On p. 4794, the incorrect plasmid was referenced. The plasmid used was pHyVec16 (GenBank Accession Number KP145000).

Developmental processes such as morphogenesis, patterning and differentiation are continuously active in the adult Hydra polyp. We carried out a small molecule screen to identify compounds that affect patterning in Hydra. We identified a novel molecule, DAC-2-25, that causes a homeotic transformation of body column into tentacle zone. This transformation occurs in a progressive and polar fashion, beginning at the oral end of the animal. We have identified several strains that respond to DAC-2-25 and one that does not, and we used chimeras from these strains to identify the ectoderm as the target tissue for DAC-2-25. Using transgenic Hydra that express green fluorescent protein under the control of relevant promoters, we examined how DAC-2-25 affects tentacle patterning. Genes whose expression is associated with the tentacle zone are ectopically expressed upon exposure to DAC-2-25, whereas those associated with body column tissue are turned off as the tentacle zone expands. The expression patterns of the organizer-associated gene HyWnt3 and the hypostome-specific gene HyBra2 are unchanged. Structure-activity relationship studies have identified features of DAC-2-25 that are required for activity and potency. This study shows that small molecule screens in Hydra can be used to dissect patterning processes.

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Studies using chemical genetics allow the researcher to perform the equivalent of classical genetics in real time using molecules that can produce a phenotype when applied to either cultured cells or a whole organism. We have initiated a chemical genetic screen using the AEP strain of Hydra vulgaris to identify bioactive molecules that modulate signaling pathways involved in development and regeneration. One compound, DAC‐2–25, induced the growth of ectopic tentacles in regenerating heads and buds. Chronic exposure to DAC‐2–25 induces ectopic tentacles in H. vulgaris AEP, H. vulgaris 950f, and H. viridissima, but not H. vulgaris Zurich. In chronically treated animals, the first ectopic tentacles appear just below the tentacle ring. Subsequent tentacles emerge in a wave down the body column. We are using AEP/Zurich chimeras to identify which cell lineage is targeted by DAC‐2–25. Structure‐activity relationship (SAR) studies have been initiated to determine what features of the molecule are required for activity. Ultimately we will use affinity chromatography coupled with mass spectrometry to identify the protein target of DAC‐2–25. Crosses of AEP and Zurich have been produced with the intention of doing bulk segregant analysis as an alternative approach to identifying the gene encoding the DAC‐2–25 target protein.

No abstract

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