Developmental Biology and Genetics – an introduction
How can a single fertilized egg cell give rise to an
entire organism?
- cell proliferation
- differentiation
- migration
- morphogenesis
- growth
- cell death
- homeostasis
Totipotent → pluripotent → multi/unipotent
→ specialized
The mammalian embryo will create
embryonic stem cells that form all the
tissues of the embryo. Cells committed to
certain lineages and become more limited in
what they can form.
Differentiated cells often leave the cell cycle.
Forward genetics → find out which genes are involved in a certain process
- search for mutants in the certain process and find out which genes are mutated
Reverse genetics → find out the function of a specific gene
- knockout the gene and look at the altered phenotype
Genetic epistasis analysis → try to order in which
series genes function, determine upstream and
downstream. Making double mutant combination.
1. Find out which genes are involved, 2. Find out in
which order these genes act.
, Totipotent cells (precursors of the germline, zygote)
can form all cell types. Inner mass cells are
pluripotent, they cannot give rise to the extra
embryonal structures such as the placenta, which is
formed by the outer layer of the blastocyst. Very
early on already some restriction in fate. Tissue
specific stem cells are very different from the
pluripotent stem cells in the inner cell mass.
Asymmetric cell division creates a new stem cell
and a differentiated cell.
Regulatory processes create variation. Signal transduction pathways (TF), gene silencing
(epigenetics, RNAi), post-translational modifications, splicing, protein localization, etc.
C. elegans
Reasons for usage of C. elegans
- simple animal
- limited number of cells (959 somatic nuclei)
- efficient genetics
- transparent
- cell lineage entirely known
From egg to adult in 3 days. Egg
→ cleavage → embryogenesis →
hatching → 4 larval stages → adult
, Horizontal line = cell division
Vertical line = cell, ends when fully
differentiated
A hermaphrodite is originally a male that
produces sperm and stores it in the
spermathecae. It switches and will only
produce oocytes after it. The oocytes will
travel through the spermathecae and get
fertilized. Gives rise to 300 progeny.
Male originate when an X chromosome is
lost during meiosis. XO individual that will
develop in a male. Used for crosses,
male hermaphrodite gives rise to 1000
progeny.
The germline is a special tissue, it maintains a
totipotent state, alteration between the mitotic
and meiotic cell cycle, immortal. It has to be
carefully protected against genomic
interference.
In L1 two germ cells after hatching,
they proliferate. Germ precursors are
formed and set aside. Granules
(PGL-1) end up in the germline,
which make in easy to recognize.
An asymmetric cell division gives rise
to the precursor of the germline
which will divide one more time,
these cells move inwards during
gastrulation. Z2/Z3 are the two germ
precursor cells from P4, somatic
cells flank them, beginning of
somatic gonad consisting of just four
, cells (Z4 – Z1). Proliferation starts, both the somatic gonad starts to form and germ cells
follow them. Red cells (DTC) migrate to the outer ends of the animal, germline follows behind
it. In the L3 stage, the direction of migration changes to the dorsal side of the animal and
back. Germline takes a U shape. Spermatogenesis starts, switch to meiosis, sperm is stored
and oocytes are formed.
Hollow tube, nuclei have a partly
shared cytoplasm. Oocyt has a
closed membrane.
In development, there are variations in the cell cycle.
During meiosis, two M phases follow each other without
DNA replication. In embryonic cell cycles, there are no
gap phases, because of which the cell cycle is very fast.
During endoreduplication cycles, mitosis is skipped
because of which the cells become more polyploid.
In meiosis the profase is very
extended in time, it can take from
days up to years. This is where
homologue chromosomes find
each other and pair, crossing
over can take place. This
happens in distinct places in C.
elegans germline.
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