QUANTIFICATION OF MYELIN BASIC-PROTEIN IN THE HUMAN FETAL SPINAL-CORDDURING THE MIDTRIMESTER OF GESTATION

The amount of myelin basic protein (MBP) was quantified in human fetal spinal cords from 12 to 24 gestational weeks (GW). MBP expression was determined by Northern blot, quantitative immunoblot, and immunocytoc hemistry. The development of compact myelin was analyzed by electron m icroscopy. Thirty-eight human fetal spinal cords were obtained after e lective termination of intrauterine pregnancies from healthy women. No rthern blot analysis showed a 15.8-fold increase in MBP mRNA between 1 2 and 18 GW. From 18 to 24 GW, MBP mRNA Increased by 2.2-fold. The mRN A data paralleled immunoblot results that showed a 90.5-fold increase in MBP (0.147 ng/mg to 13.3 ng/mg tissue) between 12 and 18 GW and an approximately 11.5-fold increase between 18 and 24 GW (13.3 ng/mg to 1 54 ng/mg tissue). Immunocytochemical analysis also showed increased st aining for MBP with advancing gestational age. At 12 GW, MBP immunorea ctivity was observed in all three spinal cord funiculi. By 18 GW, MBP was expressed throughout the spinal cord white matter with the excepti on of the lateral corticospinal tracts and in the rostral levels of th e fasciculus gracilis. With respect to myelin, at 12 GW, rare, noncomp acted myelin lamellae were observed by electron microscopy. By 18 GW, discrete areas of compact myelin were observed in areas that showed MB P immunoreactivity, and at 24 GW, compact myelin was prominent through out the white matter of the spinal cord. This study demonstrates a qua ntitative increase in MBP expression that is associated with myelin fo rmation during the second trimester of human gestation. This informati on may provide normative data that can aid in the diagnosis of myelin disorders of the preterm, neonatal, and pediatric spinal cord. (C) 199 6 Wiley-Liss, Inc.