Differential synthesis and cytolocalization of prosomes in chick embryos during development.

Prosomes, also called "multicatalytic proteinase" or proteasomes, were purified from chick embryos of different developmental stages by a simple, single-step procedure. These were characterized by their characteristic protein patterns determined by SDS polyacrylamide gel electrophoresis (SDS PAGE) and immunoblotting with four monoclonal antibodies, namely, anti-p27, -p28, -p29 and -p31, prepared against duck prosomes. In vitro labeling of embryos with 35S-methionine followed by SDS PAGE and fluorography of the purified prosomes revealed that their polypeptides are differentially synthesized at various stages during development. Among 12 polypeptides (p21 to p56), p21 is synthesized at the beginning of gastrulation (stage 2) followed by the synthesis of p24 at stage 3. Nine other polypeptides (p25 to p35) are synthesized at the head-fold stage (stage 6), while the synthesis of polypeptide p56 is only detected at stage 10 (10-somite stage). Indirect immunofluorescence studies, with the 4 monoclonal antibodies, demonstrated 3 distinct, developmental stage-specific patterns of cytodistribution of these four prosome polypeptides in the embryos. During early embryogenesis, these are uniformly nuclear in location, while at later stages (stage 4 onwards) they are also present in the cytoplasm. Interestingly, one of the antigens (p 28), although found uniformly in all types of tissues in the embryos up to the gastrulation stage, is undetectable in the neural tissues and nonuniformly distributed in other tissues of stage-10 embryos. These data suggest that there are subcomponents of prosomes which are synthesized as well as distributed in an independent manner during development, possibly reflecting subcomponent-specific multiple functions of these particles.