Spermatogenesis and related plasma androgen levels in Atlantic halibut (Hippoglossus hippoglossus L.)

Spermatogenesis in male Atlantic halibut (Hippoglossus hippoglossus L.) was investigated by sampling blood plasma and testicular tissue from 15-39-month-old fish. The experiment covered a period in which all fish reached puberty and completed sexual maturation at least once. The germinal compartment in Atlantic halibut testis appears to be organized in branching lobules of the unrestricted spermatogonial type, because spermatocysts with spermatogonia were found throughout the testis. Spermatogenesis was characterized histologically, and staged according to the most advanced type of germ cell present: spermatogonia (Stage I), spermatogonia and spermatocytes (Stage II), spermatogonia, spermatocytes and spermatids (Stage III), spermatogonia, spermatocytes, spermatids and spermatozoa (Stage IV), and regressing testis (Stage V). Three phases could be distinguished: first, an initial phase with low levels of circulating testosterone (T; quantified by RIA) and 11-ketotestosterone (11-KT; quantified by ELISA), spermatogonial proliferation, and subsequently the initiation of meiosis marked by the formation of spermatocytes (Stage I and II). Secondly, a phase with increasing T and 11-KT levels and with haploid germ cells including spermatozoa present in the testis (Stage III and IV). Thirdly, a phase with low T and 11-KT levels and a regressing testis with Sertoli cells displaying signs of phagocytotic activity (Stage V). Circulating levels of 11-KT were at least four-fold higher than those of T during all stages of spermatogenesis. Increasing plasma levels of T and 11-KT were associated with increasing testicular mass throughout the reproductive cycle. The absolute level of, or the relation between, testis growth and circulating androgens were not significantly different in first time spawners compared to fish that underwent their second spawning season. These results provide reference levels for Atlantic halibut spermatogenesis.     

Syntenic relationships between Medicago truncatula and Arabidopsis reveal extensive divergence of genome organization

Arabidopsis and Medicago truncatula represent sister clades within the dicot subclass Rosidae. We used genetic map-based and bacterial artificial chromosome sequence-based approaches to estimate the level of synteny between the genomes of these model plant species. Mapping of 82 tentative orthologous gene pairs reveals a lack of extended macrosynteny between the two genomes, although marker collinearity is frequently observed over small genetic intervals. Divergence estimates based on non-synonymous nucleotide substitutions suggest that a majority of the genes under analysis have experienced duplication in Arabidopsis subsequent to divergence of the two genomes, potentially confounding synteny analysis. Moreover, in cases of localized synteny, genetically linked loci in M. truncatula often share multiple points of synteny with Arabidopsis; this latter observation is consistent with the large number of segmental duplications that compose the Arabidopsis genome. More detailed analysis, based on complete sequencing and annotation of three M. truncatula bacterial artificial chromosome contigs suggests that the two genomes are related by networks of microsynteny that are often highly degenerate. In some cases, the erosion of microsynteny could be ascribed to the selective gene loss from duplicated loci, whereas in other cases, it is due to the absence of close homologs of M. truncatula genes in Arabidopsis.     

Evaluation of five different cDNA labeling methods for microarrays using spike controls

Background

Several different cDNA labeling methods have been developed for microarray based gene expression analysis. We have examined the accuracy and reproducibility of such five commercially available methods in detection of predetermined ratio values from target spike mRNAs (A. thaliana) in a background of total RNA. The five different labeling methods were: direct labeling (CyScribe), indirect labeling (FairPlay? – aminoallyl), two protocols with dendrimer technology (3DNA^® Array 50? and 3DNA^® submicro?), and hapten-antibody enzymatic labeling (Micromax? TSA?). Ten spike controls were mixed to give expected Cy5/Cy3 ratios in the range 0.125 to 6.0. The amounts of total RNA used in the labeling reactions ranged from 5 – 50 μg.

Results

The 3DNA array 50 and CyScribe labeling methods performed best with respect to relative deviation from the expected values (16% and 17% respectively). These two methods also displayed the best overall accuracy and reproducibility. The FairPlay method had the lowest total experimental variation (22%), but the estimated values were consistently higher than the expected values (36%). TSA had both the largest experimental variation and the largest deviation from the expected values (45% and 48% respectively).

Conclusion

We demonstrate the usefulness of spike controls in validation and comparison of cDNA labeling methods for microarray experiments.

     

Intracellular infection with Spironucleus barkhanus (Diplomonadida: Hexamitidae) in farmed Arctic char Salvelinus alpinus

A case of intracellular systemic infection with the diplomonad flagellate Spironucleus barkhanus in farmed Arctic char Salvelinus alpinus is described. The parasites were widely disseminated throughout the vasculature and in most organs. Aggregates of the parasites were seen within well-defined structures regarded as host cells in capillaries and sinusoids of the liver, spleen and head kidney. Intracellular infection with Spironucleus spp. has never previously been reported. The prevalence of infection and mortality in the affected farm was low. In contrast to systemic spironucleosis in farmed Atlantic salmon, and despite huge numbers of flagellates in the vasculature, the tissues of the organs were remarkably unaffected. The relatively few gross and histopathological lesions may indicate that Arctic char are more tolerant to this parasite than Atlantic salmon.     

Control of carbon partitioning and photosynthesis by the triose phosphate/phosphate translocator in transgenic tobacco plants (Nicotiana tabacum). II. Assessment of control coefficients of the triose phosphate/phosphate translocator

 Transgenic tobacco (Nicotiana tabacum L.) plants with decreased and increased transport capacities of the chloroplast triose phosphate/phosphate translocator (TPT) were used to study the control the TPT exerts on the flux of starch and sucrose biosynthesis, as well as CO₂ assimilation, respiration and photosynthetic electron transport. For this purpose, tobacco lines with an antisense repression of the endogenous TPT (αTPT) and tobacco lines overexpressing a TPT gene from Flaveria trinervia (FtTPT) were used. In ambient CO₂, there was no or little effect of altered TPT transport activities on either rates of photosynthetic electron transport and/or CO₂ assimilation. However, in elevated CO₂ (1500 μl · l⁻¹) and low O₂ (2%) the TPT exerted strong control on the rate of CO₂ assimilation (control coefficient for the wild type; C^JA _TPT=0.30) in saturating light. Similarly, the incorporation of ¹⁴C into starch in high CO₂ was increased in tobacco plants with decreased TPT activity, but was reduced in plants overexpressing the TPT from F. trinervia. Thus, the TPT exerted negative control on the rate of starch biosynthesis with a C^JStarch _TPT=−0.19 in the wild type estimated from a hyperbolic curve fitted to the data points. This was less than the positive control strength on the rate of sucrose biosynthesis (C^JSuc _TPT=0.35 in the wild type). Theoretically, the positive control exerted on sucrose biosynthesis should be numerically identical to the negative control on starch biosynthesis unless additional metabolic pathways are affected. The rate of dark respiration showed some correlation with the TPT activity in that it increased in FtTPT overexpressors, but decreased in αTPT plants with an apparent control coefficient of C^JRes _TPT=0.24. If the control on sucrose biosynthesis is referred to as “gain of carbon” (positive control) and the control on starch biosynthesis as well as dark respiration as a “loss of carbon” (negative control) for sucrose biosynthesis and subsequent export, the sum of the control coefficients on dark respiration and starch biosynthesis would be numerically similar to the control coefficient on the rate of sucrose biosynthesis. There was also some control on the rate of photosynthetic electron transport, but only at high light and in elevated CO₂ combined with low O₂. The control coefficient for the rate of photosynthetic electron transport was C^JETR _TPT=0.16 in the wild type. Control coefficients were also calculated for plants with elevated and lowered TPT activity. Furthermore, the extent to which starch degradation/glucose utilisation compensates for the lack of triose phosphate export was assessed. The TPT also exerted control on metabolite contents in air. Received: 26 March 1999 / Accepted: 21 August 1999     

Modelling spatial dynamics of fish

Our ability to model spatial distributions of fish populations is reviewed by describing the available modelling tools. Ultimate models of the individual's motivation for behavioural decisions are derived from evolutionary ecology. Mechanistic models for how fish sense and may respond to their surroundings are presented for vision, olfaction, hearing, the lateral line and other sensory organs. Models for learning and memory are presented, based both upon evolutionary optimization premises and upon neurological information processing and decision making. Functional tools for modelling behaviour and life histories can be categorized as belonging to an optimization or an adaptation approach. Among optimization tools, optimal foraging theory, life history theory, ideal free distribution, game theory and stochastic dynamic programming are presented. Among adaptation tools, genetic algorithms and the combination with artificial neural networks are described. The review advocates the combination of evolutionary and neurological approaches to modelling spatial dynamics of fish.