35. Reproductive Cloning and Embryonic Stem Cells

MIT OpenCourseWare

12 May 202034:28

EducationalLearning

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TLDRThe script discusses the concept of cellular differentiation, where cells acquire specialized functions as an organism develops from a fertilized egg into an adult. It describes experiments showing that this process does not involve an irreversible loss of genetic material from cells, as even the nuclei from differentiated cells can be reprogrammed to an embryonic state by factors in egg cells. The summary highlights research by Gurdon and Yamanaka proving differentiated cells can be induced into pluripotent stem cells, demonstrating the potential for regenerative medicine to create customized cells to treat diseases.

Takeaways

😀 There is a central dogma that genetic information flows from DNA to RNA to protein, and a separate dogma around cellular differentiation
😯 Cells start as totipotent stem cells and become more specialized through differentiation
🧐 Nuclear transfer experiments show differentiated cells retain ability to become other cell types
☝️ Gurdon showed nuclei from differentiated frog cells could create cloned albino frogs when put into enucleated eggs
👍 Yamanaka showed just 4 transcription factors can reprogram differentiated mouse/human cells to pluripotent stem cells
🙌 Reprogrammed induced pluripotent stem (IPS) cells can be differentiated into specialized cells like neurons or cardiac cells
🧬 IPS cells from a patient won't cause transplant rejection if transplanted back into that patient
😮 Dolly the sheep was the first cloned mammal in 1997 using somatic cell nuclear transfer
🤔 As cells differentiate, their nuclei become harder to reprogram back to a pluripotent state
💭 Goal of regenerative medicine is to replace patient's damaged cells with their own reprogrammed IPS cells

Q & A

What is the central dogma that the speaker mentions?
-The central dogma is that information flows from DNA to RNA to protein.
What does the speaker mean when he says cells acquire more specialized cell types through differentiation?
-He means that as cells develop, they take on more specific functions and lose the ability to become other cell types. This results in specialized adult cell types.
What experiment did John Gurdon do that won him the Nobel Prize?
-John Gurdon transplanted nuclei from differentiated frog cells into enucleated frog eggs. This showed that the nuclei could be reprogrammed by the egg cytoplasm to create entire organisms.
What factors did Shinya Yamanaka discover that can induce reprogramming of differentiated cells?
-Yamanaka discovered that expressing four transcription factors - Oct4, Sox2, Klf4 and c-Myc - could reprogram differentiated cells to a pluripotent state. This results in induced pluripotent stem cells.
Why is the efficiency of cloning mammals low?
-Cloning mammals by nuclear transfer is very inefficient because the nuclei from differentiated cells resist getting fully reprogrammed by the egg cytoplasm.
What is the goal of regenerative medicine using reprogrammed cells?
-The goal is to replace cells lost due to disease or injury by reprogramming a patient's cells into pluripotent stem cells, differentiating them into the needed cell type, and transplanting them back into the patient.
What is the difference between a totipotent, pluripotent and multipotent cell?
-A totipotent cell can form all cell types in an organism. A pluripotent cell can form many but not all cell types. A multipotent cell is more restricted and can only form specific related cell types.
Why won't patient-derived reprogrammed cells cause immune rejection when transplanted back into that patient?
-Because the cells contain the patient's own DNA, they will not be rejected due to genetic differences in the major histocompatibility complex.
What ethical issues are associated with human cloning or gene editing?
-Ethical issues include lack of regulation and oversight, potential risks to patients, designer babies, and playing God by altering human genomes.
What are induced pluripotent stem cells and how are they generated?
-Induced pluripotent stem cells (iPSCs) are created by expressing four transcription factors in differentiated somatic cells to reprogram them to a pluripotent state similar to embryonic stem cells.

Outlines

00:00

🧬 Introduction to Cell Differentiation and Developmental Dogmas

Adam Martin introduces key concepts related to cell differentiation during development. He discusses developmental dogmas like how cells start from a fertilized egg and undergo differentiation to become specialized adult cells. This process was previously thought to be unidirectional and irreversible.

05:02

👶 Early Mammalian Development - Formation of Blastula

Adam describes early mammalian development starting from the zygote, going through cleavage divisions to form a blastula. The blastula consists of an inner cell mass that forms the embryo proper and an outer layer of trophoblast cells that form the placenta. This represents the first differentiation event.

10:04

💡 Experiments to Test Cell Potency and Reversibility of Differentiation

Adam explains key experiments by John Gurdon and Shinya Yamanaka that overturned the dogma of irreversible differentiation. Gurdon showed nucleus transfer from differentiated to egg cells can create a whole organism. Yamanaka induced pluripotency in somatic cells by expressing four transcription factors.

15:06

👀 Example of Nuclear Transfer (Cloning)

A video example is shown of nuclear transfer from a differentiated cell to an enucleated egg cell. This reproductive cloning allows the differentiated cell nucleus to be reprogrammed and create an entire organism, demonstrating retained potency.

20:09

🐸 First Cloning Experiments in Frogs

John Gurdon's experiments are outlined where nuclei from albino frog somatic cells were transferred into wild-type frog egg cells lacking nuclei. This resulted in albino frogs, demonstrating successful reprogramming of the differentiated cell genome.

25:12

🐑 Mammalian Cloning - Dolly the Sheep

The first cloning of a mammal, Dolly the Sheep, is discussed. Though cloning mammals proved highly inefficient, it definitively demonstrated nuclei from differentiated cells can be reprogrammed for totipotency when transferred to egg cells.

30:13

🌡️ Factors that Resist Reprogramming of Differentiated Cell Nuclei

Data is shown demonstrating how nuclei from later developmental stages are less efficiently reprogrammed, likely due to changes resisting the reprogramming. However, no evidence for an actual loss of genetic material was found.

🧬 Induced Pluripotent Stem Cells and Regenerative Medicine

Shinya Yamanaka's Nobel Prize-winning work is outlined where expressing four transcription factors in differentiated cells generates induced pluripotent stem cells. Goals include differentiating these cells into tissues for transplantation into patients to replace cells lost due to disease.

Mindmap

Keywords

💡differentiation

Differentiation refers to the process by which cells acquire specialized functions during development. As the fertilized egg develops into an embryo and then into an adult organism, cells undergo changes in gene expression that direct them down specific developmental pathways towards distinct cell fates. This process of specialization is called differentiation. The video challenges the dogma that differentiation is a unidirectional, one-way process by exploring cellular reprogramming.

💡reprogramming

Reprogramming refers to the process by which differentiated adult cells can have their gene expression patterns altered to return to a more primitive, unspecialized cell state. The video discusses research by Gurdon and Yamanaka showing that introducing certain transcription factors into somatic cells can reprogram them to become pluripotent stem cells again.

💡pluripotency

Pluripotency refers to the ability of a cell to differentiate into many different cell types in the body. Pluripotent stem cells, like embryonic stem cells derived from the inner cell mass of a blastocyst, have the potential to form most adult cell types but not all cell types like a fertilized egg can.

💡totipotency

Totipotency refers to the ability of a cell to differentiate into all cell types in the body as well as extraembryonic tissues like the placenta. Only the fertilized egg and first few cells of the developing embryo are considered totipotent.

💡Oct4

Oct4 is a transcription factor that regulates pluripotency. It is highly expressed in embryonic stem cells and the inner cell mass from which they are derived. Re-expression of Oct4 and other pluripotency factors like it can reprogram differentiated somatic cells.

💡blastocyst

The blastocyst is a pre-implantation embryo around 4-5 days old in mammals. It consists of an inner cell mass that will form the future embryo proper, surrounded by an outer layer of cells called the trophoblast that will contribute to extraembryonic tissues like the placenta.

💡nuclear transfer

Nuclear transfer refers to the technique of transplanting the nucleus of a somatic cell into an enucleated egg cell, which can then be used to generate an embryo. Gurdon's experiments doing this with frog nuclei showed that differentiated cells do not irreversibly lose genetic material during development.

💡Induced pluripotent stem cells (iPSCs)

Induced pluripotent stem cells are created by expressing certain genes, like Oct4, in differentiated somatic cells to reprogram them back to a pluripotent state similar to embryonic stem cells. This allows the generation of pluripotent stem cells without the use of embryos.

💡regenerative medicine

Regenerative medicine aims to replace tissues damaged by injury or disease by transplanting stem cell-derived cells. iPSCs can be created from a patient, differentiated in vitro, and then transplanted back into the patient to regenerate lost cell types without immune rejection.

💡gene editing

Gene editing tools like CRISPR allow the DNA sequences of embryos to be precisely altered. The video discusses recent controversy surrounding the claim that the first gene-edited babies had been produced in China using CRISPR.

Highlights

The fertilized egg is totipotent, meaning it has the potential to form all cell types

The first branch point in cell differentiation occurs when the blastula forms an inner cell mass and an outer trophoblast layer

Embryonic stem cells derived from the inner cell mass are pluripotent, meaning they can form most cell types in the embryo

Differentiation relies mainly on changes in gene expression, not an irreversible loss of genetic material

John Gurdon showed nuclei from differentiated frog cells could be reprogrammed to an embryonic state by transplanting them into enucleated eggs

The first cloned mammal was Dolly the sheep, demonstrating nuclei from adult cells can be reprogrammed, but the process is very inefficient

Shinya Yamanaka discovered just four transcription factors (Oct4, Sox2, Klf4, c-Myc) can reprogram differentiated cells to a pluripotent state

Induced pluripotent stem cells (iPSCs) can differentiate into specialized cells like neurons, muscle, skin for regenerative medicine

Patient-derived iPSCs could be transplanted without risk of immune rejection since they are genetically identical

Debate whether we should allow human gene editing or cloning given a Chinese scientist's claim to have made the first gene-edited babies

The fertilized egg undergoes cleavage divisions to form a blastula consisting of an inner cell mass that will form the embryo proper

The inner cell mass expresses the Oct4 gene, marking the pluripotent state

Nuclei become more restricted in their ability to be reprogrammed as cells differentiate

iPSC technology aims to replace lost cells in patients using their own cells to avoid transplant rejection

Debate the ethics of human gene editing and cloning given recent news

Transcripts

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