Nervous systems of bilaterian animals generally consist of two cell types: neurons and glial cells. Despite accumulating data about the many important functions glial cells serve in bilaterian nervous systems, the evolutionary origin of this abundant cell type remains unclear. Current hypotheses regarding glial evolution are mostly based on data from model bilaterians. Non-bilaterian animals have been largely overlooked in glial studies and have been subjected only to morphological analysis. Here, we provide a comprehensive overview of conservation of the bilateral gliogenic genetic repertoire of non-bilaterian phyla (Cnidaria, Placozoa, Ctenophora, and Porifera). We overview molecular and functional features of bilaterian glial cell types and discuss their possible evolutionary history. We then examine which glial features are present in non-bilaterians. Of these, cnidarians show the highest degree of gliogenic program conservation and may therefore be crucial to answer questions about glial evolution.
Keyphrases
- neuropathic pain
- induced apoptosis
- cell cycle arrest
- spinal cord
- single cell
- endoplasmic reticulum stress
- genome wide
- spinal cord injury
- electronic health record
- gene expression
- big data
- oxidative stress
- quality improvement
- machine learning
- artificial intelligence
- mesenchymal stem cells
- bone marrow
- single molecule
- cell proliferation
- data analysis