Biotechnology 10/11 - Cloning & Stem Cell

Robert Bakewell

18th century breeder who pioneered selective breeding and influenced later cloning ideas

Dishley Sheep / New Leicester

Sheep line created by Bakewell to demonstrate controlled heredity

Germ plasm theory

Weismann’s concept separating hereditary germ cells from body (somatic) cells

Weismann

Biologist who proposed germ plasm theory and dismissed inheritance of acquired traits

Briggs and King

Scientists who performed first nuclear transfer experiments in frogs in 1952

Gurdon

Scientist who proved differentiated cells could be reprogrammed through nuclear transfer in 1958

Somatic cell nuclear transfer (SCNT)

Technique transferring a somatic cell nucleus into an enucleated egg

Reproductive cloning

Cloning intended to create a whole organism genetically identical to donor

Therapeutic cloning

Cloning intended to create embryos for stem cell derivation, not reproduction

Dolly the sheep

First mammal cloned from adult somatic cell using SCNT

Ian Wilmut

Lead scientist who cloned Dolly at the Roslin Institute

Roslin Institute

Research center in Scotland where Dolly the sheep was cloned

Mammal cloning successes 1990s

Series of animals cloned after Dolly including cows, mice, and goats

UN cloning declaration

2005 United Nations declaration discouraging human reproductive cloning

Totipotent

Stem cells capable of forming an entire organism

Pluripotent

Stem cells capable of forming all body cell types but not an entire organism

Multipotent

Stem cells capable of forming multiple but limited cell types

Embryonic stem cells (ESCs)

Pluripotent stem cells derived from early embryos

Adult stem cells

Multipotent stem cells found in mature tissues

Hematopoietic stem cells (HSCs)

Adult stem cells in bone marrow that form blood cells

Till and McCulloch

Scientists who discovered hematopoietic stem cells in 1963

Gail Martin

Scientist who coined the term “embryonic stem cell” in 1981

Evans and Kaufman

Scientists who derived mouse embryonic stem cells in 1981

James Thomson

Scientist who first derived human embryonic stem cells in 1998

Induced pluripotent stem cells (iPSCs)

Adult somatic cells reprogrammed to pluripotency

Shinya Yamanaka

Scientist who developed iPSCs via reprogramming factors

Dickey-Wicker Amendment

1995 law prohibiting federal funding for creation or destruction of human embryos

NIH stem cell funding guidelines

Federal policies dictating which ESC lines may receive government funding

Bush ESC policy

2001 policy restricting federal funding to preexisting embryonic stem cell lines

Obama ESC policy

2009 expansion allowing federal funding for newer ESC lines under ethical guidelines

Cell cycle

Series of phases a cell goes through to grow and divide

Mitosis

Division of a somatic cell into two genetically identical daughter cells

Meiosis

Division that produces gametes with half the chromosome number

Differentiation

Process by which unspecialized cells become specialized cell types

In vitro fertilization (IVF)

Assisted reproduction combining egg and sperm outside the body

Preimplantation embryos

Early-stage embryos used in IVF and embryonic stem cell derivation

Cloned mice

Mice created using SCNT to test reprogramming fidelity

Cloned cows

Cows cloned for agricultural or biomedical applications

Cloned goats

Goats cloned for pharmaceutical protein production (“pharm animals”)

Cloned cats

Cats cloned as part of expanding mammalian cloning experiments

Cloned mules

Hybrid equine cloned due to high economic value

Stem cell lines

Cultured stem cells that can proliferate indefinitely in vitro

Zygote

Single-cell fertilized egg capable of developing into an organism

Blastocyst

Early embryonic stage containing inner cell mass used for ESC derivation

Inner cell mass

Cluster of pluripotent cells inside the blastocyst

Embryo research debate

Ethical conflict over use of early embryos in research

Therapeutic cloning debate

Ethical controversy over creating embryos for stem cell derivation

Reproductive cloning debate

Debate over ethical, legal, and safety issues of cloning humans

Roslin technique

Specific SCNT method used to create Dolly using a quiescent somatic cell

Enucleated egg

Egg cell whose nucleus has been removed in preparation for SCNT

Nuclear transfer

Nucleus moved from donor cell into enucleated egg to initiate cloning

Reprogramming factors

Genes used to convert adult cells into pluripotent stem cells (e.g., Yamanaka factors)

Mouse iPSCs

First induced pluripotent stem cells produced in 2006 from mouse cells

Human iPSCs

Induced pluripotent stem cells first created in humans in 2007

Hematopoiesis

Process by which blood cells are formed from HSCs

ESC colony

Culture of embryonic stem cells maintained in vitro

Clonal expansion

Growth of genetically identical cells from a single ancestor cell

Embryo transfer

Placing an embryo into the uterus for pregnancy or research use

Chimera

Organism or embryo composed of genetically distinct cell populations

Genetic determinism concern

Public fear that cloning implies genes dictate identity fully

Clone identity fear

Misconception that clones would be psychological duplicates of donors

Stem cell potential

Ability of stem cells to differentiate into various cell types

Totipotency window

Early developmental stage where cells can generate entire organism

Cloning efficiency problem

Very low success rate in SCNT, with many embryos failing

Epigenetic reprogramming

Resetting chromatin and gene expression patterns during cloning

Therapeutic potential of ESCs

Use of ESCs for treating diseases through cell replacement

Therapeutic potential of iPSCs

Use of reprogrammed adult cells for personalized regenerative medicine

Parthenogenesis

Activation of egg cell without fertilization, sometimes used in research

Stem cell niche

Local environment regulating adult stem cell behavior

Embryo implantation

Stage after blastocyst formation where embryo attaches to uterine wall

ESC controversy

Public opposition focused on moral status of early embryos

NIH registry of ESC lines

Database listing federally eligible embryonic stem cell lines

SCNT in mammals

Method successfully used to clone sheep, cows, cats, goats, and other animals

Preimplantation genetic diagnosis (PGD)

Genetic testing of early embryos before implantation

Egg donation ethical issues

Concerns about risks and coercion in obtaining donor eggs

Therapeutic cloning legality

Varies by country, restricted in many nations

Moral status of embryo

Central ethical question in ESC debate

Weismann barrier

Concept that genetic information flows from germ cells to body cells, not reverse

Cloning ban proposals

National and international proposals to prohibit reproductive cloning

Human cloning fear

Fear that SCNT could lead to attempts at cloning humans

Embryo procurement

Obtaining embryos for research or medical use

Fertilization

Union of egg and sperm forming zygote

Nuclear totipotency

Concept that somatic cell nuclei retain full genetic potential

Nuclear equivalence theory

Theory that all cell nuclei contain identical genetic information

ESC derivation

Process of isolating the inner cell mass from blastocyst to make ESC lines

Human ESC controversy

Political and ethical debates surrounding derivation of human ESC lines

Stem cell therapies

Medical uses of stem cells for regeneration and repair

Cloning regulation

Government policies controlling cloning and embryo research

SCNT reprogramming problem

Errors in reprogramming somatic nuclei causing developmental failure

Cloning failure rates

Majority of cloned embryos die early or develop abnormalities

ESC pluripotency test

Assay to verify ESCs can form all three germ layers

Chimera test

Method to demonstrate pluripotency by contribution to multiple tissues

Cloned embryo anomalies

Developmental abnormalities common in cloned embryos

iPSC advantages

Bypasses embryo use and reduces immune rejection

iPSC disadvantages

Genetic/epigenetic abnormalities from reprogramming factors

HSC transplant

Therapeutic use of hematopoietic stem cells to treat blood disorders