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Isolation of a pathogenic clone of mouse mammary tumor virus
D W Morris1, H D Bradshaw, H T Billy
1Department of Pathology, School of Medicine, University of California, Davis 95616.
Abstract:
Exogenous mouse mammary tumor virus (MMTV) was cloned from a GR mammary tumor. Clone lambda GRT39 contained a full-length integrated MMTV(GR) provirus and both 5' and 3' host flanking DNA. The lambda GRT39 provirus had no apparent structural changes associated with cloning and retained the exogenous MMTV gag gene poison sequence. When introduced into rat mammary adenocarcinoma LA7 cells, the lambda GRT39 provirus was fully expressed. lambda GRT39-transfected LA7 cells made MMTV RNA, had gp52 SU protein on the cell surface, and produced B-type retrovirus particles characteristic of MMTV. Mammary tumors developed in hormone-stimulated BALB/c females injected with MMTV from lambda GRT39-transfected LA7 cells [MMTV (lambda GRT39)]. The tumors had new, clonally integrated copies of the MMTV(lambda GRT39) provirus and were expressing MMTV antigen. These data indicate that the lambda GRT39 provirus is biologically active and pathogenic.
Insights
A cloned mouse mammary tumor virus (MMTV) provirus, lambda GRT39, was biologically active. When introduced into rat cells, it caused mammary tumors in mice, indicating MMTV pathogenicity.
Area of Science:
- Virology
- Oncology
- Molecular Biology
Background:
- Mouse mammary tumor virus (MMTV) is an exogenous retrovirus associated with mammary cancer in mice.
- Cloning and characterization of infectious MMTV proviruses are crucial for understanding its role in tumorigenesis.
Purpose of the Study:
- To clone and characterize an infectious MMTV provirus from a GR mouse mammary tumor.
- To assess the biological activity and pathogenicity of the cloned MMTV provirus in a relevant experimental system.
Main Methods:
- Cloning of MMTV provirus from a GR mouse mammary tumor into lambda phage.
- Transfection of the cloned provirus (lambda GRT39) into rat mammary adenocarcinoma LA7 cells.
- Analysis of MMTV RNA expression, gp52 SU protein presence, and retrovirus particle production.
- Induction of mammary tumors in hormone-stimulated BALB/c mice injected with MMTV from transfected cells.
Main Results:
- A full-length MMTV(GR) provirus (lambda GRT39) was successfully cloned, retaining its structural integrity and gag gene sequence.
- Lambda GRT39 provirus was fully expressed in LA7 cells, leading to MMTV RNA, gp52 SU protein expression, and production of MMTV particles.
- Injected MMTV (lambda GRT39) induced mammary tumors in BALB/c mice, which contained new, clonally integrated proviruses and expressed MMTV antigen.
Conclusions:
- The cloned lambda GRT39 provirus is biologically active and capable of initiating MMTV replication.
- The lambda GRT39 MMTV provirus is pathogenic, demonstrating its ability to induce mammary tumors in susceptible mice.