Transcriptome analysis of amoeboid and ramified microglia isolated from the corpus callosum of rat brain.
BACKGROUND
Microglia, the resident immune cells of the central nervous system (CNS), have two distinct phenotypes in the developing brain: amoeboid form, known to be amoeboid microglial cells (AMC) and ramified form, known to be ramified microglial cells (RMC). The AMC are characterized by being proliferative, phagocytic and migratory whereas the RMC are quiescent and exhibit a slow turnover rate. The AMC transform into RMC with advancing age, and this transformation is indicative of the gradual shift in the microglial functions. Both AMC and RMC respond to CNS inflammation, and they become hypertrophic when activated by trauma, infection or neurodegenerative stimuli. The molecular mechanisms and functional significance of morphological transformation of microglia during normal development and in disease conditions is not clear. It is hypothesized that AMC and RMC are functionally regulated by a specific set of genes encoding various signaling molecules and transcription factors.


RESULTS
To address this, we carried out cDNA microarray analysis using lectin-labeled AMC and RMC isolated from frozen tissue sections of the corpus callosum of 5-day and 4-week old rat brain respectively, by laser capture microdissection. The global gene expression profiles of both microglial phenotypes were compared and the differentially expressed genes in AMC and RMC were clustered based on their functional annotations. This genome wide comparative analysis identified genes that are specific to AMC and RMC.


CONCLUSIONS
The novel and specific molecules identified from the trancriptome explains the quiescent state functioning of microglia in its two distinct morphological states.
Department of Anatomy, Yong Loo Lin School of Medicine, National University of Singapore, Blk MD10, 4 Medical Drive, Singapore, 117597, Singapore.
Rangarajan
R
Parakalan
Boran
B
Jiang
Baby
B
Nimmi
Manivannan
M
Janani
Manikandan
M
Jayapal
Jia
J
Lu
Samuel S W
SS
Tay
Eng-Ang
EA
Ling
S Thameem
ST
Dheen
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D002454:Cell Differentiation / Q000235:genetics; D002461:Cell Line, Transformed; D049109:Cell Proliferation; D016000:Cluster Analysis; D003337:Corpus Callosum / Q000166:cytology*; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D003599:Cytoskeleton / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D051797:Inhibitor of Differentiation Protein 2 / Q000235:genetics / Q000378:metabolism; D061346:Laser Capture Microdissection; D017628:Microglia / Q000145:classification* / Q000378:metabolism*; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013234:Stem Cells; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D016207:Cytokines; C497451:Id2 protein, rat; D051797:Inhibitor of Differentiation Protein 2; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009419:Nerve Tissue Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D014157:Transcription Factors