RNA Processing in Devlopmental biology

3. Presented by:
Sanya Yaseen
4010
Presented to:
Sir Danish Riaz

4. RNA Processing
(in cellular Differenciation)
Topic

5.  Introduction
 Overview of Gene Expression
 RNA processing in Eukaryotes
 RNA Selection
 RNA splicing
 Families of Proteins
 Sex determination in Drosophilla
Contents

6. What is Cellular Differenciation?
“Embryonic differentiation is the
process of development during which
embryonic cells specialize and diverse
tissue structures arise.”

7. What is RNA Processing?
“ The process of gene expression to
form a specific protein at a specific
place by the process of
Translation”.

8. AN OVERVIEW OF GENE
EXPRESSION
 The Different Cell Types of a Multicellular
Organism Contain the Same DNA.
 Different Cell Types Produce Different Sets
of Proteins.
 A Cell Can Change the Expression of Its
Genes in Response to External Signals.
 Gene Expression Can Be Regulated at Many
of the Steps in the Pathway from DNA to
RNA to Protein.

9. AN OVERVIEW OF GENE
EXPRESSION
 The Different Cell Types of a Multicellular
Organism Contain the Same DNA.
 Different Cell Types Produce Different Sets
of Proteins.
 A Cell Can Change the Expression of Its
Genes in Response to External Signals.
 Gene Expression Can Be Regulated at Many
of the Steps in the Pathway from DNA to
RNA to Protein.

10. cells have ability to change genes expression
without altering the nucleotide sequence of
their DNA.
If DNA were altered irreversibly during
development, differentiated cell would be
incapable of guiding the development of the
whole organism.
To test this idea, a nucleus from a skin cell of
an adult frog was injected into a frog egg
whose own nucleus had been removed.
the egg developed normally into a tadpole,
showing the normal expression of genes.

13. AN OVERVIEW OF GENE
EXPRESSION
 The Different Cell Types of a Multicellular
Organism Contain the Same DNA.
 Different Cell Types Produce Different Sets
of Proteins.
 A Cell Can Change the Expression of Its
Genes in Response to External Signals.
 Gene Expression Can Be Regulated at Many
of the Steps in the Pathway from DNA to
RNA to Protein.

14. o many proteins are common to all the cells
e.g. structural proteins of chromosomes,
RNA polymerases,
DNA repair enzymes,
ribosomal proteins,
enzymes involved in glycolysis,
cytoskelton proteins.

15.  Diferent cell types produce specialized
proteins:
e.g. Heamoglobin only produced by
reticulocytes
 a typical differentiated human cell expresses
perhaps 5000–15,000 genes.
 large variations seen in the size, shape,
behavior, and function of differentiated cells.

16. AN OVERVIEW OF GENE
EXPRESSION
 The Different Cell Types of a Multicellular
Organism Contain the Same DNA.
 Different Cell Types Produce Different Sets
of Proteins.
 A Cell Can Change the Expression of Its
Genes in Response to External Signals.
 Gene Expression Can Be Regulated at Many
of the Steps in the Pathway from DNA to
RNA to Protein.

17. Cabability to change the Gene Expression
due to External Cues.
e.g. Effect of Glucocortocoid Hormone on Liver
cells.
While some other cells of body do not
effected by that hormone e.g. fat cells
illustrate a general feature of cell
specialization

18. AN OVERVIEW OF GENE
EXPRESSION
 The Different Cell Types of a Multicellular
Organism Contain the Same DNA.
 Different Cell Types Produce Different Sets
of Proteins.
 A Cell Can Change the Expression of Its
Genes in Response to External Signals.
 Gene Expression Can Be Regulated at Many
of the Steps in the Pathway from DNA to
RNA to Protein.

19. To become an active protein, the RNA must be:
(1) processed into a messenger RNA by the
removal of introns,
(2) translocated from the nucleus to the
cytoplasm,
(3) translated by the protein-synthesizing
apparatus
(4) must be posttranslationally modified to
become active.
• Regulation can occur at any of these steps
during development

21. Processing in Eukaryotes
O Two Major Ways include:-
censoring (RNA Selection)
RNA Splicing
Censoring:-
Nuclear transcripts into mRNA
RNA Splicing:-
splicing of the mRNA into different
proteins by using different combinations of potential
exons.

23. RNA Selection
۞ mRNA transcript from pre-mRNA (nuclear
RNA (nRNA)
۞ Pre-mRNA is transcribed from DNA
۞ Pre-mRNA contains introns which are spliced
during its movement from nucleus to cytoplsm.
۞ Un-necessary segments are deleted
۞ More genes are transcribed in the nucleus than
are allowed to become mRNAs in the cytoplasm.

24. Analysis on the transcripts from
the CyIIIa genes of the sea urchin
๏ Encode calcium-binding and actin proteins,
expressed only in a particular part of the ectoderm
of the sea urchin larva.
๏ Trancribed not in ectoderm but also meso &
endoderm but only effective in ectoderm of Sea
Urchin Larva.
๏ Unprocessed genes are degraded in meso &
endoderm.

25. RNA Splicing
 nRNA contains short exons (averaging about
140 bases) & large introns.
 By splicing together, different axons form
different proteins.
 What is an intron in one cell's nucleus may be
an exon in another cell's nucleus.
 Splicing of RNA is followed by these steps:
1. 5’ capping
2. polyadenyl tail
3. removal of introns
4. editing

26. 5’ Capping

27. Polyadenyl Tail

28. Removal of Introns

29. Editing of mRNA

30. Process of Translation

31. Families of Proteins
• Deletion of different exons in different cells
forms different families of proteins.
• Instead of one gene-one polypeptide, one can
have one gene-one family of proteins.
• for example:-
α-tropomyosin gene to encode brain,
liver, skeletal muscle, smooth muscle, and
fibroblast forms of this protein.
• These are called Splicing isoforms.

33. Sex determination in Drosophilla