Nucleotide sequence and organization of the transforming region and large terminal redundancies (LTR) of avian myeloblastosis virus (AMV)

Serum-free conditions for the growth of avian granulocyte and monocyte clones and primary leukemic cells induced by AMV, and the apparent conversion of granulocytic progenitors into monocytic cells by a factor in chicken serum

The supportive activity of chicken serum for the soft-agar growth of chicken granulocyte and monocyte clones could be replaced with defined ingredients [bovine serum albumin (BSA), conalbumin, selenium, linoleic acid and for routine work, a liquid soy lecithin preparation (59% phospholipids, 39% linoleic acid, and less than 2% of inositol and choline)]. The lecithin preparation could be replaced with L-alpha-phosphatidylcholine. The source of colony-stimulating factor was medium conditioned by fibroblasts cultured under protein-free conditions. AMV-induced leukemic cells could be cloned under identical conditions. In the presence of both chicken serum (10%) and the replacement ingredients, most of the proliferative clones produced were monocytic (84%). In the presence of serum alone, all of them were monocytic. Under serum-free conditions, all the clones produced were granulocytic when a day-3 conditioned medium (CM) was used; monocytic ones were also present when a day-6 CM was used. When the serum was serially diluted in the presence of the replacement ingredients, the number of proliferative monocytic clones progressively decreased while the number of proliferative granulocytic clones progressively increased and the kinetics of each were essentially the same, only opposite in direction. Moreover, the total number of proliferative clones did not change more than 33% at any dilution (or in the absence of serum). We postulate the existence in the chick system of a serum macrophage differentiation factor (M-DF) which converts early granulocytic progenitors (or exclusively diverts a common progenitor) into monocytic cells.

Retrovirus transduction: segregation of the viral transforming function and the herpes simplex virus tk gene in infectious Friend spleen focus-forming virus thymidine kinase vectors

A series of deletions and insertions utilizing the herpesvirus thymidine kinase gene (tk) were constructed in the murine retrovirus Friend spleen focus-forming virus (SFFV). In all cases, the coding region for the SFFV-specific glycoprotein (gp55), which is implicated in erythroleukemic transformation, was left intact. These SFFV-TK and SFFV deletion vectors were analyzed for expression of tk and gp55 after DNA-mediated gene transfer. In addition, virus rescued by cotransfection of these vectors with Moloney murine leukemia virus was analyzed for infectious TK-transducing virus, gp55 expression, and erythroleukemia-inducing ability. The experiments demonstrated that deletions or insertions within the intron for the gp55 env gene can interfere with expression of gp55 after both DNA-mediated gene transfer and virus infection. In contrast, the gene transfer efficiency of the tk gene was unaffected in the SFFV-TK vectors, and high-titer infectious TK virus could be recovered. Revertant viruses capable of inducing erythroleukemia and expressing gp55 were generated after cotransfection of the SFFV-TK vectors with murine leukemia virus. The revertant viruses lost both tk sequences and the ability to transduce TK- fibroblasts to a TK+ phenotype. These experiments demonstrate that segregation of the TK and erythroleukemia functions can occur in retrovirus vectors which initially carry both markers.

Retrovirus transduction: segregation of the viral transforming function and the herpes simplex virus tk gene in infectious Friend spleen focus-forming virus thymidine kinase vectors

A series of deletions and insertions utilizing the herpesvirus thymidine kinase gene (tk) were constructed in the murine retrovirus Friend spleen focus-forming virus (SFFV). In all cases, the coding region for the SFFV-specific glycoprotein (gp55), which is implicated in erythroleukemic transformation, was left intact. These SFFV-TK and SFFV deletion vectors were analyzed for expression of tk and gp55 after DNA-mediated gene transfer. In addition, virus rescued by cotransfection of these vectors with Moloney murine leukemia virus was analyzed for infectious TK-transducing virus, gp55 expression, and erythroleukemia-inducing ability. The experiments demonstrated that deletions or insertions within the intron for the gp55 env gene can interfere with expression of gp55 after both DNA-mediated gene transfer and virus infection. In contrast, the gene transfer efficiency of the tk gene was unaffected in the SFFV-TK vectors, and high-titer infectious TK virus could be recovered. Revertant viruses capable of inducing erythroleukemia and expressing gp55 were generated after cotransfection of the SFFV-TK vectors with murine leukemia virus. The revertant viruses lost both tk sequences and the ability to transduce TK- fibroblasts to a TK+ phenotype. These experiments demonstrate that segregation of the TK and erythroleukemia functions can occur in retrovirus vectors which initially carry both markers.