Figure 1.
Schematic representation of Hydra sp.
Cross sections of two regions of the hydroid body. A: hypostome. B: pedal disk. C: detail of the nerve cells forming a net on the base of the epidermis and gastrodermis. cm: circular muscular layer formed by the contractile extensions of the nutritive muscle cells; cn: cnidocito; eg: epithelial gland cell; ep: epithelial-muscular cell; g: mucous and enzymatic gland cell; i: interstitial cell; lm: longitudinal muscle layer formed by the contractile extensions of the epithelial-muscular cells; n: nerve cell and ns: neurosensory cell.
Figure 2.
A: Panoramic view of a specimen labeled with anti-AT antiserum showing the presence of immunoreactive material in different parts of the body. B: Similar view in which the primary antibody incubation was replaced for saline solution. C: Similar view as in A showing the co-existence of f-actin filaments and immunoreactive material D: A magnified view showing the spatial relationship between AT-like nerve cells and epithelial-muscular cells. Motor nerve cells (green) and epithelial-muscular cells labeled with phalloidin (red).
Figure 3.
A: confocal 3D reconstruction showing AT-like nerve cells in a net-like arrangement and f-actin filaments. B: confocal 3D reconstruction of a cross-section of the hydroid body wall showing the anatomical relation between AT-like motor nerve cells and epithelial-muscular cells, as well as the colocalization of the cells producing the peptide, with contractile cells. C: Schematic representation of B including sensory nerve cells (blue) (modified from [69]). D and E: Panoramic (D) and detailed view (E) of an hydroid showing the presence of allatotropic-like cells in the pedal disc. Motor nerve cells (green) and epithelial-muscular cells labeled with phalloidin (red).
Figure 4.
Qdot-AT and AST-C labeling and AT-immunoreactivity.
A: Pedal disc view showing the distribution of cells labeled with Qdot-AT (*) B: Magnified view showing the cells in clusters C: View of the body wall of a hydroid showing AT recognizing epithelial-muscular cells at the stalk, as well as the distribution of the cells in a circular arrangement D: Magnified view of the epithelial-muscular circular cells at the stalk. Note the cells in two circular rows, as well as the presence of endocytic vesicles (arrow). E: View of the body wall of a hydroid showing AST-C recognizing epithelial-muscular cells at the stalk. Note that the distribution of the labeled cells is different to the labeling corresponding to the AT peptide. F: Magnified view of the same epithelial-muscular circular cells, also showing endocytic vesicles.
Figure 5.
Qdot-AT labeling and AT-immunoreactivity.
A: Panoramic view at the bottom of the stalk showing the pedal disc of a hydroid. B: Magnified view of the stalk suggesting. a morpho-functional relationship between both cell populations. Inset: detailed view of a nerve cell. Note that the morphology and spatial orientation of the cell and its projection clearly resembles the motor nature of the nerve cells. C and D: show both channels independently. Note that the position of nerve cells (C), clearly corresponding with non-labeled spaces in (D) (open circles), showing that nerve cells are intercalated between epithelial-muscular cells recognizing AT peptide and reinforcing the morpho functional relationship between these two populations. Epithelial-muscular cells recognizing AT-Qdots conjugates (red) and AT-like motornerve cells (green). Colocalization of markers (yellowish green).
Figure 6.
Myotropic activity of AT-like peptide and feeding.
A: Specimen of H. plagiodesmica after the ingestion of an A. salina egg. B: confocal 3D reconstruction of an hydroid after double labeling with AT-antiserum (green) and nanocristals (red). Note the colocalization of both markers at the level of the hypostome (arrows) and gastroenteron (arrow heads). C: Physiological assay demonstrating the AT involvement in feeding movements. Black columns: Hypostome response of 72 h starved hydroids to treatment with different doses of AT. Grey columns: Hypostome response of 72 h starved hydroids challenged with food and exposed to different doses of AT-antiserum. The results are expressed as percentage of individuals that completely extruded the hypostome. (*): Significant differences between hydroids treated with AT or AT-antiserum and controls.
Figure 7.
Species from the same phylum are labeled by a similar gray tone blocks. The tree is enrooted using the D. melanogaster FMFRamide receptor [50].