Biomedical subjects

S W Ruffins

Publications and source records attributed to S W Ruffins.

4 recordsLinked to original sources

PubMed2001

Three-dimensional digital mouse atlas using high-resolution MRI.

We present an archetypal digital atlas of the mouse embryo based on microscopic magnetic resonance imaging. The atlas is composed of three modules: (1) images of fixed embryos 6 to 15.5 days postconception (dpc) [Theiler Stages (TS) 8 to 24]; (2) an annotated atlas of the anterior portion of a 13.5 dpc (TS 22) mouse with anatomical structures delineated and linked to explanatory files; and (3) three-dimensional renderings of the entire 13.5 dpc embryo and specific organ systems. The explanatory files include brief descriptions of the structure at each volume element in the image and links to 3D reconstructions, allowing visualization of the shape of the isolated structures. These files can also contain or be linked to other types of information and data including detailed anatomical and physiological information about structures with pointers to online references, relationships between structures, temporal characteristics (cell lineage patterns, size, and shape changes), and gene expression patterns (both spatial and temporal). As an example, we have "painted" in the expression pattern of Dlx5/Dlx6 genes. This digital atlas provides a means to put specific data within the context of normal specimen anatomy, to analyze the information in 3D, and to examine relationships between different types of information.

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PubMed1996

A fate map of the vegetal plate of the sea urchin (Lytechinus variegatus) mesenchyme blastula.

Previous lineage tracing experiments have shown that the vegetal blastomers of cleavage stage embryos give rise to all the mesoderm and endoderm of the sea urchin larva. In these studies, vegetal blastomers were labeled no later than the sixth cleavage division (60-64 cell stage). In an earlier study we showed that single cells in the vegetal plate of the blastula stage Lytechinus variegatus embryo could be labeled in situ with the fluorescent, lipophilic dye, DiI(C18), and that cells labeled in the central region of the vegetal plate of the mesenchyme blastula primarily gave rise to homogeneous clones consisting of a single secondary mesenchyme cell (SMC) type (Ruffins and Ettensohn (1993) Dev. Biol. 160, 285-288). Our clonal labeling showed that a detailed fate map could be generated using the DiI(C18) labeling technique. Such a fate map could provide information about the spatial relationships between the precursors of specific mesodermal and endodermal cell types and information concerning the movements of these cells during gastrulation and later embryogenesis. We have used this method to construct the first detailed fate map of the vegetal plate of the sea urchin embryo. Ours is a latitudinal map; mapping from the plate center, where the mesodermal precursors reside, through the region which contains the endodermal precursors and across the ectodermal boundary. We found that the precursors of certain SMC types are segregated in the mesenchyme blastula stage vegetal plate and that prospective germ layers reside within specific boundaries. To determine whether the vegetal plate is radially symmetrical with respect to mesodermal cell fates, single blastomeres of four cell stage embryos were injected with lysyl-rhodamine dextran (LRD). The resulting ectodermal labeling patterns were classified and correlated with the SMC types labeled. This analysis indicates that the dorsal and ventral blastomers do not contribute equally to SMC derivatives in L. variegatus.

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PubMed1993

A clonal analysis of secondary mesenchyme cell fates in the sea urchin embryo.

The secondary mesenchyme cells (SMCs) give rise to most of the mesoderm of the sea urchin embryo. Although the early embryonic lineage of these cells has been described, the mechanisms that cause SMCs to become restricted to a particular mesodermal cell fate are unknown. To begin to address this question, we performed a clonal analysis of the fates of SMC precursors in the vegetal plate by labeling single cells with the fluorescent dye DiI (C18). Our data show that some presumptive SMCs remain pluripotent at the late blastula stage, since some cells labeled at this stage gave rise to more than one mesodermal cell type. Surprisingly, however, most labeled cells gave rise to homogeneous clones composed of a single cell type. This observation indicates that either many SMC precursors are restricted in their fate before the start of gastrulation or that all the progeny of a single vegetal plate cell are influenced by the same instructional signals during gastrulation, despite the cell divisions and extensive cell movements that occur during this time. The percentage of clones composed of a single cell type increased during the blastula stage, supporting the view that the process of SMC fate specification begins before the onset of gastrulation.

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PubMed1993

Mesodermal cell interactions in the sea urchin embryo: properties of skeletogenic secondary mesenchyme cells.

An interaction between the two principal populations of mesodermal cells in the sea urchin embryo, primary and secondary mesenchyme cells (PMCs and SMCs, respectively), regulates SMC fates and the process of skeletogenesis. In the undisturbed embryo, skeletal elements are produced exclusively by PMCs. Certain SMCs also have the ability to express a skeletogenic phenotype; however, signals transmitted by the PMCs direct these cells into alternative developmental pathways. In this study, a combination of fluorescent cell-labeling methods, embryo microsurgery and cell-specific molecular markers have been used to study the lineage, numbers, normal fate(s) and developmental potential of the skeletogenic SMCs. Previous fate-mapping studies have shown that SMCs are derived from the veg2 layer of blastomeres of the 64-cell-stage embryo and from the small micromeres. By specifically labeling the small micromeres with 5-bromodeoxyuridine, we demonstrate that descendants of these cells do not participate in skeletogenesis in PMC-depleted larvae, even though they are the closest lineal relatives of PMCs. Skeletogenic SMCs are therefore derived exclusively from the veg2 blastomeres. Because the SMCs are a heterogeneous population of cells, we have sought to gain information concerning the normal fate(s) of skeletogenic SMCs by determining whether specific cell types are reduced or absent in PMC(-) larvae. Of the four known SMC derivatives: pigment cells, blastocoelar (basal) cells, muscle cells and coelomic pouch cells, only pigment cells show a major reduction (> 50%) in number following SMC skeletogenesis. We therefore propose that the PMC-derived signal regulates a developmental switch, directing SMCs to adopt a pigment cell phenotype instead of a default (skeletogenic) fate. Ablation of SMCs at the late gastrula stage does not result in the recruitment of any additional skeletogenic cells, demonstrating that, by this stage, the number of SMCs with skeletogenic potential is restricted to 60-70 cells. Previous studies showed that during their switch to a skeletogenic fate, SMCs alter their migratory behavior and cell surface properties. In this study, we demonstrate that during conversion, SMCs become insensitive to the PMC-derived signal, while at the same time they acquire PMC-specific signaling properties.

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