Fetus Blastocyst

There are two general avenues for stem cell research pluripotent and multipotent stem cells. Pluripotent stem cells are obtained by two methods. One method is to harvest the clusters of cells from the blastocysts of human embryos. Another method is the isolation of pluripotent cells from fetuses in terminated pregnancies. Multipotent stem cells are derived from umbihcal cords or adult... 

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, whether derived from embryos, fetuses, or adults, can be simply defined as progeny of cells that are capable of differentiating into different lineages [152], Embryonic stem cells (ESCs) are isolated from the inner cell mass of blastocysts and have the ability to be cultured and maintained in an undifferentiated and pluripotent state, and directed to differentiate into all specific cell types [153,154], A variety of adult stem cells (often referred as progenitor or multipotent cells), including bone marrow-derived mesenchymal stem cells (MSCs), hematopoietic stem cells (HSCs), adipose-derived stem cells (ADSCs), and neutral stem cells (NSCs), have been found more committed but less pluripotent than ESCs. 

Implantation and subsequent placentation is a unique mammalian form of reproduction. A fertilized mammalian egg autonomously develops into a blastocyst, which must be successfully implanted in the uterus to develop further into a fetus. Initial adhesion of the embryo to the uterus occurs via the apical cell membrane of two polarized epithelial cells, the trophoblast of blastocysts, and surface epithehal cells of the endometrium. This adhesion is unique because it is apical-apical adhesion between two epithelial cells, whereas generally apical cell surfaces of epithelia are nonadhesive. 

This physical protection of the fetus by the fetal membranes is of interest due to the embryonic origin of both tissues. The fertilized egg provides the origin for both the fetus and placental membranes. The fetus is derived from the inner ceU mass and the placenta from the outer cell mass of the blastocyst. These origins are unique in the fact that they are fetally derived and as a result, should be rejected by the maternal host s immune system. However, the initial fetal cellular components and ultimately its entire physical construct are viriually unrecognized as a foreign substance. It is these remarkable characteristics of the maternal and fetal immune-privileged relationship that make these tissues so unique. 

In the mammalian egg, the synthesis of RNA starts shortly after fertilization. There is also a rapid increase in protein synthesis after fertilization, and the evidence reviewed suggests that this is probably the result of both the initiation of new mRNA synthesis as well as the activation of masked maternal mRNA in the cytoplasm or the assemblage of active ribosomes. The first morphological differentiation which may be observed is a distinction between the inner cell mass and the trophoblast cells which, in the normal mouse embryo, occurs at the late blastocyst stage at a time when the embryo contains between 30 and 60 cells. The outer trophoblast develops into the placenta and extraembryonic membranes, while the inner cell mass continues to differentiate to give rise to the fetus. 

Ability of Mouse Blastocysts to Form Viable Fetuses after in vitro Cultivation (2-4 Cell Stage Blastocyst) in the Presence of Inhibitors op Mitochondrial Nucleic Acid or Protein Synthesis"... 

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