Survival and repair of surgical and natural shell damage in the articulate brachiopod Terebratulina retusa (Linnaeus)

Living specimens of Terebratulina retusa from the Firth of Lorn, Scotland, were surgically damaged by drilling 2 mm diameter holes or narrow slits one cm long in the anterior portion of one valve, by bevelling the anterior margin of both valves, or by amputation of the anterior third of one valve. These injuries to the shell and mantle simulated the type of repaired shell damage seen in Paleozoic species, i.e., scalloped, divoted, cleft, and embayed valves. Less than ten percent of the 200 damaged specimens survived until the 25th week after surgery. Specimens of T. retusa showed the ability to repair drill holes, slits, and bevelled anterior shell regions, but not the most severe damage, i.e., amputations of the anterior third of one valve. Shell‐repair was initiated in the fourth week after surgery by the development of a membrane across the wound. The development of caeca in the new shell layer secreted to plug the drill holes became apparent by the eighth week. The punctate pattern was complete in the new, translucent shell material of bevelled and drilled specimens by the 25th week following surgery. Failure of any specimens to survive amputation of the anterior portion of a valve for more than seven weeks after surgery, and the absence of initiation of the repair process, suggests that terebratulids do not have the tolerance for, nor the ability to repair, the severe injuries (embayed valves) which were sustained and mended by extinct strophomenids.     

Ultrastructure of the metanephridia of Terebratulina retusa and Crania anomala (Brachiopoda)

Adult specimens of Terebratulina retusa and Crania anomala have one pair of metanephridia. Each metanephridium is composed of a ciliated nephridial funnel (nephrostome) and an outleading nephridial canal, thus, these organs are open ducts connecting the metacoel of the animal with the outer medium. In both species, the inner side of a nephrostome is lined by a columnar monociliated epithelium which contacts the coelothel within one of the two ileoparietal bands. The coelothel contains basal filaments (in C. anomala these are definite myofilaments). The canal epithelium also consists of monociliated columnar cells which differ from the nephrostome epithelial cells in size and some cell components. Within the nephropore, the canal epithelium makes contact with the so-called inner mantle epithelium which lines the mantle cavity. The nephrostome epithelial cells and the canal epithelial cells never contain any contractile filaments. There are always continuous transitions between these different epithelia and distinct borders cannot be observed. The present results, especially in comparison to Phoronida, do not contradict the hypothesis of a coelothelially derived nephridial funnel and an ectodermal nephridial duct in Brachiopoda. But with regard to the differences between Phoronida and Brachiopoda (larval protonephridia and podocytes in the adults are unknown in Brachiopoda), further investigations have to be done to test the hypothesis of such heterogeneously assembled metanephridia.     

Magnesium and sulphur in the calcite shells of two brachiopods, Terebratulina retusa and Novocrania anomala

This study determines the distribution of magnesium and sulphur in the shells of two species of brachiopod from the same environment to highlight environmental and biological influences on shell composition. In Terebratulina retusa there are differences in magnesium concentration between the primary layer and the outer and inner regions of the secondary layer. In contrast, Novocrania anomala has a shell composed of high magnesium calcite and there is no significant difference in magnesium concentration between the primary and the secondary shell layers. Sulphur provides an indication of the distribution of sulphated organic matrix within the shells of T. retusa and N. anomala . In T. retusa the distribution of magnesium and sulphur correlates across the shell; however, there is no evidence for a relationship between magnesium and sulphur distribution in N. anomala . The relationship between magnesium and sulphur in T. retusa indicates that a proportion of the magnesium content of the shell is associated with the sulphated fraction of the organic matrix. In these two species of brachiopod, from the same environment, magnesium and organic concentration and distribution are very different, emphasizing the importance of fully understanding the factors that control biomineral composition before the application of these biominerals to environmental studies.     

Cell patterning in the Drosophila segment: spatial regulation of the segment polarity gene patched

Intrasegmental patterning in the Drosophila embryo requires the activity of the segment polarity genes. The acquisition of positional information by cells during embryogenesis is reflected in the dynamic patterns of expression of several of these genes. In the case of patched, early ubiquitous expression is followed by its repression in the anterior portion of each parasegment; subsequently each broad band of expression splits into two narrow stripes. In this study we analyse the contribution of other segment polarity gene functions to the evolution of this pattern; we find that the first step in patched regulation is under the control of engrailed whereas the second requires the activity of both cubitus interruptusD and patched itself. Furthermore, the products of engrailed, wingless and hedgehog are essential for maintaining the normal pattern of expression of patched.     

Analysis of the complete mitochondrial DNA sequence of the brachiopod terebratulina retusa places Brachiopoda within the protostomes

Brachiopod phylogeny is still a controversial subject. Analyses using nuclear 18SrRNA and mitochondrial 12SrDNA sequences place them within the protostomes but some recent interpretations of morphological data support a relationship with deuterostomes. In order to investigate brachiopod affinities within the metazoa further, we compared the gene arrangement on the brachiopod mitochondrial genome with several metazoan taxa. The complete (15 451 bp) mitochondrial DNA (mtDNA) sequence of the articulate brachiopod Terebratulina retusa was determined from two overlapping long polymerase chain reaction products. All the genes are encoded on the same strand and gene order comparisons showed that.only one major rearrangement is required to interconvert the T. retusa and Katharina tunicata (Mollusca: Polvplacophora) mitochondrial genomes. The partial mtDNA sequence of the prosobranch mollusc Littorina saxatilis shows complete congruence with the T. rehtusa gene arrangement with regard to the ribosomal and protein coding genes. This high similarity in gene arrangement is the first to be reported within the protostomes. Sequence analyses of mitochondrial protein coding genes also support a close relationship of the brachiopod with molluscs and annelids, thus supporting the clade Lophotrochozoa. Though being highly informative, sequence analyses of the mitochondrial protein coding genes failed to resolve the branching order within the lophotrochozoa.     

Cloning and linkage mapping of resistance gene homologues in apple

Apple (Malus x domestica Borkh.) sequences sharing homology with known resistance genes were cloned using a PCR-based approach with degenerate oligonucleotide primers designed on conserved regions of the nucleotide-binding site (NBS). Sequence analysis of the amplified fragments indicated the presence of at least 27 families of NBS-containing genes in apple, each composed of several very similar or nearly identical sequences. The NBS-leucine-rich repeat homologues appeared to include members of the two major groups that have been described in dicot plants: one possessing a toll-interleukin receptor element and one lacking such a domain. Genetic mapping of the cloned sequences was achieved through the development of CAPS and SSCP markers using a segregating population of a cross between the two apple cultivars Fiesta and Discovery. Several of the apple resistance gene homologues mapped in the vicinity, or at least on the same linkage group, of known loci controlling resistance to various pathogens. The utility of resistance gene-homologue sequences as molecular markers for breeding purposes and for gene cloning is discussed.Communicated by H. Nybom     

Hyperaccumulation of nickel by Alyssum Linnaeus (Cruciferae).

Herbarium specimens of all except one of the 168 recognized species of Alyssum Linnaeus have been analysed for their nickel content in order to identify hyperaccumulators (greater than 1000 microgram per g dry mass) of nickel. A further 31 hyperaccumulators (all in section Odontarrhena) were discovered in addition to the 14 European species reported earlier. Pot trials on the non-accumulator A. serpyllifolium Desfontaines and the hyperaccumulator A. pintodasilvae Dudley in ed. involving addition of nickel to the medium in which the plants were growing, showed that not all species of of section Odontarrhena were able to act as hyperaccumulators of nickel. Hyperaccumulation occurred almost exclusively in the eastern Mediterranean area and Turkey. There appeared to be a definite correlation between species diversity, proliferation and endemism on the one hand, and extremely high nickel concentrations (greater than 1%) on the other. The data have been used to assess the evidence for promoting section Odontarrhena to generic rank.     

Cloning and characterization of the Zymobacter palmae pyruvate decarboxylase gene (pdc) and comparison to bacterial homologues

Pyruvate decarboxylase (PDC) is the key enzyme in all homo-ethanol fermentations. Although widely distributed among plants, yeasts, and fungi, PDC is absent in animals and rare in bacteria (established for only three organisms). Genes encoding the three known bacterial pdc genes have been previously described and expressed as active recombinant proteins. The pdc gene from Zymomonas mobilis has been used to engineer ethanol-producing biocatalysts for use in industry. In this paper, we describe a new bacterial pdc gene from Zymobacter palmae. The pattern of codon usage for this gene appears quite similar to that for Escherichia coli genes. In E. coli recombinants, the Z. palmae PDC represented approximately 1/3 of the soluble protein. Biochemical and kinetic properties of the Z. palmae enzyme were compared to purified PDCs from three other bacteria. Of the four bacterial PDCs, the Z. palmae enzyme exhibited the highest specific activity (130 U mg of protein(-1)) and the lowest Km for pyruvate (0.24 mM). Differences in biochemical properties, thermal stability, and codon usage may offer unique advantages for the development of new biocatalysts for fuel ethanol production.     

Drosophila segment polarity gene product porcupine stimulates the posttranslational N-glycosylation of wingless in the endoplasmic reticulum

Wnt is a family of cysteine-rich secreted glycoproteins, which controls the fate and behavior of the cells in multicellular organisms. In the absence of Drosophila segment polarity gene porcupine (porc), which encodes an endoplasmic reticulum (ER) multispanning transmembrane protein, the N-glycosylation of Wingless (Wg), one of Drosophila Wnt family, is impaired. In contrast, the ectopic expression of porc stimulates the N-glycosylation of both endogenously and exogenously expressed Wg. The N-glycosylation of Wg in the ER occurs posttranslationally, while in the presence of dithiothreitol, it efficiently occurs cotranslationally. Thus, the cotranslational disulfide bond formation of Wg competes with the N-glycosylation by an oligosaccharyl transferase complex. Porc binds the N-terminal 24-amino acid domain (residues 83-106) of Wg, which is highly conserved in the Wnt family and stimulates the N-glycosylation at surrounding sites. Porc is also necessary for the processing of Drosophila Wnt-3/5 in both embryos and cultured cells. Thus, Porc binds the N-terminal specific domain of the Wnt family and stimulates its posttranslational N-glycosylation by anchoring them at the ER membrane possibly through acylation.     

Kinetics of spermatogenesis in the wild squirrel Funambulus palmarum (Linnaeus).

The paper describes in detail the morphology and kinetics of germ cell associations, pattern of mitotic divisions, frequency distribution of different cellular associations (stages) and percent degeneration of various germ cells in the squirrel in which spermatogenesis in adults occurs all year round. Eighteen steps of spermiogenesis were identified based on the development of the acrosomal system using PAS-haematoxylin. These were appropriately divided into Golgi, acrosome, cap and maturation phases. Thirteen types of cellular associations or stages (I-XIII) were characterized along the length of the seminiferous tubule which repeated itself in space and time constituting the seminiferous epithelial cycle (CSE). Of the 18 steps of spermiogenesis, the first 13 were associated with stages I-XIII, respectively, and the rest with the first 9 stages. Spermiation occurred in stage IX. Seven types of spermatogonia [A0, A1, A2, A3, A4, intermediate (In) and B type] were identified based on their shape, size and nuclear morphology. A0 spermatogonia are pale in appearance with homogeneously distributed chromatin surrounded by a thin nuclear membrane. These are present in all stages. A1 are oval in shape and possess a thicker nuclear membrane. They are found in stages VI-X. The chromatin material undergoes progressive condensation from A1 to A4 making the last generation of spermatogonia appear darker. The In spermatogonia which are derived from A4 are morphologically similar to them but smaller in size. The B-type spermatogonia derived from the In types possess a typically round nucleus with uniformly condensed chromatin material underneath the nuclear membrane. The spermatogonia divide mitotically at fixed stages of the CSE giving rise to their next generations. Thus, A-type spermatogonia divide at stages X, XIII/I, IV and V, while In divide at stage VI. During each CSE of the squirrel, 5 peaks of mitosis occur. There is a single generation of B-type spermatogonia. These differentiate into primary spermatocytes and undergo meiosis or maturation divisions which enter to form spermatids. The A4 which divide differentially in stage VI give rise to In- and A1-type spermatogonia. Therefore, A4 spermatogonia form renewing stem cells. Based on the above pattern of spermatogonial mitosis a model for stem cell renewal in the squirrel is proposed. The percentage degeneration of germ cells varied with the cell type. During a single CSE of the squirrel, a total of 42.09% germ cells were found to degenerate. An attempt is made to compare and contrast the kinetics of spermatogenesis in the wild squirrel with that of the other rodents studied so far.     

Spatial regulation of segment polarity gene expression in the anterior terminal region of the Drosophila blastoderm embryo

The effects of mutations in five anterior gap genes (hkb, tll, otd, ems and btd) on the spatial expression of the segment polarity genes, wg and hh, were analyzed at the late blastoderm stage and during subsequent development. Both wg and hh are normally expressed at blastoderm stage in two broad domains anterior to the segmental stripes of the trunk region. At the blastoderm stage, each gap gene acts specifically to regulate the expression of either wg or hh in the anterior cephalic region: hkb, otd and btd regulate the anterior blastoderm expression of wg, while tll and ems regulate hh blastoderm expression. Additionally, btd is required for the first segmental stripe (mandibular segment) of both hh and wg at blastoderm stages. The subsequent segmentation of the cephalic segments (preantennal, antennal and intercalary) appears to be dependent on the overlap of the wg and hh cephalic domains as defined by these gap genes at the blastoderm stage. None of these five known gap genes are required for the activation of the labral segment domains of hh and wg, which are presumably either activated directly by maternal pathways or by an unidentified gap gene.