Ultrastructure of spermiogenesis in the gastropod Calliotropis glyptus Watson (Prosobranchia: Trochidae)with special reference to the embedded acrosome

Testicular spermatozoa and sperm development in the archaeogastropod Calliotropis glyptus Watson (Trochoidae: Trochidae) are examined using transmission electron microscopy and formalin-fixed tissues. During spermiogenesis, the acrosome, formed evidently through fusion of Golgi-derived proacrosomal vesicles, becomes deeply embedded in the condensing spermatid nucleus. Two centrioles (proximal and distal), both showing triplet microtubular substructure, are present in spermatids—the distal centriole giving rise to the sperm tail and its associated rootlet. During formation of the basal invagination in the spermatid nucleus, centrioles, and rootlet move towards the nucleus and come to lie totally within the basal invagination. Mitochondria are initially positioned near the base of the nucleus but subsequently become laterally displaced. Morphology of the mature spermatozoon is modified from that of the classic primitive or ect-aquasperm type by having 1) the acrosome embedded in the nucleus (the only known example within the Mollusca), 2) a deep basai invagination in the nucleus containing proximal and distal centrioles and an enveloping matrix (derived from the rootlet), 3) laterally displaced periaxonemal mitochondria, and 4) a tail extending from the basal invagination of the nucleus. Implantation of the acrosomal complex and centrioles within imaginations of the nucleus and lateral displacement of mitochondria effectively minimize the length of the sperm head and midpiece. Such modifications may be associated with motility demands, but this remains to be established. The unusual features of C. glyptus spermatozoa, though easily derivable from ‘typical’ trochoid sperm architecture, may prove useful in delineating the genus Calliotropis or tracing its relationship to other genera within the trochid subfamily Margaritinae.     

Thromboxane A2 biosynthesis in human disease

Thromboxane A2 (TxA2), the predominant cyclooxygenase product of human platelets, is a potent vasoconstrictor and platelet agonist. Although its biological properties are readily appreciable in vitro, it has been difficult to define its biological importance in vivo. To a large extent this reflected the problems associated with efforts to monitor biosynthesis of this eicosanoid and the lack of selective pharmacological probes that prevented the synthesis of TxA2 or antagonized its biological action in vivo. Recently the analysis of urinary metabolites of TxB2 has become simplified so that the methodology is readily applicable to clinical studies. This provides a noninvasive, time-integrated index of Tx biosynthesis. Although one cannot definitively establish a tissue of origin for metabolites measured in urine, indirect evidence suggests that urinary TxB2 derives primarily from the kidney whereas its dinor metabolite predominantly reflects platelet biosynthesis under physiological conditions. Although plasma concentrations of TxB2 are readily confounded by platelet activation ex vivo, the enzymatic metabolites formed from TxB2 have recently been identified and appear to bypass this problem. Combined analysis of long-lived (e.g., 11-dehydro-TxB2) and short-lived (e.g., 2,3-dinor-TxB2) metabolites in plasma promise to more accurately localize phasic increases in the biosynthesis of TxA2 and have been paralleled by the development of antagonists of the TxA2/prostaglandin endoperoxide receptor and their study of humans. The use of such specific probes in conditions characterized by abnormal biosynthesis of TxA2 promises to define the biological role of this mediator for humans.     

Identification of the mutagenic quinoxaline isomers from fried ground beef

Two mutagens isolated from fried-beef patties were compared to a series of synthetic structural isomers of 2-aminodimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-aminotrimethylimidao[4,5-f]quinoxaline (DiMeIQx). Comparison by NMR spectrometry and HPLC coelution showed that one beef mutagen (molecular weight of 213) was identical to the 8-MeIQx isomer not the 7-Me isomer. Another quinoxaline beef mutagen, having 3 methyl groups (molecular weight of 227), had an NMR spectrum different from the 5,8- or 7,8-DiMeIQx isomers, but not clearly distinguishable from the 4,8- or 4,7-DiMeIQx isomers. The HPLC separation of the DiMeIQx isomers and subsequent addition of the beef mutagen showed the beef-derived compound to coelute with the 4,8-DiMeIQx and not with the 4,7-DiMeIQx. The number and position of methyl groups was responsible for a 7-fold range of mutagenic response in the Ames/Salmonella assay. In conclusion, the major quinoxaline mutagens isolated from fried beef were identified as 8-MeIQx and 4,8-DiMeIQx isomers.     

Ultrastructure of paraspermatozoa of cerithiacean gastropods (prosobranchia: Mesogastropoda)

Using transmission electron microscopy, paraspermatozoa of representative species of the families Cerithiidae, Potamididae, Planaxidae, Dialidae and the genusAustralaba (family position uncertain) have been examined and compared with those produced by other prosobranchs, particularly other investigated cerithiaceans. Special attention is focused on the phylogenetic importance of paraspermatozoa and euspermatozoa within the superfamily Cerithiacea. The paraspermatozoa of cerithiacean gastropods fall into two structural categories: (1) those with a head region and a tail tuft (number of tails and the length of the tail tuft variable — Cerithiidae, Planaxidae, Potamididae, Modulidae, Turritellidae, Campanilidae, Pleuroceridae,Obtortio, Australaba); and (2) those with an elongate, vermiform body filled with large electron-dense vesicles and up to ninety axonemes — the latter emerging as numerous short tails from the posterior half of the paraspermatozoon body (Dialidae).     

The cyclic AMP phosphodiesterase encoded by the Drosophila dunce gene is concentrated in the mushroom body neuropil.

Drosophila dunce (dnc) flies are defective in learning and memory as a result of lesions in the gene that codes for a cAMP-specific phosphodiesterase (PDE). Antibodies to the dnc PDE showed that the most intensely stained regions in the adult brain were the mushroom body neuropil--areas previously implicated in learning and memory. In situ hybridization demonstrated that dnc RNA was enriched in the mushroom body perikarya. The mushroom bodies of third instar larval brains were also stained intensely by the antibody, suggesting that the dnc PDE plays an important role in these neurons throughout their development. The role of the dnc PDE in mushroom body physiology is discussed, and a circuit model describing a possible role of the mushroom bodies in mediating olfactory learning and memory is presented.     

The occurrence of species of semi-aquatic Enchytraeidae (Oligochaeta) in Ireland

The Enchytraeidae are essentially terrestrial oligochaetes but many species have marked aquatic tendencies. Over two thirds of recorded Irish species were found in soils which were submerged or frequently flooded and 35% showed a distinct preference for these conditions. Relatively few species were living in soils subject to drought. Red blood was present in 28 species, all but one from soils with more than 55% water. Cognettia sphagnetorum and C. glandulosa developed red blood in very wet conditions. In a survey of Irish wetlands, samples were taken from bog, heath, marsh, fen, margins of lakes and rivers, and saltmarsh. The influence of various environmental parameters was determined using ordination techniques. Magnesium and pH were found to be the most important factors. A high level of magnesium distinguished coastal sites and pH 5.2 separated two clusters representing acid peat and marsh-fen-aquatic sites. Groups of indicator species characterized each of the three clusters. The ecological distribution of the indicator species is described, and their usefulness in classifying enchytraeid communities is discussed.     

Choice of sample size in parasitological experiments

One of the most awkward practical problems confronting a research worker setting up an experiment is to decide how big the experiment should be. The larger the number of subjects then the smaller is the degree of uncertainty in the conclusions; but large trials are costly and may have to be of long duration, so there is every incentive to keep trials as small as possible. Statistics is the science of coping; with uncertainty, and in this article Michael Healy explains the statistical basis that helps to decide how big a sample size should be - how to balance minimum error rates with optimal cost efficiency.     

Ultrastructure of spermatozoa and spermiogenesis inSpirula spirula (L.): systematic importance and comparison with other cephalopods

Spermatozoa and spermiogenesis in the deep-water cephalopodSpirula sprirula (L.) are examined using transmission electron microscopy. Mature spermatozoa (taken from spermatophores) are elongate cells 115–120 μm long, composed of a conical acrosomal vesicle, cylindrical nucleus (6.8–7 μm long), flagellum and a loose mitochondrial sleeve — the latter concealing the proximal 6–8 μm of the flagellum. The acrosomal vesicle is 2.8 μm long with fibro-granular contents and an electron-lucent apical zone. Subacrosomal material, organized as closely packed granules, fills a basal invagination of the acrosomal vesicle. In early spermatids the flagellum is derived from a triplet substructure centriole positioned close to the developing nuclear invagination. As flagellum formation proceeds, the acrosomal vesicle (produced evidently through Golgi secretion) attaches to the condensing nucleus. Spermatids are connected by cytoplasmic bridges throughout their development, and exhibit a perinuclear sheath of microtubules from the onset of the fibrous stage of nuclear condensation (mid-, late spermatids). In mid-spermatids, mitochondria collect posterior to the nucleus and subsequently are packed into a cylindrical extension of the plasma membrane to form the periflagellar mitochondrial sleeve. These features of spermiogenesis and mature spermatozoa ofSpirula clearly associate the Spirulidae with the Sepiida, Teuthida and Sepiolida — particularly with the latter order. However, pending results of a thorough review of coleoid sperm morphology, the Spirulidae are here included in their own order — Spirulida (of Reitner & Engeser, 1982) — rather than in either the Sepiida or Sepiolida.     

Ultrastructure of spermiogenesis inVampyroteuthis infernalis Chun — a relict cephalopod mollusc

Spermiogenesis in the relict deep-sea cephalopodVampyroteuthis infernalis Chun is examined using transmission electron microscopy (TEM), and the results compared with available data on other cephalopods. Early spermatids ofVampyroteuthis exhibit an ovoid nucleus (with dense irregular patches), numerous mitochondria and a pair of triplet substructure centrioles (arranged parallel to each other). Subsequently, the following morphological changes take place: (1) nuclear contents condense into a fibrous reticulum, then into thick fibres; (2) the acrosomal vesicle (presumably Golgi-derived) positions itself in a shallow depression at the nuclear apex; (3) the flagellum forms from one of the two centrioles; (4) mitochondria cluster around the flagellum at the base of the nucleus; (5) a dense, fibrous plug forms within the basal invagination of the nucleus. Microtubules surround the acrosome and condensing nucleus of spermatids. The dense plug is of special systematic importance since it also occurs in spermatids and spermatozoa ofOctopus spp., but not in any investigated species of the Sepiida, Sepiolida or Teuthida. Late spermatids and mature spermatozoa ofVampyroteuthis strongly resemble developing spermatids ofOctopus, suggesting a close phylogenetic relationship betweenVampyroteuthis (and the Vampyromorpha) and octopods.     

Identification and characterization of genes controlled by the sporulation-regulatory gene spo0H in Bacillus subtilis.

We describe a general strategy for the identification of genes that are controlled by a specific regulatory factor in vivo and the use of this strategy to identify genes in Bacillus subtilis that are controlled by spo0H, a regulatory gene required for the initiation of sporulation. The general strategy makes use of a cloned regulatory gene fused to an inducible promoter to control expression of the regulatory gene and random gene fusions to a reporter gene to monitor expression in the presence and absence of the regulatory gene product. spo0H encodes a sigma factor of RNA polymerase, sigma H, and is required for the extensive reprograming of gene expression during the transition from growth to stationary phase and during the initiation of sporulation. We identified 18 genes that are controlled by sigma H (csh genes) in vivo by monitoring expression of random gene fusions to lacZ, made by insertion mutagenesis with the transposon Tn917lac, in the presence and absence of sigma H. These genes had lower levels of expression in the absence of sigma H than in the presence of sigma H. Patterns of expression of the csh genes during growth and sporulation in wild-type and spo0H mutant cells indicated that other regulatory factors are probably involved in controlling expression of some of these genes. Three of the csh::Tn917lac insertion mutations caused noticeable phenotypes. One caused a defect in vegetative growth, but only in combination with a spo0H mutation. Two others caused a partial defect in sporulation. One of these also caused a defect in the development of genetic competence. Detailed characterization of some of the csh genes and their regulatory regions should help define the role of spo0H in the regulation of gene expression during the transition from growth to stationary phase and during the initiation of sporulation.