Save Sight Institute, The University of Sydney, Sydney, NSW, 2000, Australia; Developmental Neurobiology Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, 904-0495, Japan; Molecular Cellular Biology Laboratory, Yokohama City University Graduate School of Medical Life Science, Tsurumi-ku, Yokohama, 230-0045, Japan.
Developmental Neurobiology Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, 904-0495, Japan.
Exp Eye Res. 2024 Nov;248:110066. doi: 10.1016/j.exer.2024.110066. Epub 2024 Sep 2.
The eye lens contains convexly curved fiber cells that align in concentric layers around the lens anterior-posterior pole axis. For lens fiber differentiation at the equator, cells elongate with their apical and basal tips migrating towards the anterior and posterior poles, respectively. At each pole, the fiber tips meet opposing tips of other fiber cells, to form a suture. Although umbilical or point sutures are observed in fish and birds, line, Y- or star-shaped sutures are detected in other vertebrate lenses. Sutures that do not converge at the point are thought to result from intricate movements of the fiber tips, rather than a straightforward migration along a meridional path. The triggers that give rise to these variations are currently not understood. Our findings revealed that in the mouse embryo, the early-stage lens contains only concave curved fibers, and later, a zone of concave-to-convex curve conversion develops. At this point, a nascent suture in a linear shape appears at the posterior pole and subsequently progresses into a V-shape. This V-shape appears to further develop into a Y-shape as a branch extends from the apex of the V-shape. In lens of zebrafish and Xenopus larvae that form point sutures, this curve-conversion zone is not observed. In lens of adult birds (e.g. zebra finch) that form a point suture, these too also lack a curve-conversion zone. In our previous studies, we demonstrated that murine lens fibers undergoing curve conversion extend membrane protrusions, or lamellipodia, at their basal membranes. In line with this, we did not observe protrusions at the basal tips of fibers in the non-mammalian lenses of zebrafish, Xenopus, and zebra finch in which curve conversion does not occur. We propose that the concave-to-convex conversion in rodent lenses introduces defined paths for fiber cell tips, leading to a more elaborate and complex suture formation, compared to the simple point suture of lower vertebrates.
晶状体包含凸面弯曲的纤维细胞，这些细胞沿晶状体前后极轴以同心层排列。为了在赤道处进行晶状体纤维分化，细胞伸长，其顶端和基底逐渐向前后极迁移。在每个极部，纤维尖端与其他纤维细胞的对侧尖端相遇，形成缝线。虽然在鱼类和鸟类中观察到脐状或点状缝线，但在其他脊椎动物的晶状体中检测到线状、Y 形或星形缝线。不汇聚在一点的缝线被认为是纤维尖端复杂运动的结果，而不是沿着子午线直接迁移的结果。导致这些变化的触发因素目前尚不清楚。我们的研究结果表明，在小鼠胚胎中，早期晶状体只包含凹面弯曲的纤维，随后会出现一个凹面到凸面曲线转换的区域。此时，在后端会出现一条线性的初生缝线，随后逐渐变成 V 形。随着 V 形从尖端延伸出一个分支，这个 V 形似乎进一步发育成 Y 形。在形成点状缝线的斑马鱼和非洲爪蟾幼虫的晶状体中，没有观察到这种曲线转换区。在形成点状缝线的成年鸟类（如斑胸草雀）的晶状体中，也没有观察到这种曲线转换区。在我们之前的研究中，我们证明了正在进行曲线转换的小鼠晶状体纤维在其基底膜上延伸出膜突，即片状伪足。与此一致，我们在没有发生曲线转换的非哺乳动物晶状体中，如斑马鱼、非洲爪蟾和斑胸草雀的晶状体中，没有观察到纤维基底尖端的突起。我们提出，在啮齿动物晶状体中，从凹面到凸面的转换为纤维细胞尖端引入了明确的路径，导致缝线的形成更加精细和复杂，与低等脊椎动物的简单点状缝线相比。
