Project description:Depolarization of resting membrane potential in select cells in Xenopus larvae induces striking hyperpigmentation due to dysregulation of melanocytes. Here, we show that this non-cell-autonomous process is mediated by cAMP, CREB, and the transcription factors Sox10 and Slug. Our microarray analysis reveals specific transcripts responsive to Vmem levels within a few hours of depolarization, and a set of 517 transcripts whose expression remains altered during the full hyperpigmented phenotype over a week later, linking instructor cell-depolarization to a range of developmental processes and disease states. We also show that voltage-dependent conversion of melanocytes involves the MSH-secreting melanotrope cells of the pituitary, and formulate a model for the molecular pathway linking the bioelectric properties of melanocyte cells’ microenvironment in vivo to the genetic and cellular changes induced in this melanoma-like phenotype. Remarkably, the phenotype is all-or-none: each individual animal either undergoes melanocyte conversion or not, as a whole. This group decision is stochastic, resulting in varying percentages of hyperpigmented individuals for a given experimental treatment. To understand the stochasticity and dynamic properties of this complex signaling system, we developed a novel computational method that automates the reverse-engineering of stochastic dynamic signaling models. We used this method to discover a network model that quantitatively explained our complex dataset, and even made correct predictions for new experiments that we validated in vivo. Taken together, these data (1) reveal new molecular details about a novel trigger of metastatic-like developmental cell behavior in vivo, (2) suggest new targets for biomedical intervention, and (3) demonstrate proof-of-principle of a computational method for understanding stochastic decision-making by cells during embryonic development and metastasis.
Project description:Depolarization of resting membrane potential in select cells in Xenopus larvae induces striking hyperpigmentation due to dysregulation of melanocytes. Here, we show that this non-cell-autonomous process is mediated by cAMP, CREB, and the transcription factors Sox10 and Slug. Our microarray analysis reveals specific transcripts responsive to Vmem levels within a few hours of depolarization, and a set of 517 transcripts whose expression remains altered during the full hyperpigmented phenotype over a week later, linking instructor cell-depolarization to a range of developmental processes and disease states. We also show that voltage-dependent conversion of melanocytes involves the MSH-secreting melanotrope cells of the pituitary, and formulate a model for the molecular pathway linking the bioelectric properties of melanocyte cellsâ microenvironment in vivo to the genetic and cellular changes induced in this melanoma-like phenotype. Remarkably, the phenotype is all-or-none: each individual animal either undergoes melanocyte conversion or not, as a whole. This group decision is stochastic, resulting in varying percentages of hyperpigmented individuals for a given experimental treatment. To understand the stochasticity and dynamic properties of this complex signaling system, we developed a novel computational method that automates the reverse-engineering of stochastic dynamic signaling models. We used this method to discover a network model that quantitatively explained our complex dataset, and even made correct predictions for new experiments that we validated in vivo. Taken together, these data (1) reveal new molecular details about a novel trigger of metastatic-like developmental cell behavior in vivo, (2) suggest new targets for biomedical intervention, and (3) demonstrate proof-of-principle of a computational method for understanding stochastic decision-making by cells during embryonic development and metastasis. Gene expression analysis was performed using samples treated with ivermectin from NF stage 10 onwards, collected at two developmental stages; stage 15 (early neurula) and stage 45 (free-swimming tadpole). Embryos were collected in eppendorf tubes (N=50 for stage 15, N=5 for stage 45) and frozen at -80°C. RNA extraction and microarray analysis were performed by the Beth Israel Deaconess Medical Center Genomics and Proteomics Center (Harvard) according to standard Affymetrix protocol, using a high throughput hybridization and scanning system. Microarray hybridization was performed using the Affy 3â IVT Express Kit. Fragmented and biotin labeled and amplified RNA was hybridized to the GeneChip® Xenopus laevis Genome 2.0 array as per manufacturerâs protocol. The Affymetrix GeneChip® X. laevis Genome 2.0 Array, has 32,400 probe sets representing more than 29,900 X. laevis transcripts.
Project description:Robust and efficient protocols for fertilization and early embryo care of Xenopus laevis and Xenopus tropicalis are essential for experimental success, as well as maintenance and propagation of precious animal stocks. The rapid growth of the National Xenopus Resource has required effective implementation and optimization of these protocols. Here, we discuss the procedures used at the National Xenopus Resource, which we found helpful for generation and early upkeep of Xenopus embryos and tadpoles.
Project description:Tissue regeneration is of fast growing importance in the development of biomedicine, particularly organ replacement therapies. Unfortunately, many human organs cannot regenerate. Anuran Xenopus laevis has been used as a model to study regeneration as many tadpole organs can regenerate. In particular, the tail, which consists of many axial and paraxial tissues, such as spinal cord, dorsal aorta and muscle, commonly present in vertebrates, can fully regenerate when amputated at late embryonic stages and most of the tadpole stages. Interestingly, between stage 45 when feeding begins to stage 47, the Xenopus laevis tail cannot regenerate after amputation. This period, termed "refractory period", has been known for about 20 years. The underlying molecular and genetic basis is unclear in part due to the difficult to carry out genetic studies in this pseudo-tetraploid species. Here we compared tail regeneration between Xenopus laevis and the highly related diploid anuran Xenopus tropicalis and found surprisingly that Xenopus tropicalis lacks the refractory period. Further molecular and genetic studies, more feasible in this diploid species, should reveal the basis for this evolutionary divergence in tail regeneration between two related species and facilitate the understanding how tissue regenerative capacity is controlled, thus with important implications for human regenerative medicine.
Project description:Maintenance of optimal conditions such as water parameters, diet, and feeding is essential to a healthy Xenopus laevis and Xenopus tropicalis colony and thus to the productivity of the lab. Our prior husbandry experience as well as the rapid growth of the National Xenopus Resource has given us a unique insight into identifying and implementing these optimal parameters into our husbandry operations. Here, we discuss our standard operating procedures that will be of use to both new and established Xenopus facilities.
Project description:Chromatin immunoprecipitation (ChIP) is a powerful method for analyzing the interaction of regulatory proteins with genomic loci, but has been difficult to apply to studies on early embryos due to the limiting amount of genomic material in these samples. Here, we present a comprehensive technique for performing ChIP on blastula and gastrula stage Xenopus embryos. We also describe methods for optimizing crosslinking and chromatin shearing, verifying antibody specificity, maximizing PCR sensitivity, and quantifying PCR results, allowing for the use of as few as 50 early blastula stage embryos (approximately 5x10(4) cells) per experimental condition. Finally, we demonstrate the predicted binding of endogenous beta-catenin to the nodal-related 6 promoter, binding of tagged Fast-1/FoxH1 to the goosecoid promoter, and binding of tagged Tcf3 to the siamois and nodal-related 6 promoters as examples of the potential application of ChIP to embryological investigations. Developmental Dynamics 238:1422-1432, 2009. (c) 2009 Wiley-Liss, Inc.
Project description:A Molecular Atlas of the Developing Ectoderm Defines Neural, Neural Crest, Placode and Non-Neural Progenitor Identity in Vertebrates.