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The zebrafish embryo develops rapidly, with precursors to all major organs appearing within 36 hours of fertilization. The embryo begins as a yolk with a single enormous cell on top (see image, 0 h panel), which divides into two (0.75 h panel) and continues dividing until there are thousands of small cells (3.25 h panel).
Fish embryos go through a process called mid-blastula transition which is observed around the tenth cell division in some fish species. Once zygotic gene transcription starts, slow cell division begins and cell movements are observable. [ 4 ]
Epiboly in zebrafish is the first coordinated cell movement, beginning at the dome stage late in the blastula period and continuing throughout gastrulation. [3] At this point the zebrafish embryo contains three portions: an epithelial monolayer known as the enveloping layer (EVL), a yolk syncytial layer (YSL) which is a membrane-enclosed group of nuclei that lie on top of the yolk cell, and ...
Two species of fish, zebrafish (Danio rerio) and medaka (Japanese rice fish, Oryzias latipes), are most commonly modified because they have optically clear chorions (shells), develop rapidly, the 1-cell embryo is easy to see and micro-inject with transgenic DNA, and zebrafish have the capability of regenerating their organ tissues. [9]
GM fish are widely used in basic research in genetics and development. Two species of fish- zebrafish and medaka, are most commonly modified, because they have optically clear chorions (membranes in the egg), rapidly develop, and the 1-cell embryo is easy to see and microinject with transgenic DNA. [106]
This is the same in human embryos, where they are first detected at day 27 in the aorta gonad mesonephros region, expand rapidly at day 35, then disappear at day 40. This “disappearance” correlates to the migration of these hematopoietic stem cells to the foetal liver, where it becomes the subsequent site of haematopoiesis.
In seed plants, the embryo will develop one or more "seed leaves" . By the end of embryogenesis, the young plant will have all the parts necessary to begin its life. Once the embryo germinates from its seed or parent plant, it begins to produce additional organs (leaves, stems, and roots) through the process of organogenesis.
Zebrafish embryo 48 hours after fertilization. The arrows indicate four Rohon–Beard neurons. [1] Rohon–Beard cells are specialized neurons with mechanoreceptive properties. They occur during the embryonic stage of development and are found in the dorsal part of the spinal cord in fish and amphibians. [2]