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Samenvatting Developmental Biology
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SAMENVATTING:DEVELOPMENTAL BIOLOGY
Prof. Luc Leyns
MANON UYTTENDAELE
3BA BIO-INGENIEURSWETENSCHAPPEN 2020-2021
Vrije Universiteit Brussel
, Developmental Biology – BA3: Exam questions
General questions:
A) Induction
B) French flag
C) Compare mechanisms between organisms
D) Morphogen
E) Patterning
Specific questions:
1) gastrulation: mouse Vs frog
2) gastrulation/ fate map
3) Mosaic Vs regulative development
4) Spemann Organizer
5) Zygotic A-P axis in Drosophila
6) Cytoplasmic determinants
7) Hox genes
8) Mesoderm formation
9) Maternal role in axis establishment in Drosophila
10) D-V axis in Drosophila
11) Segmental identity in Drosophila
12) Muscle formation
1
, Developmental Biology – Luc Leyns 2021
Chap.1. Overview of vertebrate development
The frog development
• LIFE CYCLE:
We will be using mostly Xenopus laevis, it’s an anuran
frog. It’s a south-african and central-African frog. It
measures between 7,5 and 14 cm. Males are generally
smaller than females.
They are entirely aquatic, so they are always in the water,
these are not jumping frogs like we have here in Belgium.
And they are also carnivorous.
They sell them in the fish shop as little albino frogs but
never buy them, because they eat all the fish inside your
aquarium.
It’s a very useful organism because before we were using the frogs from our countries, but
these frogs only lay eggs in spring period. Which means that your research on developmental
biology could only take part in spring moment.
And so, they went looking for another frog that could be used all year long. The advantage
of the frog; you have thousands of eggs, you can manipulate them, incubate them at different
temperatures, they will develop at different speed. And eventually you will get a little larva
out of this.
So, they went looking and they didn’t have to go looking very far. In the 1950’s they saw that
they were using frogs in clinics. They were using Xenopus laevis all year long because they
use it for pregnancy testing.
We know pregnancy testing now; you pee on a little strip and you will get a blue cross or not
if you are pregnant. Because it will detect a hormone in the urine, a pregnancy hormone, that
is the human Chorionic Gonadotropine.
And so, before that, to know if you were pregnant or not, they would inject a sample of your
urine into a female rabbit. And the rabbit only will ovulate if you are pregnant. It will trigger
ovulation, you would kill the rabbit, look at the ovary of the rabbit and see if there was a
recent ovulation or not.
2
, Killing the rabbit is not nice, so they went for another one and this is the Xenopus laevis.
So again, if you take a female frog and inject under the skin a little bit of urine, and if you are
pregnant, the next day this frog will lay eggs. If you are not pregnant, no eggs.
It was used in the clinics all over the world. It was a frog that was able to lay eggs all year
long. Which means that we could use it for developmental biology all year long.
We can do that because now we have purified this hormone. Human Chorionic
Gonadotropine that they purified out of urine of pregnant woman and you can inject that
under the skin of the frog, the next day you will get eggs. You can massage the belly of the
frog at different times of the day, and you will get some more eggs.
Then you take a male, kill the male and you take the testes, you crunch the testis in a little bit
of solution. And you get spermatozoids, you take a drop of these spermatozoids, you put in
top of the eggs, you mix. Fertilization will happen in vitro.
And then the development will proceed by playing with the temperature. You can slow down
or accelerate the development.
If you use a standard temperature like here you see 25°C, basically in about 1 day you will
have an embryo formed. And after 4 days you have a swimming tadpole.
So, we will have the cleavage stage leading to a blastula. We will have the gastrulation
leading to the 3-germ layer (ectoderm, mesoderm, endoderm) (anterior-posterior-dorsal-
ventral). During this class we will not talk about left-right axes.
It will then form a neural tube that’s the neurulation. And after that we will have a clear
anterior head that will develop, the heart will develop also, we will have the somites in the
anterior posterior, the tale will still elongate. And we will have a free-swimming tadpole.
This free-swimming tadpole doesn’t have yet all the neural connections but if you touch it, it
will react. It will have a cemen gland which is in the chin region, where it can stick, it’s a
sticky gland. It can stick to a plant or little rock, so it doesn’t wash away in the river for
example.
And then it will start feeding after a few days, it will feed more and more. And eventually like
in the lab for example about a month later it will metamorphose, it will lose its tale.
It will develop hind limbs and forelimbs. And then it will grow until sexual maturity. And it
will be able then to lay eggs or sperm.
This frog, and in particular the eggs of the frogs are also heavily used for cell cycle study.
A lot of cell cycles has been studied in these unfertilized eggs, you can remove the pronucleus
and have the cytoplasm. You can bring in the cytoplasm also a sperm that will decondensate
that will even start dividing. And then you can add proteins, you can add antibodies, you can
add RNA’s and you can see how that affects cell cycle and division and the formation of the
metaphase plate for example.
3
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