Basement Membranes and Associated Protein Factors In Development and Disease

基底膜是薄的细胞外基质，分隔上皮细胞和间充质细胞，并包围内皮细胞、肌肉细胞和神经细胞等细胞。基底膜是发育中第一个出现的细胞外基质，对器官发育和组织修复至关重要。它们不仅为细胞和细胞层提供支架，而且在影响细胞黏附、迁移、增殖和分化的形态发生中发挥重要作用。基底膜由IV型胶原蛋白、层粘连蛋白、粘附素、粘附素/牙本质蛋白等分子组成，它们相互作用形成超分子结构。 层粘连蛋白是一个大的多域糖蛋白家族，通常是基底膜所特有的。层粘连蛋白具有多种生物学活性，包括促进细胞黏附、迁移、分化、肿瘤细胞侵袭以及与基质分子和细胞表面受体的相互作用。层粘连蛋白-1(LN-1)又称层粘连蛋白-111，是一种由链组成的异源三聚体细胞外基质蛋白，在早期基底膜组装、胚胎着床和发育中起着至关重要的作用。层粘连蛋白-1促进不同神经细胞中的神经突起生长，并已确定在&#945；1和&#947；1链中的几个活性部位。缺乏Lama1基因的小鼠胚胎缺乏赖歇氏膜，并在胚胎第7天死亡。然而，在中枢神经系统中，Lama1的作用尚不清楚。为了研究Lama1在中枢神经系统中的体内作用，我们与Eri Arikawa-Hirasawa博士合作，利用Sox2-CRE小鼠在上皮细胞系中产生了条件Lama1基因敲除(Lama1CKO)小鼠。这些Lama1CKO小鼠存活了下来，但表现出行为障碍和小脑形成障碍。脑膜软膜基底膜Lama1缺失导致脑膜构象缺陷。在小脑发育过程中，Lama1缺乏还导致颗粒细胞前体细胞增殖和迁移减少，Bergmann神经胶质纤维和终足结构紊乱，Akt活性一过性降低。在Lama1CKO小鼠中观察到浦肯野细胞中树突状突起的数量显著减少。综上所述，这些结果表明Lama1是小脑发育和功能所必需的。 在建立转基因小鼠以研究基底膜成分Perlecan的作用时，我们发现其中一个转基因品系的后肢出现了震颤。我们将该小鼠模型命名为FURUE(FRU/FRU)。随后，我们鉴定了FUUE突变是由Teneurin-4(Ten-4/ODZ4)基因的转基因插入引起的，Ten-4/ODZ4基因编码一种功能未知的跨膜蛋白。Ten-4在野生型小鼠脊髓中强表达，在正常的少突胶质细胞分化过程中被诱导。相比之下，FURUE组小鼠没有Ten-4的表达。在FUUE小鼠的脊髓中，小直径轴突的髓鞘形成显著减少，中枢神经系统中的少突胶质细胞的分化受到抑制。皮毛/皮毛小鼠的震颤表型主要见于后肢。皮毛/皮毛脊髓背柱皮质脊髓束和股薄束的髓鞘形成严重缺陷。皮质脊髓束是主要的运动束之一，由许多小直径轴突组成。股薄束是下半身感觉神经元的小直径轴突上升的区域。因此，皮质脊髓束和股薄束中小直径轴突的髓鞘形成缺陷可能是皮毛/皮毛小鼠后肢优势震颤的原因。在多发性硬化症患者中，脊髓皮质脊髓束和感觉束中的小直径轴突受到选择性损伤。因此，Ten-4可能在多发性硬化症中起重要作用。

Basement membranes are thin extracellular matrices that separate epithelial and mesenchymal cells, and surround cells such as endothelial, muscle, and neural cells. Basement membranes are the first extracellular matrix to appear in development and are critical for organ development and tissue repair. They not only provide the scaffold for cells and cell layers, but they also play an essential role in morphogenesis that affects cell adhesion, migration, proliferation, and differentiation. Basement membranes consist of collagen IV, laminin, perlecan, nidogen/entactin, and other molecules, and they interact with one another to form supramolecular structures. Laminins are a family of large multidomain glycoproteins that are usually specific to basement membranes. Laminins perform a variety of biological activities, including promotion of cell adhesion, migration, differentiation, tumor cell invasion, and interactions with matrix molecules and cell surface receptors. Laminin-1 (also called laminin-111) is a heterotrimeric extracellular matrix protein composed of α1, β1, and γ1 chains and is crucial for early basement membrane assembly, as well as embryonic implantation and development. Laminin-1 promotes neurite outgrowth in various neuronal cells, and several active sites in the α1 and γ1 chains for neurite outgrowth have been identified. Mouse embryos that are deficient in Lama1 lack Reichert's membrane and die by embryonic day 7. In the central nervous system, however, the role of Lama1 is unknown. To study the in vivo role of Lama1 in the CNS, we generated conditional Lama1 knockout (Lama1CKO) mice in the epiblast lineage using Sox2-Cre mice in collaboration with Dr. Eri Arikawa-Hirasawa. These Lama1CKO mice survived, but displayed behavioral disorders and impaired formation of the cerebellum. Deficiency of Lama1 in the pial basement membrane of the meninges resulted in defects in the conformation of the meninges. During cerebellar development, Lama1 deficiency also caused a decrease in the proliferation and migration of granule cell precursors, disorganization of Bergmann glial fibers and endfeet, and a transient reduction in the activity of Akt. A marked reduction in the number of dendritic processes in Purkinje cells was observed in Lama1CKO mice. Together, these results indicate that Lama1 is required for cerebellar development and function. During the creation of transgenic mice to study the role of perlecan, a basement membrane component, we found that one of the transgenic lines developed tremor in the hindlimbs. We designated this mouse model as furue (fru/fru). We subsequently identified that the furue mutation was caused by a transgene insertion into the teneurin-4 (Ten-4/Odz4) gene, which encoded a transmembrane protein of unknown function. Ten-4 was strongly expressed in the spinal cord of wild-type mice and was induced during normal oligodendrocyte differentiation. In contrast, the furue mice showed no expression of Ten-4. In the spinal cord of the furue mice, myelination of small diameter axons was dramatically reduced and differentiation of oligodendrocytes in the CNS was inhibited. The tremor phenotype in fur/fur mice was predominantly observed in the hindlimbs. The dorsal column of the fur/fur spinal cord showed severe defects in myelin formation in the corticospinal tract and fasciculus gracilis. The corticospinal tract is one of the major motor tracts and consists of many small diameter axons. The fasciculus gracilis is the region from which the small diameter axons of the lower body's sensory neurons ascend. Therefore, defects in myelination of small diameter axons in the corticospinal tract and the fasciculus gracilis are likely the cause of the hindlimb-dominant tremors in the fur/fur mice. In patients with multiple sclerosis, a dysmyelinating disease, small diameter axons are selectively damaged in the corticospinal and sensory tracts of the spinal cord. Ten-4 may therefore play an important role in multiple sclerosis.