Order-disorder phenomena in myelinated nerve sheaths. II. The structure of myelin in native and swollen rat sciatic nerves and in the course of myelinogenesis

The algorithm described in the accompanying paper was applied to X-ray scattering experiments performed with rat sciatic nerves, either as a function of the age of the animal (4 to 30 days), or with adult nerves swollen in non-isotonic media. The results were all consistent with the model of disorder used in the theoretical treatment. The algorithm leads, in one step, from the data to the numerical values of the parameters, avoiding all intermediate manipulation. For each experiment a variety of parameters was determined: the average D and the variance sigma 2D of the repeat distance, the average number [N] of motifs per crystallite, the set [idiff(h/D)], which defines the diffuse scattering, the fraction alphaloose of myelin that does not belong to the compact sheaths, and the set [imotif (k/2D)], which suffices to define the continuous intensity curve of the motif imotif(s). Note the remarkable wealth of information, especially by contrast with conventional analyses which, as a rule, only yield the values of D and of the set [imotif(h/D)] (insufficient to determine the function imotif(s]. The function imotif(s) and the parameters D and sigma D (and thus the local structure of the myelin sheaths) were shown to be almost invariant in the course of myelinogenesis; what varies is mainly the total amount of myelin in the nerve and the number of membranes per sheath. Swelling agents have a dramatic influence on the X-ray scattering spectra, but in spite of the conspicuous variation of D, sigma D and [N] the structure of the motif is invariant. The structure of the motif was shown to be quite different in the native and in the swollen samples; the stacking disorder appears to involve mainly the cytoplasmic space in native myelin, the external space in swollen nerves. The very notion of electron density profile, when disorder is present, is discussed. Two criteria were proposed to select the "best" signs of the reflections: two sets came out at almost the same rank, one corresponding to Caspar & Kirschner's the other to Worthington & McIntosh's proposals, neither of which can be ruled out according to the criteria used in this work.     

Xp-duplications with and without sex reversal

Duplications in Xp including the DSS (dosage sensitive sex reversal) region cause male to female sex reversal. We investigated two patients from families with Xp duplications. The first case was one of two sisters with karyotype 46,XY, der(22), t(X;22)(p11.3;p11)mat and unambiguous female genitalia. The living sister was developmentally retarded, and showed multiple dysmorphic features and an acrocallosal syndrome. The second case was a boy with a maternally inherited direct duplication of Xp21.3-pter with the breakpoint close to the DSS locus. He had multiple abnormalities and micropenis, but otherwise unambiguous male genitalia. We performed quantitative Southern blot analysis with probes from Xp22.13 to p21.2 to define the duplicated region. Clinical, cytogenetic, and molecular data from both patients were compared with those of previously reported related cases. A comparison of the extragenital symptoms revealed no differences between patients with or without sex reversal. In both cases, the symptoms were non-specific. Among 22 patients with a duplication in Xp, nine had unambiguous female genitalia and a well-documented duplication of the DSS region. Two patients with duplication of DSS showed ambiguous external genitalia. From these data, we conclude that induction of testicular tissue may start in these patients, but that the type of genitalia depends on the degree of subsequent degeneration by a gene in DSS.     

The Health Care Ethics Consultant, edited by Françoise Baylis

The Health Care Ethics Consultant marks a stage in the development of ethics consultancy. Ethics consultancy is a manifestation of a newly secularized society in which a new discipline has developed to fill a gap created by the combination of the diminishing influence of traditional moral authorities and the growth of new problems associated with the development of new technology and changes in society and culture. The stated primary objective of the book is to focus attention on an immediate practical problem: the role and responsibilities, the education and training, and the certification and accreditation of health ethics consultants. An edited collection of articles, the book originated as a research project financed by the Social Sciences and Humanities Research Council of Canada, undertaken by a Strategic Research Network which included faculty members from Dalhousie University, McGill University, the University of Toronto, McMaster University and the University of Calgary.     

Global mangrove root production,its controls and roles in the blue carbon budget of mangroves

Mangroves are among the most carbon-dense ecosystems worldwide. Most of the carbon in mangroves is found belowground, and root production might be an important control of carbon accumulation, but has been rarely quantified and understood at the global scale. Here, we determined the global mangrove root production rate and its controls using a systematic review and a recently formalised, spatially explicit mangrove typology framework based on geomorphological settings. We found that global mangrove root production averaged ~770 ± 202 g of dry biomass m⁻² year⁻¹ globally, which is much higher than previously reported and close to the root production of the most productive tropical forests. Geomorphological settings exerted marked control over root production together with air temperature and precipitation (r² ≈ 30%, p < .001). Our review shows that individual global changes (e.g. warming, eutrophication, drought) have antagonist effects on root production, but they have rarely been studied in combination. Based on this newly established root production rate, root-derived carbon might account for most of the total carbon buried in mangroves, and 19 Tg C lost in mangroves each year (e.g. as CO₂). Inclusion of root production measurements in understudied geomorphological settings (i.e. deltas), regions (Indonesia, South America and Africa) and soil depth (>40 cm), as well as the creation of a mangrove root trait database will push forward our understanding of the global mangrove carbon cycle for now and the future. Overall, this review presents a comprehensive analysis of root production in mangroves, and highlights the central role of root production in the global mangrove carbon budget.     

The Structure of a Sessile,Stalkless Crinoid (Holopus rangii)

Specimens of Holopus rangii (order Cyrtocrinida) were collected by submersible at depths of several hundred meters in the Caribbean and fixed for light and electron microscopy. The presence of an anus is confirmed. However, the chambered organ and glandular axial organ peculiar to crinoids are lacking. The gut lumen sometimes includes partially digested prey items up to several hundred micrometers in diameter, and we propose that Holopus may feed raptorially by rapidly closing its arms over demersal zooplankton. Electron microscopy of the arm reveals a radial nerve and a radial haemal channel, which light microscopy previously failed to demonstrate. The cuticle includes bacteria that are probably symbiotic. The ten brachial nerves of the aboral nervous system unite pairwise to form five calyx nerves. The calyx nerves, one in each radial position, are connected by a pentagonal, interradial commissure and then continue to the attached end of the body where they end blindly without forming an aboral nerve center. The absence of the aboral nerve center and related internal organs strengthens the argument that no basal ossicles are included in the skeleton of the calyx and suggests that Holopus may have evolved from stalked cyrtocrinid ancestors by saltatory loss of major body parts.     

Plate 457. Mutisia Subspinosa Compositae

Mutisia subspinosa Cav. is described and illustrated and its relationships with other members of Mutisia sect. Guariruma (Cass.) Cabrera discussed. Notes on its cultivation are provided along with a historical insight into the collections of Née, made on the Malaspina expedition.