Development of the iris in the chicken embryo. I. A study of growth and histodifferentiation utilizing immunocytochemistry for muscle differentiation.
The development of the iris was studied in chicken embryos from 4 days of incubation through hatching and in chicks up to 17 days posthatching. Serial sections of the eye were stained routinely or by immunocytochemical methods using myosin antiserum to enhance detection of differentiating muscle by light microscopy. Eyes from embryos at each stage were also examined by scanning electron microscopy. Outgrowth of the iris occurs in a sequential pattern around the eye, beginning at 6 1/2 days of incubation in the region temporal to the choroid fissure and proceeding around the eye. Since differentiation of the iris follows the same pattern, similar areas of the iris were compared at each stage of development. At 6 1/2 days of incubation, pigment granules can be seen in the anterior epithelium at the root of the iris, but it is not until 8 days of incubation that pigment is identified in the same area of the posterior epithelium. As development proceeds, the pigmentation of both epithelial layers progresses from the root of the iris to the pupillary margin. Early features of the development of the sphincter muscle can first be recognized in the 7-day embryo, when epithelial buds form from the anterior epithelium adjacent to the pupillary margin. Cells from these buds detach from the epithelium and populate the entire irideal stroma; these cells are the precursors of the sphincter muscle. The epithelial buds increase in size and distribution, and coalesce into a continuous ridge of cells around the iris by 10 days of incubation. The first muscle cells differentiate at 11 days of incubation when striated fibres can be identified by immunocytochemistry. The first striated fibres of the dilator muscle are seen in the 13-day embryo. Differentiation of the dilator muscle begins near the root of the iris and proceeds toward the pupillary margin, ultimately arising from the entire anterior epithelium except near the pupillary margin. Further differentiation of the sphincter and dilator muscles continues throughout incubation and for several weeks beyond hatching.
D000818:Animals; D002454:Cell Differentiation; D002642:Chick Embryo; D002645:Chickens; D007124:Immunoenzyme Techniques; D007498:Iris / Q000196:embryology* / Q000254:growth & development / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D024510:Muscle Development; D009132:Muscles / Q000196:embryology* / Q000648:ultrastructure; D010857:Pigment Epithelium of Eye / Q000196:embryology / Q000648:ultrastructure