Inner cell mass

The blastocyst is an early embryonic stage in mammalian development. Murine blastocysts can be harvested at day 3.5 p.c. Their inner cell mass contains embryonic stem cells. Multiple murine embryonic stem cell lines have been established. Embryonic stem cells carrying genetically engineered mutations are injected into blastocysts, which are subsequently implanted into pseudopregnant foster mothers. 

Gardner RL, Squire S, Zaina S, Hills S, Graham CF 1999 Insulin-like growth factor-2 regulation of conceptus composition effects of the trophectoderm and inner cell mass genotypes in the mouse. Biol Reprod 60 190-195... 

Embryonic stem cells are derived from pre-implant-stage human embryos, usually at the blastocyst stage (the blastocyst is a thin-walled hollow structure containing a cluster of cells, known as the inner cell mass, from which the embryo arises). These embryos are invariably ones initially generated as part of in vitro fertilization procedures but which are destined to be discarded, either due to poor quality or because they are in excess to requirement. There are an estimated 400 000 in vitro fertilization-produced embryos in frozen storage in the USA alone, of which some 2.8 per cent are likely to be discarded. 

Culture of human embryonic stem cells starts with the recovery of the blastocyst s inner cell mass (Figure 14.17). One common recovery procedure is termed immunosurgery . The process... 

Blastocyst The mammalian embryo in the post-morula stage in which a fluid-filled cavity, enclosed primarily by trophoblast, contains an inner cell mass which becomes the embryonic disc. [NIH]... 

Figure 1.6 Early development of an embryo is illustrated here. The human blastocyst develops by about 4 1/2 days. Embryonic stem cells are formed from inner cell mass.

Inner cell mass cell = Embryonic stem cells... 

Figure 8.3 Specialized cells and tissues in our body develop in stages. The embryo inner cell mass develops into three layers the outer layer, or ectoderm, that will become skin, eyes, and nerves the inner cell layer, the endoderm, that develops into the lungs, liver, and the lining of our digestive system and the middle layer, the mesoderm, that develops into bones, muscle, and blood.

Stem cells are undifferentiated cells that have the ability to self-renew and differentiate into other cell types. Stem cells represent a promising model for cell-based therapy [8]. ESCs are self-renewing pluripotent cells derived from the inner cell mass (ICM) of the blastocyst. 

Early mammalian development has been hard to study because of two facts the ovum is very small, and a first priority is development of the placenta and of the layers of tissues that surround the embryo.308 311 312 This occurs in humans within the first week after fertilization. Both the trophectoderm and cells of the inner cell mass (Fig. 32-7) contribute to the extra embryonic tissues. 

The inner cell mass gives rise to the epiblast (develops into ectoderm) and the hypoblast (develops into endoderm). Cells of the epiblast migrate toward the midline of the early embryo (Figures 13.4 and 13.5). The primitive streak is active proliferation of the cells with a loss of the basement membrane separating the epiblast and endoderm. The epiblast cells migrate and intermingle with the endoderm cells. The anterior end of... 

Inner Cell Mass (I CM) will give rise to the embryo. 

Figure 13.3 Blastula containing the inner cell mass that gives rise to the embryo proper.

The cells of the inner cell mass can take part in the generation of all the tissues with the exception of the extra-embryonic structures such as trophoblast and placenta. They are the main target of the worldwide research on ESCs. To obtain these cells requires disintegration of the blastocyst. This fact has generated ethical and religious questions concerning human embryos. 

First successful bone marrow transplantation between two siblings 1978 Hematopoietic stem cells discovered in human cord blood 1981 Murine embryonic stem cells derived from mouse inner cell mass 1983 Fetal cells reported to repair spinal cord injury 1988 Isolation of murine hematopoietic stem cells 1988 Fetal pancreatic cells used in diabetic patients... 

Human embryonic stem cells (hESCs) were first derived from the inner cell mass (ICM) from the blastocyst stage (-100-200 cells) of embryos generated by in vitro fertilization [35,36]. In humans the blastocyst is an early-stage embryo, approximately 4 to 5 days old. The blastocyst can be formed by means of either in vitro fertilization or somatic cell nuclear transfer, in which the nucleus of a somatic cell is combined with an enucleated oocyte. Methods have been developed to derive hESCs from the late morula stage (30-40 cells) and from arrested embryos (16-24 cells incapable of further development), and more recently from single blastomeres isolated from 8-cell embryos (37). 

The blastocyst is a hollow, fluid-filled ball of approximately 1000 cells. The cells that form the outer layer are referred to as trophoblasts and will ultimately develop as extraembryonic tissues (e.g., placenta), while the cells of the inner cell mass are omnipotent (i.e., stem cells) and form the embryo. Depending on the species, the blastocyst arrives at the uterus within 5-10 days of fertilization, whereupon it hatches from the zona pellucida and implants into the uterine wall, which has been preconditioned by ovarian-derived steroid hormones (see Chapter 33). Shortly after implantation, the inner cell mass undergoes gastrulation to form a trilaminar embryo composed of three primary germ layers, the ectoderm, mesoderm, and endoderm. 

Stem cells normally are classified, based on their origin and differentiation capacity, as either embryonic or adult stem cells (1). Embryonic stem cells (ESCs) are derived from the inner cell mass of the blastocyst. ESCs can self-renew indefinitely and are pluripotent—(the ability to differentiate into all cell types in the embryo proper). Adult stem cells are undifferentiated (unspecialized) cells that are found in differentiated, or specialized, tissue. They have limited self-renewal capability and generally can only differentiate into the specialized cell types of the tissue in which they reside. These cells function as the reservoir for cell/tissue renewal during normal homeostasis or tissue regeneration. Sources of adult stem cells have been found in most tissues, including bone marrow, blood stream, cornea... 

Human embryonic stem cells were first collected in 1998 by two different research teams. The cells obtained from the inner cell mass of the blastocyst (4- to 5-day embryo) are embryonic stem cells (ESC) in contrast, cells cultured from the primordial germ cells of 5- to 9-week fetuses are embryonic germ cells (EGC). In the laboratory, ES or EG cells can proliferate indefinitely in an undifferentiated state but can also be manipulated to become specialized or partially specialized cell types, a process known as directed differentiation. Both ES and EG cells are pluripotent, meaning they have the potential to develop into more than 200 different known cell types. This class of human stem cells holds the promise of being able to repair or replace cells or tissues that are damaged or destroyed by many of our most devastating diseases and disabilities. 

Stem cells are progenitor cells which are not yet specifically formed. They can multiply almost infinitely and form nearly all 210 tissue types in the human being. Depending on their derivation, they are defined as follows .) embryonal (= taken from the inner cell mass of the blastocysts), (2.) foetal (= isolated from 5-9 week-old abortive foetuses, and (5.) adult (= taken from the tissue of adults or children by means of biopsy or from the umbilical cord of newborns. Adult stem cells are limited in number and life span they do, however, have a broader development potential than so far assumed. They have also been found in the liver. The transformation of stem cells from the bone marrow into hepatocytes has been carried out successfully. Liver stem cells (7-15 gm) can develop both primary cell types of the liver, (7.) mature hepatocytes and (2.) biliary epithelial cells. These stem cells are deemed to be genuine liver stem cells, and not merely derived from the activation of immature oval cells in the liver. (54,59, 60, 81) (s. fig. 2.20)... 

Embryonic Stem Cells (ESC) Inner cell mass of the blastocyst (4- to 5-day embryo) Infinite Pluripotent (Can differentiate into every cell of the organism except for the trophoblast)... 

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