Question

Phagocytic glial cells of central nervous system are derived from
(A) Mesoderm
(B) Endoderm
(C) Ectoderm
(D) Ectomesoderm​

Answer 1

Explanation:

Microglia are derived from the hematopoietic lineage and express typical pattern recognition receptors. Microglial processes interact with presynaptic boutons and dendritic spines in normal brains, and direct contacts have been observed using electron and two-photon microscopy (Nimmerjahn et al., 2005). Each microglial cell surveys several synapses simultaneously and quickly changes its motility in response to extracellular stimuli.

Notably, microglia play critical roles in shaping the neural circuit connectivity of developing and normal brains. Microglia prune synaptic connections by engulfing pre- and postsynaptic elements in the hippocampus and retinogeniculate system during postnatal development (Paolicelli and Gross, 2011; Schafer et al., 2012).

Unwanted developing synapses in the retinogeniculate system are tagged with complement protein C1q, which is the initiating protein of the classical complement cascade (Stevens et al., 2007). The binding of C1q and opsonization of unwanted synapses trigger a protease cascade, which leads to the deposition of the downstream complement protein C3 (Gasque, 2004). Deposited C3 directly activate C3 receptors on microglia, which trigger elimination via microglial phagocytosis (Stevens et al., 2007) (Fig. 1).

The relevant complement proteins are normally downregulated by adulthood in the brain, but recent studies have revealed that C1q is highly upregulated in aging brains (Stephan et al., 2013) and most neurodegenerative diseases (Hong et al., 2016), where it mediates abnormal synapse elimination