8: Zebrafish Flashcards
What are lampbrush chromosomes and where/when are they
found?
Specific type of chromosome found in growing oocytes of most animals (not mammals)
-transform into lampbrush form during diplotene stage of meiotic prophase 1 due to active transcription of many genes (since zebrafish oocytes are highly transcriptionally activs during diplotene stage of meiosis, causes distincitve lampbrush chromosomes)
the central thread is the dna, the beads are the rna pol and the branches re the nascent transcripts (ribosomal rna)
Zebrafish is a good genetic organism
large broods
breed all year
easy to maintain
transparent embryos develop outside mother
embryogenesis completed in 24h
microinjection of blastomeres permits cell labelling experiments or transgene expression
what is their spefic name
“Danio rerio”
what is the balbiani body
mitochondirial cloud, thought to be associated with maternal rna localization
What is the micropyle
hole sperm enter
follicle cells surround the oocyte (these cells secrete the vitelline envelope)
-one follicle cell maintains contact with the oocyte and this creates a small hole in the envelope in which the sperm can enter during fertilization) CALLED THE MICROPYLE
When does egg activation occur
when eggs contact water
What occurs following fertilization
1)Cortical Granule Reaction
after
2)Chorion (previously vitelline envelope) lifts from egg surface, forming fertilization envelope
then
3)cytoplasmic Streaming: results in a non yolk cytoplasm located at animal pole (called cytoplasmic cap/ blastodic)
what is the difference between the blastoderm and the blastodisc
Blastodisc: non-yolky cytoplasm located at the animal pole (clear island of yolk free cytoplasm…)
also known as cytoplasmic cap
-associated with actin/myosin streaming (at fertilization-ca++ waves stimulate contraction of the actin cytoskeleton,,, squeezing yolkfree cytoplasm to animal pole
Blastodisc: Small region at the animal pole of the telolecithal eggs of fish and chicks, containing the yolk-free cytoplasm where cleavage can occur and that gives rise to the embryo. Following cleavage, the blastodisc becomes the blastoderm.
This is where cleavage divisions occurs (meroblastic meaning incomplete cuz too yolks so only cytoplasmic regions undergo divisions (the non yolk area called the blastodisc is what divides))
-following that is when the blastodisc BECOMES BLASTODERM
(mound of cells after 12 rounds of divisions is the blastoderm, early ones remain connected andproteins can move between blastomeres)
What type of cleavage division is seen in fish?
Meroblastic division refers to a type of embryonic cleavage in which the division of the egg is incomplete due to the presence of a large amount of yolk. This results in only a part of the egg undergoing cell division while the yolk remains undivided.
this is why the blastodiscturns into the blastoderm since the blastodisc are the only part of the egg that can divide since it is yolk free area, the rest is so yolky that it doesnt divide
- Sketch the cleavage stage embryo of fish and label the three
distinct cell types
I think the three disctict cell types are
NOT THIS!!!!!!!
1) blastomere
2) yolk synticial layer (right under the blastomere)
3) Yolk (at vegetal pole)
idk tho look at slide 11 if u want
OR I THINK ITS THIS ACC NOT THAT CUZ HE DREW THIS!!!!!!!!!!!!!!!!!!!!!!!
~ 10th division – the midblastula transition occurs - three distinct cell populations:
1.yolk syncytial layer (YSL) (extra-embryonic)
2.enveloping layer (EVL) (extra-embryonic)
3.deep cells (embryo proper)
idk it was in the note but idk if this is the cleavage stage
slide 19 LOOK AT SLIDE 21!!!!!!!!!
What are maternally contributed mRNA and proteins required for?
1) establishment of POLARITY
2) Cell divisions and cleavage
Maternal mutants that disrupte microtubules also disrupt patterns of cleavage divisions so microtubules are also important
how do we know?
-maternal effect mutations showed us
What does early blastoderm cell tell us
NOTHING about determination… there is much cell mizing during cleavage so early blastoderm can become any number of tissues… fate map of blastoderm before gastrulation tells us stuff
where is the nuclei of the ysl layer cells released into
the yolky layer underneath
they get their nuceli (derived from cells at the marigin of the blastoderm)
. What type(s) of cell movement is/are most prominently
associated with gastrulation in the fish embryo?
Epiboly (movement of cells over a surface) of blastoderm cells over the yolk and involves radial intercalation fo deep cells with superficial
EVL (enveloping layer) is also joined to YSL (yolk synticial layer)
expansion of yolk synticial layers is dependent on microtubules
During epiboly, one side becomes thicker (DORSLA)
What is radial intercalation
cells from different layers between a tissue merge into one
