Isolation and characterization of the retinoblastoma protein from fish

The retinoblastoma (Rb) gene represents the first tumor suppressor gene cha racterized. The encoded protein, pRb, plays a crucial role in cell cycle co ntrol, preventing malignant cell proliferation. Recently, homologues of the Rb gene have been isolated in fish and the pocket domain, which is central to Rb function, was conserved. In our studies, using coelocanth (Latimeria chalumnae), rainbow trout (Oncorhynchus mykiss), medaka (Oryzias latipes) and English sole (Parophrys vetulus), we have developed a simple protocol f or the isolation of the Rb tumor suppressor protein and determined its' tis sue and cellular localization. Fish Rb proteins display apparent molecular weights in the range of 100-110 kDa, similar to the human pRb. The protein was detected in all tissues examined, consistent with the proteins' univers al role in cellular signalling. An interesting pattern of immunoreactive ba nds was detected in each of the cells' two main compartments, suggesting di fferential proteolysis. Immuno-analysis of the pRb in trout liver tumor mat erial revealed an additional Rb reactive product that was absent in normal liver cell extracts. (C) 2001 Elsevier Science Inc. All rights reserved.