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.