Lecture 19 - Regulation of Gene Expression Eukaryotes

What two hormones influence transcription?

1. Steroids

2. Peptides

Steroids

small and lipid soluble

ex. testosterone and estrogen

Peptides

larger in size

ex. insulin and oxytocin

Pathogens

Foreign antigens activate immune genes

What are the steps to transcription induction by peptide hormones?

1. Hormone binds to a cell membrane receptor

2. A signal cascade is activated in the cytoplasm

3. A transcription factor is activated and moves into the nucleus. It binds to response elements in the promoter region

What are the steps to transcription induced by steroid hormones?

1. Steroids can move directly through cell membrans (because they are small)

2. Steroid/receptor complex binds to hormone response elements in the promoter region

Describe how hormones influence honeybees gene expression

1. Juvenile hormone (jh) levels transitions to foraging honeybee

2. Young bees injected with JH start to forage. Removal of its JH producing glands delays transition

Describe how social regulation affects honeybees and gene regulation

1. ONLY young cohort colonies (nurses) can produce foragers

2. Lack of encounters with older forages speeds up nurse bee transition to forager role

3. Lack of foragers speeds up transition in order to compensate for absent roles

Describe how pheromone regulation affects honeybees and gene regulation

1. Transition to foraging is INHIBITED by ethyl oleic acid (external hormone)

2. Foragers transfer the chemical to nurse bees when food is transferred

   1. Nurse’s transition to foragers is slowed because it inhibits JH production

What are two mechanisms that influence eukaryote gene expression pre-transcriptional (DNA level)

1. Gene dosage

2. Nucleolus in nucleus

Gene dosage

Some housekeeping genes need to make LOTS of product (constitutively expressed). Lots of identical genes to make lots of product

Nucleolus in nucleus

visible region in nucleus where lots of rRNA genes are being expressed

What are 4 mechanisms of gene regulation on a transcriptional level?

1. Methylation in promoter

2. Basal transcription factors

3. Special transcription factors

4. ER interact with promoter

Methylation in promoter (epigenetic modification)

The addition of -CH 3 at Cs in consecutive CGs STOPS transcription on a transcriptional level

• Contributes to turning off genes during x inactivation

• Contributes to turning on genes for queen honeybee development (royal jelly)

Basal transcription factors

Can bind to response elements in the promoter region and usually activates transcription

Special transcription factors

Binds to enhancer region (ER) which becomes several hundred base pairs long

• Many hormone inducible genes

Enhancer region (ER) interaction with promoter

Assists RNA polymerase binding to promoter. It can be on either side of the gene or on different chromosomes