Julia A. Taylor

Bio: Julia A. Taylor is an academic researcher from University of Missouri. The author has contributed to research in topics: Estrogen & Estrogen receptor. The author has an hindex of 42, co-authored 69 publications receiving 9312 citations.

Increased adipose tissue in male and female estrogen receptor-α knockout mice

Abstract: Estrogen regulates the amount of white adipose tissue (WAT) in females, but its role in males and whether WAT effects involve estrogen receptor-α (ERα) or ERβ were unclear. We analyzed the role of ERα in WAT and brown adipose tissue by comparing these tissues in wild-type (WT) and ERα-knockout (αERKO) male and female mice. Brown adipose tissue weight was similar in αERKO and WT males at all ages. Progressive increases in WAT were seen in αERKO males with advancing age. Epididymal, perirenal, and inguinal WAT weighed 139–185% more in αERKO than in WT males by 270–360 days of age. Epididymal and perirenal adipocyte size was increased 20% in αERKO males. Adipocyte number was 82–168% greater in fat pads of αERKO vs. WT males. Compared with WT, 90-day-old αERKO females had increases in fat pad weights (54–103%), adipocyte size, and number. Both αERKO males and females had insulin resistance and impaired glucose tolerance, similar to humans lacking ERα or aromatase. Energy intake was equal in WT and αERKO males, indicating that obesity was not induced by hyperphagia. In contrast, energy expenditure was reduced by 11% in αERKO compared with WT males, indicating that altered energy expenditure may be important for the observed obesity. In summary, ERα absence causes adipocyte hyperplasia and hypertrophy, insulin resistance, and glucose intolerance in both sexes. These results are evidence that estrogen/ERα signaling is critical in female and male WAT; obesity in αERKO males involves a mechanism of reduced energy expenditure rather than increased energy intake.

A role for oestrogens in the male reproductive system

Abstract: Oestrogen is considered to be the 'female' hormone, whereas testosterone is considered the 'male' hormone. However, both hormones are present in both sexes. Thus sexual distinctions are not qualitative differences, but rather result from quantitative divergence in hormone concentrations and differential expressions of steroid hormone receptors. In males, oestrogen is present in low concentrations in blood, but can be extraordinarily high in semen, and as high as 250 pg ml(-1) in rete testis fluids, which is higher than serum oestradiol in the female. It is well known that male reproductive tissues express oestrogen receptors, but the role of oestrogen in male reproduction has remained unclear. Here we provide evidence of a physiological role for oestrogen in male reproductive organs. We show that oestrogen regulates the reabsorption of luminal fluid in the head of the epididymis. Disruption of this essential function causes sperm to enter the epididymis diluted, rather than concentrated, resulting in infertility. This finding raises further concern over the potential direct effects of environmental oestrogens on male reproduction and reported declines in human sperm counts.

Large Effects from Small Exposures. I. Mechanisms for Endocrine-Disrupting Chemicals with Estrogenic Activity

Abstract: Information concerning the fundamental mechanisms of action of both natural and environmental hormones, combined with information concerning endogenous hormone concentrations, reveals how endocrine-disrupting chemicals with estrogenic activity (EEDCs) can be active at concentrations far below those currently being tested in toxicological studies. Using only very high doses in toxicological studies of EEDCs thus can dramatically underestimate bioactivity. Specifically: a) The hormonal action mechanisms and the physiology of delivery of EEDCs predict with accuracy the low-dose ranges of biological activity, which have been missed by traditional toxicological testing. b) Toxicology assumes that it is valid to extrapolate linearly from high doses over a very wide dose range to predict responses at doses within the physiological range of receptor occupancy for an EEDC; however, because receptor-mediated responses saturate, this assumption is invalid. c) Furthermore, receptor-mediated responses can first increase and then decrease as dose increases, contradicting the assumption that dose-response relationships are monotonic. d) Exogenous estrogens modulate a system that is physiologically active and thus is already above threshold, contradicting the traditional toxicological assumption of thresholds for endocrine responses to EEDCs. These four fundamental issues are problematic for risk assessment methods used by regulatory agencies, because they challenge the traditional use of extrapolation from high-dose testing to predict responses at the much lower environmentally relevant doses. These doses are within the range of current exposures to numerous chemicals in wildlife and humans. These problems are exacerbated by the fact that the type of positive and negative controls appropriate to the study of endocrine responses are not part of traditional toxicological testing and are frequently omitted, or when present, have been misinterpreted.

Components of plastic: experimental studies in animals and relevance for human health

Abstract: Components used in plastics, such as phthalates, bisphenol A (BPA), polybrominated diphenyl ethers (PBDE) and tetrabromobisphenol A (TBBPA), are detected in humans. In addition to their utility in plastics, an inadvertent characteristic of these chemicals is the ability to alter the endocrine system. Phthalates function as anti-androgens while the main action attributed to BPA is oestrogen-like activity. PBDE and TBBPA have been shown to disrupt thyroid hormone homeostasis while PBDEs also exhibit anti-androgen action. Experimental investigations in animals indicate a wide variety of effects associated with exposure to these compounds, causing concern regarding potential risk to human health. For example, the spectrum of effects following perinatal exposure of male rats to phthalates has remarkable similarities to the testicular dysgenesis syndrome in humans. Concentrations of BPA in the foetal mouse within the range of unconjugated BPA levels observed in human foetal blood have produced effects in animal experiments. Finally, thyroid hormones are essential for normal neurological development and reproductive function. Human body burdens of these chemicals are detected with high prevalence, and concentrations in young children, a group particularly sensitive to exogenous insults, are typically higher, indicating the need to decrease exposure to these compounds.

Roles of estrogen receptor-alpha gene expression in reproduction-related behaviors in female mice.

Abstract: The role of gene expression of the estrogen receptor-alpha form (ER alpha) in the regulation of female reproductive behavior was investigated in estrogen receptor knockout (ERKO) mice, deficient specifically for the ER alpha, but not the ER beta, gene. Estrogen- or estrogen- plus progesterone-treated gonadectomized ERKO mice did not show any lordosis response. Detailed behavioral analysis revealed that ERKO females were also deficient in sexual behavioral interactions preceding the lordosis response. They were extremely rejective toward attempted mounts by stud male mice, which could not show any intromissions. During resident-intruder aggression tests, gonadally intact ERKO females were more aggressive toward female intruder mice than wild-type (WT) mice. Gonadectomy did not influence the levels of aggressive behavior, and their genotype differences when mice were tested both before and after gonadectomy. However, when mice were tested after gonadectomy for the first time, very few ERKO mice showed aggression. In contrast to aggression, male-type sexual behavior shown by resident mice toward female intruder mice during aggression tests was not different between ERKO and WT mice and was completely abolished after gonadectomy of the resident mice. Finally, it was also found that ERKO females showed greatly reduced levels of parental behavior toward newborn pups placed in their home cage. These changes in parental behavior were not influenced by gonadectomy. ERKO females retrieved significantly fewer numbers of pups with longer latencies compared with wild-type (WT) or heterozygous (HZ) littermates when they were tested as gonadally intact or 20-65 days after gonadectomy. In addition, during parental behavior tests, a significantly higher percentage of ERKO mice exhibited infanticide compared with WT and HZ mice, which rarely showed infanticide. Taken together, these findings suggest that ER alpha gene expression plays a key role in female mice, not only for sexual behavior but also for other interrelated behaviors, such as parental and aggressive behaviors. In addition, persistence of genotype differences in parental and aggressive behavior after gonadectomy indicates that ER alpha activation during neural developmental processes may also be involved in the regulation of these behaviors.

Brown Adipose Tissue: Function and Physiological Significance

Abstract: Cannon, Barbara, and Jan Nedergaard. Brown Adipose Tissue: Function and Physiological Significance. Physiol Rev 84: 277–359, 2004; 10.1152/physrev.00015.2003.—The function of brown adipose tissue i...

Accumulation and fragmentation of plastic debris in global environments.

Abstract: One of the most ubiquitous and long-lasting recent changes to the surface of our planet is the accumulation and fragmentation of plastics. Within just a few decades since mass production of plastic...

The Environmental Protection Agency

Abstract: The Environmental Protection Agency (EPA) provides access to information on a variety of topics related to the environment and strives to inform citizens of health risks. The EPA also has an extensive library network that consists of 26 libraries throughout the United States, which provide access to a plethora of information to EPA employees, scientists, and researchers. The EPA implemented a reorganization project to digitize their materials so they would be more accessible to a wider range of users, but this plan was drastically accelerated when the EPA was threatened with a budget cut. It chose to close and reduce the hours and services of some of their libraries. As a result, the agency was accused of denying users the “right to know” by making information unavailable, not providing an adequate strategic plan, and discarding vital materials. This case study explores the background of the digitization project, the practices implemented, and the critiques of the project.