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| Unit 3: Demos |
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Operon Tutorial Positive v. negative control of prokaryotic gene transcription Transcription of eukaryotic vs. prokaryotic genomes (6c) How Does Methylation Control Synthesis of Proteins? optional: Diagram showing how Dolly was made (from
Liem et al. Functional Anatomy of the Vertebrates, 3rd ed.) Yolk content and cleavage in human eggs (14c) Notochord
development (16a) Comparative development (17b) Determinate v. indeterminate cleavage & embryonic induction Unit 3 Slides (accompanying text can be found in your Survival Manual on pages 57-59.) |
Neural Crest Cells Although derived from ectoderm, the neural crest has sometimes been called the “fourth germ layer” because of its importance. Neural crest cells have also been considered the developmental factors (along with input from Hox genes) that “make humans human” because of their role in determining facial structure. Neural crest cells are unique to vertebrates and give rise to a variety of important structures in the adult body. Their name suggests their origin. As neurulation proceeds and the neural tube begins to form, neural crest cells are groups of cells positioned on the top (dorsal) edges of the forming neural folds (see diagram below). Once the neural tube has formed and invaginated, the neural crest cells form a distinct population of cells resting on top of (just dorsal to) the neural tube. These cells will migrate away along defined routes to a number of locations as development proceeds. In the end, neural crest cells form a wide array of different cell types including skin pigment cells (melanocytes and others), neurons of the dorsal root ganglia of spinal nerves, the autonomic nervous system (both sympathetic and parasympathetic ganglia - think about the paths these nerves take from the spinal cord to their target organs? These paths are formed during the initial migration of the neural crest cells away from the nerve tube), Schwann cells responsible for myelination of peripheral nerves, and the adrenal medulla - which is so intimately connected to the sympathetic nervous system via hormonal signaling with epinephrine and norepinephrine. Neural crest cells are also important in the head - forming some bones and cartilage in the lower jaw as well as portions of the eyes, ears, and teeth.
Neural crest cells. Successive stages of amphibian neurulation diagrammed in transverse sections. Each of the drawings shows the neural ectoderm, the epidermal ectoderm, and the neural crest. When the neural folds fuse, they close the neural tube under a continuous layer of epidermis. The cells originally located at the crests of the neural folds, known as neural crest cells, then come to lie on top of the neural tube, from where they migrate to different locations and have a wide variety of fates. Figure 13.22 from K. Kalthoff. 2001. Analysis of Biological Development. McGraw Hill, Boston.
Fig. 34.7 from Campbell 7th Edition
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