The nematode gonad is an exemplary system for the study of organogenesis and fundamental problems in developmental and cellular biology. Nematode gonads vary dramatically across species (Chitwood, B.G., Chitwood, M.B., 1950. Introduction to Nematology." University Park Press, Baltimore; Felix, M.A., Sternberg, P.W., 1996. Symmetry breakage in the development of one-armed gonads in nematodes. Development 122, 2129-2142). As such, comparative developmental biology of gonadogenesis offers the potential to investigate changes in developmental and cellular processes that result in novel organ morphologies and thus may give insights into how these changes can affect animal bauplane. Pristionchus pacificus is a free-living nematode that diverged from the model nematode Caenorhabditis elegans around 200-300 million years ago. The morphology and development of P. pacificus is highly homologous to that of C. elegans. However, many differences in morphology and the underlying molecular signaling networks are easy to identify, making P. pacificus ideal for a comparative approach. Here, we report a detailed description of the P. pacificus hermaphrodite gonad using electron and fluorescent microscopy that will provide a basis for both phenotypic studies of genetic mutations and in vivo molecular studies of cloned genes involved in P. pacificus gonad development. We report that the morphology of the P. pacificus gonad is distinct from that of C. elegans. Among these differences are germ line patterning differences, heterochronic differences, novel gonadal arm-migrations, novel cellular composition of some somatic tissues (e.g., the number of cells that comprise the sheath and different spermathecal regions are different), the absence of a somatic tissue (e.g., the spermathecal valve cells), a novel architecture for the sheath, and changes in the cellular and sub-cellular morphology of the individual sheath cells. Additionally, we report a set of cell ablations in P. pacificus that indicate extensive cell communication between the somatic gonadal tissues and the germ line. Individual ablation experiments in P. pacificus show significant differences in the effects of individual somatic tissues on germ line patterning in comparison to C. elegans.

Over the past two to three decades, developmental biology has demonstrated that all multicellular organisms in the animal kingdom share many of the same molecular building blocks and many of the same regulatory genetic pathways. Yet we still do not understand how the various organisms use these molecules and pathways to assume all the forms we know today. Evolutionary developmental biology tackles this problem by comparing the development of one organism to another and comparing the genes involved and gene functions to understand what makes one organism different from another. In this review, we revisit a set of seven concepts defined by Lewis Wolpert (fate maps, asymmetric division, induction, competence, positional information, determination, and lateral inhibition) that describe the characters of many developmental systems and supplement them with three additional concepts (developmental genomics, genetic redundancy, and genetic networks). We will discuss examples of comparative developmental studies where these concepts have guided observations on the advent of a developmental novelty. Finally, we identify a set of evolutionary frameworks, such as developmental constraints, cooption, duplication, parallel and convergent evolution, and homoplasy, to adequately describe the evolutionary properties of developmental systems.

Northwestern University (nickel speciation in sediment), and Marnix Vangheluwe of ARCHE Consultants (sediment risk assessment). Members of the European Union Technical Conclusion (i) Group (Derivation of Predicted No-Effect Concentrations for Nickel in Sediment) provided guidance and feedback on project planning and interpretation of results, notably Henrik Tyle and Janeck Scott-Fordsmand of the Denmark Environmental Protection Agency and Colin Jansson of the University of Ghent. Dave Mount and Russ Hockett of U.S. Environmental Protection Agency collected and shipped the West Bearskin Lake sediment. Paul Sibley of the University of Guelph provided technical advice on sediment spiking and toxicity test methods, while on sabbatical at CERC. Many USGS scientists and technicians contributed to the success of this project and report. Ryan Warbritton and Dave White maintained invertebrate cultures; Doug Hardesty, Eric Brunson, Jamie Hughes, Rebecca Consbrock, and Ning Wang assisted with toxicity tests; and Tom May, Mike Walther, and Rui Sun assisted with chemical analyses. James Fairchild and Robert Seal provided technical reviews of the manuscript.

Increased sensitivity and accuracy of a single-stranded DNA splint-mediated ligation assay (sPAT) reveals poly(A) tail length dynamics of developmentally regulated mRNAs, RNA Biology, 11:2, 111-123,