Tig1 regulates proximo-distal identity during salamander limb regeneration.

Salamander limb regeneration is an accurate process which gives rise exclusively to the missing structures, irrespective of the amputation level. This suggests that cells in the stump have an awareness of their spatial location, a property termed positional identity. Little is known about how positional identity is encoded, in salamanders or other biological systems. Through single-cell RNAseq analysis, we identified Tig1/Rarres1 as a potential determinant of proximal identity. Tig1 encodes a conserved cell surface molecule, is regulated by retinoic acid and exhibits a graded expression along the proximo-distal axis of the limb. Its overexpression leads to regeneration defects in the distal elements and elicits proximal displacement of blastema cells, while its neutralisation blocks proximo-distal cell surface interactions. Critically, Tig1 reprogrammes distal cells to a proximal identity, upregulating Prod1 and inhibiting Hoxa13 and distal transcriptional networks. Thus, Tig1 is a central cell surface determinant of proximal identity in the salamander limb.

ALK and GSK3: Shared Features of Neuroblastoma and Neural Crest Cells.

Neuroblastoma is one of the most common and deadly childhood cancers. Neuroblastoma arises from transformed cells of the neural crest lineage. Outcomes of the disease vary greatly, ranging from spontaneous regression to aggressive metastases. While this variability may reflect the inherent migratory capabilities and multipotency of neural crest cells, there have been few direct comparisons between neuroblastoma and embryonic neural crest cells, in part because of the limited in vivo accessibility of the mammalian neural crest lineage. Our recent studies demonstrate a novel link between anaplastic lymphoma kinase (ALK) and glycogen synthase kinase 3 (GSK3). Our work suggests that ALK-dependent regulation of GSK3 via tyrosine phosphorylation may alter the substrate specificity of GSK3, thus regulating cytoskeletal dynamics in migrating neural crest cells.

Glycogen synthase kinase 3 controls migration of the neural crest lineage in mouse and Xenopus.

Neural crest migration is critical to its physiological function. Mechanisms controlling mammalian neural crest migration are comparatively unknown, due to difficulties accessing this cell population in vivo. Here we report requirements of glycogen synthase kinase 3 (GSK3) in regulating the neural crest in Xenopus and mouse models. We demonstrate that GSK3 is tyrosine phosphorylated (pY) in mouse neural crest cells and that loss of GSK3 leads to increased pFAK and misregulation of Rac1 and lamellipodin, key regulators of cell migration. Genetic reduction of GSK3 results in failure of migration. We find that pY-GSK3 phosphorylation depends on anaplastic lymphoma kinase (ALK), a protein associated with neuroblastoma. Consistent with this, neuroblastoma cells with increased ALK activity express high levels of pY-GSK3, and blockade of GSK3 or ALK can affect migration of these cells. Altogether, this work identifies a role for GSK3 in cell migration during neural crest development and cancer.

Identification of Flavin-Containing Monooxygenase 5 (FMO5) as a Regulator of Glucose Homeostasis and a Potential Sensor of Gut Bacteria.

We have previously identified flavin-containing monooxygenase 5 (FMO5) as a regulator of metabolic aging. The aim of the present study was to investigate the role of FMO5 in glucose homeostasis and the impact of diet and gut flora on the phenotype of mice in which the Fmo5 gene has been disrupted (Fmo5-/- mice). In comparison with wild-type (WT) counterparts, Fmo5-/- mice are resistant to age-related changes in glucose homeostasis and maintain the higher glucose tolerance and insulin sensitivity characteristic of young animals. When fed a high-fat diet, they are protected against weight gain and reduction of insulin sensitivity. The phenotype of Fmo5-/- mice is independent of diet and the gut microbiome and is determined solely by the host genotype. Fmo5-/- mice have metabolic characteristics similar to those of germ-free mice, indicating that FMO5 plays a role in sensing or responding to gut bacteria. In WT mice, FMO5 is present in the mucosal epithelium of the gastrointestinal tract where it is induced in response to a high-fat diet. In comparison with WT mice, Fmo5-/- mice have fewer colonic goblet cells, and they differ in the production of the colonic hormone resistin-like molecule ßFmo5-/- mice have lower concentrations of tumor necrosis factor α in plasma and of complement component 3 in epididymal white adipose tissue, indicative of improved inflammatory tone. Our results implicate FMO5 as a regulator of body weight and of glucose disposal and insulin sensitivity and, thus, identify FMO5 as a potential novel therapeutic target for obesity and insulin resistance.

The phenotype of a knockout mouse identifies flavin-containing monooxygenase 5 (FMO5) as a regulator of metabolic ageing.

We report the production and metabolic phenotype of a mouse line in which the Fmo5 gene is disrupted. In comparison with wild-type (WT) mice, Fmo5(-/-) mice exhibit a lean phenotype, which is age-related, becoming apparent after 20 weeks of age. Despite greater food intake, Fmo5(-/-) mice weigh less, store less fat in white adipose tissue (WAT), have lower plasma glucose and cholesterol concentrations and enhanced whole-body energy expenditure, due mostly to increased resting energy expenditure, with no increase in physical activity. An increase in respiratory exchange ratio during the dark phase, the period in which the mice are active, indicates a switch from fat to carbohydrate oxidation. In comparison with WT mice, the rate of fatty acid oxidation in Fmo5(-/-) mice is higher in WAT, which would contribute to depletion of lipid stores in this tissue, and lower in skeletal muscle. Five proteins were down regulated in the liver of Fmo5(-/-) mice: aldolase B, ketohexokinase and cytosolic glycerol 3-phosphate dehydrogenase (GPD1) are involved in glucose or fructose metabolism and GPD1 also in production of glycerol 3-phosphate, a precursor of triglyceride biosynthesis; HMG-CoA synthase 1 is involved in cholesterol biosynthesis; and malic enzyme 1 catalyzes the oxidative decarboxylation of malate to pyruvate, in the process producing NADPH for use in lipid and cholesterol biosynthesis. Down regulation of these proteins provides a potential explanation for the reduced fat deposits and lower plasma cholesterol characteristic of Fmo5(-/-) mice. Our results indicate that disruption of the Fmo5 gene slows metabolic ageing via pleiotropic effects.

The phenotype of a flavin-containing monooyxgenase knockout mouse implicates the drug-metabolizing enzyme FMO1 as a novel regulator of energy balance.

Flavin-containing monooxygenases (FMOs) of mammals are thought to be involved exclusively in the metabolism of foreign chemicals. Here, we report the unexpected finding that mice lacking Fmos 1, 2 and 4 exhibit a lean phenotype and, despite similar food intake, weigh less and store less triglyceride in white adipose tissue (WAT) than wild-type mice. This is a consequence of enhanced whole-body energy expenditure, due mostly to increased resting energy expenditure (REE). This is fuelled, in part, by increased fatty acid ß-oxidation in skeletal muscle, which would contribute to depletion of lipid stores in WAT. The enhanced energy expenditure is attributed, in part, to an increased capacity for exercise. There is no evidence that the enhanced REE is due to increased adaptive thermogenesis; instead, our results are consistent with the operation in WAT of a futile energy cycle. In contrast to FMO2 and FMO4, FMO1 is highly expressed in metabolic tissues, including liver, kidney, WAT and BAT. This and other evidence implicates FMO1 as underlying the phenotype. The identification of a novel, previously unsuspected, role for FMO1 as a regulator of energy homeostasis establishes, for the first time, a role for a mammalian FMO in endogenous metabolism. Thus, FMO1 can no longer be considered to function exclusively as a xenobiotic-metabolizing enzyme. Consequently, chronic administration of drugs that are substrates for FMO1 would be expected to affect energy homeostasis, via competition for endogenous substrates, and, thus, have important implications for the general health of patients and their response to drug therapy.