Stem Cells

Features of Stem Cells

1. Unspecialised

2. Able to self-renew (cell div)

3. Able to differentiate

4. Behaviour is regulated by stem cell niche

Totipotency

Have the capacity to differentiate into all cell types including extraembryonic tissues (placenta), can form an organism

EG fertilised egg (zygote)

Pluripotency

Have the potential to differentiate into almost any cell type, but lacks self-organising ability to form an organism

EG embryonic stem cells (from inner cell mass of blastocyst)

Multipotency

Capable of differentiating into several related cell types for the tissue they reside in

EG Lymphoid, myeloid stem cells

Function of stem cells

1. Self-renew to ensure a constant pool of stem cells

2. Support growth and development

3. Repair by replenishing cells that are damaged

Embryonic Stem Cells

• found from inner cell mass of blastocyst

• can differentiate into any cell except trophoblast

Structure of germ layers (EEM)

Ectoderm: generates outer layer of embryo, produces skin, brain and nervous system

Endoderm: becomes innermost layer of embryo, produces epithelium of digestive tube and organs

Mesoderm: sandwiched between above 2, generates the rest of the important organs (heart, lungs, kidney etc)

Blood Stem Cells

Lymphoid progenitor cells —> B cells, T cells

Myeloid progenitor cells —> basophils, eosinophils, platelets, neutrophils, erythrocytes, monocytes

Bioethics

Respect for autonomy

Nonmaleficence

Beneficence

Justice

Respect for autonomy

allows individuals to make informed decisions for themselves without interference

Nonmaleficence

Avoid causing harm intentionally, minimise harm

Beneficence

Work to the best interests of individuals

Justice

ensure fairness and equity of resources

FOR embryonic stem cells

• embryos are not equivalent to human life as it only starts at heartbeat

• embryonic stem cells can treat a wide range of diseases due to its range of differentiation

• there are surplus embryos created from IVF that would otherwise be destroyed

AGAINST embryonic stem cells

• embryo is human as it has potential

• disrespect to life to treat it as a tool

• unforeseen consequences (eg tumours)

• expensive

embryonic VS adult stem cells

Induced Pluripotent Stem Cells (iPSCs)

• normal adult cells that are reprogrammed to embryonic stem cell-like state

• erasing and remodelling epigenetic marks like DNA methylation to reverse potency level

Advantages of iPSCs

• can be obtained from adult tissue, hence no embryos destroyed

• can be obtained easily from donor

• derived from patient, less chance of immune rejection

Problems w iPSCs

• low efficiency: conversion rate is very slow

• genetic modification may result in cancer