The mitochondrial prohibitin complex is essential for embryonic viability and germline function in Caenorhabditis elegans

Prohibitins in eukaryotes consist of two subunits (PHB1 and PHB2) that together form a high molecular weight complex in the mitochondrial inner membrane. The evolutionary conservation and the ubiquitous expression in mammalian tissues of the prohibitin complex suggest an important function among eukaryotes. The PHB complex has been shown to play a role in the stabilization of newly synthesized subunits of mitochondrial respiratory enzymes in the yeast Saccharomyces cerevisiae. We have used Caenorhabditis elegans as model system to study the role of the PHB complex during development of a multicellular organism. We demonstrate that prohibitins in C. elegans form a high molecular weight complex in the mitochondrial inner membrane similar to that of yeast and humans. By using RNA-mediated gene inactivation, we show that PHB proteins are essential during embryonic development and are required for somatic and germline differentiation in the larval gonad. We further demonstrate that a deficiency in PHB proteins results in altered mitochondrial biogenesis in body wall muscle cells. This paper reports a strong loss of function phenotype for prohibitin gene inactivation in a multicellular organism and shows for the first time that prohibitins serve an essential role in mitochondrial function during organismal development.     

A Gondwanan origin of passerine birds supported by DNA sequences of the endemic New Zealand wrens

Zoogeographic, palaeontological and biochemical data support a Southern Hemisphere origin for passerine birds, while accumulating molecular data suggest that most extant avian orders originated in the mid-Late Cretaceous. We obtained DNA sequence data from the nuclear c-myc and RAG-1 genes of the major passerine groups and here we demonstrate that the endemic New Zealand wrens (Acanthisittidae) are the sister taxon to all other extant passerines, supporting a Gondwanan origin and early radiation of passerines. We propose that (i) the acanthisittids were isolated when New Zealand separated from Gondwana (ca. 82-85 Myr ago), (ii) suboscines, in turn, were derived from an ancestral lineage that inhabited western Gondwana, and (iii) the ancestors of the oscines (songbirds) were subsequently isolated by the separation of Australia from Antarctica. The later spread of passerines into the Northern Hemisphere reflects the northward migration of these former Gondwanan elements.     

Uridine 5′-Diphosphate-Glucose Dehydrogenase from Soybean Nodules

A highly purified preparation of uridine 5′-diphosphate (UDP)-glucose (Glc) dehydrogenase (DH; EC 1.1.1.22) has been characterized from soybean (Glycine max L.) nodules. The enzyme had native and subunit molecular masses of approximately 272 and 50 kD, respectively. UDP-Glc DH displayed typical hyperbolic substrate kinetics and had K_m values for UDP-Glc and NAD⁺ of 0.05 and 0.12 mm, respectively. Thymidine 5′-diphosphate-Glc and UDP-galactose could replace UDP-Glc as the sugar nucleotide substrate to some extent, but the enzyme had no activity with NADP⁺. Soybean nodule UDP-Glc DH was labile in the absence of NAD⁺ and was inhibited by a heat-stable, low-molecular-mass solute in crude extracts of soybean nodules. UDP-Glc DH was also isolated from developing soybean seeds and shoots of 5-d-old wheat and canola seedlings and was shown to have similar affinities for UDP-Glc and NAD⁺ as those of the soybean nodule enzyme. UDP-Glc DH from all of these sources was most active in young, rapidly growing tissues.     

Timing and duration of moult in three populations of Purple Sandpipers Calidris maritima with different moult/migration patterns

Timing and duration of primary moult in three populations of Purple Sandpipers Calidris maritima were described and discussed in relation to the birds’ need to complete moult before the onset of winter, when resources are required for survival. We predicted that moult would be completed earlier by birds wintering at higher latitudes. The south Norwegian breeding population, which moults and winters along the coast of east Britain (54–57°N) had a mean starting date of 21 July for primary moult (16 July for females and 24 July for males), a mean duration of 61 days, and completed on 20 September. Resident Icelandic (64–65°N) birds had a mean starting date of 22 July for primary moult (17 July for females and 25 July for males), a mean duration of 51 days, and completed on 11 September. Birds moulting in north Norway (70°N) arrived in north Norway in suspended primary moult or without having started moult, and completed it there. They had a mean completion date of 2 November for primary moult (31 October for females and 3 November for males). Starting date and duration could not be estimated because some suspended moult for an undetermined period, but it was thought that they started in late August. It is likely that most originated from Russia. The onset of moult appears to be set by the end of breeding and there is little overlap in these two events. The earlier start of moult by females in all three populations may be because they abandon the males when the chicks hatch, leaving the males to attend the chicks. Although the duration of primary moult followed the expected trend, being fastest in north Norway and slowest in Britain, the onset of moult was so late in north Norway that they had an unexpectedly late completion date, despite their rapid moult. The late completion of primary moult in north Norway suggests that wintering in the far north may not pose the energetic constraints on Purple Sandpipers that had previously been supposed.     

VLA-2 mediates the interaction of collagen with endothelium during in vitro vascular tube formation.

A confluent endothelial monolayer can be induced to form vascular tubes in response to collagen. We investigated possible mechanisms of collagen-induced tube formation by using antibodies to the VLA-2 integrin receptor and protein kinase C inhibitors. Pre-incubation of cells with anti-VLA-2 (which recognises both the α2 and β1 chains) and AK7 (which recognises only the α2 chain) showed a dose-dependent inhibition of tube formation. At 50 μg/ml, anti-VLA-2 completely inhibited collagen-induced tube formation, whereas AK7 caused only partial inhibition. Both chlorpromazine and trifluoperazine, at concentrations of 10μM, prevented tube formation (> 40% inhibition), In summary, the VLA-2 integrin receptor plays a role in the induction of tube formation by type I collagen. Protein kinase C may be activated during this process.     

The use of species abundance estimates in marine benthic studies

The application of species abundance estimates, commonly used in terrestrial plant ecology, to marine benthic dredge data is advocated. Two possible scales were tested for their ability to measure adequately the structure of an assemblage by computing measures of evenness diversity McNaughton's dominance index, and Morisita's index of dispersion using both real counts obtained from grab samples and these counts transformed into the two respective abundance estimates. It is concluded that species abundance estimators, when applied to grab or dredge data result in significant savings in sample processing time with only a minimal loss of information about assemblage structure.     

BIOCHEMICAL BASIS OF FLORAL COLOR POLYMORPHISM IN A HETEROCYANIC POPULATION OF TRILLIUM SESSILE (LILIACEAE)

A study of flavonoids occurring within a heterocyanic population of Trillium sessile was made to determine the chemical basis of a common floral color polymorphism in this species. In the study population, three floral color phenotypes (red, pink, yellow) are determined primarily by the presence or absence of anthocyanin compounds in the petal tissue, and secondarily by quantitative differences in the concentration of several flavonol glycosides. Petals of red phenotypes contain both cyanidin 3-arabinoside and 3-diarabinoside, petals of pink phenotypes contain only cyanidin 3-arabinoside, and petals of yellow phenotypes lack cyanidin entirely. Quercetin 3-0-glucoside, quercetin 3-0-arabinoglucoside, quercetin 3–0-arabinogalactoside, and quercetin 3-0-arabinogalactosyl, 7-0-glucoside occur in petals of all three phenotypes but differ in relative amounts. Petals of the red phenotype have mostly 3-0-biosides, but lesser amounts of both quercetin 3-0-glucoside and the 3,7-0-triglycoside. Petals of the pink phenotype contain relatively equal amounts of quercetin mono-, di-, and triglycosides. Petals of the yellow phenotypes contain mostly quercetin 3,7-0-triglycosides, and less mono- and di-glycosides. Small amounts of a quercetin tetraglycoside were detected in petals of both yellow and pink phenotypes, but not in red phenotypes. The enhancement of quercetin polyglycoside biosynthesis in yellow petal phenotypes is attributed to the shunting of dihydroflavonol precursors to synthesis of quercetin compounds when their conversion to anthocyanins is blocked genetically.     

Holistic Pattern Analysis as an Alternative to Pattern Cladistics in Hypothesizing Crustacean Phylogenetic Sequences

There has been a growing realization that ‘true’ phylogenetic relationships cannot be determined using pattern cladistical methods alone. The applications of such techniques to the problem of crustacean evolution is first examined using the results presented by Wilson (in this issue). It is found that the degree of correlation of characters in the head vs trunk regions explains very well the grouping of taxa in the cladograms, suggesting that the groups are nothing more than mathematical constructs. The argument is presented that functions of different parts of the crustacean body need to be determined, along with an understanding of how the body morphology is designed in accordance with the dominant functions. A method for producing hypothesized phylogenetic sequences from an analysis of body morphology is proposed and examined using the amphipod family Iphimediidae. It is suggested that cladograms are merely hypotheses and can be tested using functional morphological information of the type outlined.