V-MYB ONCOGENE AND C-MYB PROTOONCOGENE EXPRESSION IN AVIAN CELLS - MORPHOLOGICAL-CHANGES OF THE CELLS AND TOPOGRAPHIC LOCALIZATION OF MYB PROTEINS

Morphological changes of avian cells expressing the v-myb oncogene or c-myb proto-oncogene were studied by means of electron microscopy. Exp ression of both genes lead to distinct morphological changes of these cells. The nucleus of LSCC-BM2 cells expressing v-myb gene was of norm al size but usually of irregular shape. It contained large unravelled nucleoli with typical interstices in some cells. Small nucleolar struc tures were also localized in the periphery of nuclear membrane. Nuclea r envelope revealed reduced perinuclear space between two membranes. L SCC-BK3 cells expressing the c-myb gene were characterized by distinct ly enlarged nucleus, in most cases of irregular shape. It contained on ly one nucleolus markedly enlarged, often unravelled, with apparent in terstitial area. Nucleoli with nucleolonemas were observed in some cel ls. Nuclear envelope formed by two obscure membranes showed reduced pe rinuclear space. Topographic localization of v-Myb and c-Myb protein p roducts was not basically different, both being detected in the nucleu s of avian cells. v-Myb and c-Myb markers were distributed mostly in c lusters, usually associated with interchromatin granules, but some mar ker was associated also with the nuclear membrane. Both Myb products w ere never detected in nucleolar structures of avian cells. Morphologic al changes of avian cells expressing myb genes and topographic localiz ation of Myb proteins in these cells were different from those found i n the insect cells expressing myb genes. The observed differences are discussed.