54 research outputs found
Hedgehog Signaling Regulates Apical Actin Morphology
poster abstractStereocilia are highly patterned actin based cell protrusions found on the apical surface of auditory hair cells. They are formed mainly from bundled filamentous actin and its associated actin cross-linking proteins. Interestingly, stereocilia develop around another cell appendage, the microtubule based kinocilium, which is the primary cilium for a hair cell. Primary cilia are found on most somatic cells and play a significant role in the regulation and proper transduction of the Hedgehog (Hh) pathway. In the current study, we are testing the hypothesis that Hh pathway activity can alter actin bundling and elongation. In support of this idea, ectopic activation or repression of Hh signaling changed the morphology of stereocilia in vivo. To further test our hypothesis, we used a CL4 porcine kidney epithelial cell culture system stably expressing the actin crosslinking protein ESPN fused to green fluorescent protein. These cells serve as an in vitro model of apical actin protrusions similar to mature stereocilia in vivo. We manipulated Hh signaling in these cells using both a genetic and a pharmacological approach. In the pharmacological approach, CL4 cells were treated with the hedgehog agonist (Purmophamine) and antagonist (Cyclopamine), at varying concentrations for 48 hours. Genetically, the Hh pathway was ectopically activated by overexpressing the transcription factor Gli1, Gli2, Gli3, and SmoA1 repressed by expressing Gli3R. Immunofluorescent (IF) and scanning electron microscopy (SEM) revealed that CL4 cells dramatically altered the apical actin structures under these conditions. In particular, activating Gli transcription decreased apical actin-based structures while antagonizing activity resulted in more actinbased protrusions. This data strongly supports the hypothesis that the Hh signaling pathway can regulate the actin cytoskeleton
Use of an Episodic Food Intake Monitoring System to Evaluate Feeding Behavior in Mice
poster abstractThe measurement of food consumption in laboratory animals is critical to studies in metabolism and obesity. Unfortunately, feeding behavior is very sensitive to the environment. Many factors such as the change of cages, diet, and human interactions can introduce undesired experimental variation. Here we describe our experiences with a commercially available episodic food intake monitoring system, the BioDAQ Monitor. This system is designed to quantitatively record feeding behavior in mice. It continuously monitors the weight of the food and uses this information to determine bout length and size. Bouts that occur soon after one another can then be defined as meals. When an animal jostles the food hopper while eating, the weight of the hopper fluctuates and eating is considered to be in progress.
Once the hopper weight has been stable for a specified time, that period of feeding is considered to be concluded. The system also has the capability to assess either food or liquid choice paradigms and to directly measure the administration of orally available drugs in either the feed or the water. In addition to these functions, the system uses an environment monitor to record temperature, humidity and lighting of the room every five minutes. Here we present data showing measurements taken in hyperphagic mutant mice, altered feeding paradigms, and under different drug and protein hormone treatments. Future studies using this system will continue to focus on the hyperphagia associated obesity phenotype observed in mice upon conditional disruption of primary cilia
Cilia and Obesity
The ciliopathies Bardet-Biedl syndrome and Alström syndrome cause obesity. How ciliary dysfunction leads to obesity has remained mysterious, partly because of a lack of understanding of the physiological roles of primary cilia in the organs and pathways involved in the regulation of metabolism and energy homeostasis. Historically, the study of rare monogenetic disorders that present with obesity has informed our molecular understanding of the mechanisms involved in nonsyndromic forms of obesity. Here, we present a framework, based on genetic studies in mice and humans, of the molecular and cellular pathways underlying long-term regulation of energy homeostasis. We focus on recent progress linking these pathways to the function of the primary cilia with a particular emphasis on the roles of neuronal primary cilia in the regulation of satiety
Understanding Cilia Function on POMC Neurons in Appetite and Satiety
poster abstractOver one-third of adults in the United States are obese. Obese individuals are at an
increased risk for cardiovascular diseases, type 2 diabetes, cancer, and other health
conditions, resulting in premature death. Interestingly, cilia have been linked to controlling
satiety in both mice and humans, and individuals with dysfunctional cilia are often obese.
Cilia are cellular appendages composed of microtubules and can be motile or immotile.
Primary (immotile) cilia function as sensors for important signaling pathways. The loss of
cilia, specifically from hypothalamic proopiomelanocortin (POMC) expressing cells,
disrupts satiety, leading to overeating and obesity. While it is known that cilia loss in POMC cells in the hypothalamus causes obesity, the age or developmental stage at which cilia loss is important for this phenotype remains unclear. The aim of this research is to determine the time point critical for proper cilia function on POMC neurons to maintain normal feeding behaviors. To do this, we utilize an inducible POMC-CreER mouse model. This model allows us to disrupt cilia formation and maintenance at specific stages of life. We take a multifaceted approach to analyze the impact of cilia loss by measuring longterm body weight and feeding behavior in adult mice, studying changes in embryonic development, as well as analyzing physiological changes in cultured primary neurons. These studies will contribute to a better understanding of the role of cilia in satiety signaling which will help lead to the development of effective treatments for weight related diseases
Hedgehog Pathway Activation Alters Ciliary Signaling in Primary Hypothalamic Cultures
Primary cilia dysfunction has been associated with hyperphagia and obesity in both ciliopathy patients and mouse models of cilia perturbation. Neurons throughout the brain possess these solitary cellular appendages, including in the feeding centers of the hypothalamus. Several cell biology questions associated with primary neuronal cilia signaling are challenging to address in vivo. Here we utilize primary hypothalamic neuronal cultures to study ciliary signaling in relevant cell types. Importantly, these cultures contain neuronal populations critical for appetite and satiety such as pro-opiomelanocortin (POMC) and agouti related peptide (AgRP) expressing neurons and are thus useful for studying signaling involved in feeding behavior. Correspondingly, these cultured neurons also display electrophysiological activity and respond to both local and peripheral signals that act on the hypothalamus to influence feeding behaviors, such as leptin and melanin concentrating hormone (MCH). Interestingly, we found that cilia mediated hedgehog signaling, generally associated with developmental processes, can influence ciliary GPCR signaling (Mchr1) in terminally differentiated neurons. Specifically, pharmacological activation of the hedgehog-signaling pathway using the smoothened agonist, SAG, attenuated the ability of neurons to respond to ligands (MCH) of ciliary GPCRs. Understanding how the hedgehog pathway influences cilia GPCR signaling in terminally differentiated neurons could reveal the molecular mechanisms associated with clinical features of ciliopathies, such as hyperphagia-associated obesity
Mammalian Clusterin associated protein 1 is an evolutionarily conserved protein required for ciliogenesis
BACKGROUND: Clusterin associated protein 1 (CLUAP1) was initially characterized as a protein that interacts with clusterin, and whose gene is frequently upregulated in colon cancer. Although the consequences of these observations remain unclear, research of CLUAP1 homologs in C. elegans and zebrafish indicates that it is needed for cilia assembly and maintenance in these models. To begin evaluating whether Cluap1 has an evolutionarily conserved role in cilia in mammalian systems and to explore the association of Cluap1 with disease pathogenesis and developmental abnormalities, we generated Cluap1 mutant mice. METHODS: Cluap1 mutant embryos were generated and examined for gross morphological and anatomical defects using light microscopy. Reverse transcription PCR, ÎČ-galactosidase staining assays, and immunofluorescence analysis were used to determine the expression of the gene and localization of the protein in vivo and in cultured cell lines. We also used immunofluorescence analysis and qRT-PCR to examine defects in the Sonic hedgehog signaling pathway in mutant embryos. RESULTS: Cluap1 mutant embryos die in mid-gestation, indicating that it is necessary for proper development. Mutant phenotypes include a failure of embryonic turning, an enlarged pericardial sac, and defects in neural tube development. Consistent with the diverse phenotypes, Cluap1 is widely expressed. Furthermore, the Cluap1 protein localizes to primary cilia, and mutant embryos were found to lack cilia at embryonic day 9.5. The phenotypes observed in Cluap1 mutant mice are indicative of defects in Sonic hedgehog signaling. This was confirmed by analyzing hedgehog signaling activity in Cluap1 mutants, which revealed that the pathway is repressed. CONCLUSIONS: These data indicate that the function of Cluap1 is evolutionarily conserved with regard to ciliogenesis. Further, the results implicate mammalian Cluap1 as a key regulator of hedgehog signaling and as an intraflagellar transport B complex protein. Future studies on mammalian Cluap1 utilizing this mouse model may provide insights into the role for Cluap1 in intraflagellar transport and the association with colon cancer and cystic kidney disorders
Testing Therapeutic Candidates in a Mouse Model of Polycystic Kidney Disease
poster abstractApproximately 1 in 500 middle aged people in the United States will be diagnosed with Polycystic Kidney Disease (PKD), an inherited genetic disorder that results in extreme cysts on the kidneys. PKD eventually leads to end-stage kidney failure and current treatments are limited to dialysis or transplantation. Thus, a pharmacological approach to prevent, delay, or slow the progression of PKD would revolutionize treatment and improve mortality. Interestingly, many proteins associated with PKD have been found in and around the primary cilia of renal epithelial cells. Cilia are small microtubule-based cellular appendages found on the surface of most cell types in the human body and are broadly classified as either âmotileâ or âprimaryâ (immotile). Primary cilia are known to be mechano- and environmental sensors, and play a critical role in cell-to-cell communication. The aim of this proposed research is to use potential therapeutics identified in silico and in vitro in animal models of PKD to determine if the compound can delay or prevent cystogenesis. Here we test Sildenafil citrate (Viagra) in an animal model of rapidly progressing cyst formation for its ability to ameliorate the phenotype. Further research directed at understanding the cilia, cell-cycle, and cilia-mediated signalling activity will hopefully provide important insights into the mechanisms of renal cyst pathogenesis and lead to better approaches for therapeutic intervention for PKD
Coiled-coil domain containing 42 (Ccdc42) is necessary for proper sperm development and male fertility in the mouse
Spermiogenesis is the differentiation of spermatids into motile sperm consisting of a head and a tail. The head harbors a condensed elongated nucleus partially covered by the acrosome-acroplaxome complex. Defects in the acrosome-acroplaxome complex are associated with abnormalities in sperm head shaping. The head-tail coupling apparatus (HTCA), a complex structure consisting of two cylindrical microtubule-based centrioles and associated components, connects the tail or flagellum to the sperm head. Defects in the development of the HTCA cause sperm decapitation and disrupt sperm motility, two major contributors to male infertility. Here, we provide data indicating that mutations in the gene Coiled-coil domain containing 42 (Ccdc42) is associated with malformation of the mouse sperm flagella. In contrast to many other flagella and motile cilia genes, Ccdc42 expression is only observed in the brain and developing sperm. Male mice homozygous for a loss-of-function Ccdc42 allele (Ccdc42(KO)) display defects in the number and location of the HTCA, lack flagellated sperm, and are sterile. The testes enriched expression of Ccdc42 and lack of other phenotypes in mutant mice make it an ideal candidate for screening cases of azoospermia in humans
The Hedgehog Signaling Pathway is Expressed in the Adult Mouse Hypothalamus and Modulated by Fasting
The hedgehog signaling pathway is best known for its role in developmental patterning of the neural tube and limb bud. More recently, hedgehog signaling has been recognized for its roles in growth of adult tissues and maintenance of progenitor cell niches. However, the role of hedgehog signaling in fully differentiated cells like neurons in the adult brain is less clear. In mammals, coordination of hedgehog pathway activity relies on primary cilia and patients with ciliopathies such as Bardet-Biedl and Alström syndrome exhibit clinical features clearly attributable to errant hedgehog such as polydactyly. However, these ciliopathies also present with features not clearly associated with hedgehog signaling such as hyperphagia-associated obesity. How hedgehog signaling may contribute to feeding behavior is complex and unclear, but cilia are critical for proper energy homeostasis. Here, we provide a detailed analysis of the expression of core components of the hedgehog signaling pathway in the adult mouse hypothalamus with an emphasis on feeding centers. We show that hedgehog pathway genes continue to be expressed in differentiated neurons important for the regulation of feeding behavior. Furthermore, we demonstrate for the first time that pathway activity is regulated at the transcriptional level by fasting. These data suggest that hedgehog signaling is involved in the proper functioning of brain regions that regulate feeding behavior and that hedgehog pathway dysfunction may play a role in the obesity observed in certain ciliopathies
A CreER Mouse to Study Melanin Concentrating Hormone Signaling in the Developing Brain
The neuropeptide, melanin concentrating hormone (MCH), and its G proteinâcoupled receptor, melanin concentrating hormone receptor 1 (Mchr1), are expressed centrally in adult rodents. MCH signaling has been implicated in diverse behaviors such as feeding, sleep, anxiety, as well as addiction and reward. While a model utilizing the Mchr1 promoter to drive constitutive expression of Cre recombinase (Mchr1âCre) exists, there is a need for an inducible Mchr1âCre to determine the roles for this signaling pathway in neural development and adult neuronal function. Here, we generated a BAC transgenic mouse where the Mchr1 promotor drives expression of tamoxifen inducible CreER recombinase. Many aspects of the Mchr1âCre expression pattern are recapitulated by the Mchr1âCreER model, though there are also notable differences. Most strikingly, compared to the constitutive model, the new Mchr1âCreER model shows strong expression in adult animals in hypothalamic brain regions involved in feeding behavior but diminished expression in regions involved in reward, such as the nucleus accumbens. The inducible Mchr1âCreER allele will help reveal the potential for Mchr1 signaling to impact neural development and subsequent behavioral phenotypes, as well as contribute to the understanding of the MCH signaling pathway in terminally differentiated adult neurons and the diverse behaviors that it influences
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