Background: Skeletal muscle-derived myokines modulate metabolic, inflammatory, and other processes. Results: Myonectin, a novel myokine whose expression and circulating levels are regulated by diet, metabolic state, and exercise, functions to control lipid metabolism. Conclusion: Myonectin is a potential nutrient-responsive metabolic regulator secreted by muscle. Significance: Myonectin links muscle to systemic lipid metabolism via its action on adipocytes and hepatocytes, providing insight into complex tissue cross-talk.

This study addresses the role of sonic hedgehog (shh) in increasing oral pharyngeal constructive traits (jaws and taste buds) at the expense of eyes in the blind cavefish Astyanax mexicanus. In cavefish embryos, eye primordia degenerate under the influence of hyperactive Shh signaling. In concert, cavefish show amplified jaw size and taste bud numbers as part of an adaptive change in feeding behavior. To determine whether pleiotropic effects of hyperactive Shh signaling link these regressive and constructive traits, sonic hedgehog (shh) expression was compared during late development of the surface- (surface fish) and cave-dwelling forms of Astyanax. After an initial expansion along the midline of early embryos, shh was elevated in the oral pharyngeal region in cavefish and later was confined to taste buds. The results of shh inhibition and overexpression experiments indicate that Shh signaling has an important role in oral and taste bud development. Heat shock mediated activation of an injected shh transgene at specific times in development showed that taste bud amplification and eye degeneration are sensitive to shh overexpression during the same early developmental period, although taste buds are not formed until much later. Genetic crosses between cavefish and surface fish revealed an inverse relationship between eye size and jaw size/taste bud number, supporing the linkage between oral pharyngeal constructive traits and eye degeneration. The results suggest that hyperactive Shh signaling increases oral and taste bud amplification in cavefish and suggest that selection for constructive oral pharyngeal traits may be responsible for eye loss via pleiotropic function of the Shh signaling pathway.

SUMMARY Vertebrate circadian rhythms are organized by the hypothalamic suprachiasmatic nucleus (SCN). Despite its physiological importance, SCN development is poorly understood. Here, we show that Lim homeodomain transcription factor 1 (Lhx1) is essential for terminal differentiation and function of the SCN. Deletion of Lhx1 in the developing SCN results in loss of SCN-enriched neuropeptides involved in synchronization and coupling to downstream oscillators, among other aspects of circadian function. Intact, albeit damped, clock gene expression rhythms persist in Lhx1-deficient SCN; however, circadian activity rhythms are highly disorganized and susceptible to surprising changes in period, phase, and consolidation following neuropeptide infusion. Our results identify a factor required for SCN terminal differentiation. In addition, our in vivo study of combinatorial SCN neuropeptide disruption uncovered synergies among SCN-enriched neuropeptides in regulating normal circadian function. These animals provide a platform for studying the central oscillator's role in physiology and cognition.