4/11/2023 0 Comments Embryonic stem cells![]() ![]() ![]() Clonally isolated EC cells retained the capacity for differentiation and could produce derivatives of all three primary germ layers: ectoderm, mesoderm, and endoderm. After transplantation to extrauterine sites of appropriate mouse strains, these “funny little tumors” produced benign teratomas or malignant teratocarcinomas ( 107, 345). Embryonic stem (ES) cells, derived from the ICM, have the developmental capacity to differentiate in vitro into cells of all somatic cell lineages as well as into male and female germ cells.ĮS cell research dates back to the early 1970s, when embryonic carcinoma (EC) cells, the stem cells of germ line tumors called teratocarcinomas ( 344), were established as cell lines (135, 173, 180 see Fig. At present, it is not known to what extent adult stem cells may also develop (transdifferentiate) into cells of other lineages or what factors could enhance their differentiation capability (dashed lines). In adult tissues, multipotent stem and progenitor cells exist in tissues and organs to replace lost or injured cells. At the blastocyst stage, only the cells of the inner cell mass (ICM) retain the capacity to build up all three primary germ layers, the endoderm, mesoderm, and ectoderm as well as the primordial germ cells (PGC), the founder cells of male and female gametes. Zygote and early cell division stages (blastomeres) to the morula stage are defined as totipotent, because they can generate a complex organism. The embryonic origin of mouse and human ES cells is the major reason that research in this field is a topic of great scientific interest and vigorous public debate, influenced by both ethical and legal positions.įIG. Cells of the ICM are no longer totipotent but retain the ability to develop into all cell types of the embryo proper (pluripotency Fig. Subsequently, cell differentiation results in the formation of a blastocyst composed of outer trophoblast cells and undifferentiated inner cells, commonly referred to as the “inner cell mass” (ICM). This capacity, defined as totipotency, is retained by early progeny of the zygote up to the eight-cell stage of the morula. The first entity of life, the fertilized egg, has the ability to generate an entire organism. Many of these advances are based on developmental studies of mouse embryogenesis. Because of these breakthroughs, cell therapies based on an unlimited, renewable source of cells have become an attractive concept of regenerative medicine. Several seminal discoveries during the past 25 years can be regarded not only as major breakthroughs for cell and developmental biology, but also as pivotal events that have substantially influenced our view of life: 1) the establishment of embryonic stem (ES) cell lines derived from mouse ( 108, 221) and human ( 362) embryos, 2) the creation of genetic mouse models of disease through homologous recombination in ES cells ( 360), 3) the reprogramming of somatic cells after nuclear transfer into enucleated eggs ( 392), and 4) the demonstration of germ-line development of ES cells in vitro ( 136, 164, 365). This review therefore focuses both on mouse and human ES cells with respect to in vitro propagation and differentiation as well as their use in basic cell and developmental biology and toxicology and presents prospects for human ES cells in tissue regeneration and transplantation. Recent molecular and cellular advances with mouse ES cells, however, portend the successful use of these cells in therapeutics. The number of human ES cell lines available for research may also be insufficient to adequately determine their therapeutic potential. Transplanted ES cell progeny may not function normally in organs, might retain tumorigenic potential, and could be rejected immunologically. Current techniques for directed differentiation into somatic cell populations remain inefficient and yield heterogeneous cell populations. Ethical issues surround the derivation of human ES cells from in vitro fertilized blastocysts. Before therapeutic applications can be realized, important problems must be resolved. ![]() Human ES cell lines, which have recently been derived, may additionally serve as an unlimited source of cells for regenerative medicine. Mouse ES cells, which are established as permanent cell lines from early embryos, can be regarded as a versatile biological system that has led to major advances in cell and developmental biology. Embryonic stem (ES) cells, in particular, possess a nearly unlimited self-renewal capacity and developmental potential to differentiate into virtually any cell type of an organism. Stem cells represent natural units of embryonic development and tissue regeneration. ![]()
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