During animal development, cells differentiate into specific cell types to form tissue and organs. Visualization of specific components of individual cell types is useful for studying developmental processes. For this purpose, a number of antibodies and GFP-transgenic lines as molecular markers have been generated in the C. elegans community. In particular, monoclonal antibodies (mAbs) that recognize specific cellular components, such as K76 (anti-P granule; Strome & Wood, 1983) and MH27 (anti-AJM-1, an apical junction protein; Francis & Waterston, 1985), have been extensively used for over 20 years. Furthermore, mAbs can potentially be used for biochemical/proteomic application, for example, to isolate and to identify components of the protein complexes detected by the mAb. The repertoire of such useful mAb markers, however, is still limited, thus we aimed to generate a new panel of mAbs that recognize cell-type- or cellular component-specific structures. As antigens, we used embryonic extracts that were immunologically depleted of abundant cell-type-non-specific components. Hybridoma lines were visually screened by immunofluorescence of C. elegans embryos, and thus far 35 mAbs (the ""KT mAb"" series) have been obtained. Recognized structures include: P-granules, muscle fiber components, muscle-epidermal attachment structures, subsets of epidermal cells, pharyngeal lumen, basement membrane, centrosomes, nuclear envelope, eggshell, and other undefined structures/positions. Preliminary results from double staining and staining of mutant embryos indicate that many of the KT mAbs appear to recognize antigens distinct from previously available mAbs. We have started distributing KT mAbs (currently 17 of them) upon request. Data for each KT mAbs including immunofluorescent images at each stage of embryogenesis are available from our website
(http://www.cdb.riken.jp/dge/KTmAbDB/KTtop.html).