Table 1.

Comparision of Neuronal and Astrocytic Primary Cilia in the Mature Brain

Features	Neurons	Astrocytes
Origination	Ectoderm [119] Neuroepithelial Cells and Radial Glial Cells [27]	Ectoderm [119] Neuroepithelial Cells and Radial Glial Cells[27]
Excitability	Excitable	Non-excitable
Connectivity	Highly connected via synapses	Not wired to one another via chemical synapses; albeit gap junctions found [120, 121]
Differentiation	Terminally differentiate upon maturation	Regional differentiation & become reactive in response to insults
Proliferative Capacity	Lose mitotic ability in maturation [52]	Maintain proliferative capacity throughout life [26]
Primary Cilia Markers	AC3 (Figure 1), SSTR3, 5-HT6, & MCHR1 [15]	Arl13B (Figure 1) [15]
AC3	Highly expressed in neuronal primary cilia [45]	Faintly expressed in immature astrocyte cilia, few in adult astrocyte cilia [45]
ARL13B	Faintly expressed in immature neurons, not prominent in mature neurons [45]	Highly expressed in astrocyte primary cilia in the mature brain [45] (Figure 1)
Cilia Length (Hippocampus)	5.0–5.91 μm (AC3-positive) [15]	2.8–3.2 μm (ARL13B-positive) [15]
Shh Components	Smoothened [17], Patched1 [63], GPR161 [64,56] and Gli transcription factors [63] detected in primary cilia in the neural tube. Presence in primary cilia of mature neurons not shown.	Smoothened and Patched1 detected in primary cilia of astrocytes in the postnatal brain [122]
Structural Dynamics	Relatively stable	Subject to dynamic change during astrocyte proliferation
Ciliogenesis	Research confined to embryonic neuronal ciliogenesis; Lack of de novo ciliogenesis in mature neurons	5 known stages of ciliogenesis in adult astrocytes [53, 54]
Ciliary Disease Implications	Obesity, cognitive impairment & mental disorders [89]	Astrocytoma/glioblastoma [53, 54]