Cell differentiation and gene expression

Question 1

Define cell differentiation

Answer 1

The process through which a cell undergoes changed in gene expression and gene activity to specialise and take on specific roles within an organism

Question 2

Give an overview of cell differentiation

Answer 2

1. Different cell types are produced
2. Originally multicellular organisms consist of masses of undifferentiated cells.
3. not reversible

Question 3

What is cell determination?

Answer 3

Cell determination is the stability of cell differentiation even after cessation of induced signaling.

Transmitted to daughter cells after division

e.g white blood cells are in the same environment but they remember which cell type they are

Question 4

What is cell lineage?

Answer 4

The series of successive cell types leading from the zygote to a particular mature cell type.

Differentiation occurs in steps. At each step, an immature (precursor or progenitor - any immature cell types able to differentiate into another cell type(s)) cell type changes into a more mature one (which may still be a precursor). The series of cell types leading from the zygote to a particular cell type is called a cell lineage

• Cell lineages can branch, where precursor cells are able to produce more than one daughter cell type. Such precursor cells are called pluripotent.
• The branches here do not represent cell division, just the particular cell types that each precursor type is able to differentiate into, given the right signals.
• “Cell differentiation” also refers to each step-in lineage – that is, a precursor cell type is said to differentiate to the next cell type.

Question 5

How can cell types become different?

Answer 5

Different cell types express different sets of genes.

Question 6

What does gene expression mean?

Answer 6

Synthesis of the product of a given gene – a protein or a functional RNAs like a tRNA. Involves transcription and (for proteins) translation. Different cell types make very different sets of gene products, which is what makes the cells different.

Question 7

Is a change in gene expression always differentiation?

Answer 7

No, there is also modulation.

Proportion of dividing cells falls as we approach to maturity.

Question 8

What is modulation and compare differentiation and modulation?

Answer 8

• A simple, reversible change in gene expression, with no change in cell type.
• E.g. upregulation of alcohol dehydrogenase in liver cells: a transcriptional change that is reversible, and dependent on a continuing external stimulus: in this case increased blood alcohol.
• Or gene expression changes during the cell cycle – reversibly.
• Also called adaptation.

Question 9

Define stem cell

Answer 9

undifferentiated and unspecialized cells of the human body. Found in embryos (embryonic stem cells) and in adults (adult stem cells).

Question 10

What can stems cell do?

Answer 10

• Able to differentiate into any cell of an organism and have the ability to renew themselves by cell division

Question 11

Define embryonic stem cell

Answer 11

Embryonic stem cell, a cell type found in very early embryos, able to differentiate into all cell types of the body.

o Totipotent or pluripotent*
o Derived from a four- or five- day-old human embryo in the blastocyst phase of development.
o - *Pluripotent cells of the embryo have been shown to be transiently existing cells, not stem cells.

Question 12

Define Pluripotent, Postnatal stem cells, and totipotent

Answer 12

• Pluripotent - Able to produce several functional cell types (e.g., bone marrow stem cells). Also used for embryonic stem cells that can produce cell types of all three germ layers.
• Postnatal (or adult) stem cell - An immature cell that can both divide to produce further cells like itself and differentiate to replace functional cells that are worn out or lost.
• Totipotent- Able to produce all cell types of both the body and the extra-embryonic parts (placenta, membranes).

Question 13

What are Multipotent cells, what is the purpose of them and where are they found?

Answer 13

Multipotent cells can differentiate into a limited number of cell types, they replace dead cells, and are found in areas with a high turnover rate of cells e.g rbs, epithelium and intestine

Question 14

What is a unipotent cell?

Answer 14

A unipotent cell can only differentiate into one specific cell type e.g spermatological cells and dermatocytes

Question 15

What is asymmetric and symmetric stem cells

Answer 15

On image

Question 16

Where are tissue-specific stem cells found? Give an example e.g bone marrow

Answer 16

Tissue-specific stem cells are maintained in special supportive microenvironments called stem cell niches.
Supporting ECM, neighbouring niche cells, secreted soluble signalling factors (such as growth factors and cytokines), physical parameters (such as shear stress, tissue stiffness, and topography), and environmental signals (metabolites, hypoxia, inflammation, etc.).

• Blood cells are initially made in certain embryonic structures. From foetal week 20 onward they originate from the bone marrow.
• Hematopoietic stem cells (HSCs): multipotent stem cells anchored to fibroblast-like osteoblasts of the marrow of long bones. Produce all blood cells and some immune system cells. Regular self-renewal. Produce RBCs and immune system
• Mesenchymal stem cells (MSCs): stromal cells found in bone marrow and other organs. Poorly defined and heterogeneous. They do not self-renew very regularly. Give rise to cartilage, bone and fibrous connective tissue.

Question 17

Describe transcription factors in terms of gene expression regulation and differential transcription

Answer 17

• Cell differentiate through differential gene expression.
• The types and number of proteins a cell generates help to determine how a cell differentiates.
• RNA sequencing and microarrays assays allow to analyse the transcription profile of each cell.
• Some genes need to be switched off and others, switched on = transcription factors

Detected by probes, microassays and RNA sequencing to look at differences in mRNA between 2 cells