NEURULATION INDUCTION Neural plate stage http www lawrence

NEURULATION & INDUCTION

Neural plate stage http: //www. lawrence. edu/dept/biology/embryoatlas/Frognpltneurula 2. jpg

Neural Fold Stage - Amphibian Pictures from digital lab manual

Neural Tube Stage - Amphibian Picture from digital lab manual

Neural Fold Stage - Aves (Birds) Picture from digital lab manual Neural Tube Stage - Aves (Birds) Picture from digital lab manual

Neurulation movie from digital lab manual

Neurulation - Amphibian Movie of frog neurulation from digital lab manaul http: //www. esb. utexas. edu/kalthoff/bio 349/Wallingford_MOVIE 1. mov

Neurulation - Aves (Birds) Whole mount pictures of 24 hr and 33 hr chick embryo from web links below http: //www. uoguelph. ca/zoology/devobio/210 labs/33 hrwm. htm http: //www. uoguelph. ca/zoology/devobio/210 labs/24 hrwm. htm

Neurulation - Aves (Birds) Movie of chick neurulation. Time-lapse movie (1 frame every 15 min. ) of early chicken development showing neurulation.

Terminology Totipotent cell - a cell that has the ability to form a complete organism through embryogenesis (e. g. the zygote, one of the first two blastomeres formed during cleavage in frogs or mammals). Pleuripotent cell - a cell that has the ability to differentiate into any type of tissue if exposed to the appropriate chemical signals (e. g. stem cells derived from the inner cell mass of an early mammalian embryo). Multipotent cell - a cell that has the ability to differentiate into a limited number of tissue types if exposed to the appropriate chemical signals (e. g. stem cells obtained from adult tissues)

Induction and Neurulation - The Classic Story

Perhaps the first recorded example of induction

Induction Definitions 1. Dictionary - Production of an effect elsewhere than at the original locus of activity. 2. Developmental Biology text - The ability of one tissue to influence the fate of nearby cells. . . by a chemical signal (Purves and Lichtman, 1985) 3. Developmental Biology text - The process whereby an inducing tissue interacts with a responding tissue, causing the tissue to differentiate (Oppenheimer and Lefevre Jr. , 1984)

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Spemann and Mangold, 1924. http: //www. hhmi. ucla. edu/derobertis/

Morphogen A substance secreted by one group of cells that influences the differentiation of another group of cells. Morphogens are chemical factors that regulate the expression of genes during development. This regulation may be direct or indirect.

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“Over the next three quarters of a century, vigorous searches have been made to identify the molecules liberated by the organizer that induce overlying cells to become nerve tissue. One candidate after another has been put forward and then found not to be responsible. Part of the problem has been that not until just recently has it become clear that the organizer does NOT induce the central nervous system but, instead, it prevents signals originating from the ventral side of the blastula from inducing skin (epidermis) there. This is how it works: ”

MODERN RESEARCH ON NEURULATION & INDUCTION 23

Unfortunately, simplicity is not the answer. Proteins secreted by dorsal (Spemann organizer) or ventral gastrula signaling centers and neurulation http: //www. hhmi. ucla. edu/derobertis/ Dorsal gastrula signaling center Spemann organizer = cells of grey crescent region Ventral gastrula signaling center 24

• Bone Morphogenetic Protein-4 ( BMP-4 ) and other proteins are secreted by the ventral gastrula signaling center. • BMP-4, as well as some other proteins, bind to receptors on ectodermal cells and induce them to become epidermis. • If the activity of BMP-4 is blocked, ectoderm will follow the default pathway and differentiate into central nervous system structures. Picture from web link below. • Cells in the dorsal gastrula signaling center secrete the proteins chordin and noggin. • Chordin and noggin bind to BMP-4 in the region where the neural plate forms and block its activity, thus freeing the presumptive neural ectoderm to follow the central nervous system pathway of differentiation. http: //users. rcn. com/jkimball. ma. ultranet/Biology. Pages/S/Spemann. html