Presentation on theme: "Jamie Gunnarson and Jena Arne"— Presentation transcript:
1Jamie Gunnarson and Jena Arne Cell Movements of Early Zebrafish Development and Important Signaling PathwaysNote-this is actually a mouse embryoJamie Gunnarson and Jena ArneAll images are taken from S. Gilbert, “Developmental Biology, 8th edition, Sinauer and Associates
2zebrafish from the one-cell zygote to vertebrate embryo EmbryogenesisEarly development ofzebrafish from the one-cell zygote to vertebrate embryo
4Cleavage StageThe fertilized egg undergoes synchronous cleavage. This egg is telolecithal, meaning only a small region is free of yolk. This yolk-free region is termed the blastodisc and divides by meroblastic, discoidal cleavage.
5Blastula Stage Mid-Blastula Transition Blastula stages begin at the eighth division (128 cell stage). The pulsing characteristic of synchronous division stops and asynchronous division begins. At this point transcription of the zygotic genome begins. Between the ninth and tenth division, the Yolk Syncytial Layer (YSL) is formed by the fusion of cells with yolk.
6Blastula Stage continued The blastomeres begin to mix randomly and mixing continues through late gastrulation. Dorsal YSL begins to express the nodal signal Squint when nuclear beta-catenin accumulates.
7Blastula Stage Fate map The mixing of the cells finally allows for fate mapping during late-blastula.Text
8Blastula Stage Late Blastula VentralDorsalVegetal PoleNodalAnimal PoleAll embryonic cells undergo epiboly driven by the expansion of the YSL. The outermost layer of blastomeres (the enveloping layer) surrounds the yolk cell.Marginal blastomeres express Znr proteins (squint and cyclops) creating a nodal gradient causing different cell fate specification. Cells with very high nodal become prechordal plate, while cells with decreased nodal become notochord.
9Gastrulation Embryonic Shield Formation Cells undergo dorsal convergence to form the embryonic shield. This structure organizes gastrulation. The embryonic shield secretes nodal which sets up the dorsal-ventral gradient, in which high nodal produces dorsal structures and low nodal produces ventral structures.
10Gastrulation Mesendoderm Formation Cells of the embryonic margin begin to involute, giving rise to the mesendoderm. These specified cells involute to form the inner cell layer (hypoblast).Cells of the embryonic margin begin to involute, giving rise to the mesendoderm. These specified cells involute to form the inner cell layer (hypoblast).
11Gastrulation D/V Axis Formation by BMP Inhibitors VentralDorsalVegetal PoleAnimal PoleBMPBMP is high on the ventral side and turned off on the dorsal side by the BMP inhibitors Noggin, Chordin, and Follistatin. Inhibitors are expressed from the embryonic shield, and cell fates are specified along the dorsal-ventral axis.
12Gastrulation Anterior-Posterior Axis Formation The anterior-posterior axis is formed by involution. The first cells to involute make anterior structures and the last cells to involute make posterior structures.
13Gastrulation Convergent Extension Mesendoderm and ectoderm converge to the dorsal side and extend along the anterior-posterior axis.Convergent extension, epiboly and involution occur at the same time.Courtesy of Dr. Jennifer Liang Spring 2010
24AnswerEpiboly is driven by the expansion of the YSL and causes the enveloping layer to surround the yolk.
25Question 6Which structure secretes nodal and how does this signal affect dorsal-ventral axis formation?
26AnswerThe embyronic shield secretes nodal. Regions with high nodal produce dorsal structures and regions with low nodal produce ventral structures.
27Question 7Which cells involute to form the inner cell layer (hypoblast)?
28AnswerMesoderm and endoderm, termed mesendoderm cells, involute to form the inner cell layer and are derived from the embryonic margin.
29Question 8Explain the role of BMP inhibitors in dorsal- ventral axis formation.
30AnswerThe role of BMP inhibitors in dorsal-ventral axis formation is to turn off BMP signaling. This occurs on the dorsal side, thus causing BMP to accumulate on the ventral side, forming ventral structures.
31Question 9Which cell movement is responsible for anterior-posterior axis formation? Explain how this occurs.
32AnswerInvolution is responsible for anterior-posterior axis formation. The first cells to involute give rise to anterior structures and the last cells to involute give rise to posterior structures.
33Question 10What occurs during convergent extension?
34AnswerDuring convergent extension all germ layers converge to the dorsal side of the developing embryo and extend along the anterior- posterior axis.