Animal development-lower vertebrates Flashcards
General overview if animal development
fertilization
fusion of egg and sperm (formation of the zygote)
cellular cleavage
- formation of blastula
- Under maternal control (especially in lower vertebrates)
Gastrulation
formation of the three germ layers-ectoderm, mesoderm, endoderm
Organogenesis
- organ formation
- Under zygotic control
Maternal sygotic transition (MZT)
- activation of zygoticgene expression
- cell cycle slows down
- Tissue movements initiate
Descruptive enbryology terms
- The animal- vegetak axis
Early Xenopus
Zygote-8 cell- mid blastula- early gastrula- mid gastrula- early neurula- late neurula
Mid blastula
Actication of zygotic gene expression
Cleavage stage
- 1st and 2nd cleavage= vertical
- 3rd cleavage= equatorial (closer to animal pole)
- cells of the blastula= blastomeres
- cavity that form at the center of the blastula= blastocoel
Notice the cells at the vegetal poel are larger why is this so?
- more cells
It is not bith, marriage or death is the most important them in your life, but gastrulation
- lewis wolpert
What is gastrulation?
- Formation of the three primary germ layers
- Ectoderm, Mesoderm, and Endoderm
The nechanism of gatrulation can vary among species
- Invertebrates
- lowe invertebrates (frogs and fish)
- higher vertebrates (birds and mammals)
Important tissue movements involved in gastrulation
Invagination: Inforlding of cell sheet into embryo
- Sea urchins
- fruit dlies
Involution:
- Inturning of cell sheet over the basal surface of an outer layer
- Frogs
- fish
Ingression
- Migration of individual cells into the embryo
- Amniotes
- birds and mammals
Apical construction of epithelial cells lead to tissue invagination
- note: this involves the actin cytoskeleton at apicla face (red)
Fate map of the frog (xenopus) blastula
Axial
- notochord (important signaling tissue for inducing the CNS and somites)
Paraxial
- somites
- 9form segmented strictures- vertebrae, musculature, dermis)
Fate map of the frog (xenopus) blastula
Intermediate
kidneys, gonads
Fate map of the frog (xenopus) blastula
Lateral plate
- body wall, limb buds (presursors to the limbs)
Fate map of the frog (xenopus) blastula
Ventral
blood cells and vessels
Fate map of the frog (xenopus) blastula
Much happens during gastrulation (frog example)
- cells of the animal hemisphere migrate over the whole embryonic surface in a process known as epiboly lower vertebrates)
- ## marginal zone cells involute to form the archenteron (develping gut)
During involution
- The mesoderm separates from the endoderm and involutes as a separate tissues layer between the ectoderm and endoderm
- towards the end the dorsal axial mesoderm elongates in the anteroposterior direction faciliated by convergent extension:
- The ventrolateral mesoderm moves towards the dorsal midline (converges) and the dorsal midline elongates (extends)
Gatrulation:
- formation of the three germ layers
Initiation of gastrulation
- marked by the formation of the dorsal lip in the dorsal vegetal quadrant
The gastrulating cells interact with
- fibronectin tracks secreted into the ECM b y the lastocoel roof
Fibronenic
tracks promote the migraHng of involuted deep cells to the animal pole
The dorsal lip elongates
laterally and then ventrally encircling the whole embryon forming the blastopore
The fates of the three gern layers
Ectoderm
- epidermis
- Cenetral nervous system
- lens
- neural crest:
- melanocytes
- craniofacial cartilage and bone
- smooth muscle
- peripheral neurons
- some glial cells
Mesoderm
- heaed mesoderm
- notochord
- somites
- kidneys
- limbs
- blood vessels
- skeletal muscle
- heart
Endoderm
- Epithelial linings of:
- liver
- gut
- pancreas
- bladder
- lungs
Neurolation:
The ectoderm on the dorsal side becomes the centrao nervous system
Notochord
- Signals to the overlying ectoderm to become the neural plate
Neural folds
form on the outer edges of the neural plate
Neural folds
fuse at the dorsal midline forming the neural tube and the overlying epidermis
Neural crest cells form
at the end of neurulation
Neural crest forms:
- Melanocytes
- craniofacial cartilage and bone
- smooth muscle
- peripheral neurons
- some glial cells
Tissue
Tissue invaginates all around the circumference of the embryo forming the blastopore
During and after neurulation
there is significant elongation of the body
Somites
are segmented pairs of paraxial mesodermal 1ssue that give rise to a variety of structures
Subdivisions and Bssues derived from
the somite
Somites are composed of:
- Sclerotome
- Epaxial myotome
- Hypaxial myotome
- dermatome
the vertebrae are formed initially of
cartilage-> which is later replaced by bone
Epaxial myotome
forms the segmental muscles of the main body axis
Dermatome
Forms the dorsal dermis
