Understanding the fate of adult-generated neurons and the mechanisms that influence them requires consistent labeling and tracking of large numbers of stem cells. We generated a nestin-CreER T2 /R26R-yellow fluorescent protein (

In several species, including rat and vole, the proliferation of new neurons in the adult dentate gyrus (DG) subgranular zone (SGZ) is influenced by both gender and endogenous levels of the gonadotropic steroid hormone estradiol. However, little is known about how adult neurogenesis is regulated by these factors in the mouse. We report here that adult C57BL/6 mice do not have gender differences in hippocampal proliferation or neurogenesis. In addition, the production of new SGZ cells in female mice was not influenced by estrous cycle or after ovariectomy, suggesting that fluctuations in endogenous estradiol levels do not alter adult neurogenesis in the mouse. Both male and female mice had a greater number of BrdU-immunoreactive SGZ cells following chronic treatment with fluoxetine. This demonstrates a parallel proliferation response in both genders, and opens avenues for addressing the neurogenesis hypothesis of depression in female rodents. These findings underscore a distinct regulation of adult neurogenesis in mice vs. other rodents, and are discussed in regard to their implications for the study of adult hippocampal neurogenesis.

CCAAT/enhancer-binding protein ␤ (C/EBP␤) plays a key role in initiation of adipogenesis in adipose tissue and gluconeogenesis in liver; however, the role of C/EBP␤ in hepatic lipogenesis remains undefined. Here we show that C/EBP␤ inactivation in Lepr db/db mice attenuates obesity, fatty liver, and diabetes. In addition to impaired adipogenesis, livers from C/EBP␤ ؊/؊ x Lepr db/db mice had dramatically decreased triglyceride content and reduced lipogenic enzyme activity. C/EBP␤ deletion in Lepr db/db mice down-regulated peroxisome proliferator-activated receptor ␥2 (PPAR␥2) and stearoyl-CoA desaturase-1 and up-regulated PPAR␣ independent of SREBP1c. Conversely, C/EBP␤ overexpression in wild-type mice increased PPAR␥2 and stearoyl-CoA desaturase-1 mRNA and hepatic triglyceride content. In FAO cells, overexpression of the liver inhibiting form of C/EBP␤ or C/EBP␤ RNA interference attenuated palmitate-induced triglyceride accumulation and reduced PPAR␥2 and triglyceride levels in the liver in vivo. Leptin and the anti-diabetic drug metformin acutely down-regulated C/EBP␤ expression in hepatocytes, whereas fatty acids up-regulate C/EBP␤ expression. These data provide novel evidence linking C/EBP␤ expression to lipogenesis and energy balance with important implications for the treatment of obesity and fatty liver disease.Obesity is the most common nutritional disorder in Western societies. Today in the United States, more than 60% of people are either overweight (body mass index (BMI) Ͼ 25) or obese (BMI Ͼ 30) (1). Obesity is frequently associated with type II diabetes, hypertension, and hyperlipidemia, all known risk factors for cardiovascular disease (2). Obesity is also a major risk factor for non-alcoholic fatty liver disease, one of the most common emerging liver diseases in Western countries coinciding with the worldwide obesity epidemic (3, 4). The underlying transcriptional events that contribute to obesity and its associated disorders are not well understood. Some of the genes that regulate body weight have been identified as well as additional neuropeptides, hormones, and nutritional factors that play a role in body weight regulation, particularly through the ␤-adrenergic system (5, 6). Discovery of the hormone leptin and its receptors, which suppress appetite and reduce fat mass, has dramatically increased our understanding of the regulation of energy balance (7,8). More recently, the study of specific transcription factor genes and their metabolism has provided powerful new tools for understanding the integrated mechanisms underlying obesity and diabetes (9 -11). This is most elegantly illustrated using tissue-specific gene knockouts and overexpression models to elucidate the mechanism of action of the PPAR 5 family of nuclear hormone receptors (12). The CCAAT/enhancer-binding protein (C/EBP) family includes five nuclear transcription factors, C/EBP ␣, ␤, ␥, ␦, and ⑀, encoded by separate genes located on different chromosomes (13,14). Collectively, C/EBPs are expressed across a variety of cell types, and...

Insulin resistance is a cardinal feature of normal pregnancy and excess growth hormone (GH) states, but its underlying mechanism remains enigmatic. We previously found a significant increase in the p85 regulatory subunit of phosphatidylinositol kinase (PI 3-kinase) and striking decrease in IRS-1-associated PI 3-kinase activity in the skeletal muscle of transgenic animals overexpressing human placental growth hormone. Herein, using transgenic mice bearing deletions in p85␣, p85␤, or insulin-like growth factor-1, we provide novel evidence suggesting that overexpression of p85␣ is a primary mechanism for skeletal muscle insulin resistance in response to GH. We found that the excess in total p85 was entirely accounted for by an increase in the free p85␣-specific isoform. In mice with a liverspecific deletion in insulin-like growth factor-1, excess GH caused insulin resistance and an increase in skeletal muscle p85␣, which was completely reversible using a GH-releasing hormone antagonist. To understand the role of p85␣ in GH-induced insulin resistance, we used mice bearing deletions of the genes coding for p85␣ or p85␤, respectively (p85␣ ؉/؊ and p85␤ ؊/؊ ). Wild type and p85␤؊/؊ mice developed in vivo insulin resistance and demonstrated overexpression of p85␣ and reduced insulin-stimulated PI 3-kinase activity in skeletal muscle in response to GH. In contrast, p85␣ ؉/؊ mice retained global insulin sensitivity and PI 3-kinase activity associated with reduced p85␣ expression. These findings demonstrated the importance of increased p85␣ in mediating skeletal muscle insulin resistance in response to GH and suggested a potential role for reducing p85␣ as a therapeutic strategy for enhancing insulin sensitivity in skeletal muscle.Insulin resistance is a common feature associated with growth hormone excess; however, the cellular mechanism underlying insulin resistance remains elusive. We previously demonstrated that transgenic mice overexpressing human placental growth hormone (TG-hPGH), 2 at levels comparable with the third trimester of pregnancy, were severely insulin-resistant and display increased amounts of the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase) in skeletal muscle (1).Several recent studies have suggested that a disrupted balance between the levels of the PI 3-kinase subunits may alter insulin-stimulated PI 3-kinase activity (2-6). This enzyme consists of a regulatory subunit, p85, and a catalytic subunit, p110 (7). Normally, the regulatory subunit exists in stoichiometric excess to the catalytic one, resulting in a pool of free p85 monomers not associated with the p110 catalytic subunit. The p85 monomers bind to phosphorylated IRS proteins, blocking access to p85-p110 heterodimers. Thus, there exists a balance between the free p85 monomer and the p85-p110 heterodimer with the latter being responsible for the PI 3-kinase activity. Increases or decreases in expression of p85 shift this balance in favor of either free p85 or p85-p110 complexes (3-6). Because the monomer and the heterod...

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