Leung Doreen Siu Yi, Unsicker Klaus, Reuss Bernhard
Neuroanatomy and Interdisciplinary Center for Neurosciences (IZN), University of Heidelberg, Im Neuenheimer Feld 307, D-69120 Heidelberg, Germany.
Int J Dev Neurosci. 2002 Feb;20(1):63-75. doi: 10.1016/s0736-5748(01)00056-9.
Connexins (cx) constitute a family of transmembrane proteins that form gap junction channels allowing metabolic and electrical coupling of cellular networks. Initial studies on the expression of cx in the developing brain have suggested that cx may undergo dynamic changes and may possibly be implicated in synchronizing development and differentiation of neural progenitor cells and young neurons. We have investigated expression of cx26, cx32, cx43, and cx45 in the midbrain floor, where nigrostriatal dopaminergic neurons originate and differentiate. This neuron population is of major importance in regulating motor-functions. Semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) revealed low levels of cx26-mRNA in the midbrain floor at E12, which gradually increased during pre- and postnatal development, reaching a maximum in the adult. Cx32-mRNA-levels reached a first peak at E16, and showed highest levels in adulthood. Cx43 was highly expressed at E12, decreased until E18, and subsequently increased again until adulthood. Cx45 mRNA was prominent at all developmental ages, but slightly decreased after the first postnatal week. Double-labeling for the dopaminergic neuronal marker tyrosine hydroxylase (TH), and cx-immunoreactivities (ir) evaluated by quantitative confocal laser microscopy revealed both distinct and similar developmental patterns for the individual cx investigated. Cx26 was highest at E14, decreased towards birth, and subsequently increased again reaching about 50% of the E14 level in the adult. Cx32-ir peaked at E16 and dropped to low levels after birth. Cx43-ir was highest at E12, decreased sharply at E14, reached its lowest levels at birth, but modestly increased again afterwards. Cx45-ir showed a biphasic pattern, with two prominent peaks at E12 and E18, followed by a massive postnatal decrease. Taken together, our results reveal that expression and ir of cx in the midbrain floor and dopaminergic neurons, respectively, follow cx-type specific patterns that temporally coincide with important steps of midbrain morphogenesis, as e.g. progenitor cell formation and migration (E12), early differentiation (E14-16), target encounter (E16-18) and postnatal functional maturation of the nigrostriatal system.
连接蛋白（Cx）构成了一个跨膜蛋白家族，它们形成间隙连接通道，使细胞网络实现代谢和电偶联。对发育中的大脑中Cx表达的初步研究表明，Cx可能会发生动态变化，并且可能与神经祖细胞和年轻神经元的发育和分化同步有关。我们研究了黑质纹状体多巴胺能神经元起源和分化的中脑底部中Cx26、Cx32、Cx43和Cx45的表达。这一神经元群体在调节运动功能方面至关重要。半定量逆转录聚合酶链反应（RT-PCR）显示，在胚胎第12天（E12）时，中脑底部Cx26 mRNA水平较低，在出生前和出生后的发育过程中逐渐升高，在成年时达到最高值。Cx32 mRNA水平在E16时达到第一个峰值，并在成年期表现出最高水平。Cx43在E12时高表达，到E18时下降，随后在成年前再次升高。Cx45 mRNA在所有发育阶段都很突出，但在出生后第一周后略有下降。通过定量共聚焦激光显微镜对多巴胺能神经元标记物酪氨酸羟化酶（TH）和Cx免疫反应性（ir）进行双重标记，结果显示，所研究的各个Cx呈现出既不同又相似的发育模式。Cx26在E14时最高，出生时下降，随后再次升高，在成年时达到E14水平的约一半。Cx32-ir在E16时达到峰值，出生后降至低水平。Cx43-ir在E12时最高，在E14时急剧下降，出生时达到最低水平，但之后又适度升高。Cx45-ir呈现双相模式，在E12和E18时有两个突出峰值，随后在出生后大幅下降。综上所述，我们的结果表明，中脑底部和多巴胺能神经元中Cx的表达和ir分别遵循Cx类型特异性模式，这些模式在时间上与中脑形态发生的重要步骤相吻合，例如祖细胞形成和迁移（E12）、早期分化（E14 - 16）、靶点接触（E16 - 18）以及黑质纹状体系统的出生后功能成熟。
