A presentation on the relation between differential RNA processing and animal development.

1. Differential RNA Processing
& Animal Development
SYED MUHAMMAD KHAN
(BS HONS. ZOOLOGY)

2. Introduction
• In bacteria, differential gene expression can be
effected at the following levels:
1. Transcription
2. Translation
3. Protein modification
• In eukaryotes there is another possible level of
regulation: control at the level of RNA processing and
transport.

3. Introduction
• There are two major ways in which differential RNA
processing can regulate development:
1. Nuclear RNA Selection / Selecting which RNA gets
translated.
2. Differential RNA Splicing / Using various
combinations of exons to code for multiple proteins
from just one nuclear RNA.

4. Nuclear RNA Selection
• More genes are transcribed in the nucleus than are
allowed to become mRNAs in the cytoplasm.
• A particular cell type only needs to produce particular
proteins that will help it in performing its function.
• If any irrelevant genes are transcribed, their transcripts
(RNAs) are discarded.

5. Nuclear RNA Selection
• 5’ cap is added to the first nucleotide in the transcript
during transcription (7-methyl Guanosine).
• It protects the transcript from being broken down.
• It also helps the ribosome attach to the mRNA and start
reading it to make a protein.
• Poly-A tail is added to the 3’ end.
• The tail makes the transcript more stable and helps it get
exported from the nucleus to the cytosol.

6. Nuclear RNA Selection
Left – Nuclear RNA Selection. Right – 5’ cap and 3’ poly A tail of mRNA

7. Differential RNA Splicing
• Splicing - introns are excised out of the primary
messenger RNA transcript, and the exons are joined
together to generate mature messenger RNA.

8. Differential RNA Splicing
• Alternative/Differential nRNA splicing can produce a
wide variety of proteins from the same gene.
• By splicing together different sets of exons, different
cells can make different types of mRNAs, and hence,
different proteins.
• Recognizing a sequence of nRNA as either an exon or
an intron is a crucial step in gene regulation.

9. Differential RNA Splicing
• Spliceosomes are complex molecular machines
involved in splicing of nRNA, they are found in the
nucleus of eukaryotic cells.
• Spliceosomes are made up of snRNPs (small nuclear
ribonucleo proteins), i.e. U1, U2, U4, U5, U6, etc.
• snRNPs are made up of small nuclear RNAs (snRNAs)
and proteins called splicing factors, which combine to
form.

10. Differential RNA Splicing
• Most genes contain consensus sequences at the 5' and
3' ends of the introns.
• These sequences are the splice sites of the intron.
• Lariats are discarded by-products of RNA splicing;
these are usually introns that are cut out of the RNA to
make the final transcript.

11. Differential RNA Splicing
• Different proteins encoded by the same gene are
called splicing isoforms of the protein.
• Splicing Enhancers are sequences (present in nRNA)
that promote the assembly of spliceosomes at RNA
cleavage sites.
• Splicing Silencers act to inhibit splicing.

12. Differential RNA Splicing
Some of the types of alternative splicing are as follows:
1. Exon Skipping/Cassette Exon
2. Mutually Exclusive Exons
3. Alternate 3’ Splice Site
4. Alternative 5’ Splice Site

13. Differential RNA Splicing
Example of Differential RNA Splicing