Developmental Biology Final

• Amniote vertebrates


  Extra embryonic membranes: Amnion, chorion, allantois, and yolk sac
• Fertilization


  1. Cortical rotation

  2. Cleavage - starts at animal pole
• Blastocoel


  Migration and separation of animal and vegetal cells
• Mid-blastula transition


  1. Activation of the embryos genome - late in 12th cycle in Xenopus

  2. Gap phases added to mitosis
• amphibians and fish

  • No one specific way they gastrulate
  • Begins in marginal zone - equatorial region
  • Cells of blastocoel floor move up toward the roof
  • Vegetal rotation and invagination of bottle cells - deep vs. superficial cells
  • Superficial - ectoderm and endoderm
  • Deep - mesoderm (can be superficial)
  • Point opposite sperm entry - region of the gray crescent
• Noggin, chordin, BMPs, cerberus


  Factors involved in gastrulation
• Amphibians


  • Undergo external fertilization
  • Eggs laid in water, sperm released over them
  • Cleavage forms a hollow ball of cells called a blastula
  • Gastrulation reorganizes blastula into 3 germ layers
  • Organogenesis forms organs and tissues
  • Metamorphosis transforms larval tadpoles into adults
• Fish


  • Undergo external fertilization in water
  • Cleavage forms a blastula
  • Gastrulation establishes 3 germ layers
  • Neurulation forms neural tube
  • Organogenesis forms organs and tissues
  • Many have distinct larval stages
• Fish cleavage


  • Telolecithal
  • Meroblastic
  • Blastodisc - discoidal cleavage
  • Alternating meridional and equatorial cleavage
  • 12 rapid divisions - blastoderm on the yolk cell
  • Syncytial at the base
• Model species - Fish


  Zebra fish
• Birds


  • Undergo internal fertilization
  • Cleavage forms a blastoderm on top of the yolk
  • Develop extraembryonic membranes (amnion, chorion, allantois)
  • Organogenesis forms organs and tissues
• Mammals


  • Undergo internal fertilization
  • Cleavage forms a blastocyst
  • Implantation of blastocyst into uterus
  • Gastrulation reorganizes blastocyst into 3 germ layers
  • Organogenesis forms organs and tissues
  • Placenta supports embryo/fetus
• Teratogen


  An agent or factor that can disrupt normal embryonic/fetal development, leading to birth defects
• Alcohol as a teratogen


  Alcohol can interfere with gene expression involved in critical developmental pathways
• Glyphosate (Roundup) treatment reduced Sonic hedgehog (Shh) expression in chick embryos
• Gain of function experiment to restore Shh expression in Glyphosate exposed embryos


  1. Obtain fertilized chicken eggs

  2. Treat experimental group with glyphosate

  3. Introduce exogenous Shh proteins into embryos using microinjection or electroporation

  4. Monitor Shh expression using in situ hybridization and immunohistochemistry

  5. Analyze phenotypic outcomes and compare between groups
• Diethylstilbestrol (DES)


  Synthetic estrogen that disrupted female reproductive tract development
• Effects of DES on female rodents


  • Reproductive tract abnormalities
  • Reduced fertility
  • Increased ectopic pregnancies
  • Increased reproductive tract cancer risk
• Experiment to investigate substance in alien soda can causing infertility


  1. Identify and isolate the substance

  2. Establish control group

  3. Expose groups to different concentrations of the substance

  4. Monitor exposed groups and control for reproductive health and offspring development

  5. Perform histological and molecular analyses
• Temperature-dependent sex determination (TSD)


  • Mechanism where the sex of an organism is determined by the temperature during a critical period of embryonic or larval development
  • Common in many reptile species, such as turtles, crocodiles, and alligators
• Phenotypic plasticity


  The ability of an organism to change its phenotype (morphology, physiology, or behavior) in response to environmental cues or stimuli
• Yellow crescent/fate mapping
• Tools - immunohistochemistry, antibodies, cDNA libraries, CRISPR, in-situ hybridization
• Hans Speeman - inductive interactions in regulative development
• Hans Speeman and Hilde mangold - primary embryonic induction

  They transplanted a group of cells from the dorsal lip of the blastopore (a region known as the "organizer") from an early gastrula embryo of a newt into the ventral side of another newt embryo. The result was the formation of a second, complete embryonic body axis, including a notochord, neural tube, and somites
• Dorsal blastopore lip transplantations
• Induction of neural ectoderm and dorsal mesoderm: BMP inhibitors
• Syncytial cleavage pattern - drosophila 

  Fish cleavage pattern - discoidal 

  Chick cleavage pattern - discoidal 

  Mammal cleavage pattern - rotational 

  Frog cleavage pattern - radial 

  Fish yolk descriptor - telolecithal 

  Chick yolk descriptor - telolecithal 

  Mammal yolk descriptor - isolecithal 

  Frog yolk descriptor - telolecithal 

  Fish cleavage extent - meroblastic 

  Chick cleavage extent - meroblastic 

  Mammal cleavage extent - holoblastic

  Frog cleavage extent - holoblastic
• The first cell division in the frog embryo occurs at the animal pole (animal hemisphere) while the second cell division occurs at the vegetal pole (vegetal hemisphere). This results in an unequal distribution of cytoplasmic components between the two daughter cells.
• Telolecithal eggs have one large yolk mass located on one side of the egg, resulting in asymmetrical cleavage patterns.
• Cleavage patterns can be classified based on their shape, such as syncytial or radial.
• Yolk descriptors refer to the location of the yolk within the egg, with telolecithal eggs having most of the yolk concentrated at one end and isolecithal eggs having evenly distributed yolk throughout the egg.
• Isolecithal eggs have evenly distributed yolk throughout the entire egg, leading to symmetrical cleavage patterns.
• Meroblastic cleavage involves only part of the zygote undergoing mitosis, leaving some unfertilized ooplasm behind.
• Holoblastic cleavage involves all parts of the zygote undergoing mitosis, with no unfertilized ooplasm remaining.
• Cleavage refers to the process by which a fertilized ovum divides into smaller cells through mitosis.
• Yolk location within the egg can also influence cleavage patterns, with telolecithal eggs having more asymmetry compared to isolecithal eggs.
• There are three main types of cleavage: syncytial, discoidal, rotational, radial, and holoblastic.
• Syncytial cleavage involves multiple nuclei within a single cytoplasm.
• During gastrulation, the blastula undergoes invagination, forming a three-layered structure called the gastrula.