Morphological diversity and development of glia in Drosophila

Abstract

Insect glia represents a conspicuous and diverse population of cells and plays a role in controlling neuronal progenitor proliferation, axonal growth, neuronal differentiation and maintenance, and neuronal function. Genetic studies in Drosophila have elucidated many aspects of glial structure, function and development. Just as in vertebrates, it appears as if different classes of glial cells are specialized for different functions. Based on topology and cell shape, glial cells of the central nervous system fall into three classes (Fig. 1A–C): (i) surface glia that extend sheath-like processes to wrap around the entire brain; (ii) cortex glia (also called cell body-associated glia) that encapsulate neuronal somata and neuroblasts which form the outer layer (cortex) of the central nervous system; (iii) neuropile glia that are located at the interface between the cortex and the neuropile, the central domain of the nervous system formed by the highly branched neuronal processes and their synaptic contacts. Surface glia is further subdivided into an outer, perineurial layer, and an inner, subperineurial layer. Likewise, neuropile glia comprises a class of cells that remain at the surface of the neuropile (ensheathing glia), and a second class that forms profuse lamellar processes around nerve fibers within the neuropile (astrocyte-like or reticular glia). Glia also surrounds the peripheral nerves and sensory organs; here, one also recognizes perineurial and subperineurial glia, and a third type called “wrapping glia” that most likely corresponds to the ensheathing glia of the central nervous system. Much more experimental work is needed to determine how fundamental these differences between classes of glial cells are, or how and when during development they are specified. To aid in this work the following review will briefly summarize our knowledge of the classes of glial cells encountered in the Drosophila nervous system, and then survey their development from the embryo to adult.

Glial cells in neuronal development: recent advances and insights from Drosophila melanogaster

“…Surface glia, the outermost layer of protection surrounding the larval and adult CNS, comprises two subtypes, the perineurial and subperineurial glia (SPG). These glial cells exclusively function as a blood-brain-barrier to prevent unwanted molecules over a certain size from entering the CNS [2,5,16] .…”

“…Distinct classes of glia are based on their morphology and function similar to their mammalian counterparts [10,13,[15][16][17] (Table 1 and Fig. 1).…”

“…Two types of neuropil glia are present in Drosophila: ensheathing glia, which surround the synaptic neuropil, and astrocyte-like glia that infiltrate into the inner region of the neuropil volume. Finally, CNSderived peripheral glia are also subcategorized into three types [3][4][5]16] . The innermost type in contact with axons is termed wrapping glia; this is also considered to be a subtype of neuropil glia due to its association with nerves.…”

“…Surface glia, the outermost layer of protection surrounding the larval and adult CNS, comprises two subtypes, the perineurial and subperineurial glia (SPG). These glial cells exclusively function as a blood-brain-barrier to prevent unwanted molecules over a certain size from entering the CNS [2,5,16] .The protection is mainly mediated by SPG, which form [3,18] . In regards to size, SPGs have large and flatted cell bodies and are few in number, whereas perineurial glia have smaller cell bodies and higher numbers (Fig.…”

Analysis of Glial Distribution in Drosophila Adult Brains

“…Furthermore, Drosophila glia are morphologically and functionally similar to their mammalian counterparts [14]. A plethora of studies have given thorough descriptions of the diverse types of Drosophila adult glia [16][17][18]. Particularly, glia associated with the antennal lobes (ALs) have been discussed [19].…”