Heterochromia (also known as a heterochromia iridis or heterochromia iridium) is an ocular condition in which one iris is a different color from the other iris (complete heterochromia), or where the part of one iris is a different color from the remainder (partial heterochromia or sectoral heterochromia). It is a result of the relative excess or lack of pigment within an iris or part of an iris, which may be inherited or acquired by disease or injury. This uncommon condition usually results due to uneven melanin content. A number of causes are responsible, including genetic, such as chimerism, Horners Syndrome and Waardenburg syndrome.
Depictions of chick developmental anatomy. (A) Dorsal view (looking “down” at what will become the back) of a 2-day chick embryo, as depicted by Marcello Malpighi in 1672. (B) Ventral view (looking “up” at the prospective belly) of a chick embryo at a similar stage, seen through a dissecting microscope and rendered by F. R. Lillie in 1908. (C) Eduard d’Alton’s depiction of a later stage 2-day chick embryo in Pander (1817). (D) Modern rendering of a 3-day chick embryo. Details of the anatomy will be discussed in later chapters. (A from Malpighi 1672; B from Lillie 1908; C from Pander 1817, courtesy of Ernst Mayr Library of the Museum of Comparative Zoology, Harvard; D after Carlson 1981.)
Primary neurulation: neural tube formation in the chick embryo. (A, 1) Cells of the neural plate can be distinguished as elongated cells in the dorsal region of the ectoderm. Folding begins as the medial neural hinge point (MHP) cells anchor to notochord and change their shape, while the presumptive epidermal cells move towards the center. (B, 2) The neural folds are elevated as presumptive epidermis continues to move toward the dorsal midline. (C, 3) Convergence of the neural folds occurs as the dorsolateral hinge point (DLHP) cells become wedge-shaped and epidermal cells push toward the center. (D, 4) The neural folds are brought into contact with one another, and the neural crest cells link the neural tube with the epidermis. The neural crest cells then disperse, leaving the neural tube separate from the epidermis. (Photographs courtesy of K. Tosney and G. Schoenwolf; drawings after Smith and Schoenwolf 1997.)
Findings Point to Clues for Regenerative Therapies
June 25, 2009 - In a new study, published this week in Science, researchers investigated a trio of cell-signaling pathways that work simultaneously, converging to direct pancreas and liver progenitor cells to mature into their final state. They looked at how BMP, TGF-beta, and FGF signaling pathways turn on genes that guide cells to ultimately become pancreas or liver tissue.
The Science paper addresses how chemical signals from neighboring cells in the embryo tell early progenitor cells to activate genes encoding the regulatory proteins. The regulatory proteins, in turn, guide the cells to become a liver cell or a pancreas cell. “In the current study we mapped the signaling pathways being turned on before they connected with the target genes,” explains Zaret. “We monitored these cues before the cell displayed any overt signs of differentiation. While my lab and others had previously looked at individual signals that influence development, in this paper we simultaneously mapped three signal paths that converge to induce liver and pancreas cells. We’re starting to construct a network of the common signals that govern development of these specific cell types. The complexity of this system is somewhat like our 26-letter alphabet being able to encode Shakespeare or a menu at a restaurant.” (found on Penn Medicine)
Picture : Distribution of the genetic regulatory protein, Smad4, in a mouse embryo at 8.5 days gestation. The green stain in the center is Smad4 expressed in the liver and pancreas progenitor cells. The green on the periphery is Smad4 in the extraembryonic yolk sac tissue.
Credit: Ken Zaret, PhD; Ewa Wandzioch, PhD, University of Pennsylvania School of Medicine
Human Development Timeline
Heterotopic Tissue Recombination Assay
This assay is used to demonstrate that ectoderm-derived mesenchyme, when combined with epithelium from another organ, directs organogenesis for ectoderm-derived appendages (mammary gland, tooth, hair follicle, salivary gland).
via Jiménez-Rojo et al., 2012
Chick embryo intestine (20X)
(embryos are so cool you guys)