6: Gastrulation and the Formation of the Primary Organ Rudiments
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germ layers are formed through cell movements is called
gastrulation
ectoderm forms
• epidermis of the skin • epithelium of the oral and nasal cavities • nervous system • sense organs
mesoderm forms
• muscle and connective tissue: bone • components of circulatory • urinary • genital systems
endoderm forms
• mucosal epithelium • glands of respiratory • glands of digestive
Gastrulation came from greek means
gastrula meaning “belly” or “little stomach”
a diagram of an egg or blastula, indicating the fate of each cell or region, at a later stage of development
Fate Maps
analysis of the fate of each blastomere after first and second cleavage is called
cytogeny or cell lineage study
the first fate maps date back to the 1880s and in 1905 the first comprehensive collection of Ascidian (sea squirt) fate maps was published by
Edwin Conklin
importance of fate maps • essential tool in most embryological experiments • provide researchers with information on which portions of the embryo will normally become which larval or adult structure • way of tracing a particular region as it develops from an early embryo into a differentiated body plan • understanding an organism’s developmental pathway • understanding the lineage and migration of progenitor cells can lead to the discovery of _ • determining the function of each specific region
gene regulatory networks and signaling pathways
Construction of Fate Map by following methods
• Observing Living Embryos/ Natural Markings • Vital Dye Marking/ Vital Staining • Carbon Particle Marking • Radioactive (Isotope) Labelling and Fluorescent Dyes
radioactive isotope such as _ are used to label the early blastomeres
C14 and P
Carbon Particle Marking - s introduced by
Spratt (1946)
A sort of “mark” can be made on, or inside the egg or embryo using agents such as:
a. charcoal b. dye c. soot d. fluorescent molecules (rhodamine-conjugated dextran) e. proteins like green fluorescent protein (GFP) f. enzymes encoded by injected genes or mRNAs
one way of making the fate map is by staining the various parts of the early embryo with a lipophilic dye such as _ and observe where the labelled regions end up
dil
another sophisticated way of labelling the blastomeres is by injection of high molecular weight molecules such as _ , which cannot pass through cell membrane and are, therefore, **restricted to the injected cell ** and its progeny
rhodamine-labelled dextran these cells can be easily detected later, under a UV microscope