Temporal and spatial patterns of glial differentiation in the surgically induced spinal open neural tube defect of chick embryos: astrocytic, radial glial and microglial differentiations.

Abstract

There are controversies over the pattern of glial differentiation in spinal open neural tube defect (ONTD) at the prenatal stage. A surgical model of ONTD allows a more precise comparison of glial differentiation between the ONTD and control groups than chemical and genetic models. To investigate the influence of ONTDs on the patterns of glial differentiation, ONTDs were induced by surgery using Hamburger and Hamilton stage 18 or 19 chick embryos. The spinal cord tissues on postoperative days (POD) 5, 7, 10, and 14 were processed to observe astrocytic, radial glial, and microglial differentiations by glial fibrillary acid protein (GFAP), vimentin and ricinus communis agglutinin-I (RCA-I) stainings, respectively. Four embryos were assigned to subgroups of each POD. Control embryos ( n=4) were staged but the neural tubes were not incised. In the control group, GFAP positivity was shown faintly at the dorsal midline on embryonic day (E) 10 (corresponding to POD 7), in the ventral one-third of the white matter on E 13 and in the whole white matter on E 17. Embryos with ONTDs showed earlier and stronger GFAP positivity from POD 7-14, especially at the dorsal surface and the adjacent gray matter. In the control group, vimentin staining demonstrated a positive reaction at the midline with positivity in a faint, radial pattern on E 8 and E 10. This had all disappeared by E 13 and 17. In embryos with ONTDs, vimentin positivity was enhanced and persisted from POD 5-14. These findings were prominent along the dorsal surface of ONTDs. No difference in RCA-I staining was found between the control and ONTD groups. The results reveal that ONTD promotes astrocytic differentiation and prolongs expression of radial glial fibers, which seems to be a reaction to the damage caused by exposure of the spinal cord tissue to amniotic fluid.