In cnidarians, axial patterning is not restricted to embryogenesis but continues throughout a prolonged life history filled with unpredictable environmental changes. How this developmental capacity copes with fluctuations of food availability and whether it recapitulates embryonic mechanisms remain poorly understood. Here we utilize the tentacles of the sea anemone Nematostella vectensis as an experimental paradigm for developmental patterning across distinct life history stages. By analyzing over 1000 growing polyps, we find that tentacle progression is stereotyped and occurs in a feeding-dependent manner. Using a combination of genetic, cellular and molecular approaches, we demonstrate that the crosstalk between Target of Rapamycin (TOR) and Fibroblast growth factor receptor b (Fgfrb) signaling in ring muscles defines tentacle primordia in fed polyps. Interestingly, Fgfrb-dependent polarized growth is observed in polyp but not embryonic tentacle primordia. These findings show an unexpected plasticity of tentacle development, and link post-embryonic body patterning with food availability.

The antennal lobe (AL) of Drosophila is the first olfactory processing center in which olfactory input and output are spatially organized into distinct channels via glomeruli to form a discrete neural map. In each glomerulus, the axons of a single type of olfactory receptor neurons (ORNs) synapse with the dendrites of a single type of projection neurons (PNs). The AL is an ideal place to study how the wiring specificity between specific types of ORNs and PNs is established during development. During the past two decades, the involvement of diverse molecules in the specification and patterning of ORNs and PNs has been reported. Furthermore, local interneurons-another component of glomeruli-have been recently catalogued and their functions have been gradually dissected. Although there is accumulating knowledge about the involvement of these three cell types in the wiring specificity of the olfactory system, in this review, we focus especially on the development of PN dendrites.

Proper function of the neural network results from the precise connections between axons and dendrites of presynaptic and postsynaptic neurons, respectively. In the Drosophila olfactory system, the dendrites of projection neurons (PNs) stereotypically target one of ∼50 glomeruli in the antennal lobe (AL), the primary olfactory center in the brain, and form synapses with the axons of olfactory receptor neurons (ORNs). Here, we show that Eph and Ephrin, the well-known axon guidance molecules, instruct the dendrodendritic segregation during the discrete olfactory map formation. The Eph receptor tyrosine kinase is highly expressed and localized in the glomeruli related to reproductive behavior in the developing AL. In one of the pheromone-sensing glomeruli (DA1), the Eph cell-autonomously regulates its dendrites to reside in a single glomerulus by interacting with Ephrins expressed in adjacent PN dendrites. Our data demonstrate that the trans interaction between dendritic Eph and Ephrin is essential for the PN dendritic boundary formation in the DA1 olfactory circuit, potentially enabling strict segregation of odor detection between pheromones and the other odors.

In cnidarians, axial patterning is not restricted to embryonic development but continues throughout a prolonged life history filled with unpredictable environmental changes. How this developmental capacity copes with fluctuations of food availability and whether it recapitulates embryonic mechanisms remain poorly understood. To address these questions, we utilize the tentacles of the sea anemone Nematostella vectensis as a novel paradigm for developmental patterning across distinct life history stages. As a result of embryonic development, Nematostella polyps feature four primary tentacles, while adults have 16 or more. By analyzing over 1000 growing polyps, we find that tentacle progression is remarkably stereotyped and occurs in a feeding-dependent manner. Mechanistically, we show that discrete Fibroblast growth factor receptor b (Fgfrb)-positive ring muscles prefigure the sites of new tentacles in unfed polyps. In response to feeding, a Target of Rapamycin (TOR)-dependent mechanism controls the expansion of Fgfrb expression in oral tissues which defines tentacle primordia. Using a combination of genetic, cellular and molecular approaches, we demonstrate that FGFRb regionally enhances TOR signaling activity and promotes polarized growth, a spatial pattern that is restricted to polyp but not to embryonic tentacle primordia. These findings reveal an unexpected plasticity of tentacle development, and show that the crosstalk between TOR-mediated nutrient signaling and FGFRb pathway couples post-embryonic body patterning with food availability.3