Olfactory ensheathing cells are the main phagocytic cells that remove axon debris during early development of the olfactory system

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Author(s)
Nazareth, Lynnmaria
Lineburg, Katie E
Chuah, Meng Inn
Velasquez, Johana Tello
Chehrehasa, Fatemeh
St John, James A
Ekberg, Jenny AK
Year published
2015
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During development of the primary olfactory system, axon targeting is inaccurate and axons inappropriately project within the target layer or over-project into the deeper layers of the olfactory bulb. As a consequence there is considerable apoptosis of primary olfactory neurons during embryonic and postnatal development and axons of the degraded neurons need to be removed. Olfactory ensheathing cells (OECs) are the glia of the primary olfactory nerve and are known to phagocytose axon debris in the adult and postnatal animal. However it is unclear when phagocytosis by OECs first commences. We have investigated the onset of ...
View more >During development of the primary olfactory system, axon targeting is inaccurate and axons inappropriately project within the target layer or over-project into the deeper layers of the olfactory bulb. As a consequence there is considerable apoptosis of primary olfactory neurons during embryonic and postnatal development and axons of the degraded neurons need to be removed. Olfactory ensheathing cells (OECs) are the glia of the primary olfactory nerve and are known to phagocytose axon debris in the adult and postnatal animal. However it is unclear when phagocytosis by OECs first commences. We have investigated the onset of phagocytosis by OECs in the developing mouse olfactory system by utilizing two transgenic reporter lines: OMP-ZsGreen mice which express bright green fluorescent protein in primary olfactory neurons and S100߭DsRed mice which express red fluorescent protein in OECs. In crosses of these mice, the fate of the degraded axon debris is easily visualized. We found evidence of axon degradation at E13.5. Phagocytosis of the primary olfactory axon debris by OECs was first detected at E14.5. Phagocytosis of axon debris continued into the postnatal animal during the period when there was extensive mis-targeting of olfactory axons. Macrophages were often present in close proximity to OECs but they contributed only a minor role to clearing the axon debris, even after widespread degeneration of olfactory neurons by unilateral bulbectomy and methimazole treatment. These results demonstrate that from early in embryonic development OECs are the primary phagocytic cells of the primary olfactory nerve.
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View more >During development of the primary olfactory system, axon targeting is inaccurate and axons inappropriately project within the target layer or over-project into the deeper layers of the olfactory bulb. As a consequence there is considerable apoptosis of primary olfactory neurons during embryonic and postnatal development and axons of the degraded neurons need to be removed. Olfactory ensheathing cells (OECs) are the glia of the primary olfactory nerve and are known to phagocytose axon debris in the adult and postnatal animal. However it is unclear when phagocytosis by OECs first commences. We have investigated the onset of phagocytosis by OECs in the developing mouse olfactory system by utilizing two transgenic reporter lines: OMP-ZsGreen mice which express bright green fluorescent protein in primary olfactory neurons and S100߭DsRed mice which express red fluorescent protein in OECs. In crosses of these mice, the fate of the degraded axon debris is easily visualized. We found evidence of axon degradation at E13.5. Phagocytosis of the primary olfactory axon debris by OECs was first detected at E14.5. Phagocytosis of axon debris continued into the postnatal animal during the period when there was extensive mis-targeting of olfactory axons. Macrophages were often present in close proximity to OECs but they contributed only a minor role to clearing the axon debris, even after widespread degeneration of olfactory neurons by unilateral bulbectomy and methimazole treatment. These results demonstrate that from early in embryonic development OECs are the primary phagocytic cells of the primary olfactory nerve.
View less >
Journal Title
Journal of Comparative Neurology
Copyright Statement
© 2014 Wiley Periodicals, Inc.. This is the pre-peer reviewed version of the following article: Olfactory ensheathing cells are the main phagocytic cells that remove axon debris during early development of the olfactory system, Journal of Comparative Neurology, which has been published in final form at dx.doi.org/10.1002/cne.23694.
Subject
Zoology
Neurosciences
Central nervous system
Peripheral nervous system
Medical physiology