Genome-Wide Analyses Reveal a Role for Peptide Hormones in Planarian Germline Development

Howard Hughes Medical Institute and Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.
PLoS Biology (Impact Factor: 9.34). 10/2010; 8(10):e1000509. DOI: 10.1371/journal.pbio.1000509
Source: PubMed


Bioactive peptides (i.e., neuropeptides or peptide hormones) represent the largest class of cell-cell signaling molecules in metazoans and are potent regulators of neural and physiological function. In vertebrates, peptide hormones play an integral role in endocrine signaling between the brain and the gonads that controls reproductive development, yet few of these molecules have been shown to influence reproductive development in invertebrates. Here, we define a role for peptide hormones in controlling reproductive physiology of the model flatworm, the planarian Schmidtea mediterranea. Based on our observation that defective neuropeptide processing results in defects in reproductive system development, we employed peptidomic and functional genomic approaches to characterize the planarian peptide hormone complement, identifying 51 prohormone genes and validating 142 peptides biochemically. Comprehensive in situ hybridization analyses of prohormone gene expression revealed the unanticipated complexity of the flatworm nervous system and identified a prohormone specifically expressed in the nervous system of sexually reproducing planarians. We show that this member of the neuropeptide Y superfamily is required for the maintenance of mature reproductive organs and differentiated germ cells in the testes. Additionally, comparative analyses of our biochemically validated prohormones with the genomes of the parasitic flatworms Schistosoma mansoni and Schistosoma japonicum identified new schistosome prohormones and validated half of all predicted peptide-encoding genes in these parasites. These studies describe the peptide hormone complement of a flatworm on a genome-wide scale and reveal a previously uncharacterized role for peptide hormones in flatworm reproduction. Furthermore, they suggest new opportunities for using planarians as free-living models for understanding the reproductive biology of flatworm parasites.

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    • "AChE activity (Gustafsson, 1987; Gustafsson et al., 1995; S. C. Sukhdeo and M. V. Sukhdeo, 1994; V. C. Wilson and Schiller, 1969). However, considering that neuropeptides have been shown to play important roles in the regulation of reproductive development and function in planarians (Collins et al., 2010), it is premature to rule out innervation in these structures. "
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    • "For some RNAi experiments, the beef liver homogenate was mixed with dsRNA-expressing bacteria and directly added to the worms (Reddien et al., 2005b). For other experiments, RNAi knockdowns were generated by feeding in vitro transcribed dsRNA (Collins et al., 2010). As a control RNAi group, worms were fed unc22 double-stranded RNA. "
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    • "Histological analysis (Figure 6—figure supplement 1) of FoxA(RNAi) animals demonstrated that this dorsal outgrowth lacked any recognizable anatomical features of control pharynges, such as radial symmetry or clear laminar structure. Consistent with this observation, these dorsal outgrowths also failed to express either of two pharynx-specific markers (Smed-laminin and Smed-npp-1) (Collins et al., 2010) or the intestinespecific marker Smed-porcupine (Figure 6F), indicating that this aberrantly produced tissue does not acquire pharyngeal or endodermal fate. However, we did identify enrichment of neuronal markers (Smed-PC2 and Smed-ndk) and the muscle marker Smed-collagen, which suggests that in the absence of FoxA, differentiation into neurons and muscle remains intact. "
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