This preview shows page 1. Sign up to view the full content.
Unformatted text preview: e of pluripotential cells from mouse embryos, Nature, 1981, 292: 154156), demonstrated that stem cells could be cultured directly from
(C) Gail R. Martin normal mouse embryos. The isolation of these embryonic stem cell lines paved the way to genetic manipulation and analysis of mouse development, as well as to the possible use of human embryonic stem cells in transplantation therapy. The Experiments
Based on the premise that embryonal carcinoma cells were derived from normal embryonic stem cells, Martin attempted to culture cells from normal mouse blastocysts. Starting with cells from approximately 30 embryos, she initially isolated four colonies of growing cells after a week of culture. These cells could be repeatedly passaged into mass cultures, and new cell lines could be reproducibly derived when the Embryonic stem cells differentiate in culture to a variety of cell types, including neuronlike cells (A), endodermal cells (B), and cartilage (C). (Continued on next page.) This material cannot be copied, reproduced, manufactured, or disseminated in any form without express written permission from the publisher. 2009 Sinauer Associates, Inc. UNCORRECTED PAGE PROOFS
CHAPTER 17 KEY EXPERIMENT Culture of Embryonic Stem Cells (continued )
experiment was repeated with additional mouse embryos. The cell lines derived from normal embryos (embryonic stem cells) closely resembled the embryonal carcinoma cells derived from tumors. Most importantly, the embryonic stem cells could be induced to differentiate in culture into a variety of cell types, including endodermal cells, cartilage, and neuron-like cells (see figure). Moreover, if the embryonic stem cells were injected into a mouse, they formed tumors containing multiple differentiated cell types. It thus appeared that embryonic stem cell lines, which retained the ability to differentiate into a wide array of cell types, could be established in culture from normal mouse embryos. The Impact
The establishment of embryonic stem cell lines has had a major impact on studies of mouse genetics and development as well as opening new possibilities for the treatment of a variety of human diseases. Subsequent experiments demonstrated that embryonic stem cells could participate in normal mouse development following their injection into mouse embryos. Since gene transfer techniques could be used to introduce or mutate genes in cultured embryonic stem cells, these cells have been used to investigate the role of a variety of genes in mouse development. As discussed in Chapter 4, any gene of interest can be inactivated in embryonic stem cells by homologous recombination with a cloned DNA, and the role of that gene in mouse development can then be determined by introducing the altered embryonic stem cells into mouse embryos. In 1998 two groups of researchers developed the first lines of human embryonic stem cells. Because of the proliferative and differentiative capacity of these cells, they offer the hope of providing new therapies for the treatment of a variety of diseases. Although a number of technical problems and ethical concerns need to be addressed, transplantation therapies based on the use of embryonic stem cells may provide the best hope for eventual treatment of diseases such as Parkinson's, Alzheimer's, diabetes, and spinal cord injuries. Embryonic Stem Cells
Embryonic stem cells were first cultured from mouse embryos in 1981 (Figure 17.23). They can be propagated indefinitely in culture and, if reintroduced into early embryos, are able to give rise to cells in all tissues of the mouse. Thus they retain the capacity to develop into all of the different types of cells in adult tissues and organs (referred to as pluripotency). In addition, they can be induced to differentiate into a variety of different types of cells in culture. As discussed in Chapter 4, mouse embryonic stem cells have been an important experimental tool in cell biology because they can be used to introduce altered genes into mice (see Figure 4.36). Moreover, they provide an outstanding model system for studying the molecular and cellular events associated with embryonic cell differentiation, so embryonic stem cells have long been of considerable interest to cell and developmental biologists. Interest in these cells reached a new peak of intensity, however, in 1998 when two groups of researchers reported the isolation of stem cells (A) Embryo Culture of embryonic stem cells (B) FIGURE 17.23 Culture of mammalian embryonic stem cells (A) Embryonic stem cells are cultured from the inner cell mass of an early embryo (blastocyst). (B) Scanning electron micrograph of cultured embryonic stem cells. (Yorgos Nikas/Photo Researchers, Inc.) Inner cell mass This material cannot be copied, reproduced, manufactured, or disseminated in any form without express written permission from the publisher. 2009 Sinauer Associates, Inc. UNCORRECTED PAGE PROOFS
CELL DEATH AND CELL RENEWAL 25 Undifferentiated ES cells maintained in LIF Removal of LIF FIGURE 17.24 Differentiation of embryonic stem cells Mouse embryonic stem (ES) cells are maintained in the undifferen...
View Full Document