °C. The acclimation period was associated with the synthesis of at least one specific protein and accumulation of lipids. Profiles of protein synthesis in rotifers incubated at 10 °C revealed a 94 kD protein, which did not appear in rotifers cultured at 25 or 37 °C. Immunoisolation, using a polyclonal antibody that was prepared against HSP60, revealed that this protein was synthesized in rotifers kept at 10, 25 or 37 °C. However, this antibody did not react with the 94 kD peptide.In addition, rotifers kept at 10 °C accumulated substantial amounts of lipids, including eicosapentaenoic acid (EPA), which is found in the algae fed to them. These results support the hypothesis of specific adaptations to survival at low temperatures during an acclimation period.     

Looking back at a quarter-century of research at the Maurice E. Müller Institute for Structural Biology

The Maurice E. Müller Institute, embedded in the infrastructure of the Biozentrum, University of Basel, was founded in 1985 and financed by the Maurice E. Müller Foundation of Switzerland. For 26 years its two founders, Ueli Aebi and Andreas Engel, pursued the vision of integrated structural biology. This paper reviews selected publications issuing from the Maurice E. Müller Institute for Structural Biology and marks the end of this era.     

Observations on the clypeasteroid Echinocyamus pusillus (O. F. Müller)

The tiny echinoid Echinocyamus pusillus (O. F. Müller) is equipped with specialized external structures that suit it for a wide variety of environments. Special features include the ability to burrow in sediments of fine sand to shell gravel and to climb vertically.Specimens dredged off the west coast of Scotland were observed in aquaria and with the SEM. E. pusillus is characterized by three kinds of spines, and by two of pedicellariae. In contrast to sand dollars, the spines play a passive rôle in the feeding and burrowing operation, probably retaining a defensive nature as in the regular urchins. It is the podia that are chiefly involved in climbing, burrowing, righting, and probably feeding. Surface ciliary currents transport particles, but not to the mouth; they may have a respiratory or cleansing function. Experimental animals did not burrow in either very fine or very coarse sand, probably because a certain relationship exists between particle weight and podia size.E. pusillus shares behavioural and structural characteristics with regular and irregular urchins. It is not a true sand dollar, but may illustrate an evolutionary stage towards such a form.     

Effects of tissue extract of adults on metamorphosis in Ascidia mentula O.F. Müller and Ascidiella scabra (O.F. Müller)

Unhatched, but fully developed larvae of two solitary ascidians Ascidia mentula O.F. Müller and Ascidiella scabra (O.F. Müller) were incubated in a variety of adult tissue extracts, which an earlier study had shown to accelerate metamorphosis. Our study confirmed this observation and showed, furthermore, that tissue extracts induce tail resorption in unhatched larvae of Ascidiella. For both species, the most active induction of metamorphosis was obtained with tunic tissue extracts. The results indicate that chemical stimulation without the presence of tactile cues may initiate metamorphosis. We suggest that the ability of tunic extracts to induce metamorphosis may explain juvenile establishment on adult ascidians and their aggregated distribution found in nature.     

Effect of water temperature on the excystment of the dinoflagellate Ceratium hirundinella (O. F. Müller) Bergh

The effect of water temperature on the excystment of the dinoflagellate Ceratium hirundinella (O. F. Müller) Bergh was studied in the laboratory. Excystment was observed between 15–30 °C and was 2% at an optimum water temperature of 20 °C–25°C. Little excystment occurred between 5 and 10 °C. The results at low temperatures are not in accordance with those obtained in an English lake. This disagreement suggests an adaptability of excystment to the temperature regime of the lake.     

Studies of the fine structure of β-d-glucans of barleys extracted at different temperatures

Enzymic analyses of aqueous extracts of barley obtained at 25–100° demonstrated an exponential relationship between β-d-glucan content and temperature. Purified β-d-glucans, in particular those from extracts made at 40° and 100°, were compared by the Smith-degradation method followed by g.l.c. analysis of the methyl and the trimethylsilyl ethers of the products. All extracts yielded qualitatively the same products, including oligosaccharides which were characteristic of sequences of adjacent (1→3)-linkages. The material extracted at 100° contained relatively more of these sequences, and also showed a much higher specific viscosity, than did the material extracted at low temperatures. The structural implications of these findings are discussed.     

Purification and properties of beta-N-acetylhexosaminidase from the mollusc Helicella ericetorum Müller.

1. A beta-N-acetylhexosaminidase was purified 330-fold from the digestive gland of the terrestrial mollusc Helicella ericetorum Müller. 2. Its pH optimum is 4.5 for both beta-N-acetylglucosaminidase and beta-N-acetylgalactosaminidase activities in two buffer solutions; it is fully stable at 37 degrees C for 2h in the pH range 3.8--4.6 and shows one isoelectric point (pH 4.83). 3. The estimated mol.wt. is between 120,000 and 145,000. 4. The enzyme shows an endo-beta-N-acetylhexosaminidase activity on natural substrates such as ovalbumin, ovomucoid, chondroitin 4-sulphate, chitin and hyaluronic acid. 5. Two forms of the enzyme were separated by preparative polyacrylamide-gel electrophoresis. 6. Km and Vmax. for p-nitrophenyl 2-acetamido-2-deoxy-beta-D-glucopyranoside and p-nitrophenyl 2-acetamide-2-deoxy-beta-D-galactopyranoside are 0.43 mM, 30.1 micronmol of p-nitrophenol/min per mg and 0.19 mM, 8.6 micronmol of p-nitrophenol/min per mg respectively. 7. It is inhibited by Hg2+, Fe3+, acetate, some lactones, N-acetylgalactosamine, N-acetylglucosamine and mannose. 8. Mixed-substrates analysis and Ki values for competitive inhibitors indicated that beta-N-acetylglucosaminidase and beta-N-acetylgalactosaminidase activities are catalysed by the enzyme at the same active site.     

Studies on sex-organ development. Ontogeny of cytoplasmic oestrogen receptor in chick Müllerian duct.

Oestradiol receptors were observed in the cytoplasm of the chick Müllerian duct at several embryonic stages. The sedimentation coefficients and the dissociation constants of the receptor protein remained unchanged throughout the various stages of development. Specific binding of cytoplasmic receptor to [3H]oestradiol assayed in vitro was shown to be saturable at concentration of 10nM or higher. The number of oeastradiol-binding sites on a per-cell basis increased linearly from day 8 to day 12 of incubation and then levelled off from day 12 to the fourth day after hatching. These results indicate that in the developing embryonic sex organ, the same receptor protein is present throughout prenatal development. The concentration of the oestradiol receptor increases and reaches a constant value, but the capacity for the receptor to interact with the hormone does not change.     

Preservation of resting eggs of the euryhaline rotifer Brachionus plicatilis O. F. Müller by canning

Recent research has indicated that the hatchability of mass-producedrotifer (Brachionus plicatilis) resting eggs (stored in sea water in thedark at 4°C) gradually decreases due to bacterialinfection of the porous egg surface. We investigated whether lyophilizationas well as a canning treatment could solve the problem of bacterialinfection of resting eggs. The canning method preserves eggs in a dry form,after lyophilization at –40°C. The resting eggs werepacked in cans under various pressures: 21, 34, 48, 61, 75, 88 and 101 kPa.The viability of the canned resting eggs was tested by hatching experimentsdone 6 and 12 months after canning and storage at 5°C.When partial pressures were less than 88 kPa, percent hatching after 6months ranged between 16 and 20%, similar to that of uncanned eggs(19% hatching), but significantly lower (9 and 11%, P <0.01) at 88 and 101 kpa. Even after 12 months, percent hatching remained at35% when canning was at 61 kpa. Lyophilization and canning at partialpressure lower than 88 kPa could therefore preserve resting eggs, andhatchability was maintained. Canned eggs that were treated with NaClO (1 mgl^–1) or NFS-Na (5 mg l^–1) showed a significantlyhigher percent hatching (68% and 80%, respectively, each P<0.05) than untreated eggs.     

Studies on sex-organ development. Oestrogenic effect on ornithine decarboxylase activity in the differentiating Müllerian ducts and other organs of the chick embryo.

The activity of ornithine decarboxylase in the differentiating left and right Müllerian ducts was assayed and compared with that in other embryonic organs, i.e. the liver and the brain throughout the stages of development. In general the enzyme activity was high in the early stages and decreased extensively in the late stages of development. Specifically, in the left and righ Müllerian ducts, the enzyme activity was high from day 8 to day 9 of incubation. In the right duct the enzyme activity started to decline on day 9 and then continuously decreased to an almost undetectable value on day 18 of incubation. In the left duct the enzyme activity also decreased slightly from day 9 to day 12; however, it increased from day 13 to day 15 and finally decreased to a constant value from day 18 until hatching. The alteration in enzyme activity in the Müllerian duct as assayed in vitro during development is not due to the effect of the size of the endogenous ornithine pool. When the enzyme activity was subjected to oestrogen stimulation, an increase of 5--10-fold for the left duct and of 5--3-fold for the right duct was observed during the course of development. No such stimulation was observed with the treatment of progesterone. Testosterone consistently caused a 25--30% inhibition of the enzyme activity in the Müllerian duct. Oestrogen slightly stimulated the enzyme activity in the developing liver but inhibited that of the brain. The concentration of the three polyamines measured in the Müllerian duct corresponds to the activity of the enzyme determined.     

Influence of the age of algae fed to rotifers (Brachionus plicatilis O.F. Müller) on the expression of mixis in their progenies

Summary The sequence of the appearance of mixis in the rotifer Brachionus plicatilis was followed among the descendents of amictic rotifers transferred from a high salinity media (40 S) to a low one (9 S). All the neonates that hatched from the amictic eggs, after being transferred to a low salinity, were amictic. Each one of these neonates was cultured individually and its offspring removed periodically every 8–10 h. It was observed that throughout their reproductive phase, these parental females retained their potential to produce either mictic or amictic offspring. All the first produced neonates developed into amictic females, but among those produced later, three patterns were prevalent. The prevalent pattern (type A) was one in which the probability of a neonate being mictic increased towards the middle of the parents' reproductive phase and was followed by a slow decline. In the second pattern (type B), the probability of a daughter being mictic was constant throughout the parents' reproductive phase. It is suspected that the quality of food supplied to the rotifers determines the appearance of patterns, A, B or C. It is postulated that the innate capacity of rotifers to undergo mixis is genetically controlled, while its expression is modulated by environmental conditions.