lec 15- intro to vertebrates and xenopus part 1 Flashcards
do all vertebrate have a similar body plan with the AP axis, the DV axis, and left and right axes?
yes
what does the vertebral column, which surrounds the spinal cord, define?
the AP axis with the head located at the anterior end
what is the DV axis defined by?
the vertebral column on the dorsal side
does the left side and right side of the body plan have appendages, and do they look symmetrical but aren’t?
yes they have appendages and look symmetrical but internally aren’t due to different organ places
what are the similarities and differences between all vertebrate embryos?
-differences: eggs vary in size, embryos look different at the blastula stage, development diverges at the end
-similarities: they all look similar after gastrulation during a stage called plylotypic stage, all embryos have a neutral tube, somites, a notochord, and a head
why is xenopus used as a model organism?
-fertilized eggs are easy to obtain when a female or male are injected with the hormone gonadotropin
-the eggs are large
-have a dark animal and a yellow vegetal region
-eggs are laid in water
what happens during early development/cleavage in Xenopus?
-at fertilization, sperm enters the egg at the animal region
-the cleavages occur at different rates, the first cleavage is oriented parallel with animal vegetal axis
-the embryo is bisected into left and right halves, the second cleavage also occurs along the AV axis but at right angles to the first
-the third cleavage occurs in the equatorial plane, an unequal division that produces four smaller animal cells and four larger vegetal cells
-at the blastula stage, an embryo with a few large cells in the vegetal half and more, smaller cells in the animal half are produced
what exist in xenopus gastrulation and where are the different cells located?
-the blastula contains a fluid filled cavity called the blastocoel
-ectoderm is located at the animal pole
-cells that give rise to mesoderm are located around the equator in the marginal zone
-endoderm is located in vegetal region
-first sign of gastrulation is a small infolding called the blastopore (forms future dorsal side)
what does the blastopore correspond to?
to the site of the embryonic organizer and Spemann-Mangold orgnizer
what does the transplanted dorsal lip of the blastopore induce?
the formation of a second embryo
what is induction?
one cell or tissue directs development of adjacent cells or tissues
what is the grafted dorsal lip of the blastopore called?
Spemann-Mangold Organizer
what happens during gastrulation?
-blastopore is formed
-cells at the site of the future blastopore move inside of the embryo, these are called bottle cells
-the presumptive endoderm and mesoderm involute around the lip of the blastopore and move along under the ectoderm
-during involution, a sheel of cells roll over an edge around itself
-ingression follows invagination, cells separate from one another and begin to move away freely
-the ectoderm spreads downward and eventually covers the whole embryo, epiboly and emboly take place
-as the cells move into the interior through the blastopore, another cavity forms, the archenteron which is the precursor of the gut
-the leading edge of the tissue will become the anterior (head) of the embryo
what is epiboly?
the process by which a layer of cells spreads or expands to enclose deeper layers of the embryo
what is emboly?
internalization or movement of mesoderm and endoderm precursors from the surface of the embryo to the inside
what is convergent extension?
a process that drives cells move underneath the ectoderm inside the embryo
what happens during convergent extension?
the tissue narrows along one axis while elongating along a perpendicular axis, can also occur when two populations of cells migrate towards one another
what happens during neurulation?
-occurs after gastrulation, this is when the neural tube forms, it is the precursor of the central nervous system and this embryonic stage is called a neurula
-the earliest visible sign of neurulation is the formation of the neural folds, they form on the dorsal side of the embryo
-the neural folds move upwards, fold towards the midline and fuse together to form the neural tube, the neural tube sinks below the epidermis
-the anterior portion of the neural tube will form the brain and posterior forms the spine
what changes occur inside the embryo during neurulation?
-the blastocoel is displaced by the cells that are entering the embryo and it eventually disappears
-the notochord forms the midline of the embryo
-it is an important skeletal element of the embryo and it sends signals that pattern surrounding tissues
what is organogenesis and what occurs?
-during neurulation, the embryo elongates along the AP axis and by the end of this stage it begins to look like a tadpole, this is organogenesis and it results in the tailbud stage of the embryo
-in the tailbud stage, the beginnings of many organs are present, including eyes, ears and the brain as well as somites (block tissue that give rise to muscle and skeleton)
-tadpole formed when organogenesis is complete
