McMenamin P G, Krause W J
Department of Anatomy and Human Biology, University of Western Australia, Nedlands.
J Anat. 1993 Oct;183 ( Pt 2)(Pt 2):343-58.
Marsupials are unique models for developmental biology-oriented research because of the immature state of their development at birth. The North American opossum (Didelphis virginiana) has several advantages over other marsupials, including large litter size, short prenatal period (12.5 d), an extended postnatal period while accessible in the pouch, and its ability to reproduce reliably in captivity. Studies of ocular development in this species have not been reported previously. The aim of the present investigation was therefore to document the major landmarks in prenatal and postnatal development of the cornea, lens, iris, ciliary body and retina. Fifteen embryos (10.5, 10.7 and 11 d postconception and 6 h after birth [12 d]) were studied by paraffin histology. Eyes of pouch young at 8 d, 2, 6, 9 and 13 wk were studied by transmission electron microscopy and light microscopy. The study revealed a similar pattern of ocular development in Didelphis to other metatherian and eutherian mammals. Differentiation of the eye is particularly rapid in the 2 d before birth. For example, although the lens vesicle separates from the surface ectoderm on d 10, by birth (2.5 d later) a primitive cornea and fused eyelids have formed, presumably to protect the eye during migration to the pouch. At birth the retinal pigment epithelium (RPE) contains melanin; however, the inner layer of the optic cup does not differentiate into an inner and outer neuroblastic layer until 8 d after birth. Around 6 wk after birth most components of the adult eye are identifiable, albeit in an immature form. These include the corneal layers, the iris (including the sphincter pupillae), ciliary processes, RPE tapetum, and a fully laminated retina with immature photoreceptors. A knowledge of the timing of major events in eye development in Didelphis and their comparison with equivalent events in human eye development should allow the appropriate choice of stages for any future experimental studies utilising this marsupial species.
有袋类动物是发育生物学导向研究的独特模型，因为它们出生时发育处于未成熟状态。北美负鼠（弗吉尼亚负鼠）相较于其他有袋类动物具有多个优势，包括产仔数多、孕期短（12.5天）、产后在育儿袋中可接触的时间长，以及能够在圈养环境中可靠繁殖。此前尚未有关于该物种眼部发育的研究报道。因此，本研究的目的是记录角膜、晶状体、虹膜、睫状体和视网膜在产前和产后发育的主要标志性事件。通过石蜡组织学研究了15个胚胎（受孕后10.5、10.7和11天以及出生后6小时[12天]）。通过透射电子显微镜和光学显微镜研究了育儿袋幼崽在8天、2、6、9和13周时的眼睛。研究发现，弗吉尼亚负鼠的眼部发育模式与其他有袋类和真兽类哺乳动物相似。在出生前2天，眼睛的分化尤为迅速。例如，尽管晶状体泡在第10天与表面外胚层分离，但到出生时（2.5天后），原始角膜和融合的眼睑已经形成，大概是为了在迁移到育儿袋的过程中保护眼睛。出生时，视网膜色素上皮（RPE）含有黑色素；然而，视杯内层直到出生后8天才分化为内、外神经母细胞层。出生后约6周，成年眼睛的大多数组成部分都可辨认，尽管其形态尚未成熟。这些组成部分包括角膜各层、虹膜（包括瞳孔括约肌）、睫状突、RPE反光层，以及具有未成熟光感受器的完全分层视网膜。了解弗吉尼亚负鼠眼睛发育主要事件的时间安排，并将其与人类眼睛发育中的相应事件进行比较，应该能够为未来利用这种有袋类动物进行的任何实验研究选择合适的阶段。
