We are combining genetic and immunological approaches to study male tail morphogenesis. Currently, we are developing a panel of monoclonal antibodies directed against male tail components. There are two reasons for developing these antibodies. First, they can serve as molecular markers for normal development, so that the phenotype of male tail mutants can be rapidly and precisely defined. Secondly, these antibodies may identify important morphogenic components which cannot be easily identified genetically, either because they are polygenic, or because they are involved in other essential developmental processes. To illustrate the latter point, one could imagine a cuticle protein essential for maintenance of the fan-like shape of the bursa. If this protein was encoded by a multigene family, or served an essential function earlier in development, it would be difficult to identify mutations in the gene coding for this protein. For our initial fusion, mice were immunized with L4 males. Hybridomas were prepared and screened by immunofluorescence microscopy of whole mounts of methanol-fixed animals. As expected, most positive hybridomas produced antibodies directed against antigens present throughout the animal. However, two hybridomas produced antibodies with interesting specificities. One (A117) appears to bind to the entire bursal fan as well as some material in and around the ventral nerve cord. The other (A27) binds to a ring-like structure which surrounds the cloaca. In hermaphrodites, two posterior cell bodies appear to react with this antibody. Since the A27 antibody recognizes a clearly sexually dimorphic structure, it may be useful in distinguishing male tail mutants that result from partial sexual transformation. We have recently generated hybridomas from a mouse which was first injected with L4 hermaphrodites, immunosuppressed with cyclophosphamide, and then immunized with L4 males and used to prepare hybridomas. From the initial screening of these hybridomas, the immunosuppression regimen appears to have been successful in reducing the number of hybridomas producing antibody to common antigens (e.g., muscle). However, we have not observed a concomitant increase in the number of male tail-specific clones. We have also been screening for new mab (male abnormal) mutations, primarily in mutator backgrounds ( of course!). For our initial, brutally inelegant screen, we have constructed mut;him-5 strains, using MT2878 (Mike Finney's version of Phil Anderson's TR674 mutator). We have been screening under the dissecting microscope for clones producing males with defective tails; initial results suggest that this is a feasible approach. If anyone has recovered any unwanted, mutator-induced mab mutations (sometimes they are hard to avoid), please let us know.