M2. development of xenopus laevis Flashcards
the vertebrate body plan
-similar basic body plan
vertebral column
segmented backbone surrounding the spinal cord
anterior-posterior axis
- head - trunk - tail
- head end enclosed in a skull (bone or cartilage)
dorsal-ventral axis
- spinal cord (d)
- mouth (v)
bilateral symmetry
dorsal midline
phylotypic stage
-all chordate embryos pass through the phylotypic stage
(embryos are similar in appearance)
-common features : head, notochord, neural tube (earliest appearance of nervous system), somites (blocks of mesoderm)
all vertebrate embryos undergo a similar pattern of development
- gametogenesis
- fertilization
- cleavage
- gastrulation
- notochord formation
- neurulation
- somitogenesis
- organogenesis
cleavage
earliest cell division, rapid cell division through which embryo becomes divided into smaller cells
gastrulation
dynamic process through three germ layeter (ectoderm, mesoderm, endoderm) organize themselves
notochord formation
column of mesoderm located just ventral to neural tube
neurulation
formation of the neural tube - precursor to nerve cord
somitogenesis
formation of regularly spaced blocks of mesoderm (somites) flaking notochord that give rise to skeleton and muscle
organogenesis
development of organs
model amphibian embryo: xenopus laevis
- basis for what we know about early development of the embryo
- embryos are large (scaled bar 0.5mm) - allowed for dissection of the early embryo
- dissected tissues easy to culture
xenopus laevis: egg
- egg has a distinct polarity –> animal to vegetal axis (bar 1mm)
- dark pigmented animal region and heavier yolk vegetal region
- sperm enters animal region
- zygote is diploid (2N)
- first cleavage along animal -vegetal axis
xenopus blastulation: cleavage of the embryo to form blastomeres
- first cleavage along A/V axis, divides egg in left -right
- second cleavage 90 degrees to first cleavage
- third cleavage equatorial and asymmetric - four small animal and four small vegetal cells, eight total blastomeres
blastula
germ layers start to form
(ectoderm, endoderm, mesoderm)
an animal embryo at the early stage of development when it is a hollow ball of cells.
blastula stage :
- reached after 12 divisions (~4096 cells)
- has radial symmetry (ie. no visible sign of A/P or D/V axis)
- has blastocoel
- marginal zone
blastocoel
a fluid filled cavity in animal region
marginal zone
equatorial ring around embryo separating animal and vegetal region
ectoderm
animal region- epidermis and nervous system
mesoderm
marginal zone - muscle, bone, blood, heart
endoderm
vegetal zone - intestine , lungs, liver, pancreas
xenopus laevis : gastrulation
the morphogenic process occurring in three dimensions where endoderm and mesoderm are internalized
-blastopore
blastopore
small slit like in folding of marginal zone on dorsal side, site of embryonic organizer (i.e. Spemann-Mangold organizer)
-organized dorsal development and antero-posterior axis
gastrula mesoderm and endoderm
enter blastopore and migrate (via involution) to the future anterior of the embryo
-first tissues to enter the embryo are most anterior
involution
germ layer migrate as a coherent sheet of cells
gastrula : ventral and dorsal
ventral side initiates involution after dorsal side - delayed but similar cell movement occur on ventral side
- epiboly
- all three layers change shape and elongate
epiboly
ectoderm spreads to cover embryo
gastrula: archentron
a second cavity forms during gastrulation (future gut cavity) –> blastocoel reduces in size
-mesoderm and endoderm spread to the left and right of the midline
-lateral mesoderm spreads ventrally to cover inside of archenteron
late gastrulation
- blastopore closed (future anus)
- the mesoderm contacts both the ectoderm and endoderm along the antero -posterior axis
- mesoderm is patterned along its antero-posterior axis via the action of the organizer
- ectoderm covers embryo
- yolk cells remain as food source
neurulation
- dorsal mesoderm starts to develop into notochord (rod along dorsal midline) and somites (segmented blocks of mesoderm along notochord)
- lateral mesoderm (lateral plate mesoderm) will form mesoderm derived organs (i.e. heart (A) kidneys (P))
neurulation: neurula stage
formation of the neural tube (precursor to central nervous system)
neurulation: nerual plate
is the ectoderm located above notochord and somites
- edge of the neural plate forms neural folds which rise towards midline and fuse to form neural tube
- the neural tubes sinks below epidermis
- the anterior neural tube becomes brain- middle and posterior neural tube becomes spinal cord
early tail bud stage: dorsal part of somites
become dermatome (future dermis)
early tail bud stage : ventral somite
becomes vertebrae, trunk and limb muscles
early tail bud stage : lateral plate mesoderm
heart, kidney, gonads and gut muscles
early tail bud stage: ventral mesoderm blood
forming tissues
early tail bud stage : endoderm
lining of the intestine, liver, pancreas, and lungs
early tail bud stage: after neurulation
neural tube closure, the tail bud stage occurs
early tail bud stage: the brain
anterior neural tube, is divided into forebrain, midbrain and hindbrain
early tail bud stage: organogenesis initiates
eyes and ears start to develop
early tail bud stage: three branchial arches form
form jaws and bones of the face
early tail bud stage: neural crest cells
come from the edges of the neural folds after neural tube fusion
-they detach and migrate as single cells b/w the mesodermal tissues to become the sensory and autonomic nervous system pigment cells and some cartilage of skull
