The role of transgenic animals in the analysis of various biological aspects of normal and pathologic states

The introduction of foreign genes into the germ line of mammals has been a practical reality now for a number of years. This form of experimentation allows the creation of lines of animals tailor-made to answer specific molecular genetic questions. Manipulation of the mammalian embryos has been enormously important in developmental biology in recent years and that experience has brought about the possibility of new experiments allowing the molecular analysis of many biological processes. The methodologies involved in constructing transgenic animals have been published extensively in a number of comprehensive reviews. In typical experiments, pronuclear stage (one cell) embryos (Figs. 1 and 2) are collected after fertilization, but prior to the onset of cleavage. Exogenous cloned linearized DNA is injected into one of the two pronuclei by means of a finely drawn injection pipet. The manipulated embryo is transferred into the oviduct or ovarian bursal space of a surrogate mother previously mated with a sterile male. Alternative methods include retroviral transfection of cleavage stage embryos or insertion of genetically engineered embryo-derived embryonal stem cells into blastocysts. Offspring from these procedures are screened by standard molecular analyses to determine presence of the foreign genetic material. The present report explores the application of this methodology to a specific set of problems: (i) regulation of gene expression in vivo, (ii) the establishment of disease models for the study of pathogenesis. (iii) the use of exogenous genetic elements to correct specific genetic defects, (iv) the role of insertional mutangenesis in disruption of normal development, (v) analysis of genetic ablation, (iv) the use of transgenic animals to modulate carcinogens.