Early Vert Development (2) Flashcards
Why might test results say that a mother’s kids are not biologically hers even if they are?
- mother could be a chimera (organism with two distinct cell types)
- father had halotype 1 and 2
- mother had halotype 3 and 4
- the mother was derived from two eggs (3 and 4) and two sperm (1 and 2)
- would typically give rise to fraternal twins but the eggs fused together
- blood shows (1 and 3) but germline show (2 and 4) making all offspring (2 and 4)
What is an interesting case of twinning?
- twins: a phenotypic male and a hermaphrodite
- both shared 100% maternal alleles and 50% paternal alleles
- this means they came from 1 egg and 2 sperm
- pathenogenetic activation and cleavage of ovum then fertilization by two sperm or 3n egg that later split to 2 2n eggs
What study was conducted by Wilhelm Roux in the late 1800’s?
- at the 2-cell stage, a hot needle was put into one cell to kill it
- the cell died and no longer divided or developed, however the other cell continued to develop normally according to fate map
- he believed this to be evidence towards mosaic development
What is a problem with Wilhelm Roux’s experiment?
- he left the dead cell there and it could be having an effect on the living cell
- if the dead cell is removed, you get a proper left and right axis forming
- this provides evidence towards regulative development
What occurs if you split cells of mice at the 2-cell stage? At the 4-cell stage?
- 2-cell: both cells can form a new embryo
- 4-cell: do not develop
What are the 3 cleavages of an amphibian embryo like?
- mesolecithal: displace radial cleavage
- first two cleavages are longitudinal
- the third cleavage is equatorial (splitting the embryo so that the vegetal pole is larger)
How were frog late blastula fate maps formed?
- generated using different dyes and markers
What are different layers where the blastopore will form?
- chorda-mesoderm: notochord
- head mesoderm: prechordal plate
- pharyngeal endoderm: pharynx, tongue
What occurs during xenopus gastrulation?
- bottle cells form and involution starts which forms the blastopore
- cells crawl to the animal pole
Where do the axis lie in the gastrula of the xenopus?
- blastopore is posterior (anus) opposite to pharyngeal endoderm that is now anterior
- animal pole is dorsal and vegetal pole is ventral
How is ectoderm regionalized after gastrulation?
- ventral: epidermis
- dorsal: neural plate
What occurs during neurulation?
- neural plate stage to neural tube formation
- neural groove forms and neural fold brings two sides together
- brings us to the neurula stage
Does a fate map tell us what cells are at an earlier stage?
- no, it tells us what they will become at the end point
- fate map is more of a guideline since cells can be influenced
What type of experiment can we do to see if a cell is specified and determined?
- transplant to see if it changes
- separate cells from embryo and simply observe
What was the golden age of embryology?
- early 1900’s
- addressed fundamental questions underlying vertebrate body plan formation
- “simple” questions and “simple” experiments
- used large embryos and simple tools
- amphibian embryos great for physical manipulation (big and heal fast)
What experiment did Hans Spemann do?
- transplant neural tissue to epidermis during early gastrula stage: became epidermis (also happens if grown in isolation)
- transplanted neural tissue to epidermis during late gastrula stage: became neural tissue
- sometime between these two times the neural tissue fate became determined
Following Hans Spemann experiment, what hypothesis might one come up with?
- the underlying mesoderm has an instructive role in the formation of neural tissue
What is Spemann/Mangold’s dorsal lip transplantation experiment?
- remove the dorsal lip (fated to become dorsal mesoderm) from one embryo and transplant it to where epidermis is likely to form (opposite to dorsal lip)
- results in embryo with a twinned axis
- some cells of host changed their fate to become neural tissue
What was the dorsal lip named?
- Spemann’s organizer
- dorsal lip-axis inducing property
What might the molecular mechanism underlying the Spemann Organizer be?
- neural inducing factor
- without the neural inducing factor, the default state of the ectoderm is epidermis
What conclusions can be made about the neural induction/ectoderm regionalization?
- neural tissue is not determined until late gastrulation
- default state of the ectoderm is skin (epidermis)
- the dorsal lip of the blastopore is sufficient to induce secondary axis formation and neural tissue from ectoderm that had been fated to become epidermis
What study did Nieuwkoop conduct in 1963?
- he removed the animal cap and cultured it in isolation: this resulted in epidermis
- he also removed the animal cap and dissociated it, then reaggregated it which resulted in neural tissue
What molecular mechanism combines Nieuwkoop’s results and Spemann’s organizer experiments? **
- if you add LiCl to an blastula, you get dorsalized embryos (only neural ectoderm, no epidermis)
- used subtractive hybridization to identify mRNAs enriched in dorsal tissue
- noggin
Where is noggin mRNA localized?
- dorsolateral region
- prechordal mesoderm
- notochord
