Animal Development Process of development from a single cell to an entire multi-cellular organism

Animal Development Fertilization Cleavage Gametogenesis Gastrulation Organogenesis Neurulation

1: Fertilization Haploid egg and haploid sperm combine to form a diploid zygote. Eggs have 2 ways to block polyspermy Fast Block: Change in the electrical potential of the egg plasma membrane Slow Block: Creation of a ‘fertilization envelope’ that acts as a physical barrier keeping other sperm away from the fertilized egg

Vitelline Layer Plasma Membrane 1n

Fast Block to Polyspermy 1n

1: One sperm penetrates the egg

2: The plasma membrane changes its permeability and Na+ ions flood into the egg

3: The egg is now (+)-charged and repels the (+)-charged proteins on other sperm surfaces Na+ Na+ Na+ 1n 1n + Na+ Na+ + Na+

Slow Block to Polyspermy 1n

1: One sperm penetrates the egg

2: Cortical vesicles inside the egg fuse with the plasma membrane

2: The vesicles release enzymes into the space between the vitelline and plasma membranes

3: The enzymes break the bonds between the vitelline and the plasma membranes. Water floods the space between the two layers and the vitelline layer rises. 1n 1n

4: The vitelline layer hardens and becomes impermeable to sperm, thus forming the “fertilization envelope”. 1n 1n

The egg on the left is unfertilized, and has no envelope. In eggs like the sea urchin and starfish, the fertilization envelopes are visible as a halo around the egg. The egg on the left is unfertilized, and has no envelope. invert-embryo.blogspot.com

2: Cleavage & Blastulation Egg and sperm fuse to create a diploid single-celled zygote. The zygote goes through many rapid MITOTIC cell divisions resulting in a ball (or disc) of cells called a blastula www.wired.com www.cathylaw.com www.lifesci.ucsb.edu greenmicroscope.wordpress.com

The Blastula Through rapid divisions, the zygote develops into a blastula, a hollow ball (or disc) of cells The individual cells are referred to as blastomeres The empty space in the center is referred to as a blastocoel

Egg Type vs. Pattern of Cleavage Early development is affected by the amount and distribution of yolk in an egg Eggs with small amounts of evenly distributed yolk are called ISOLECITHAL Isolecithal eggs divide evenly through Holoblastic Cleavage

Egg Type vs. Pattern of Cleavage Eggs with large amounts of yolk concentrated at one end of the egg are called TELOLECITHAL. MODERATELY telolecithal eggs divide by Holoblastic Cleavage, but the size of the cells differs between the two poles as does the placement of the blastocoel. www.mainsgate.com

Holoblastic Cleavage in an Isolecithal egg vs Holoblastic Cleavage in an Isolecithal egg vs. a Moderately Telolethical egg Adapted from http://biology.kenyon.edu/courses/biol114/Chap13/blastula.gif

Meroblastic Cleavage Strongly Telolechithal eggs, like chicken eggs, have a large amount of yolk. The nucleus is surrounded by a very small area devoid of yolk called the Active Cytoplasm. These eggs divide by Meroblastic Cleavage: only the Active Cytoplasm divides and the blastula forms as a disc resting on the surface of the yolk.

Moderately Telolecithal Strongly Telolecithal Holoblastic Meroblastic Moderately Telolecithal Strongly Telolecithal Isolecithal http://locolobo.org/frog_egg.gif http://cas.bellarmine.edu/tietjen/AnimalDiversity/img3.gif http://www.eb.tuebingen.mpg.de/departments/3-genetics/zebrafish_embryo

3: Gastrulation Beginning of cell differentiation Characterized by cell migration, rather than division Results in a Gastrula which will eventually develop into the digestive tract of the organism The Gastrula is made up of 3 embryonic (or, germ) layers called the Endoderm, Ectoderm and Mesoderm.

3: Gastrulation Blastocoel 1)The surface cells of the Blastula begin to move into the inside of embryo through a process called INVOLUTION. Blastocoel http://upload.wikimedia.org/wikipedia/commons/3/31/Gastrulation.png

3: Gastrulation Remnant of Blastocoel 2)The inverted cells push into the blastocoel forming a new internal cavity, the ARCHENTERON Remnant of Blastocoel http://upload.wikimedia.org/wikipedia/commons/3/31/Gastrulation.png

3: Gastrulation Remnant of Blastocoel BLASTOPORE 2)The inverted cells push into the blastocoel forming a new internal cavity, the ARCHENTERON The opening of the Archenteron is called the BLASTOPORE Remnant of Blastocoel

3: Gastrulation 3) The resulting Gastrula has two embryonic (or, germ) layers: The ECTODERM on the outside, and The ENDODERM on the inside. http://upload.wikimedia.org/wikipedia/commons/3/31/Gastrulation.png

3: Gastrulation 3) The resulting Gastrula has two embryonic (or, germ) layers: The ECTODERM on the outside, and The ENDODERM on the inside. The Mesoderm will form later, between the Ecto- and Endo-derm layers.

3: Gastrulation BLASTOPORE ARCHENTERON 4) The Archenteron will eventually become the digestive tract and the blastopore either develops into the mouth or the anus. In the case of Deuterosomes, like the Sea Urchin, the Starfish and humans, it will become the anus. ARCHENTERON BLASTOPORE

Development in a Starfish You will use slides to examine the stages of development in a Starfish from Fertilization to Gastrula http://www.youtube.com/watch?v=GqM6a7ijocw&feature=related

4: Neurulation Neurulation only occurs in Chordates (all vertebrates and some closely related invertebrates) Forms the brain and nerve (spinal) cord

4: Neurulation The Process begins with the Ectoderm. Certain cells of the Ectoderm flatten into a long NEURAL PLATE ECTODERM NEURAL PLATE http://www.biog1105-1106.org/demos/106/unit03/media/neuralcrestdev.jpg

4: Neurulation The Neural Plate sinks and the edges of the ectoderm rise forming the Neural Groove and Neural Folds NEURAL GROOVE NEURAL FOLDS

4: Neurulation The Neural Folds approach each other, and fuse

4: Neurulation NEURAL TUBE The sides of the Neural Plate fuse and become the Neural Tube. The anterior end of this becomes the Brain and the posterior end becomes the spinal cord. NEURAL TUBE

Development in a Frog You will use slides to examine the stages of development in a Frog from Cleavage to Neurulation Note the differences in blastulation between the isolethical and telolethical eggs http://www.youtube.com/watch?v=dXpAbezdOho&feature=related

Development in the Zebrafish The Zebrafish has a very telolecithal egg Note how the Blastodisc forms like a cap on the surface of the yolk. Gastrulation is different from the frog. The blastula surface slides down and engulfs the yolk, which ends up inside the embryo In the live fish, observe the Somites, Nervous system (notochord and developing brain) and the circulatory system (beating heart and circulating blood) http://www.youtube.com/watch?v=l4hk6wI9avw