Glial Cell Biology ILO 2 - Understand the cellular and genetic differences between various glial cells in the brain

Question 1

What % of brain cells are astrocytes in mice and in humans?

Answer 1

Mice - 10-20%

Humans 20-40%

Question 2

Name the 8 morphological classes of astrocytes and some of their features.

Answer 2

Protoplasmic astrocytes - found in white matter and show classic star morphology
Fiberous astrocyte - found in the white matter and show the classic star morphology
Radial astrocyte/Bergmann glia - found in the cerebellum, extremely polarised with end feet interacting with pia matter
Velate astrocyte - found in cerebellum and olfactory bulb surrounded by tightly packed neurons
Interlaminar astrocytes - cell body in molecular layer, branches extend through lamina of cortical layers
Marginal and perivascular astrocytes - extensive end feed connected to pia matter (marginal) to blood vessel (perivascular). Perivascular astrocytes have no neuronal connections (do not participate in tripartite synapse), only enwrap blood vessels
Immature astrocyte/glioblast - give rise to mature astrocytes

Question 3

What are the characteristic markers of astrocytes?

Answer 3

Glial fibrillary acidic protein (GFAP)
Calcium binding protein (S100b)
Aldehyde dehydrogenase 1 family L1 (Adlh1L1)

Question 4

What is the main issue with astrocyte markers?

Answer 4

Not all astrocytes express them e.g. only 10-20% of all cortex astrocytes express GFAP

Question 5

What are the four microglia states and how does their morphology differ?

Answer 5

Silent/resting microglia - actively scan environment, thin processes
Activated microglia - more ‘bushy’ morphology, increased number and thicker processes
Phagocytic microglia - round, large body, less processes
Dystrophic microglia - segmented, dying

Question 6

What %/number of brain cells are microglia in humans and mice?

Answer 6

Humans - 5-10%

3.5x10^6 in mice

Question 7

What are the characteristic markers of resting microglia?

Answer 7

Proliferation +/-
Iba1 +
CD11b +
Vimentin -
MHC Class I antigen -

Question 8

What are the characteristic markers of activated microglia?

Answer 8

Proliferation +
Iba1 +
CD11b+
Vimentin +
MHC Class I antigen +

Question 9

What are the characteristic markers of phagocytic microglia?

Answer 9

Proliferation +
Iba1 +
CD11b+
Vimentin +
MHC Class I antigen +

Question 10

What are the characteristic markers of dystrophic microglia?

Answer 10

Proliferation -
Iba1 +
CD11b+
Vimentin +
MHC Class I antigen +

Question 11

How many types of oligodendrocyte are there?

Answer 11

4

Question 12

What are the similarities and differences between Type1 and Type2 oligodendrocytes?

Answer 12

Similarities - relatively small cell body, 4-5 processes from soma, enwrap axons with diameter <2um, wrap up to 30 axons
Most common in the CNS
Differences - Type 1 enwrap axons in any direction, type 2 - enwrap parallel axons

Question 13

What are the 3 different morphologies of type 1 oligodendrocytes?

Answer 13

Ramified
Stellar
Smooth

Question 14

What are the features of type 3 oligodendrocytes?

Answer 14

Small body, few branches, 1-2 primary processes, enwrap thicker axons ~50uM in diameter, enwrap fewer axons

Question 15

What are the features of type 4 oligodendrocytes?

Answer 15

Enwrap very thick axons, only a single branch extending from cell body
Rarely found in mice - nerves not thick enough

Question 16

What are the characteristics of NG2 glia/polydendrocytes?

Answer 16

Morphologically similar to astrocytes
Cell marker is neuroglia antigen 2 (NG2)
Cannot produce myelin
Important in generating new brain cells

Question 17

What are the characteristic markers of oligodendrocytes?

Answer 17

Olig2 - oligodendrocyte transcription factor
Myelin basic protein (MBP)
Myelin oligodendrocyte glycoprotein (MOG)
Myelin proteolipid protein (PLP)