@article {5820, title = {Early embryogenesis of planaria: a cryptic larva feeding on maternal resources.}, journal = {Development Genes \& Evolution}, volume = {216}, year = {2006}, month = {2006 Nov}, pages = {667-81}, abstract = {

The early planarian embryo presents a complete ciliated epidermis and a pharynx and feeds on maternal yolk cells. In this paper, we report on all the elements involved in the formation of such an autonomous embryo, which we name cryptic larva. First, we provide a description of the spherical and fusiform yolk cells and their relationship with the blastomeres, from the laying of the egg capsule up to their final fate in mid embryonic stages. Then, we describe the early cleavage and the subsequent development of the tissues of the cryptic larva, namely, the primary epidermis, the embryonic pharynx, and a new cell type, the star cells. Finally, we discuss the possibility that the cryptic larva either constitutes a vestigial larva or, more likely, is the evolutionary result of the competition between multiple embryos for the limited and shared maternal resources in the egg capsule.

}, keywords = {Animals, Electron, Feeding Behavior, In Situ Hybridization, Larva, Microscopy, Planarians}, issn = {0949-944X}, doi = {10.1007/s00427-006-0094-3}, author = {Cardona, Albert and Hartenstein, Volker and Romero, Rafael} } @article {5822, title = {The embryonic development of the triclad Schmidtea polychroa.}, journal = {Development Genes \& Evolution}, volume = {215}, year = {2005}, month = {2005 Mar}, pages = {109-31}, abstract = {

Triclad flatworms are well studied for their regenerative properties, yet little is known about their embryonic development. We here describe the embryonic development of the triclaty 120d Schmidtea polychroa, using histological and immunocytochemical analysis of whole-mount preparations and sections. During early cleavage (stage 1), yolk cells fuse and enclose the zygote into a syncytium. The zygote divides into blastomeres that dissociate and migrate into the syncytium. During stage 2, a subset of blastomeres differentiate into a transient embryonic epidermis that surrounds the yolk syncytium, and an embryonic pharynx. Other blastomeres divide as a scattered population of cells in the syncytium. During stage 3, the embryonic pharynx imbibes external yolk cells and a gastric cavity is formed in the center of the syncytium. The syncytial yolk and the blastomeres contained within it are compressed into a thin peripheral rind. From a location close to the embryonic pharynx, which defines the posterior pole, bilaterally symmetric ventral nerve cord pioneers extend forward. Stage 4 is characterized by massive proliferation of embryonic cells. Large yolk-filled cells lining the syncytium form the gastrodermis. During stage 5 the external syncytial yolk mantle is resorbed and the embryonic cells contained within differentiate into an irregular scaffold of muscle and nerve cells. Epidermal cells differentiate and replace the transient embryonic epidermis. Through stages 6-8, the embryo adopts its worm-like shape, and loosely scattered populations of differentiating cells consolidate into structurally defined organs. Our analysis reveals a picture of S. polychroa embryogenesis that resembles the morphogenetic events underlying regeneration.

}, keywords = {Animals, Blastomeres, Embryo, Epidermis, Female, Morphogenesis, Nonmammalian, Ovum, Turbellaria}, issn = {0949-944X}, doi = {10.1007/s00427-004-0455-8}, author = {Cardona, Albert and Hartenstein, Volker and Romero, Rafael} } @article {5821, title = {An in situ hybridization protocol for planarian embryos: monitoring myosin heavy chain gene expression.}, journal = {Development Genes \& Evolution}, volume = {215}, year = {2005}, month = {2005 Sep}, pages = {482-88}, abstract = {

The monitoring of gene expression is fundamental for understanding developmental biology. Here we report a successful experimental protocol for in situ hybridization in both whole-mount and sectioned planarian embryos. Conventional in situ hybridization techniques in developmental biology are used on whole-mount preparations. However, given that the inherent lack of external morphological markers in planarian embryos hinders the proper interpretation of gene expression data in whole-mount preparations, here we used sectioned material. We discuss the advantages of sectioned versus whole-mount preparations, namely, better probe penetration, improved tissue preservation, and the possibility to interpret gene expression in relation to internal morphological markers such as the epidermis, the embryonic and definitive pharynges, and the gastrodermis. Optimal fixatives and embedding methods for sectioning are also discussed.

}, keywords = {Animals, Developmental, Dose-Response Relationship, Drug, Embryo, Epidermis, Gene Expression Regulation, In Situ Hybridization, Myosin Heavy Chains, Nonmammalian, Planarians, Time Factors, Tissue Preservation}, issn = {0949-944X}, doi = {10.1007/s00427-005-0003-1}, author = {Cardona, Albert and Fern{\'a}ndez, Juani and Solana, Jordi and Romero, Rafael} } @article {5823, title = {A novel invertebrate trophic factor related to invertebrate neurotrophins is involved in planarian body regional survival and asexual reproduction.}, journal = {Developmental biology}, volume = {252}, year = {2002}, month = {2002 Dec 15}, pages = {188-201}, abstract = {

Trophic factors are a heterogeneous group of molecules that promote cell growth and survival. In freshwater planarians, the small secreted protein TCEN49 is linked to the regional maintenance of the planarian central body region. To investigate its function in vivo, we performed loss-of-function and gain-of-function experiments by RNA interference and by the implantation of microbeads soaked in TCEN49, respectively. We show that TCEN49 behaves as a trophic factor involved in central body region neuron survival. In planarian tail regenerates, tcen49 expression inhibition by double-stranded RNA interference causes extensive apoptosis in various cell types, including nerve cells. This phenotype is rescued by the implantation of microbeads soaked in TCEN49 after RNA interference. On the other hand, in organisms committed to asexual reproduction, both tcen49 mRNA and its protein are detected not only in the central body region but also in the posterior region, expanding from cells close to the ventral nerve chords. In some cases, the implantation of microbeads soaked in TCEN49 in the posterior body region drives organisms to reproduce asexually, and the inhibition of tcen49 expression obstructs this process, suggesting a link between the central nervous system, TCEN49, regional induction, and asexual reproduction. Finally, the distribution of TCEN49 cysteine and tyrosine residues also points to a common evolutionary origin for TCEN49 and molluscan neurotrophins.

}, keywords = {Amino Acid, Amino Acid Sequence, Animals, Biological Factors, Immunohistochemistry, In Situ Hybridization, In Situ Nick-End Labeling, Molecular Sequence Data, Nerve Growth Factors, Planarians, Reproduction, Sequence Homology}, issn = {0012-1606}, author = {Bueno, David and Fern{\`a}ndez-Rodr{\'\i}guez, Juana and Cardona, Albert and Hern{\`a}ndez-Hern{\`a}ndez, Victor and Romero, Rafael} }