Frog Development

• Overview of the Frog Development

  Gametogenesis

  Mating

  Fertilization

  Cleavage

  Morulation

  Blastulation

  Gastrulation

  Organogenesis
• Gametogenesis

  Structure: small, elongated, and typically have a streamlined shape

  Size: smaller than frog eggs and require a microscope to be seen

  Mobility: highly motile, equipped with a flagellum for propulsion

  Function: to fertilize the frog eggs

  Composition: contains genetic material in the form of DNA, as well as enzymes (acrosome) to aid in penetration of the egg's protective jelly

  Production: produced in the testes of male frogs and released during the breeding season when they enter the female's cloaca during amplexus (the mating embrace)

  
• Gametogenesis

  b. Egg

  Structure: also known as ova or oocytes, are large, spherical cells

  Size: relatively large, often visible to the naked eye

  Protection: encased in a jelly-like substance that provides protection and support.

  Composition: composed of cytoplasm, which contains nutrients and organelles.

  Function: non-motile and serves as the female gametes, waiting to be fertilized by sperm
• In egg, animal pole is located in Upper hemisphere of the egg or embryo
• in egg, vegetal pole is located in Lower hemisphere of the egg or embryo
• cytoplasmic components of animal pole

  Higher concentration; metabolically active; less yolk
• cytoplasmic components of vegetal pole

  Lower concentration; metabolically less active; more yolk
• Animal pole: associated embryonic layer

  Ectoderm (outer tissues, e.g., skin, nervous system)
• Vegetal pole: associated embryonic layer

  Endoderm (inner tissues, e.g., digestive organs)
• just read

  
• Mating

  Amplexus

  distinctive behavior in frog mating where the male frog grasps the female from behind in a tight embrace 

  helps to position the male's cloaca (a reproductive opening) close to the female's cloaca for efficient sperm transfer
• Fertilization

  External fertilization

  the male releases sperm into the water

  as the female releases her eggs, they are fertilized externally

  the male's sperm fertilizes the eggs as they are laid (ponds or streams)
• Cleavage

  series of successive mitotic divisions

  after successful fertilization, the frog egg undergoes its first cleavage, dividing into two equal-sized blastomeres (individual cells formed during cleavage)

  cleavage continues, a gray crescent forms (marks the future location of the notochord and nervous system)

  undergo rapid cleavage with successive cell divisions

  divisions are holoblastic, which means that the entire egg is divided into smaller blastomeres

  frog egg is mesolecithal, yolk is moderately distributed throughout the egg
• Just read

  
• Morulation

  Morula

  compacted mass of blastomeres

  composed of a tightly packed cluster of cells and lacks a central fluid-filled cavity (blastocoel)

  the gray crescent, a key developmental marker, remains positioned on the dorsal side of the morula

  important for establishing the future dorsal-ventral axis and specifying tissue differentiation during later development

  mulberry shape stage
• Stage: Morulation

  
• Stage: Blastulation

  
• Blastulation

  Blastula

  a small central fluid filled cavity or space appears within an embryo, called blastocoel or segmentation cavity

  the embryo appears as a hollow ball and is now called a blastula
• How to identify if an embryo is in its blastula stage?

  when a central cavity develops within the morula
• what stage?

  Blastula stage

  
• Identify the zones?

  Blue - animal pole

  Green - Marginal pole

  Yellow - vegetal pole

  
• Presumptive fates of each zone?

  animal -

  marginal -

  vegetal -

  Cell zones

  
• aim of gastrulation?

  to form the 3 germ layers
• name the germ layers?

  ecto, meso, endo
• What is the movement of cells to form different tissues or organs in the organisms?

  Morphogenetic movement
• what stage?

  §Initiation of gastrulation.

  §Ectodermal cells on the animal pole spread and cover the blastocoel.

  §Thinning of the blastula's outer layer.

  epiboly
• what stage?

  §Cells at the dorsal marginal zone begin to move inward.

  §Formation of the blastopore and dorsal lip.

  §Gives rise to the endoderm and mesoderm germ layers.

  invagination
• what stage?

  §Continuation of inward cell movement.

  §Cells spread over the blastopore lip.

  §Contributes to the formation of endoderm and mesoderm.

  involution
• what stage?

  §Result of invagination and involution.

  §Endoderm: Innermost germ layer, lining the future gut.

  §Mesoderm: Middle germ layer, giving rise to muscles and organs.

  §Ectoderm: Outermost germ layer, forming skin and nervous system.

  germ layer formation
• just read

  
• How to identify if an embryo is in its gastrula stage?

  Cell movement or structure rearrangement is evident

  Blastopore is present
• just read

  
• What happens to the blastocoel during gastrulation?

  It disappears and is replaced by the archenteron.

  
• Yolk plug - as cells move inward and the blastopore forms, some of the underlying yolk material gets enclosed within the developing embryo
• Give location and main derivatives of endoderm?

  innermost

  
• give the location and derivatives of mesoderm?

  middle

  
• give the location of the ectoderm and its derivatives?

  outermost

  
• what happens during 8. Organogenesis?

  Neural tube formation

  Notochord development

  Formation of specific tissues and organs

  
• Neurulation

  Formation of the neural plate

  Ectodermal cells at the upper dorsal side become specialized.

  Form a raised "neural plate" along the dorsal surface.
• Neurolation

  Neural groove formation

  Neural plate changes to have a groove down the middle (neural groove).