Investigating Zebrafish Microglia with Confocal Microscopy to Understand Brain Development
Researchers identify two distinct subtypes of microglia in the developing zebrafish brain.
Microglia are the dominant immune cells in the central nervous system (CNS). They play a critical role in brain development by both trimming and promoting synapse formation, which makes our brains more efficient as we transition out of childhood. Additionally, microglia clear apoptotic neurons, which is an essential task both in brain development and disease. One outstanding question in developmental neuroscience research is whether there are distinct subsets of microglia that perform these diverse functions.
Dr. Anna Molofsky is an Associate Professor at the Weill Institute for Neurosciences at the University of California, San Francisco, USA. Her lab's publication in Nature Communications studied microglia in zebrafish using confocal microscopy along with sequencing methods to identify two phenotypically and functionally distinct subtypes of microglia in the developing zebrafish brain.
We are interested in understanding how innate immune cells known as microglia shape the healthy brain. Our goal is to identify key cellular and molecular processes that regulate postnatal synaptic development in hopes to inform new immune-based therapies for psychiatric and neurodevelopmental illnesses.
Two Subtypes of Zebrafish Microglia
In N.J. Silva et al., the Molofsky lab identifies two unique subtypes of microglia during brain development in zebrafish; one subtype is located within the midline optic tectum (OT) and the other from the hindbrain.
They show that microglia found in the OT are condensed and amoeboid in shape, remove apoptotic neurons, and express lysosomal cathepsin genes. In contrast, microglia in the hindbrain are branched out in shape, engulf synapses, and express synaptic pruning genes.
Identification of Microglia Subtypes
Essential Data Provided by Confocal Microscopy
Microglia Within the Hindbrain Region
Ramified microglia within the hindbrain region of the zebrafish brain showing the enriched gene cd74a (MHC class II). Labels: Zebrafish microglia (4C4: white), cd74a (red), and DNA (blue)
Microglia Enriched in the Optic Tectum (OT)
Amoeboid microglia enriched in the optic tectum (OT) with catalytic activity of cathepsin b and l, which is indicated by fluorescence probe Prosense 680. Labels: Zebrafish microglia (mpeg: green), Prosense 680 (white), and DNA (blue)
These findings suggest that not all microglia are created equal and their function is dictated by their location within the brain. The identification of microglia subpopulations within the brain will aid in our understanding of biological functions for future immune-based therapies.