褪黑素与绵羊的季节性生殖

绵羊是一种短光照型生殖动物,具有明显的生殖季节性。人们普遍认为,绵羊生殖周期与环境光周期的同步变化是通过褪黑素作用于下丘脑－垂体－性腺轴系统来实现的。近年来的不少研究结果表明,绵羊对光周期的感受性还受褪黑素受体的调控。现从生态学（光周期的生殖效应）、神经内分泌学和分子生物学（褪黑素受体）等领域的研究进展出发,对褪黑素调控绵羊自然季节性生殖的作用及机制进行系统综述。     

Transferrin types and reproduction in sheep

Transferrin types were determined for flocks of Finnish Landrace, Clun Forest, Soay and Merino sheep and gene frequencies were calculated. Analysis of ratios of transferrin types in segregating matings of Finnish Landrace and Clun Forest revealed a significant excess of heterozygotes in matings of heterozygous rams with heterozygous and with homozygous ewes. In Finnish Landrace, matings of sheep homozygous for Tf ^c to those heterozygous for Tf ^C gave a significant excess of homozygous male lambs and heterozygous female lambs. Finnish Landrace ewes of transferrin type BD had smaller litters than ewes of other types.     

Genomic prediction of reproduction traits for Merino sheep

Economically important reproduction traits in sheep, such as number of lambs weaned and litter size, are expressed only in females and later in life after most selection decisions are made, which makes them ideal candidates for genomic selection. Accurate genomic predictions would lead to greater genetic gain for these traits by enabling accurate selection of young rams with high genetic merit. The aim of this study was to design and evaluate the accuracy of a genomic prediction method for female reproduction in sheep using daughter trait deviations (DTD) for sires and ewe phenotypes (when individual ewes were genotyped) for three reproduction traits: number of lambs born (NLB), litter size (LSIZE) and number of lambs weaned. Genomic best linear unbiased prediction (GBLUP), BayesR and pedigree BLUP analyses of the three reproduction traits measured on 5340 sheep (4503 ewes and 837 sires) with real and imputed genotypes for 510 174 SNPs were performed. The prediction of breeding values using both sire and ewe trait records was validated in Merino sheep. Prediction accuracy was evaluated by across sire family and random cross‐validations. Accuracies of genomic estimated breeding values (GEBVs) were assessed as the mean Pearson correlation adjusted by the accuracy of the input phenotypes. The addition of sire DTD into the prediction analysis resulted in higher accuracies compared with using only ewe records in genomic predictions or pedigree BLUP. Using GBLUP, the average accuracy based on the combined records (ewes and sire DTD) was 0.43 across traits, but the accuracies varied by trait and type of cross‐validations. The accuracies of GEBVs from random cross‐validations (range 0.17–0.61) were higher than were those from sire family cross‐validations (range 0.00–0.51). The GEBV accuracies of 0.41–0.54 for NLB and LSIZE based on the combined records were amongst the highest in the study. Although BayesR was not significantly different from GBLUP in prediction accuracy, it identified several candidate genes which are known to be associated with NLB and LSIZE. The approach provides a way to make use of all data available in genomic prediction for traits that have limited recording.     

Seasonality of reproduction in sheep and its control by photoperiod

Seasonality of the reproductive cycle in sheep is a general phenomenon for mid-latitude breeds. The proximal part (breeding season) and also partially distal part (end of gestation and beginning of lactation) of this cycle is controlled by photoperiod, whatever the form of light regimens. Data are presented which indicate that male and female do not necessarily have the same photoperiodic sensitivity. Gonadal stimulation in the ram starts 1.5-2 months earlier than in the ewe under annual variations. Photoperiod controls the reproductive cycle by the intermediary of the hypothalamo-pituitary axis. There are both a steroid-independent and a steroid-dependent effect of light, depending on both decreasing and increasing daylength in mid-latitudes. Data are also presented which support Bunning's hypothesis on photoperiodic time measurement in mammals. Sheep measure photoperiodic time by using a circadian rhythm of photosensitivity. Daylength is not measured by the total duration of exposure to light but by the illumination of two special set points during the day, one of them entraining the circadian rhythm of photosensitivity and the other inducing or not inducing a physiological response if it is coincident, or not coincident, with photoinducible phase of that rhythm. A photoinducible phase has been found for prolactin secretion, and perhaps also for LH secretion. Melatonin secretion is used by sheep for measuring daylength. However, that secretion disappears during two set points during the day, thus raising the possibility of using alternatively melatonin and light pulse for controlling the reproductive cycle in sheep.     

External and internal complexity of complex adaptive systems

We introduce concepts of external and internal complexity to analyze the relation between an adaptive system and its environment. We apply this theoretical framework to the construction of models in a cognitive system and the selection between hypotheses through selective observations performed on a data set in a recurrent process and propose a corresponding neural network architecture.     

External and internal diffusion in heterogeneous enzymes systems

The intrusion of diffusion in heterogeneous enzyme reactions, which follow. Michaelis-Menten kinetics, is quantitatively characterized by dimensionless parameters that are independent of the substrate concentration. The effects of these parameters on the overall rate of reaction is illustrated on plots commonly employed in enzyme kinetics. The departure from Michaelis-Menten kinetics due to diffusion limitations can be best assessed by using Hofstee plots which are also suitable to distinguish between internal and external transport effects. A graphical method is described for the evaluation of the reaction rate as a function of the surface concentration of the substrate from measured data.     

External and internal forms of yeast aminopeptidase II.

1. Intact cells of Saccharomyces cerevisiae catalyze the hydrolysis of various aminopeptidase substrates. This activity is not due to permeation of substrates and products but exerted by an external enzyme. 2. From its substrate specificity and the effects of pH and inhibitors the enzyme was identified as aminopeptidase II. 3. About 40% of total aminopeptidase II activity is detectable with untreated exponentially growing cells. Up to two thirds of the external enzyme is released into the medium during enzymic digestion of the cell wall, while little enzyme is liberated by osmotic shock. Membrane preparations contained only small amounts of aminopeptidase II; thus, the localization of the external enzyme appears to be similar to that of the so-called 'periplasmic' yeast hydrolases. 4. By cytochemical methods the presence of aminopeptidase II in the cell envelope was visualized. 5. In contrast to aminopeptidase II, yeast dipeptidase is an entirely intracellular enzyme.     

Influence of exogenous melatonin on seasonality of reproduction in sheep

Two experiments were performed to examine the effects of exogenous melatonin on seasonality of reproduction in ewes. To simulate the secretory pattern observed on the shortest day of the year, 2.5 mg melatonin were administered i.m. at 1600 hr each day. This dosage has been shown to keep serum concentrations of melatonin elevated until the onset of darkness on the longest day of the year (i.e. ～ 6 hr). In experiment 1, ewes were administered melatonin (n=10) or vehicle (n=10) from June 20 until the onset of the breeding season. Jugular blood samples were collected three times weekly and the serum was stored for analysis of progesterone by radioimmunoassay. The interval from the first day of treatment until serum concentrations of progesterone remained above 1 ng/ml in two consecutive samples (indicative of the formation of a corpus luteum) was 39.3 ± 4.1 days in the melatonin-treated ewes and 61.4 ± 4.6 days in the ewes receiving vehicle (P < 0.05). In the second experiment, ewes were given injections of melatonin (n=6) or vehicle (n=6) from December 21 until September 1. Again, jugular blood samples were collected three times weekly for analysis of progesterone. The interval from initiation of treatment until serum concentrations of progesterone remained below 1 ng/ml for at least 5 consecutive samples was 80.2 ± 3.3 days in the melatonin-treated ewes and 37.8 ± 6.5 days in the control ewes (P < 0.05). However, when treatment was begun on January 1 the interval from the initiation of treatment until serum concentrations of progesterone were greater than 1 ng/ml in two consecutive samples after June 1 was not different between melatonin-treated and control ewes. These data indicate that adminis-tration of melatonin to ewes can hasten the onset of the breeding season in the fall or extend the length of the breeding season in the spring, but after prolonged administration the ewes may become refractory to the treatment.     

Identification of sheep ovary genes potentially associated with off-season reproduction

Off-season reproduction is a favorable economic trait for sheep industry.Hu sheep,an indigenous Chinese sheep breed,demonstrates a higher productivity of lambs and displays year-around oestrous behavior under proper nutrition and environment.The genetic basis behind these traits,however,is not well understood.In order to identify genes associated with the off-season reproduction,we constructed a suppression subtractive hybridization(SSH) cDNA library using pooled ovary mRNAs of 6 oestrous Hu females as a tester and the pooled ovary mRNAs of 6 non-oestrous Chinese Merino females as a driver.A total of 382 resulting positive clones were obtained after the SSH.We identified 114 differentially up-regulated genes in oestrous Hu sheep by using subsequent screening and DNA sequencing,of which 8 were previously known,93 were reported for the first time in sheep,and 13 were novel with no significant homology to any sequence in the DNA databases.Functions of the genes identified are related to cell division,signal transduction,structure,metabolism,or cell defense.To validate the results of SSH,6 genes(Ntrk2,Ppap2b,Htra1,Nid1,Serpine2 and Foxola) were selected for conformational analysis using quantitative real-time PCR(qRT-PCR),and two of them(Htral and Foxola) were verified by Northern blot.All of the 6 genes were differentially up-regulated in the ovary of oestrous Hu.It is obvious that off-season reproduction is a complex trait involving multiple genes in multiple organs.This study helps to provide a foundation for the final identification of functional genes involved in the sheep ovary.     

External and internal tags for the green sea urchin

Two internal and three external tags were tested on the green sea urchin. Desirable qualities of a tag were high sea urchin survival, retention for at least a few months, detection on the sea floor by divers, identification of individuals, quick application, and low cost. These objectives were met by an external nylon screw tag visible to divers and two internal aluminum tags detectable with an underwater metal detector. Successful tags were inserted through a hole drilled in the test and were tested in the laboratory and field. All internal tags were retained for the full duration of the 4-month trial and did not retard growth or affect survival. Divers could identify individual urchins with nylon screw tags, but the tag retention rate was lower.     

The dual klepsydra model of internal time representation and time reproduction

We present a model of the internal representation and reproduction of temporal durations, the 'dual klepsydra' model (DKM). Unlike most contemporary models operating on a 'pacemaker-counter' scheme, the DKM does not assume an oscillatory process as the internal time-base. It is based on irreversible, dissipative processes in inflow/outflow systems (leaky klepsydrae), whose states are continuously compared; if their states are equal, durations are subjectively perceived as equal. Model-based predictions fit experimental time reproduction data with good accuracy, and show qualitative features not accounted for by other models. The deterministic model is characterized by two parameters, kappa (outflow rate coefficient) and eta (ratio of inflow rates). A stochastic version of the model (SDKM) assumes randomly fluctuating inflows, involves two more parameters, and accounts for intra-individual variance of reproduced durations. Analysis of the SDKM leads to non-trivial problems in the stochastic theory, briefly sketched here. Methods of parameter estimation for both deterministic and stochastic versions are given. Applying the DKM to the subjective experience of time passage, we show how subjective measure of elapsed time is constituted. Finally, essential features of the model and its possible neurophysiological interpretation are discussed.     

Genetic mapping of quantitative trait loci for aseasonal reproduction in sheep

The productivity and economic prosperity of sheep farming could benefit greatly from more effective methods of selection for year-round lambing. Identification of QTL for aseasonal reproduction in sheep could lead to more accurate selection and faster genetic improvement. One hundred and twenty microsatellite markers were genotyped on 159 backcross ewes from a Dorset × East Friesian crossbred pedigree. Interval mapping was undertaken to map the QTL underlying several traits describing aseasonal reproduction including the number of oestrous cycles, maximum level of progesterone prior to breeding, pregnancy status determined by progesterone level, pregnancy status determined by ultrasound, lambing status and number of lambs born. Seven chromosomes (1, 3, 12, 17, 19, 20 and 24) were identified to harbour putative QTL for one or more component traits used to describe aseasonal reproduction. Ovine chromosomes 12, 17, 19 and 24 harbour QTL significant at the 5% chromosome-wide level, chromosomes 3 and 20 harbour QTL that exceeded the threshold at the 1% chromosome-wide level, while the QTL identified on chromosome 1 exceeded the 1% experiment-wide significance level. These results are a first step towards understanding the genetic mechanism of this complex trait and show that variation in aseasonal reproduction is associated with multiple chromosomal regions.     

The influence of haemoglobin types on reproduction and production in Hungarian Merino sheep

Fewer Hb A and AB lambs were born than expected in the investigated Hungarian Merino population but the factors responsible for these differences could not be identified. The Hb A and AB breeding ewes were not inferior to their B type herd mates with respect to average daily weight gain (when lambs), reproductive performance (prolificacy) and survival rate. Their reproductive performance was, in some cases, even better than that of the ewes with other haemoglobin types. The haemoglobin types cannot be used as markers when selecting for higher prolificacy.     

Cytogenetics and reproduction of sheep with multiple centric fusions (Robertsonian translocations)

The significance of centric fusions (Robertsonian translocations) in domestic animals, with special reference to sheep, is reviewed. The mating is described of a further 856 ewes with either a normal chromosome number 2n = 54 or carrying one or more of the three different translocations (centric fusions) t1, t2 and t3 in various heterozygous and homozygous arrangements. Rams which were used in the matings were homozygous for one of the translocation chromosomes (2n = 52), double heterozygotes (2n = 52), triple heterozygotes (2n = 51) or were carriers of 4 translocation chromosomes (2n = 50) and 5 translocation chromosomes (2n = 49). A remarkably even distribution of segregation products was recorded in the progeny of all combinations of translocation ewes x translocation rams in those groups in which sufficient animals were available for statistical analysis. Forty-eight chromosomally different groups of animals were mated. Further, the overall fertility of the translocation sheep, measured by conception rate to first service, lambing percentage and number of ewes which did not breed a lamb, was not significantly different from New Zealand national sheep breeding data. In some groups the poorer reproductive performance could be explained by the age structure of the flock and inbreeding depression, which probably affected the performance of some animals. Sheep with progressively decreasing chromosome numbers, due to centric fusion, 2n = 50, 2n = 49 and 2n = 48, are reported. The 2n = 48 category represents a triple homozygous ewe and a triple homozygous ram and is the first report of the viable evolution of such domestic animals. Less than 1% of phenotypically abnormal lambs were recorded in a total of 1995 progeny born over 10 years. It is now considered that there is little or no evidence to suggest that centric fusions in a variety of combinations affect the total productive fitness of domestic sheep. It is suggested that future research should be more actively directed to understanding their genetic significance.     

The role of omega-3 polyunsaturated fatty acids in reproduction of sheep and cattle

The positive effects of fat and energy supplementation on improvements in reproduction are well documented. However, the specific effects of omega-3 polyunsaturated fatty acids (n-3) on reproductive success in ruminants have not been examined in detail. While the link between n-3 and markers associated with reproduction, in particular, prostaglandin F(2α) (PGF(2α)) and the link between PGF(2α) and reproductive outcomes are well established, evidence of a direct effect of high n-3 diets on measurable reproductive outcomes in ruminants is lacking. Therefore, the aim of the current review was to examine the effect of n-3 on a number of reproductive markers and measurable outcomes in sheep and cattle. There is strong evidence linking consumption of diets high in n-3 with reduced circulating peripheral inflammatory markers such as PGF(2α). Inflammatory eicosanoids including PGF(2α), in particular, can significantly affect reproduction outcomes such as the onset of oestrus, embryo survival and parturition. While there is also evidence linking n-3 supplementation with longer time to oestrus and parturition associated with reduced PGF(2α), the effects of n-3 on other measurable outcomes of reproductive success, such as pregnancy rate, embryo survival and intergenerational effects on the health and production of offspring are largely unknown. Similarly, the effects of diets high in n-3 or n-6 polyunsaturated fatty acids on male fertility are also unknown.     

星天牛成虫复眼外部形态和内部超微结构

星天牛Anoplophora chinensis能够取食上百种植物,以幼虫蛀干危害为主。本研究使用扫描电镜、透射电子显微镜和光学显微镜研究了星天牛成虫复眼外部形态和内部超微结构。结果表明星天牛复眼着生于触角基部,为不规则的肾形,表面光滑,由1 211~1 270个小眼组成,大部分小眼呈六边形,少数位于复眼边缘的小眼为不规则的五边形,小眼间角为6.90~9.56°。每个小眼由角膜、晶锥、视网膜细胞和基膜组成。角膜厚度为84.03±3.82 μm,晶锥被初级色素细胞包围,色素颗粒直径为0.41~0.97 μm。每个小眼包括8个视网膜细胞,其中6个周缘细胞（R1~R6）包围2个中央细胞（R7~R8）,视网膜细胞的感杆小体在向心侧形成半融合的感杆束,次级色素细胞色素颗粒将相邻小眼的视网膜细胞隔离,色素颗粒直径为0.41~1.06 μm。星天牛成虫复眼为并列像型,复眼分辨率较低,但视觉角度广,能够感受强度较低的光照。