A presentation on translational regulation of development.

1. Translational
Regulation of
Development
SYED MUHAMMAD KHAN
(BS HONS. ZOOLOGY)

2. Introduction
 Control of gene expression at the level of
translation can occur by:
1. Differential mRNA Longevity
2. Selective Inhibition of mRNA Translation
(Stored oocyte mRNAs)
3. micro-RNAs
4. Cytoplasmic Localization
5. Stored mRNAs in Brain Cells

3. Differential mRNA Longevity
 The longer an mRNA persists, the more
protein can be translated from it.
 More time in cytoplasm = More translation
 Poly A-tail (post transcriptional
processing/on 3’ end) increases the life of
mRNA.

4. Differential mRNA Longlivety
 In female rats, casein (milk protein)mRNA
is normally short lived.
 But when the rat is lactating (feeding milk
to babies), prolactin is released.
 Prolactin increases the life of caesin
mRNA.

5. Selective Inhibition of mRNA
Translation: Stored oocyte mRNAs
 The oocyte makes and stores mRNAs that
will be used only after fertilization.
 These mRNAs remain dormant.
 They are activated when
ovulation/fertilization takes place
(depending on mRNA).

6. Selective Inhibition of mRNA
Translation: Stored oocyte mRNAs
 These stored mRNAs encode proteins that:
1. Are needed during cleavage.
2. Regulate the timing of early cell division.
3. Determine the fates of cells. These include
the bicoid, caudal, nanos, etc. in
Drosophila.

7. Selective Inhibition of mRNA
Translation: Stored oocyte mRNAs
 mRNAs are in cytoplasm, hence they are
available for translation.
 Inhibitors prevent the translation of these
mRNAs in the oocyte
 These inhibitors must be removed at the
time around fertilization.

8. Selective Inhibition of mRNA
Translation: Stored oocyte mRNAs
Before fertilization, inhibitors such as Maskin inhibit translation of
mRNA. But upon fertilization, Maskin (inhibitor) is displaced by
an enzyme, translation can now proceed.

9. micro-RNAs
 microRNAs (miRNAs) are RNAs of about 22
nucleotides.
 Made from precursor RNA.
 They form a RNA-protein complex: RNA
induced silencing complex (RISC) and bind
with a target mRNA (with complementary
base pairs) and inhibit translation.

10. micro-RNAs (Synthesis)
 The miRNA gene encodes a pri-miRNA
(primary micro RNA) that has several hairpin
regions.
 The pri-miRNA is processed into individual pre-
miRNA "hairpins" by a RNAase enzyme.
 These pre-miRNA hairpins are exported from
the nucleus.

11. micro-RNAs (Synthesis)
 Once in the cytoplasm, another RNAase,
separates the single stranded miRNA.
 The strand is packaged with proteins into
the RNA-induced silencing complex
(RISC).
 RISC binds with target RNA to inhibit
translation.

12. micro-RNAs
Model for the formation
and use of microRNAs.

13. micro-RNAs (Action)
The miRNA complex can inhibit
tanslation by:
(A) Blocking binding of RNA
with ribosomes or initiation factors.
(B) Recruiting endonucleases to
Digest poly A tail of target RNA,
this will destroy it.
(C) Recruiting proteases to destroy
nascent (in process) protein.

14. Cytoplasmic Localization
 A majority of mRNAs (about 70% in
Drosophila embryos) are localized to
specific places in the cell .
 There are three major mechanisms for the
localization of an mRNA:
1. Diffusion & Local Anchoring
2. Localized Protection
3. Active transport along cytoplasm

15. Cytoplasmic Localization
Diffusion & Local Anchoring:
The nanos (mRNA), produced in
Drosophila oocyte, are free to
roam around the cytoplasm, but
they when they reach the
posterior end, they are anchored
and their translation is initiated.

16. Cytoplasmic Localization
Localized Protection:
The hsp83 mRNA is degraded in all
regions of Drosophila embryo
except the posterior region where
it is offered protection and is
Translated.

17. Cytoplasmic Localization
Active Transport Along The
Cytoskeleton:
In Drosophila oocyte, bicoids
(mRNAs) are actively (using ATP)
transported to the anterior portion
by the cytoskeleton.

18. Stored mRNAs in Brain Cells
 The storage of long-term memory, in
brain, requires new protein synthesis.
 The local translation of mRNAs in the
dendrites of brain neurons, increases the
strength of synaptic connections

19. Stored mRNAs in Brain Cells
 One of the proteins responsible for
constructing specific synapses is brain-derived
neurotrophic factor, or BDNF.
 BDNF regulates neural activity and is critical
for new synapse formation.
 BDNF induces local translation of previously
mentioned neural messages in the dendrites.

20. Stored mRNAs in Brain Cells
 Several mRNAs are transported along the
cytoskeleton to the dendrites of neurons.
 These include RNAs coding for:
1. Receptors for neurotransmitters
2. Enzymes
3. Cytoskeleton Components

21. Post-translational Regulation of
Development
 Several changes can take place in a protein
even after translation:
1. Cleavage of inhibitory sections (to activate
protein).
2. Transporting proteins to their required
location (where they have to function).
3. Assembling with other proteins
(Haemoglobin consists of 4 peptide chains).
4. Attachment of cofactor (i.e. ions like Ca2+)