Platyhelminthes are excellent models for the study of stem cell biology, regeneration and the regulation of scale and proportion. In addition, parasitic forms infect millions of people worldwide. Therefore, it is puzzling that they remain relatively unexplored at the molecular level. We present the characterization of similar to3000 non-redundant cDNAs from a clonal line of the planarian Schmidtea mediterranea. The obtained cDNA sequences, homology comparisons and high-throughput whole-mount in situ hybridization data form part of the S. mediterranea database (SmedDb; http://planaria.neuro.utah.edu). Sixty-nine percent of the cDNAs analyzed share similarities with sequences deposited in GenBank and dbEST. The remaining gene transcripts failed to match sequences in other organisms, even though a large number of these (similar to80%) contained putative open reading frames. Taken together, the molecular resources presented in this study, along with the ability of abrogating gene expression in planarians using RNA interference technology, pave the way for a systematic study of the remarkable biological properties displayed by Platyhelminthes.

Thyroid hormone (TH) is required for limb development in Xenopus laevis. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb.

Cajal bodies (CBs) are complex organelles found in the nuclei of a wide variety of organisms, including vertebrates, invertebrates, plants, and yeast. In most cell types CBs are <1 mum in diameter, severely limiting the range of experimental observations that can be made on them. By contrast, CBs in the amphibian oocyte nucleus (also called the germinal vesicle) are 2-10 mum in diameter. We have taken advantage of this large size to carry out kinetic studies on coilin, a protein that is specifically enriched in CBs. We labeled coilin with photoactivatable green fluorescent protein and analyzed the movement of the protein by confocal microscopy in unfixed germinal vesicles isolated in oil. We showed that coilin leaves the CB relatively slowly (minutes rather than seconds) with kinetics similar to earlier measurements on its entrance. We also showed that coilin diffuses very slowly within the CB, consistent with its being in a large macromolecular complex. Finally, we found that the movement of coilin is not directly affected by the transcriptional state of the nucleus or ongoing nucleocytoplasmic exchange. These data on the kinetics of coilin reinforce the conclusion that CB components are in a constant state of flux, consistent with models that postulate an active role for CBs in nuclear physiology.

Cajal bodies (CBs) are nuclear organelles that occur in a variety of organisms, including vertebrates, insects, and plants. They are most often identified with antibodies against the marker protein coilin. Because the amino acid sequence of coilin is not strongly conserved evolutionarily, coilin orthologues have been difficult to recognize by homology search. Here, we report the identification of Drosophila melanogaster coilin and describe its distribution in tissues of the fly. Surprisingly, we found coilin not only in CBs but also in histone locus bodies (HLBs), calling into question the use of coilin as an exclusive marker for CBs. We analyzed two null mutants in the coilin gene and a piggyBac insertion mutant, which leads to specific loss of coilin from the germline. All three mutants are homozygous viable and fertile. Cells that lack coilin also lack distinct foci of other CB markers, including fibrillarin, the survival motor neuron (SMN) protein, U2 small nuclear RNA (snRNA), U5 snRNA, and the small CB-specific (sca) RNA U85. However, HLBs are not obviously affected in coilin-null flies. Thus, coilin is required for normal CB organization in Drosophila but is not essential for viability or production of functional gametes.