Snake yolk sac as a site for in vivo organ incubation: A new method in the research of snake embryo development

The snake embryo yolk sac served as a culture medium for the development of isolated reptilian organs. Isolated upper jaws of Natrix tessellata and Vipera palaestinae embryos at the early stages of jaw organogenesis were implanted into the yolk, close to the yolk sac blood vessels of Natrix tessellata embryos in order to determine natural conditions for long‐term incubation of organ culture. Tissues were incubated in the yolk for approximately 1 month until 1 day before host embryo hatching. Histological inspection showed full morphological differentiation of all tissues including scales, bones, teeth, glands, and connective tissue. The biochemical marker phosphodiesterase showed the typical developmental pattern in the main oral gland, Duvernoy's gland, and was comparable to the same gland in the host embryo. Vipera implants developed almost normally, except for differentiation of the skin which remained in the stage of one to two cell undifferentiated layers. Natrix was chosen for these experiments owing to the special chemical composition of its yolk that allows the penetration of blood vessels. This characteristic is probably crucial for the success of angiogenesis, which in turn is an essential condition for tissue survival. The ability of the yolk to support normal differentiation of isolated organs provides a valuable tool for the long‐term incubation experiments that are indispensable in order to achieve maximal tissue differentiation. © Wiley‐Liss, Inc.