----- Original Message ----- From: Science-Week <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, 24 December 1999 10:04 PM Subject: Science Week BULLETIN December 20, 1999 > ScienceWeek BULLETIN - December 20, 1999 > **************************************************************** > This is SW BULLETIN, a free publication published each Monday by > the Editors of SCIENCE-WEEK, the weekly Email research digest. > Subscribe to ScienceWeek: If you want to understand new basic > research, read the online Email publication that selectively > reports and explains new research without ballyhoo or compromise. > Subscription details at URL: http://scienceweek.com/subinfo.htm > **************************************************************** > Table of Contents of the current issue of ScienceWeek will be > found near the end of this file. > **************************************************************** > The following new free reports from SW back issues have been > posted at the ScienceWeek website (links on the main page). > These reports are available on the main page only one week, and > are usually changed over the weekend. Four weeks after posting > they will be in the SW archive, where they can be retrieved via > the ScienceWeek search engine: > -------------------------------------- > Science & Society: Ammonia and the Population Explosion > Earth Science: On the Natural Occurrences of Diamond > Materials Science: On Rotating Superfluid Helium-3 > Astrobiology: Polarized Starlight and Amino Acid Homochirality > Cell Biology: Protein Sorting and Golgi Components > > -------------------------------------- > SW main page URL: http://www.scienceweek.com > **************************************************************** > > SW BULLETIN - December 20, 1999 > --------------------------------------------- > > This Week's Report: > > Science Policy: Human Embryonic Stem Cell Research > > --------------------------------------------- > > [The following report first appeared in ScienceWeek 20 Aug 99] > > ON HUMAN EMBRYONIC STEM CELL RESEARCH > In a multicellular living organism such as a human or a mouse, > what differentiates one cell type from another is apparently not > the genome, since the genome is the same in every cell, but which > parts of the genome are operational. In other words, each cell > type, skin cell, muscle cell, etc., has a particular gene profile > characteristic of that cell type. Cells of a particular cell type > are said to be "differentiated". Stem cells, present in all early > embryos and in some tissues, are undifferentiated cells that in > response to appropriate signals differentiate and give rise to a > variety of cell types. Embryonic stem cells are "totipotent", > i.e., they have the potential to differentiate into any type of > tissue cell. These cells form at a very early stage in human > development and remain in an undifferentiated state for only a > short period of time. They are first clearly recognizable > approximately 5 to 7 days after fertilization, when a human > embryo forms a structure called a "blastocyst", a hollow fluid- > filled sphere consisting of only 140 cells. There are two types > of cells in the blastocyst at this stage: a) "trophoblast cells", > which form the wall of the sphere, and which will become > supporting tissues of the fetus (e.g., the placenta); b) "inner- > cell-mass cells", a clump of cells located at one end within the > blastocyst interior, and which are the undifferentiated cells > (stem cells) that will divide and develop into the individual. > The expected future medical applications of stem cells, > particularly embryonic stem cells, are extremely promising, but > because of the involvement of embryos and certain other > considerations, basic stem cell research has provoked intense > controversy. ... ... Shirley J. Wright (University of Dayton, US) > presents a review of those aspects of human embryonic stem cell > research that have been the focus of science policy controversy, > the author making the following points: > 1) Human blastocysts -- each capable of developing into a > complete human being -- are a potential source of embryonic stem > cells, undifferentiated cells with the potential to develop into > any cell type in the body. These cells have enormous therapeutic > potential for the replacement of damaged or diseased tissues, but > current legal and ethical concerns limit the nature of the > research that can be performed with these cells because of their > source. > 2) At the 5 day stage, the human blastocyst is approximately > 200 microns in diameter. Cells of the inner cell mass can give > rise to all 3 germ layers -- the ectoderm, mesoderm, and endoderm > -- which in turn give rise to all the tissues in the body. The > ectoderm cells develop into skin, nerves and eyes; the mesoderm > cells develop into bone, blood, and muscles; the endoderm cells > develop into the lungs, liver, and the lining of the intestines. > At the 5 to 7 day stage, the inner cell mass can be removed from > the blastocyst and cultured in a dish as embryonic stem cells. > 3) Early human embryos can also provide undifferentiated > pluripotent cells (i.e., cells capable of differentiating into > certain cell types but not all cell types) in the form of > primordial germ cells, the precursors of eggs and sperm cells. > The primordial germ cells do not differentiate early, remaining > in the yolk sac until approximately the 6th to 8th week of > development, when they migrate to the developing gonads in the > embryo. These primordial germ cells may be extracted as > pluripotent embryonic germ cells beginning approximately 24 days > after fertilization. > 4) Embryonic stem cells obtained from the inner cell mass of > a blastocyst can be grown in a culture dish on a layer of > "feeder" cells derived from irradiated mouse *fibroblasts. The > layer of feeder cells arrests the differentiation of the stem > cells by releasing various inhibitory factors. Cell lines derived > in this manner are immortal -- they can divide indefinitely to > form more undifferentiated cells, thus providing a ready source > for future research. > 5) Fusing a human somatic cell (i.e., any human non-germ > cell) with an enucleated egg cell allows the creation of person- > specific embryonic stem cells, thus avoiding the complications of > tissue incompatibility. In this technique, a patient's somatic > cell is placed next to an enucleated egg cell, and the two cells > are fused by application of an electric current, the somatic cell > nucleus entering the egg cytoplasm. The egg is then activated and > develops into a blastocyst embryo, and the blastocyst can now > provide embryonic stem cells compatible with the patient. This is > the technique that was used Ian Wilmut and his group to produce > the cloned sheep Dolly. > 6) Transfer of a human somatic-cell nucleus (such as a cheek > *epithelial-cell nucleus) to an enucleated bovine egg cell > produces a "*chimera" that could be the source of embryonic stem > cells. Such an experiment was successfully performed by Robl and > Cibelli in 1996. The embryo developed to the 32-cell stage, but > was not allowed to develop further. > 7) Production of human replacement tissue (e.g., neural > cells, pancreatic cells, or heart-muscle cells) in a culture dish > is one of the important potential clinical applications of > embryonic stem-cell technology. Once cultured, the differentiated > cells would be injected into the damaged organ, where they would > replace the damaged tissue. But this has not yet been achieved, > and the clinical technology will require years of development. > 8) The author concludes: "As a society we must identify the > ethical, social, legal, medical, theological, and moral issues > that surround this research. People from all walks of life -- > scientists, lawyers, ethicists, clergy, and the general public -- > should be involved in making the decision. We are also at the > crossroads where further scientific evidence is needed to explore > the full potential of these cells, and yet many of the necessary > experiments raise further ethical issues. The question of how we > should use these powerful cells remains a challenging problem for > the next century." > ----------- > Shirley J. Wright: Human embryonic stem-cell research: Science > and ethics. > (Amer. Scientist Jul/Aug 99 87:352) > QY: Shirley J. Wright [[EMAIL PROTECTED]] > ----------- > Text Notes: > ... ... *fibroblasts: A type of connective tissue cell, secreting > structural proteins (e.g., collagen) that form certain tissue > components, including the extracellular matrix. > ... ... *epithelial-cell: In animals, epithelial cells > (epithelium) compose the cell layers that form the interface > between a tissue and the external environment, for example, the > cells of the skin, the lining of the intestinal tract, and the > lung airway passages. > ... ... *chimera: In general, a "chimera" is any cell or organism > with genetic material from two or more genotypes (e.g., two or > more species). > ------------------- > Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 20Aug99 > ------------------- > Related Background: > PATENT ON UMBILICAL-CORD STEM CELLS REJECTED IN EUROPE > Stem cells are undifferentiated cells that give rise to all the > varieties of cells. Bone marrow stem cells are undifferentiated > cells in bone marrow that give rise to all the varieties of blood > cells, including the various leukocytes (white blood cells) of > the immune system: B-cells, T-cells, and macrophages. Umbilical > cord stem cells can produce red and white blood cells and > platelets, and their transplantation is more effective and > cheaper than conventional methods involving stem cells from bone > marrow donors. Umbilical cord stem cells, for example, have lower > immunogenicity, which reduces the risk of rejection by the > patient. A group of international researchers and international > biotechnology companies have won a legal challenge against a > European patent on the use of stored umbilical cord stem cells. > The patent was granted 3 years ago to the US company Biocyte, but > it has now been rejected in Europe, with the primary reason for > the rejection apparently the existence of previous use of such > cells by others. Researchers in the field say the winning of this > legal battle lifts the threat of expensive patent infringement > litigation, a threat that has intimidated the exploration of new > uses for umbilical cord blood cells. > (Nature 99/399:626) (SW Bulletin 25 Jun 99) > ------------------- > Related Background: > CONVERSION OF NEURAL STEM CELLS INTO BLOOD CELLS > ... Stem cells are common in embryos, but they have also been > identified in adult tissues that undergo extensive cell > replacement due to physiological turnover or injury, e.g., the > *hematopoietic, intestinal, and *epidermal systems. Stem cells > have also been found in the central nervous system, a tissue > believed to be capable of only extremely limited self-repair. > Central nervous system stem cells can generate the 3 major cell > types found in the adult brain: *astrocytes, *oligodendrocytes, > and neurons. This is consistent with the view that the > developmental potential of stem cells is restricted to the > differentiated elements of the tissue in which they reside. But > some developmental peculiarities suggest certain cells may be > able to differentiate into cell types that are not of the same > origin. ... ... C.R.R. Bjornson et al (5 authors at 4 > installations, CA IT) now report an investigation to determine > whether stem cells are restricted to produce specific cell types, > namely, those from the tissue in which they reside. The authors > report that after transplantation into *irradiated host mice, > genetically labelled mouse neural stem cells were found to > produce a variety of blood cell types, including *myeloid and > *lymphoid cells, as well as early hematopoietic cells. The > authors suggest that neural stem cells appear to have a wider > differentiation potential than previously thought, and that if > they behave similarly to their mouse counterparts, human neuronal > stem cells may provide a renewable and characterized source of > cells that could be used in approaches aimed at hematopoietic > reconstitution in various blood diseases and disorders. > ----------- > C.R.R. Bjornson et al: Turning brain into blood: A hematopoietic > fate adopted by adult neural stem cells in vivo. > (Science 22 Jan 99 283:534) > QY: Christopher R.R. Bjornson [[EMAIL PROTECTED]] > ----------- > Text Notes: > ... ... *hematopoietic: From hematopoiesis (hemopoiesis, > hematogenesis) Refers to the formation and development of the > various types of blood cells. > ... ... *epidermal: The term "epidermal" refers to the > superficial epithelial portion of the skin. In animals, > epithelial cells compose the cell layers that form > the interface between a tissue and the external environment, for > example, the cells of the skin, the lining of the intestinal > tract, and the lung airway passages. > ... ... *astrocytes: (astroglia, macroglia) Glial cells are more > numerous than neurons in the brain, but their function has been > generally characterized as "metabolic" or "supportive", without > much discussion of details. Astrocytes are the largest glial > cells, with many extensions radiating outward like a starburst, > and at least one of their functions is apparently to maintain the > so-called "blood-brain barrier" effectively separating neural > tissue from blood. > ... ... *oligodendrocytes: (oligodendroglia) Glial cells > characterized by sheet-like processes that are wrapped around > individual neuron axons to form the myelin sheath of nerve fibers > in the central nervous system. (The myelin sheath of a nerve > fiber is effectively a periodically interrupted insulation which > increases the propagation velocity of nerve impulses.) > ... ... *irradiated host mice: In this investigation, host > animals were radiated before transplantation in order to reduce > the population of immune system blood cells, this reduction > apparently intensifying the signals resulting in donor stem cell > differentiation. > ... ... *myeloid: Refers to bone marrow cells or cells derived > from bone marrow cells. > ... ... *lymphoid cells: Refers to cells of the lymphatic system. > The lymphatic system is a complex network for the distribution of > lymph fluid (which is similar to blood plasma -- blood without > red cells). > ------------------- > Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 2Apr99 > ------------------- > Related Background: > RESEARCH USE OF STEM CELLS APPROVED BY NIH > It is probable that one of the major public debates in the coming > months will concern the use of human stem cells in research (see > related background report below). On 19 January 1999, the US > Department of Health and Human Services announced that a > Congressional ban on human embryo research does not apply to > human stem cells, and federally financed researchers will soon > be able to work on these cells. In its ruling, the Office of > the General Counsel of the US health department said that because > stem cells by themselves do not have the capacity to develop into > a human being, they cannot be considered embryos. Deriving the > cells from human embryos is legal, provided it is not done with > federal money. Harold E. Varmus, director of the US National > Institutes of Health, has stated it would still be illegal for > researchers to use federal money to derive their own stem cells > from human embryos, but they can now use federal money to work on > the cells obtained by others, in particular the stem cells > obtained by James Thompson (University of Wisconsin, US) from > human embryos created in surplus amounts in a fertility clinic. > The new US government ruling on the use of human stem cells is > opposed by the US National Conference of Catholic Bishops, and > the ruling is still subject to modification or elimination by the > new US Congress. > (New York Times 20 Jan 1999) > ------------------- > Summary by SCIENCE-WEEK [http://scienceweek.com] 29Jan99 > ------------------- > Related Background: > EMBRYONIC STEM CELLS DERIVED FROM HUMAN BLASTOCYSTS > *Embryonic stem cells are derived from *totipotent cells of the > early mammalian embryo and are capable of *unlimited and > undifferentiated proliferation in vitro. In *chimeras with intact > embryos, mouse embryonic stem cells contribute to a wide range of > adult tissues, including *germ cells, providing a powerful > approach for introducing specific genetic changes into the mouse > *germ line. ... ... J.A. Thompson et al now report the production > of human *blastocyst-derived *pluripotent cell lines that have > normal chromosome characteristics, express high levels of > *telomerase activity, and express *cell surface markers that > uniquely characterize primate embryonic stem cells. The authors > report that after undifferentiated proliferation in vitro for 4 > to 5 months, these cells still maintained the developmental > potential to form *trophoblast, and to form derivatives of *all 3 > embryonic germ layers, including gut *epithelium (mesoderm) and > neural epithelium, embryonic *ganglia, and *stratified squamous > epithelium (ectoderm). The authors suggest these cell lines > should be useful in human developmental biology, drug discovery, > and transplantation medicine. ... ... In a related commentary in > the same journal, J. Gearhart makes the following points: 1) A > renewable tissue-culture source of human cells capable of > differentiating into a wide variety of cell types would have > broad applications in basic research and transplantation > therapies. A major step in realizing this goal has now been taken > with the demonstration that human embryonic stem cells can be > grown in culture. 2) In the work of J.A. Thompson et al, four > cell lines tested produced *teratomas when grown in > *immunosuppressed mice. Histology of the tumors revealed > differentiated cells derived from all 3 embryonic germ layers > (ectoderm, mesoderm, and definitive endoderm) -- a result > consistent with pluripotency. 3) The derivation of human > embryonic stem cells now raises a whole new set of expectations. > On the basis of the already completed use and study of mouse > embryonic stem cells, the research and clinical potential for > human embryonic stem cells is enormous. They will be important > for in vitro studies of normal human embryogenesis, abnormal > development (through the generation of cell lines with targeted > gene alterations and engineered chromosomes), human gene > discovery, drug and *teratogen testing, and as a renewable source > of cells for tissue transplantation, cell replacement, and gene > therapies. These latter applications could eventually make > unnecessary the direct use of fetal tissue in transplantation > therapies [*Note #1]. > ----------- > J.A. Thompson et al (7 authors at 2 installations, US IL) > Embryonic stem cell lines derived from human blastocysts. > (Science 6 Nov 98 282:1145) > QY: James A. Thompson, University of Wisconsin 608-262-3961. > ----------- > J. Gearhart (Johns Hopkins University, US) > New potential for human embryonic stem cells. > (Science 6 Nov 98 282:1061) > QY: John Gearhart [[EMAIL PROTECTED]] > ----------- > Text Notes: > ... ... *Embryonic stem cells: In general, the term "stem cells" > refers to undifferentiated cells that upon differentiation can > give rise to various specialized cell lines such as blood cells, > skin cells, nerve cells, etc. Adult bone marrow, for example, > contains stem cells that are the precursors of the various > specialized types of blood cells. "Embryonic" stem cells are > specifically stem cells derived from the embryo only. > ... ... *totipotent cells: Cells that have the ability to > differentiate into any type of cell and thus form a new organism > or regenerate any part of an organism. > ... ... *unlimited and undifferentiated proliferation in vitro: > In general, differentiated "normal" cells in tissue culture > produce a limited number of replications. In contrast, embryonic > stem cells and many types of cancer cells in tissue culture show > unlimited replications, and are thus called "immortal" cell > lines. In this context, "undifferentiated" proliferation is > simply proliferation without cell differentiation > (specialization). > ... ... *chimeras: In this context, an animal that has received a > transplant of genetically and immunologically different tissue. > In this report, the transplant involves the injection of human > cultured stem cells into mice. > ... ... *germ cells: In general, reproductive cells. All other > cells are "somatic" cells. > ... ... *germ line: In general, this refers to the line of > differentiated germ cells. > ... ... *blastocyst: A mammalian egg in the later stages of > *cleavage but before implantation in the uterus. The blastocyst > consists of a hollow fluid-filled ball of cells and an inner cell > mass (embryonic stem cells) from which the embryo develops. > ... ... *cleavage: The early and rapid division stage that > divides the fertilized egg into smaller and smaller cells > (blastomeres) while retaining the same overall size of the > embryo. > ... ... *pluripotent cell: A cell that has the potential, > depending on conditions, to give rise to many differentiated cell > lines but which lacks complete totipotency. > ... ... *telomerase: Telomeres are defined ends of chromosomes > that contain specific repeated DNA sequences. They are essential > for normal chromosome replication, and since their length > shortens a bit with each replication, they are believed to be > involved in the aging of the cell. Telomerase is an enzyme that > repairs damage to telomeres, and it is thought by some that > cancerous cells may have mutant telomerase, the mutant enzyme > conferring immortality on the cancer cell. > ... ... *cell surface markers: Cell surface proteins or protein > components that can be chemically identified. > ... ... *trophoblast: In the early vertebrate embryo, the outer > ectodermal cell layer of the blastocyst. In mammals, it is the > trophoblast that attaches to the uterus and forms the placenta. > ... ... *all 3 embryonic germ layers: In the embryos of higher > animals, there occurs the transformation of a single-layer > blastula into a 3-layered gastrula consisting of ectoderm, > mesoderm, and endoderm surrounding a cavity with one opening. The > 3 layers are called the "germ layer", and these layers, via > further cell differentiation and proliferation, determine the > development of all the major body systems and organs. > ... ... *epithelium: In animals, epithelial cells (epithelium) > compose the cell layers that form the interface between a tissue > and the external environment, for example, the cells of the skin, > the lining of the intestinal tract, and the lung airway passages. > ... ... *ganglia: (singular: ganglion) In the context of cells, > the original meaning of "ganglion" was any cluster of nerve cell > bodies in the central or peripheral nervous system. Currently, > the term "ganglion" refers to a aggregation of nerve cell bodies > located in the peripheral nervous system. Unfortunately, many > neuroanatomy texts still label certain neuron clusters in the > central nervous system in the old way (e.g., basal ganglia). > ... ... *stratified squamous epithelium: The cells of the > epithelium are for the most part closely packed cells with little > extracellular material between adjacent cells, the cells arranged > in continuous sheets in either single or multiple layers. The > cells may be flat, cubelike, columnar, or a combination of > shapes, and "squamous" cells are flattened and scalelike. In this > context, "stratified squamous epithelium" refers to a structure > consisting of distinctly layered epithelial cells (layers varying > in size and shape of cells), the top layer of which are squamous > cells. > ... ... *teratomas: A teratoma is a neoplasm (tumor) composed of > multiple tissues, including tissues not normally found in the > organ in which it arises. A teratoma in the adult human ovary, > for example, can contain hair, teeth, skin, heart muscle, nerve > cells, and so on -- all a result of "wild" cellular > differentiation of neoplastic cells, but with enough regulation > so that distinct tissues are formed. In the context of this > report, the teratomas occurred in mice after injection of > cultured human stem cells, thus demonstrating the ability of > those stem cells to differentiate into organized specific tissue- > producing cells. > ... ... *immunosuppressed mice: In general, this refers to mice > whose immune system response has been suppressed by chemical, > biological, or physical means. In this report, the purpose of the > immunosuppression was to allow the development of a mouse > teratoma provoked by injection of human stem cells. Without > immunosuppression, the human stem cells would be immediately > attacked and possibly destroyed by the mouse immune system before > the stems cells could differentiate. > ... ... *teratogen: Any drug or other agent that causes abnormal > fetal development. > ... ... *Note #1: We repeat here a quotation that appeared at the > head of a recent issue of SW: "Between the fifth and tenth days > the lump of stem cells differentiates into the overall building > plan of the mouse embryo and its organs. It is a bit like a lump > of iron turning into the space shuttle. In fact it is the > profoundest wonder we can still imagine and accept, and at the > same time so usual that we have to force ourselves to wonder > about the wondrousness of this wonder." -- Miroslav Holub > ------------------- > Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 27Nov98 > > [SW Bulletin 20 Dec 99] > > **************************************************************** > If you have questions or comments about SW BULLETIN, > send Email to: [EMAIL PROTECTED] > Claire Haller, Managing Editor > **************************************************************** > > What you are now reading is SW BULLETIN, a free publication > sponsored by ScienceWeek. SW BULLETIN is published on Mondays, > delivered by Email, and also posted each week on the SW website. > Each week the Bulletin provides an in-depth report on a single > topic of general scientific interest, the text usually amplified > by notes and background material from ScienceWeek. Anyone can > receive SW BULLETIN free via Email. To subscribe to SW Bulletin, > transmit SUB BULLETIN as the subject of an Email message to: > [EMAIL PROTECTED] To unsubscribe, transmit REMOVE BULLETIN > to the same address. > > SCIENCE-WEEK, the main publication, is now in its 3rd year. > ScienceWeek is an Email digest of new research in the sciences. > Each weekly issue contains in-depth summaries, explicating texts, > glossaries, and related background reports. A free sample > issue and subscription details are available at the SW website: > http://www.scienceweek.com > > Contents of the current issue of ScienceWeek (24 December 99): > -------------------------------------------------------------- > 1. Science Policy: On the Regulation of Human Genetic Tests > 2. Applied Mathematics: Conformal Mapping > 3. Astrophysics: On the Complexity of the Death of Stars > 4. Neurobiology: Modification of Dendritic Spines by Calcium > 5. Paleoanthropology: Dating of Late Pleistocene Hominid Remains > 6. Evolutionary Biology: Two Species of Living Coelacanths > In Focus: On the Foundations of Quantum Mechanics > > You will always find the table of contents of the current issue > at the SW website: http://www.scienceweek.com > The website also includes a search engine to search the SW > archive of back issues, with free access to over 1000 reports. > > ================================================================ > Copyright > Copyright (c) 1999 ScienceWeek > All Rights Reserved > > We encourage you to share SW BULLETIN with colleagues who may > have an interest in its contents. SW BULLETIN may be > redistributed for non-commercial purposes, in printed or > electronic form, as long as the contents of the publication are > not changed in any way, the document is not offered for sale, and > the document is complete (including front and end matter. > ================================================================ > > SCIENCEWEEK, a weekly Email research digest devoted to improving > communication between the sciences, and between scientists, > science educators, and science policy-makers. www.scienceweek.com > -----end file >
