Expression of a neuropeptide similar to allatotropin in free living turbellaria (platyhelminthes).

Mechanisms coordinating cell-cell interaction have appeared early in evolution. Allatotropin (AT), a neuropeptide isolated based on its ability to stimulate the synthesis of juvenile hormones (JHs) in insects has also been found in other invertebrate phyla. Despite this function, AT has proved to be myotropic. In the present study we analyze its expression in two groups of Turbellaria (Catenulida, Macrostomida), and its probable relationship with muscle tissue. The results show the presence of an AT-like peptide in the free living turbellaria analyzed. The analysis of the expression of the peptide together with phalloidin, suggests a functional relationship between the peptide and muscle tissue, showing that it could be acting as a myoregulator. The finding of immunoreactive fibers associated with sensory organs like ciliated pits in Catenulida and eyes in Macrostomida makes probable that AT could play a role in the physiological mechanisms controlling circadian activities. Furthermore, the existence of AT in several phyla of Protostomata suggests that this peptide could be a synapomorphic feature of this group. Indeed, the presence in organisms that do not undergo metamorphosis, could be signaling that it was first involved in myotropic activities, being the stimulation of the synthesis of JHs a secondary function acquired by the phylum Arthropoda.

The first ultrastructural description of the Haswell cells in Temnocephalidae (Platyhelminthes, Temnocephalida), with insights into their function.

This paper provides the first description of the Haswell cells at the ultrastructural level, as well as giving an insight into their function. Two species of Temnocephalidae were studied, Temnocephala iheringi and T. haswelli. Haswell cells are identical in both species, and their structure indicates that they have a secretory function. They are highly interdigitated with parenchymal cells and are usually joined to them by cup-like desmosomes. Nuclei are irregular, with a honeycomb structure and perichromatin granules. The most prominent organelle is granular endoplasmic reticulum, which is typically arranged in concentric rings that usually encircle a conspicuous Golgi complex. Secretion bodies are secreted via projections of the Haswell cells that reach the surface in the anterior portion of the body and in the tentacles. Distinct pores with a size and distribution consistent with the TEM observations were seen under SEM in these regions.