Analysis of glial fibrillary acidic protein, neurofilament protein, actin and heat shock proteins in human fetal brain during the second trimester

Glial fibrillary acidic protein (GFAP), the 66 kDa neurofilament protein (NF-66), actin, the 27 kDa heat shock protein (HSP27) and the 70 kDa constitutive heat shock protein (HSC70) were analyzed in human fetal brain during the second trimester, from 10 to 24 gestational weeks (GW). By immunohistochemistry, cell-type specific localization of GFAP and NF-66 in astrocytes and neurons, respectively, was confirmed. HSP27 was expressed mostly in the nuclear region of neurons and non-neuronal cells, and HSC70 was widely distributed throughout the tissue. By quantitative immunoblotting, GFAP was not detectable in gray matter of prefrontal cortex prior to 16 GW. Between 16 and 21 GW, the content of GFAP rose slowly. Thereafter, GFAP accumulated rapidly. The content of GFAP in different brain regions (prefrontal, parietal, and occipital cortices) differed significantly at 22 GW. In contrast, NF-66 was already highly expressed at 10 GW, slowly rose to maximal values by 18 GW, and thereafter remained stationary. In contrast to GFAP, the content of NF-66 was similar in different brain regions at 22 GW. Although actin was abundant throughout the second trimester, a sharp drop in its content in the prefrontal cortex was detected at 17 GW. To explain such a decrease, two heat shock proteins were analyzed. HSP27, known to modulate actin polymerization, was found to increase sharply at 16-17 GW. In contrast, HSC70 remained constant during the second trimester and was highly expressed in the fetal brain, at a level comparable to that in the adult brain.