ch. 16 - select topics (embronic development, cloning, stem cells)

transformation from zygote to adult involves…

• cell division

• cell differentiation

• morphogenesis

cell division

process from zygote to embryo

cell differentiation

the process by which cells become specialized in structure and function

• e.g. production of tissue

cell morphogenesis

the physical processes that give an organism it's 3-dimensional shape

apoptosis

described as programmed cell death

• occurs in mature organisms in cells that are infected, damaged or at the end of their functional lives

  • occurs in vertebrates but can also occur in fungi and yeasts

process of apoptosis

• DNA, organelles and other cytoplasmic components are fragmented

• cells become multilobed and the contents are packaged into vesicles called blebs

  • these blebs get engulfed by scavenger cells

what is apoptosis used for?

• protects neighbouring cells from damage by nearby dying cells

• essential for development and maintenance

  • such as morphogenesis of hands and feet

apoptosis in morphogenesis

• the embryonic region that develops into feet has a solid, platelike structure

  • apoptosis eliminates the cells in the interdigital region

    • the space in between appendages/digits (fingers and toes)

is apoptosis the same in every organism?

no, the level of apoptosis will vary

• e.g. in ducks the level is lower between the developing digits because webbed feet for ducks is more useful to them more than it is in feet of chickens (land bird)

cloning animals: nuclear transplantation

process where the nucleus of an unfertilized egg cell is replaced with the nucleus from another cell

• may produce organisms that are genetically identical to the “parent" that donated the nucleus

  • experiements were done by John Gurdon

what did the nuclear transplantation show?

showed that a transplanted nucleus can support normal development of the egg

• however older the donor nucleus, the lower the percentage of normally developing tadpoles

  • John Gurden concluded from this work that nuclear potential is restricted

reproductive cloning of mammals

• 1997 scottish researchers announced the birth of Dolly

  • a lamb cloned from an adult sheep via nuclear transplantation from a different cell

    • Dolly had a premature death in 2003 and arthritis led to speculation that her cells were not as healthy as those of a normal sheep

how was dolly made?

1. they took mammary cells from one sheep

2. they then took a egg cell from another sheep and removed the nucleus

3. once they have both they fuse the cells together (aka. insert the mammary cell's nucleus inside the egg cell)

4. they allow the egg cell with the nucleus from the mammary cell to grow in an early embryo

5. the early embryo will then be implanted into the uterus of a surrogate sheep

6. then the embryo will grow into a lamb and will be birthed

• the lamb that is birthed from the surrogate mother is a clone of the sheep they took mammary cells from

  • b/c cells/nucleus came from the first sheep

stem cells

a relatively unspecialized cell that can reproduce itself forever and can differentiate into specialized cells of one or more type

• can change into different specialized cells like, fat cells, WBC, bone cells, etc.

types of stem cells

• embryonic (ES0

• adult or somatic

embryonic

isolated from early embryos at the blastocyst stage (blastula)

blastula

cells that are constantly dividing

e.g. onion root tip

adult or somatic

used for repair and replacement

• e.g. skin cells or bone marrow cells

  • only able to generate a limited number of cell types

    • e.g. can only generate what it was taken from → not pluripotent ability

reason for research with embryonic/adult stem cells

they have enormous potential for medical applications

• goal is to supply cells to repair damaged or diseased organs (due to accidents or diseases

  • e.g. nerve cells for parkinson's or huntington's, insulin producing pancreatic cells for type 1 diabetes

why is taking embryonic stem cells controversial?

this is because you can only take it from babies or the actual embryo

• this can cause the embryo to die if taken from it.

  • however it is more promising than taking adult stem cells

In vitro fertilization (IVF)

process of fertilization outside of the female body

• creates 7 embryos

  • can be implanted into the female → leads to multiple babies or not if it did not implant

  • sometimes they are sent for research

  • can be frozen and preserved for pregnancy

induced pluripotent stem (iPS) cells

when researchers are able to transform fully differentiated adult stem cells to act like ES cells using retroviruses

• this work was done by John Gurdon and Shinya Yamanaka (received Nobel prize)

how does iPS cells relate to regenerative medicine?

the cells from the patient can be turned into iPS cells to potentially replace diseased (nonfunctional) cells

• e.g. Masayo Takahasi studied patients with age-related macular degeneration (disease of the retina)

  • obtained skin cells from the patient and turned them into iPS cells which turned into retinal cells, which was used to transplant them into the patient's eye

John Gurdon

scientist who studied stem cells and nuclear transplantation

• established the basis for cloning and regenerative medicine