Stem cells 2 - Niches

Question 1

Describe the structure of a germarium is drosophila

Answer 1

going from top to bottom
- terminal filament
- cap cell
- germline stem cell
- cyctoblast

Question 2

What is the niche of a stem cell?

Answer 2

the environment of a stem cell that provides the factors needed for stem cell maintenance

Question 3

Explain the divisions of drosophilla female germline stem cells (GSC)

Answer 3

• 2-3 GSC per germanium undergo asymmetric division
• produces a cyctoblast
• cystoblast divided 4x to produce progenitors of 15 nurse cells and 1 oocyte

Question 4

What is the niche of GSC?

Answer 4

• cap cells

Question 5

Explain GSC and somatic cells

Answer 5

• male and female GSC are closely associated with somatic cells

Question 6

Name 2 main features of the regulation of the drosophila germline

Answer 6

• maintenance of no stem cells by environment
• asymmetric divisions segregating local determinants

Question 7

How is the number of GSCs controlled in drosophila germline?

Answer 7

• BAM - bag of marbles
• off in GSC, on in cystoblasts
• secreted factors from cap cells and terminal filaments bind to receipts and activate signalling pathways to keep bam off

Question 8

How does the asymmetric division of GSCs happen?

Answer 8

• spindles are orientated so one cell is near hub (males) or cap cells
• cell that inherits spectrosome becomes GSC
• GSC anchored to cap cells by adhering junctions

Question 9

What is a spectrosome?

Answer 9

a condensed organelle made of spectral (actinobinding contractile in cell division)

Question 10

Are asymmetric divisions in mammal cell types rare or common?

Answer 10

rare

Question 11

Name 4 differentiated cells in the gut and their roles?

Answer 11

• enterocyte - absorbs nutrients
• goblet cell - secretes mucus
• enteroendocrine - secreted hormones
• panted cell - mediates microbial immunity

Question 12

Where are cells expressing Lgr5 found and what are they called?

Answer 12

• bottom of the crypt
• crypt based columnar cells (CBC)

Question 13

How was it determined that Lgr5 cells are stem cells?

Answer 13

• permanently mark the cells and track their dependents
• Lgr5 promoter expresses recombination enzyme
• all decendents will express LacZ
• Recombination enzyme is called creERT2
• only active in presence of tamoxifen
• creERT2 then removes the stop transcription signal on the Rosa26 gene (which has LacZ)
• when tamoxifen is added, all offspring will express LacZ
• all different cell types in the crypt and villus contained LacZ

Question 14

Draw out the set up of the Lgr5 and Rosa26 experiment

Answer 14

look at notes

Question 15

What is the niche for Lgr5+ cells?

Answer 15

• Paneth cells secreting Wnt3
• Lrg5+ cells require Wnt3

Question 16

Do Lgr5+ cells divide asymmetrically?

Answer 16

• no they divide symmetrically
• neural drift happens

Question 17

What is neutural drift?

Answer 17

• when there is a small population you end up with a smaller genetic pool (genetic drift)