Cep215 is essential for morphological differentiation of astrocytes

Cep215 (also known as Cdk5rap2) is a centrosome protein which is involved in microtubule organization. Cep215 is also placed at specific subcellular locations and organizes microtubules outside the centrosome. Here, we report that Cep215 is involved in morphological differentiation of astrocytes. Cep215 was specifically localized at the glial processes as well as centrosomes in developing astrocytes. Morphological differentiation of astrocytes was suppressed in the Cep215-deleted P19 cells and in the Cep215-depleted embryonic hippocampal culture. We confirm that the microtubule organizing function of Cep215 is critical for the glial process formation. However, Cep215 is not involved in the regulation of cell proliferation nor cell specification. Based on the results, we propose that Cep215 organizes microtubules for glial process formation during astrocyte differentiation.

The role of epidermal growth factor receptor in human gliomas: II. The control of glial process extension and the expression of glial fibrillary acidic protein

✓ Our earlier investigations of the biology of the epidermal growth factor receptor (EGFR) in human gliomas demonstrated that the level of EGFR expression did not directly predict the glioma growth response to EGF, suggesting that the function of the EGFR in glioblastomas might not be limited to mediating the growth effects of EGF. We conducted the current studies to investigate the function(s) of the EGFR not related to growth control in human gliomas. These investigations show that the EGFR mediates the stimulative effects of EGF on glial process extension and glial fibrillary acidic protein (GFAP) expression. In addition, the level of EGFR expression correlates inversely with glioma cell responsiveness to differentiation promoting agents (for example, nerve growth factor and transforming growth factor-β) that act through transmembrane tyrosine kinase receptors. Thus, glioma lines with a high level of EGFR expression (for example, T-98G cells) responded to fewer differentiation promoting factors than lines with a low level of EGFR expression (such as U-373MG cells). Our results suggest that the EGFR in gliomas may participate in mediating the process extension and GFAP stimulative effects of both EGF and other differentiation promoting agents. These properties represent components of the differentiated state in glia because their expression is stimulated by dibutyryl cyclic adenosine monophosphate in normal astrocytes. The involvement of the EGFR in the expression of these glial specific properties suggests that the EGFR may play an important role in glial differentiation.

Astroglial cells provide a template for the positioning of developing cerebellar neurons in vitro.

Indirect immunocytochemical staining with antisera raised against purified glial filament protein and a neurofilament polypeptide was used to study cell interactions between astrocytes and neurons dissociated from embryonic and early postnatal cerebellum. Staining with antibodies raised against purified glial filament protein revealed that greater than 99% of all processes present in cerebellar cultures during the 1st wk in vitro were glial in origin. After 1 wk in culture, unstained processes that were presumably neuronal were observed. Stained astroglial processes formed a dense network that served as a template for cerebellar neurons, identified by indirect immunocytochemical localization of tetanus toxin. More than 90% of neurons from postnatal days 1 or 7 were positioned within one cell diameter of a glial process. In contrast, less than 40% of the neurons dissociated from early embryonic cerebellum were located adjacent to a glial process. Staining with antibodies raised against purified glial filament protein also revealed differences in astroglial morphology that were under developmental regulation. Astroglial cells from embryonic cerebellum were fewer in number and had thick, unbranched processes. Those from postnatal day 1 were more slender, branched, and stellate. Those from postnatal day 7 were highly branched and stellate. Some veil-like astroglial processes were also observed in cells from postnatal animals. These morphological changes were also observed when cells from embryonic day 13 were maintained for a week in vitro. No specific staining of embryonic or postnatal cerebellum cells was observed with antibodies raised against purified neurofilament polypeptides.

ULTRASTRUCTURAL STUDY OF REMYELINATION IN AN EXPERIMENTAL LESION IN ADULT CAT SPINAL CORD

This report presents ultrastructural observations on the cytological events that attend myelin formation occurring in the wake of demyelination in adult cat spinal cord. Lesions were induced in subpial cord by cerebrospinal fluid (c.s.f.) exchange (1, 2). Tissue from eleven cats at nine intervals from 19 to 460 days was fixed in situ by replacing c.s.f. with buffered OsO4 and embedded in Araldite. After demyelination, axons are embraced by sheet-like glial processes. An occasional myelin sheath is first seen at 19 days; by 64 days, all axons are at least thinly myelinated. The cytoplasm of the myelin-forming cells, unlike that of either oligodendrocyte or fibrous astrocyte in normal cord, is dense with closely packed organelles and fine fibrils. Many of the myelinogenic cells become scarring astrocytes and at 460 days the lesion teems with their fibril-filled processes. Oligodendrocytes appear in the lesion after remyelination is under way. Phagocytes disappear gradually. A myelin sheath is formed by spiral wrapping of a sheet-like glial process around an axon. Where the first turn of the spiral is completed, a mesaxon is formed. As cytoplasm is lost from the process, the plasma membrane comes together along its outer and cytoplasmic surfaces to form compact myelin. Only a small amount of cytoplasm is retained; it is confined to the paramesaxonal region and, on the sheath exterior, to a longitudinal ridge which appears in profile as a small loop. This outer loop has the same rotational orientation as the inner mesaxon. These vestiges of spiral membrane wrapping are also found in normal adult and new-born cat cord. Nodes are present in all stages of remyelination and in normal adult cat and kitten cord. These observations suggest that myelin is reformed in the lesion in the same way it is first formed during normal development. The mechanism of myelin formation is basically similar to that proposed for peripheral nerve and amphibian and mammalian optic nerve; it does not agree with present views on the mechanism of myelinogenesis in mammalian brain and cord. This is the first demonstration of remyelination in adult mammalian central nervous tissue.