Egg size-dependent expression of growth hormone receptor accompanies compensatory growth in fish

Large egg size usually boosts offspring survival, but mothers have to trade off egg size against egg number. Therefore, females often produce smaller eggs when environmental conditions for offspring are favourable, which is subsequently compensated for by accelerated juvenile growth. How this rapid growth is modulated on a molecular level is still unclear. As the somatotropic axis is a key regulator of early growth in vertebrates, we investigated the effect of egg size on three key genes belonging to this axis, at different ontogenetic stages in a mouthbrooding cichlid (Simochromis pleurospilus). The expression levels of one of them, the growth hormone receptor (GHR), were significantly higher in large than in small eggs, but remarkably, this pattern was reversed after hatching: young originating from small eggs had significantly higher GHR expression levels as yolk sac larvae and as juveniles. GHR expression in yolk sac larvae was positively correlated with juvenile growth rate and correspondingly fish originating from small eggs grew faster. This enabled them to catch up fully in size within eight weeks with conspecifics from larger eggs. This is the first evidence for a potential link between egg size, an important maternal effect, and offspring gene expression, which mediates an adaptive adjustment in a relevant hormonal axis.     

Timing of nuclear maturation and postovulatory aging in oocytes of in vitro-grown mouse follicles with or without oil overlay

Meiotic maturation of the oocyte is a timed sequence of events induced by the ovulatory LH surge. In vitro maturation of oocytes is known to alter the meiotic time course. This study documented the timing of meiosis in oocytes grown in vitro for 12 days, from the preantral follicle stage onward, and the influence of an oil overlay. In the oil-free culture, the stability of the metaphase II spindle was further explored to determine the postovulatory aging events. After the maturation stimulus, in vitro-grown oocytes were collected at 2-h intervals spanning the period of meiosis (0-18 h) and at 3-h intervals during early postovulatory aging (18-27 h). Stage of maturation was assessed both morphologically and by detailed spindle analysis and chromosome alignment. Results revealed that oil overlay did not impair the competence of cultured oocytes to proceed to meiosis II, but delayed meiosis I progression. Oil overlay during culture causes a different hormonal exposure of the follicles by a differential segregation into the oil overlay. The use of a progesterone receptor antagonist, however, did not induce a delay in meiotic progression. Aging effects in oil-free cultured follicles were detected 5 h after the establishment of the metaphase II spindle, comparable to their in vivo grown counterparts. The predominant effect of aging was an interphase-like appearance of the cytoskeleton. So an optimal time window for fertilization after in vitro follicular growth was determined to be 16-21 h after maturation induction.     

A biogeographical analysis of rotifers of the genus Trichocerca Lamarck, 1801 (Trichocercidae,Monogononta, Rotifera), with notes on taxonomy

An analysis of distribution patterns reveals a unique group of Nearctic endemics in Trichocerca Lamarck, 1801. This group, comprising 13.4% of all taxa analysed in the genus, is of diverse origin. A glacial origin is postulated for one species. The observed biogeographic pattern of eight others, and possibly two New World taxa, suggests a pre-Pleistocene origin followed by differential extinctions during glaciations in the Nearctic and Palaearctic. In general, endemism in Trichocerca is strongly biased towards the Northern hemisphere, with no endemism in tropical regions. This suggests a Laurasian origin of the genus. The analysis further reveals a majority (65.7%) of widely distributed taxa, with strict cosmopolitanism in more than a third of the species analysed. Latitudinal variation is evident in 26.9% of Trichocerca, and a warm-water preference appears to be indicated for a majority of these. Although the results should be interpreted with caution due to confused taxonomy, a Southern hemisphere, warm-water and Northern hemisphere, cold water component appear to be present. Comments on the taxonomy and distribution of several species are provided, along with illustrations of poorly known species. Suggestions include elevating T. maior (Hauer, 1936) to species rank, and several new cases of synonymy.     

Fifteen species in one: deciphering the <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> species complex (Rotifera,Monogononta) through DNA taxonomy

Understanding patterns and processes in biological diversity is a critical task given current and rapid environmental change. Such knowledge is even more essential when the taxa under consideration are important ecological and evolutionary models. One of these cases is the monogonont rotifer cryptic species complex Brachionus plicatilis, which is by far the most extensively studied group of rotifers, is widely used in aquaculture, and is known to host a large amount of unresolved diversity. Here we collate a dataset of previously available and newly generated sequences of COI and ITS1 for 1273 isolates of the B. plicatilis complex and apply three approaches in DNA taxonomy (i.e. ABGD, PTP, and GMYC) to identify and provide support for the existence of 15 species within the complex. We used these results to explore phylogenetic signal in morphometric and ecological traits, and to understand correlation among the traits using phylogenetic comparative models. Our results support niche conservatism for some traits (e.g. body length) and phylogenetic plasticity for others (e.g. genome size).     

Vitamin E and selenium treatment of monocrotaline induced hepatotoxicity in rats

Monocrotaline (MCT) is a hepatotoxic pyrrolizidine alkaloid that is derived from plants; exposure may occur by consumption of contaminated grains, herbal teas and medicines. MCT can cause liver damage. We investigated the antioxidant effects of selenium (Se) and vitamin E against the toxic effects of MCT. Female Wistar albino rats were divided into four groups: a control group, an MCT group, an MCT + Se group, and an MCT + vitamin E group. Liver tissues were harvested, fixed, processed to paraffin and sections were cut. Anti-von Willebrand factor (vWF) immunohistochemistry, terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL), and hematoxylin and eosin staining were performed. Serum and liver tissue glutathione (GSH), catalase (CAT), and glutathione peroxidase (GPx) levels were measured. Histopathological and TUNEL data showed significantly increased liver damage in the MCT group compared to controls. Histopathological and TUNEL staining indicated significant improvements in the MCT + vitamin E and MCT + Se groups compared to the MCT group. MCT significantly reduced the serum GSH level and GPx activity, and liver GPx activity. Biochemical data indicated a significant improvement in serum GSH level in the MCT + vitamin E group compared to the MCT group. We suggest that vitamin E and Se afford limited protection against MCT hepatotoxicity.     

A plant-specific cyclin-dependent kinase is involved in the control of G2/M progression in plants

Cyclin-dependent kinases (CDKs) control the key transitions in the eukaryotic cell cycle. All the CDKs known to control G(2)/M progression in yeast and animals are distinguished by the characteristic PSTAIRE motif in their cyclin-binding domain and are closely related. Higher plants contain in addition a number of more divergent non-PSTAIRE CDKs with still obscure functions. We show that a plant-specific type of non-PSTAIRE CDKs is involved in the control of the G(2)/M progression. In synchronized tobacco BY-2 cells, the corresponding protein, accumulated in a cell cycle-regulated fashion, peaking at the G(2)/M transition. The associated histone H1 kinase activity reached a maximum in mitosis and required a yet unidentified subunit to be fully active. Down-regulation of the associated kinase activity in transgenic tobacco plants using a dominant-negative mutation delayed G(2)/M transition. These results provide the first evidence that non-PSTAIRE CDKs are involved in the control of the G(2)/M progression in plants.     

Expression of CKS1At in Arabidopsis thaliana indicates a role for the protein in both the mitotic and the endoreduplication cycle

Although endoreduplication is common in plants, little is known about the mechanisms regulating this process. Here, we report the patterns of endoreduplication at the cellular level in the shoot apex of Arabidopsis thaliana L. Heynh. plants grown under short-day conditions. We show that polyploidy is developmentally established in the pith, maturing leaves, and stipules. To investigate the role of the cell cycle genes CDC2aAt, CDC2bAt, CYCB1;1, and CKS1At in the process of endoreduplication, in-situ hybridizations were performed on the vegetative shoot apices. Expression of CDC2aAt, CDC2bAt, and CYCB1;1 was restricted to mitotically dividing cells. In contrast, CKS1At expression was present in both mitotic and endoreduplicating tissues. Our data indicate that CDC2aAt, CDC2bAt, and CYCB1;1 only operate during mitotic divisions, whereas CKS1At may play a role in both the mitotic and endoreduplication cycle. Received: 11 May 1998 / Accepted: 29 September 1998     

Construction and characterization of an ovine BAC contig spanning the callipyge locus

We describe the construction of an ovine BAC contig spanning a 4.6 centimorgan (cM) chromosome segment known to contain the callipyge (CLPG) locus. The contig comprises 21 ovine BAC clones jointly covering approximately 900 kilobases (Kb). Two gaps in the BAC contig, spanning 10 and 7.5 Kb, respectively, were bridged by long range PCR. The corresponding chromosome region was shown to be characterized by an unusually low Kb to cM ratio (164 Kb/cM) and a high density of Not1 sites (1:126 Kb) possibly reflecting a high gene density in the corresponding chromosome region. Equivalent amplification of 64 sequence tagged sites spanning the corresponding region from homozygous +/+ and CLPG/CLPG individuals disproves the hypothesis of a major deletion causing the CLPG mutation.     

Role of tapering in aortic wave reflection: hydraulic and mathematical model study

Pressure and flow have been measured simultaneously at six locations along the aorta of an anatomically correct 1:1 scale hydraulic elastic tube model of the arterial tree. Our results suggest a discrete reflection point at the level of the renal arteries based on (i) the quarter-wavelength formula and (ii) the comparison of foot-to-foot (c(ff)) and apparent phase velocity (c(app)). However, separation of the pressure wave into an incident and reflected wave at all six locations indicates continuous reflection: a reflected wave is generated at each location as the forward wave passes by. We did a further analysis using a mathematical transmission line model with a simple tapering geometry (length 50 cm, 31 and 11 mm proximal and distal diameter, respectively) for a low (0.32 ml/mmHg), normal (1.6 ml mmHg) and high (8 ml/mmHg) value of total arterial compliance. Using the quarter-wavelength formula, a discrete reflection point is found at x = 33 cm, the level of the renal arteries, independent of the value of total compliance. However, local analysis comparing c(ff) and c(app) does not reveal a marked reflection site, and the analysis of incident and reflected waves merely suggests a continuous reflection. We therefore conclude that the measured in vivo aortic wave reflection indices are the result of at least two interacting phenomena: a continuous wave reflection due to tapering, and local reflections arising from branches at the level of the diaphragm. The continuous reflection is hidden in the input impedance pattern. Using the quarter-wavelength formula or the classical wave separation theory, it appears as a reflection coming from a single discrete site, confusingly also located at the level of the diaphragm. Therefore, the quarter-wavelength formula and the linear wave separation theory should be used with caution to identify wave reflection zones in the presence of tapering, i.e., in most mammalian arteries.