Severe appetite and weight loss define the eating disorder anorexia nervosa, and can also accompany the progression of some neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS). Although acute loss of hypothalamic neurons that produce appetite-stimulating neuropeptide Y (Npy) and agouti-related peptide (Agrp) in adult mice or in mice homozygous for the anorexia (anx) mutation causes aphagia, our understanding of the factors that help maintain appetite regulatory circuitry is limited. Here we identify a mutation (C19T) that converts an arginine to a tryptophan (R7W) in the TYRO3 protein tyrosine kinase 3 (Tyro3) gene, which resides within the anx critical interval, as contributing to the severity of anx phenotypes. Our observation that, like Tyro3−/− mice, anx/anx mice exhibit abnormal secondary platelet aggregation suggested that the C19T Tyro3 variant might have functional consequences. Tyro3 is expressed in the hypothalamus and other brain regions affected by the anx mutation, and its mRNA localization appeared abnormal in anx/anx brains by postnatal day 19 (P19). The presence of wild-type Tyro3 transgenes, but not an R7W-Tyro3 transgene, doubled the weight and lifespans of anx/anx mice and near-normal numbers of hypothalamic Npy-expressing neurons were present in Tyro3-transgenic anx/anx mice at P19. Although no differences in R7W-Tyro3 signal sequence function or protein localization were discernible in vitro, distribution of R7W-Tyro3 protein differed from that of Tyro3 protein in the cerebellum of transgenic wild-type mice. Thus, R7W-Tyro3 protein localization deficits are only detectable in vivo. Further analyses revealed that the C19T Tyro3 mutation is present in a few other mouse strains, and hence is not the causative anx mutation, but rather an anx modifier. Our work shows that Tyro3 has prosurvival roles in the appetite regulatory circuitry and could also provide useful insights towards the development of interventions targeting detrimental weight loss.

CAMP factor is an extracellular cytolytic protein produced by Streptococcus agalactiae. CAMP factor has been reported to bind the Fc fragments of immunoglobulin G (IgG) and has therefore also been called protein B, in analogy to protein A of Staphylococcus aureus. We attempted to characterize the interaction of protein B with IgG in more detail. In contrast to protein A, CAMP factor does not inhibit the activation of complement by hemolysin antibodies bound to sheep red cell surfaces. IgG also failed to inhibit the co-hemolytic activity of CAMP factor, which is in disagreement with previous findings. After co-incubation, CAMP factor and IgG were cleanly separated by gel filtration, indicating that no binding had occurred.

The serotonergic (5-HT) system modulates many behaviors and has been implicated in psychiatric disorders, but the density of 5-HT processes has complicated analyses. We have used regulatory regions from the Tryptophan hydroxylase 1 (Tph1) gene to drive expression of LoxP-flanked placental alkaline phosphatase (PLAP) to generate the Tph1-Lox-PLAP reporter mouse line. In these mice, PLAP is expressed in the hindbrain raphe nuclei and in peripheral tissues known to express Tph1. Tph1 is expressed at low levels in neurons. While, in Tph1-Lox-PLAP mice, most PLAP-expressing neurons are monoaminergic, PLAP was expressed in only 5-10% of neurons expressing the predominant neuronal 5-HT biosynthetic enzyme Tph2, serotonin transporter (SERT) or aromatic amino acid decarboxylase (AADC). To test this reporter further, we examined the brains of mice carrying the anorexia (anx) mutation, in which increased overall density of 5-HT immunoreactivity had been previously observed at P21. PLAP-labeling of processes in anx/anx and anx/+ mice was reduced at P0. By P10, distribution of PLAP-labeled processes in anx/+ and +/+ cortices was indistinguishable, but differed markedly from that seen in the cortical layers of anx/anx mice. Thus, the Tph1-LoxP-PLAP reporter revealed a dosage sensitive role of the anx mutation in the early 5-HT system and later cortical layer-specific differences in 5-HT process distribution in anx/anx mice. Thus, the Tph1-LoxP-PLAP reporter provides a sensitive indicator for analyses of serotonergic cells in the brain and periphery.