Dalmau Ishar, Vela José Miguel, González Berta, Finsen Bente, Castellano Bernardo
Departmet of Histology, Faculty of Medicine, Autonomous University of Barcelona, E-08193-Bellaterra, Spain.
J Comp Neurol. 2003 Mar 31;458(2):144-57. doi: 10.1002/cne.10572.
Entrance of mesodermal precursors into the developing CNS is the most well-accepted origin of microglia. However, the contribution of proliferation and death of recruited microglial precursors to the final microglial cell population remains to be elucidated. To investigate microglial proliferation and apoptosis during development, we combined proliferating cell nuclear antigen (PCNA) immunohistochemistry, in situ detection of nuclear DNA fragmentation (TUNEL), and caspase-3 immunohistochemistry with tomato lectin histochemistry, a selective microglial marker. The study was carried out in Wistar rats from embryonic day (E) 16 to postnatal day (P) 18 in cerebral cortex, subcortical white matter, and hippocampus. Proliferating microglial cells were found at all ages in the three brain regions and represented a significant fraction of the total microglial cell population. The percentage of microglia expressing PCNA progressively increased from the embryonic period (25-51% at E16) to a maximum at P9, when the great majority of microglia expressed PCNA (92-99%) in all the brain regions analyzed. In spite of the remarkable proliferation and expansion of the microglial population with time, the density of microglia remained quite constant in most brain regions because of the considerable growth of the brain during late prenatal and early postnatal periods. In contrast, apoptosis of microglia was detected only at certain times and was restricted to some ameboid cells in white matter and primitive ramified cells in gray matter, representing a small fraction of the microglial population. Therefore, our results point to proliferation of microglial precursors in the developing brain as a physiological mechanism contributing to the acquisition of the adult microglial cell population. In contrast, microglial apoptosis occurs only locally at certain developmental stages and thus seems less crucial for the establishment of the final density of microglia.
中胚层前体细胞进入发育中的中枢神经系统是小胶质细胞最被广泛接受的起源。然而，募集的小胶质前体细胞的增殖和死亡对最终小胶质细胞群体的贡献仍有待阐明。为了研究发育过程中小胶质细胞的增殖和凋亡，我们将增殖细胞核抗原（PCNA）免疫组织化学、核DNA片段原位检测（TUNEL）、半胱天冬酶-3免疫组织化学与番茄凝集素组织化学（一种选择性小胶质细胞标记物）相结合。该研究在Wistar大鼠中进行，从胚胎第16天（E16）到出生后第18天（P18），取材于大脑皮层、皮层下白质和海马体。在所有年龄段的这三个脑区均发现有增殖的小胶质细胞，且它们在小胶质细胞总数中占相当大的比例。表达PCNA的小胶质细胞百分比从胚胎期（E16时为25%-51%）开始逐渐增加，在出生后第9天达到最高，此时在所有分析的脑区中，绝大多数小胶质细胞（92%-99%）表达PCNA。尽管随着时间推移小胶质细胞群体显著增殖和扩大，但由于产前后期和产后早期大脑的显著生长，大多数脑区中小胶质细胞的密度保持相当恒定。相比之下，仅在特定时间检测到小胶质细胞凋亡，且仅限于白质中的一些阿米巴样细胞和灰质中的原始分支细胞，它们在小胶质细胞群体中占一小部分。因此，我们的结果表明，发育中的大脑中小胶质前体细胞的增殖是一种生理机制，有助于获得成年小胶质细胞群体。相比之下，小胶质细胞凋亡仅在特定发育阶段局部发生，因此对于建立小胶质细胞的最终密度似乎不太关键。
