Ghrelin gene in cichlid fish is modulated by sex and development

We have identified the complementary and genomic DNA sequences of the novel growth hormone-releasing peptide, ghrelin, in the cichlid fish (tilapia Oreochromis niloticus). The tilapia ghrelin precursor cDNA was 855 bp long, consisting of 119 bp of 5(')-untranslated region, 324 bp open reading frame, and 412 bp of 3(')-untranslated region. The serine residues at positions 2 and 3 of the "active core" (GSSF) of the ghrelin mature peptide are conserved between tilapia and the mammalian species. The tilapia ghrelin gene has four exons and three introns and resembles the structure of other known ghrelin genes. RT-PCR analysis revealed ghrelin mRNA predominantly expressed in the stomach but absent in the brain, pituitary, heart, kidney, ovary, and testis. Real-time PCR analysis showed an age/body size dependent increase in gastric ghrelin, which stagnated at 7 cm body size (onset of maturation). Ghrelin mRNA levels were unchanged in food-deprived sexually mature animals but were significantly higher in females compared to males. The present study shows that the structure of ghrelin peptide is highly conserved, and the reported differences in somatic and gonadal growth in tilapia could be a consequence of age- and sex-related synthesis of gastric ghrelin.     

Size,sex and social experience: Experimental tests of multiple factors mediating contest behaviour in a rockpool fish

Aggressive contests amongst conspecifics are important to understand from an ecological and evolutionary perspective as contest dynamics can directly influence individual fitness. For some species, individual attributes such as relative body size closely predict the outcome, intensity and duration of contests, whereas for others, prior social experiences play a key role. However, disentangling the relative effects of individual attributes and social experiences is challenging from an experimental perspective, and because of this, few studies have investigated relative effects of multiple factors. Rockpool fishes have been well studied in terms of factors governing abundance, distribution and community structure, but much less so in terms of contest behaviour. This is surprising because contest dynamics are likely to directly affect the distribution of fishes along the rocky shore, and hence indirectly govern population and community composition. Here, we explored multiple factors potentially influencing contest behaviour in a numerically dominant, resident intertidal fish species, Bathygobius cocosensis (Gobiidae). Using a series of staged pairwise contest trials, we investigated the effect of size, sex and social experiences (namely prior residency and winner–loser experiences) on contest dynamics. We found no evidence that prior residency influenced contest outcome, suggesting social experiences play a minor role in contest dynamics. Previous winner/loser experience also did not influence contest outcome, although this is likely a product of low sample size. In addition, the likelihood of winning was unrelated to contestant sex, and the combination of sexes in paired contests did not influence contest intensity or duration. Instead, body size was related to contest outcome, intensity and duration in the majority of experimental trials. These results suggest that body size rather than sex or social experiences is the key determinant of contest dynamics in this species. We suggest that the dynamic biotic and abiotic environment inhabited by intertidal fish may reduce the influence of prior social experiences in modulating contest dynamics.     

Multiple paternity is related to adult sex ratio and sex determination system in reptiles

The adult sex ratio (ASR, the proportion of males in the adult population) is an emerging predictor of reproductive behaviour, and recent studies in birds and humans suggest it is a major driver of social mating systems and parental care. ASR may also influence genetic mating systems. For instance male-skewed ASRs are expected to increase the frequency of multiple paternity (defined here as a clutch or litter sired by two or more males) due to higher rates of coercive copulations by males, and/or due to females exploiting the opportunity of copulation with multiple males to increase genetic diversity of their offspring. Here, we evaluate this hypothesis in reptiles that often exhibit high frequency of multiple paternity although its ecological and life-history predictors have remained controversial. Using a comprehensive dataset of 81 species representing all four non-avian reptile orders, we show that increased frequency of multiple paternity is predicted by more male-skewed ASR, and this relationship is robust to simultaneous effects of several life-history predictors. Additionally, we show that the frequency of multiple paternity varies with the sex determination system: species with female heterogamety (ZZ/ZW sex chromosomes) exhibit higher levels of multiple paternity than species with male heterogamety (XY/XX) or temperature-dependent sex determination. Thus, our across-species comparative study provides the first evidence that genetic mating system depends on ASR in reptiles. We call for further investigations to uncover the complex evolutionary associations between mating systems, sex determination systems and ASR.     

Sexual behaviour: a receptor for sex control in Drosophila females

Male Drosophila manipulate the sexual behaviour of their female mating partners by release of a Sex-peptide, but how does this work? A G-protein-coupled receptor has now been identified which acts in the female flies to detect male Sex-peptide and trigger increased egg laying and reduced sexual receptivity.     

鳜肿瘤坏死因子相关的凋亡诱导配体Trail基因的原核表达

肿瘤坏死因子相关的凋亡诱导配体(Tumor related apoptosis inducing ligand,TRAIL),亦称Apo-2L,是由Wiley,et al.在1995年搜索EST数据库时首次发现并成功克隆的,是继TNF和FasL之后发现的第三个TNF家族的凋亡分子[1].     

Acute exposure to ultraviolet‐B radiation modulates sex steroid hormones and receptor expression in the skin and may contribute to the sex bias of melanoma in a fish model

Using the Xiphophorus fish melanoma model, we show a strong male bias for sunlight‐induced malignant melanoma, consistent with that seen in the human population. To examine underlying factors, we exposed adult X. couchianus fish to a single, sublethal dose of UVB and measured circulating sex steroid hormones and expression of associated hormone receptor genes over a 24‐h period. We found that a single exposure had profound effects on circulating levels of steroid hormones with significant decreases for all free sex steroids at 6 and 24 h and increases in conjugated 2‐estradiol and 11‐ketotestosterone at 6 and 24 h, respectively. Whereas ARα expression increased in male and female skin, neither ARβ nor either of the ERs showed significant responses to UVB in either sex. The rapid response of male androgens and their receptors in the skin after UVB irradiation implicates hormones in the male bias of skin cancer and suggests that the photoendocrine response immediately after UV exposure may be relevant to melanomagenesis.     

Reduced opsin gene expression in a cave-dwelling fish

Regressive evolution of structures associated with vision in cave-dwelling organisms is the focus of intense research. Most work has focused on differences between extreme visual phenotypes: sighted, surface animals and their completely blind, cave-dwelling counterparts. We suggest that troglodytic systems, comprising multiple populations that vary along a gradient of visual function, may prove critical in understanding the mechanisms underlying initial regression in visual pathways. Gene expression assays of natural and laboratory-reared populations of the Atlantic molly (Poecilia mexicana) revealed reduced opsin expression in cave-dwelling populations compared with surface-dwelling conspecifics. Our results suggest that the reduction in opsin expression in cave-dwelling populations is not phenotypically plastic but reflects a hardwired system not rescued by exposure to light during retinal ontogeny. Changes in opsin gene expression may consequently represent a first evolutionary step in the regression of eyes in cave organisms.     

Growth hormone differentially regulates growth and growth-related gene expression in closely related fish species

Zebrafish (Danio rerio) have become an important model organism for developmental biology and human health studies. We recently demonstrated differential growth patterns between the zebrafish and a close relative the giant danio (Danio aequipinnatus), where the giant danio appears to exhibit indeterminate growth similar to most fish species important for commercial production, while zebrafish exhibit determinate growth more similar to mammalian growth. This study focused on evaluating muscle growth regulation differences in adult zebrafish and giant danio utilizing growth hormone treatment as a mode of growth manipulation. Growth hormone treatment resulted in increased overall growth in giant danio, but failed to increase growth in the zebrafish. Growth hormone treatment increased muscle IGF-I and GHrI gene expression in both species, but to a larger degree in the giant danio. In contrast, zebrafish exhibited a larger increase in IrA and IGF-IrB gene expression in muscle in response to GH treatment. In addition muscle myostatin levels were differentially regulated between the two species, with a down-regulation observed in rapidly growing, GH-treated giant danio and an up-regulation in zebrafish not actively growing in response to GH. This is the first report of differential expression of growth-regulating genes in closely related fish species exhibiting opposing growth paradigms. These results further support the role that the zebrafish and giant danio can play important model organisms for determinate and indeterminate growth.     

Provisioning in western bluebirds is not related to offspring sex

Parents should invest more in one sex of offspring if the fitnessreturn per unit investment is higher for that sex. Sex-biasedprovisioning may occur when sons and daughters differ in theirneeds or when there is local resource competition or enhancement.We used feeding observations and sex-ratio manipulations todetermine if sex-biased provisioning occurs in western bluebirds(Sialia mexicana). The sex ratio of the brood had no effecton feeding rates by adults at unmanipulated nests over a 6-yearperiod. Adult males and females also did not differ in the numberof feedings made to sons and daughters in 13 videotaped nests.Likewise, adult feeding rates to nests experimentally biasedtoward sons or daughters did not differ significantly. Nesdingsthat were closest to the nest hole and that reached highestwere the most likely to be fed. Sons and daughters did not differin the begging behaviors most likely to result in a feeding.We conclude that sex-biased provisioning does not occur in thispopulation of western bluebirds and diat nesding behavior maybe a more important determinant of feeding.     

Facial movement varies by sex and is related to attractiveness

Facial movement has received little attention in studies of human attractiveness, yet dynamic displays are an important aspect of courtship in many species. This experiment investigated whether facial movement could be used to identify sex, and whether the ease of identification was associated with attractiveness. We removed shape cues to sex by applying movement from individual faces to a standardised facial model. Participants were able to distinguish between male and female animations of this model at levels above chance. Furthermore, there was a positive association between ease of sex identification and attractiveness for female, but not male, faces. Analysis of facial movement suggested several behaviours that are more frequent in women than men (blinking, tilting, nodding, shaking, and amount of movement). Although some of these behaviours may be cues to sex identification, none alone was directly linked to attractiveness. Our findings suggest that feminine motion is attractive in female faces, but sexually recognisable movement has no clear influence on male attractiveness, in agreement with work on static faces employing composite images.     

Loss of calcitonin binding in rat is not related to calcitonin receptor gene abnormality.

C-cell tumors occur frequently (50%) in old WAG/Rij rats. Interestingly, genetically transmitted loss of CT binding sites in the kidney has also been demonstrated in WAG/Rij rats. To determine if these issues are resulted from mutation of calcitonin receptor (CTR), we analyzed the CTR genomic abnormality in WAG/Rij rat. We demonstrated that both Wistar and WAG/Rij rats expressed type-C1a CTR by RT-PCR analysis and their mRNA expressions were approximately equal by Northern blotting analysis. Direct sequence of RT-PCR products for CTR showed no different nucleotide sequences between the two strains. There were three polymorphisms at the first transmembrane domain and the fourth intracellular membranes, which are different from Sprague-Dawley rat. We concluded that the loss of CT binding in WAG/Rij rat is not related to CTR gene abnormality. Abnormal system of CTR amino acid modification may be occurred in WAG/Rij rat.     

Corticosteroid receptor mRNA expression in the brains of patients with epilepsy

The effects of corticosteroids in the brain are mediated through the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). We used a sensitive competitive RT-PCR assay to quantify the amounts of GR and MR mRNA in human brain tissue specimens from patients with focal epilepsies. GR and MR mRNAs were expressed at approximately the same levels in the temporal lobe, frontal lobe, and hippocampus as compared to tissues with high glucocorticoid/mineralocorticoid receptor expression (liver/kidney). GR and MR mRNA concentrations in the temporal lobe increased markedly during childhood and reached adult levels at puberty. GR and MR mRNA expression was significantly higher in the temporal lobe and frontal lobe cortex of women than in those of men. In women, MR and GR mRNA concentrations were markedly lower in hippocampal tissue than in frontal and temporal lobe cortex tissue. In conclusion, our data demonstrate sex- and site-dependent expression of corticosteroid receptor mRNA in the human brain.     

The distance between Escherichia coli genes is related to gene expression levels.

It is shown that the distance between Escherichia coli genes oriented in the same direction on the chromosome is positively correlated to the expression level of the downstream gene. It is suggested that this could be a strategy to avoid interference between ribosomes translating two different genes.