Endocrine disruptors affect larval zebrafish behavior: Testing potential mechanisms and comparisons of behavioral sensitivity to alternative biomarkers.

Larval zebrafish (Danio rerio) are a tool for assessing endocrine disruption during early development. Here, we investigated the extent to which a simple light/dark behavioral test at five days post fertilization could compliment current methods within the field. We exposed fertilized embryos to hormones (17ß-estradiol, testosterone, dihydrotestosterone, 11-ketotestosterone, thyroxine, triiodothyronine, progesterone, and hydrocortisone) and other relevant compounds (17α ethinylestradiol, bisphenol A, bisphenol S, nonylphenol, flutamide, nilutamide, linuron, drospirenone, potassium perchlorate, mifepristone, and fadrozole) to screen for behavioral effects between 96 and 118h post fertilization (hpf). With the exception of progesterone, all the hormones tested resulted in altered behaviors. However, some inconsistencies were observed regarding the age of the larvae at testing. For example, the xenoestrogens 17α- ethinylestradiol and nonylphenol had behavioral effects at 96hpf, but not at 118hpf. Furthermore, although thyroxine exposure had pronounced effects on behavior, the thyroid disruptor potassium perchlorate did not. Finally, we were unable to demonstrate a role of nuclear receptors following testosterone and 17α- ethinylestradiol exposure, as neither the androgen receptor antagonist flutamide nor the general estrogen receptor inhibitor fulvestrant (ICI) could rescue the observed behavioral effects, respectively. Similarly, molecular markers for androgen and estrogen disruption were upregulated at concentrations below which behavioral effects were observed. These results demonstrate hormones and endocrine disruptors can alter the behavior of larval zebrafish, but the mechanistic pathways remain unclear.

Local Populations of Arabidopsis thaliana Show Clear Relationship between Photoperiodic Sensitivity of Flowering Time and Altitude.

Adaptation of plants to local conditions that vary substantially within their geographic range is essential for seasonal timing of flowering, a major determinant of plant reproductive success. This study investigates photoperiodic responses in natural populations of Arabidopsis thaliana from high northern latitudes and their significance for local adaptation. Thirty lineages from ten local A. thaliana populations, representing different locations across an altitudinal gradient (2-850 m a.s.l.) in Norway, were grown under uniform controlled conditions, and used to screen for responses to five different photoperiods. We studied relationships between variation in photoperiodic sensitivity of flowering time, altitude, and climatic factors associated with the sites of origin. We found that variation in response to photoperiod is significantly correlated with altitude and climatic variables associated with the sites of origin of the populations. Populations originating from lower altitudes showed stronger photoperiodic sensitivity than populations from higher altitudes. Our results indicate that the altitudinal climatic gradient generates clinal variation in adaptive traits in A. thaliana.

Toxicant induced behavioural aberrations in larval zebrafish are dependent on minor methodological alterations.

Alterations in zebrafish motility are used to identify neurotoxic compounds, but few have reported how methodology may affect results. To investigate this, we exposed embryos to bisphenol A (BPA) or tetrabromobisphenol A (TBBPA) before assessing larval motility. Embryos were maintained on a day/night cycle (DN) or in constant darkness, were reared in 96 or 24 well plates (BPA only), and behavioural tests were carried out at 96, 100, or 118 (BPA only) hours post fertilisation (hpf). We found that the prior photo-regime, larval age, and/or arena size influence behavioural outcomes in response to toxicant exposure. For example, methodology determined whether 10µM BPA induced hyperactivity, hypoactivity, or had no behavioural effect. Furthermore, the minimum effect concentration was not consistent between different methodologies. Finally, we observed a mechanism previously used to explain hyperactivity following BPA exposure does not appear to explain the hypoactivity observed following minor alterations in methodology. Therefore, we demonstrate how methodology can have notable implications on dose responses and behavioural outcomes in larval zebrafish motility following identical chemical exposures. As such, our results have significant consequences for human and environmental risk assessment.

Fine mapping of a QTL on bovine chromosome 6 using imputed full sequence data suggests a key role for the group-specific component (GC) gene in clinical mastitis and milk production.

BACKGROUND: Clinical mastitis is an inflammation of the mammary gland and causes significant costs to dairy production. It is unfavourably genetically correlated to milk production, and, thus, knowledge of the mechanisms that underlie these traits would be valuable to improve both of them simultaneously through breeding. A quantitative trait locus (QTL) that affects both clinical mastitis and milk production has recently been fine-mapped to around 89 Mb on bovine chromosome 6 (BTA6), but identification of the gene that underlies this QTL was not possible due to the strong linkage disequilibrium between single nucleotide polymorphisms (SNPs) within this region. Our aim was to identify the gene and, if possible, the causal polymorphism(s) responsible for this QTL through association analysis of high-density SNPs and imputed full sequence data in combination with analyses of transcript and protein levels of the identified candidate gene. RESULTS: Associations between SNPs and the studied traits were strongest for SNPs that were located within and immediately upstream of the group-specific component (GC) gene. This gene encodes the vitamin D-binding protein (DBP) and has multiple roles in immune defense and milk production. A 12-kb duplication that was identified downstream of this gene covered its last exon and segregated with the QTL allele that is associated with increased mastitis susceptibility and milk production. However, analyses of GC mRNA levels on the available samples revealed no differences in expression between animals having or lacking this duplication. Moreover, we detected no differences in the concentrations of DBP and its ligand vitamin D between the animals with different GC genotypes that were available for this study. CONCLUSIONS: Our results suggest GC as the gene that underlies the QTL for clinical mastitis and milk production. However, since only healthy animals were sampled for transcription and expression analyses, we could not draw any final conclusion on the absence of quantitative differences between animals with different genotypes. Future studies should investigate GC RNA expression and protein levels in cows with different genotypes during an infection.

Hematological shift in goat kids naturally devoid of prion protein.

The physiological role of the cellular prion protein (PrP(C)) is incompletely understood. The expression of PrP(C) in hematopoietic stem cells and immune cells suggests a role in the development of these cells, and in PrP(C) knockout animals altered immune cell proliferation and phagocytic function have been observed. Recently, a spontaneous nonsense mutation at codon 32 in the PRNP gene in goats of the Norwegian Dairy breed was discovered, rendering homozygous animals devoid of PrP(C). Here we report hematological and immunological analyses of homozygous goat kids lacking PrP(C) (PRNP(Ter/Ter) ) compared to heterozygous (PRNP (+/Ter)) and normal (PRNP (+/+)) kids. Levels of cell surface PrP(C) and PRNP mRNA in peripheral blood mononuclear cells (PBMCs) correlated well and were very low in PRNP (Ter/Ter), intermediate in PRNP (+/Ter) and high in PRNP (+/+) kids. The PRNP (Ter/Ter) animals had a shift in blood cell composition with an elevated number of red blood cells (RBCs) and a tendency toward a smaller mean RBC volume (P = 0.08) and an increased number of neutrophils (P = 0.068), all values within the reference ranges. Morphological investigations of blood smears and bone marrow imprints did not reveal irregularities. Studies of relative composition of PBMCs, phagocytic ability of monocytes and T-cell proliferation revealed no significant differences between the genotypes. Our data suggest that PrP(C) has a role in bone marrow physiology and warrant further studies of PrP(C) in erythroid and immune cell progenitors as well as differentiated effector cells also under stressful conditions. Altogether, this genetically unmanipulated PrP(C)-free animal model represents a unique opportunity to unveil the enigmatic physiology and function of PrP(C).