Two aspects of the regulation of gene expression : transcription and mrna polyadenylation

Transcription

1 Two aspects of the regulation of gene expression : transcription and mrna polyadenylation Laboratoire de Génétique moléculaire de la Neurotransmission, Paris Director : Pr. Mallet Division of Molecular Neurobiology, University of Tokyo Director : Pr. Mikoshiba Supervisor : Pr. Mizutani Hélène Kiefer Shimizu Higashi High School November 28,

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4 University High school 3-10 years 3 years Mathematics Mathematics Sciences Sciences Medical studies Law studies Economy Economy Foreign languages Litterature History Litterature, etc 4

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6 Agricultural science and technology university (5 years) Production, improvement and transformation of agricultural products Biology Economy European rules for agriculture and environment Company Research PhD 6

7 Why did I choose to do a PhD rather than to work in a company? Aim of research = to better understand the world, in order to improve the quality of life Research is exciting (for me) and may be usefull (for our children or grandchildren!) Good balance between manual and intellectual work, at least in experimental sciences Less money but more independency 7

8 Why am I interested in studying the regulation of gene expression? 8

9 We all come from one cell... that will give an organism after many division and differentiation steps 9

10 All the cells in our body contain the same genetic information... But they have different appearance and function 10

11 How is this diversity possible? B A Same genetic information but different environment B A Gene expression A B A Different proteins different functions B B A 11

12 What is gene expression? Dinner Let s take an example... 12

13 What is gene expression? Books = information Dinner Selection of one book Cooking Copy of the book Library Kitchen 13

14 What is gene expression? Genes = information Proteins Selection of one gene Protein synthesis Copy of the gene = messenger RNA (mrna) Nucleus Cytoplasm 14

15 What is gene expression? Genes = information Original paper = DNA sequence Amino acids Proteins Selection of one gene Protein synthesis Copy of the gene = messenger RNA (mrna) Copy paper = RNA sequence Nucleus Cytoplasm 15

16 What is gene expression? DNA sequence = INFORMATION Protein synthesis = FUNCTION Genes TRANSCRIPTION TRANSLATION mrna Nucleus Cytoplasm 16

17 Why do two cells in a different environment have a different gene expression pattern? B A Same genetic information but different environment B A Gene expression A B A Different proteins different functions B B A 17

18 Because extracellular environment contains signals that regulate gene expression 1 Modification of the environment 2 Signal transmission 3 Gene expression regulation 4 Answer : division, death or differentiation

19 Because environment changes, the regulation of gene expression is : Time-dependent : Steps of the development (regulation of cell cycle, differentiation) Physiological state of the cell (stimulus) Space-dependent Different cell types in the organism Deregulation of gene expression leads to pathology (ex : cancer, neurodegenerative disease...) 19

20 Regulation of transcription by transcription factors 20

21 What is gene expression? DNA sequence = INFORMATION Protein synthesis = FUNCTION Genes TRANSCRIPTION TRANSLATION mrna Nucleus Cytoplasm 21

22 Transcription requires many DNA sequences and proteins DNA Regulatory sequences Gene Proteins Transcription factors Transcription machinery 22

23 Transcription requires many DNA sequences and proteins Regulatory sequences Gene Transcription factors Transcription machinery 23

24 Transcription requires many DNA sequences and proteins Regulatory sequences Gene TRANSCRIPTION TRANSCRIPTION FACTORS HELP OR PREVENT TRANSCRIPTION MACHINERY TO INITIATE TRANSCRIPTION Transcription factors Transcription machinery 24

25 The combination of regulatory sequences is unique for one gene during all the life B B A A 25

26 The combination of transcription factors is unique for one cell at one time point + B A + B A 26

27 Regulation of transcription is due to specific interactions between transcription factors and regulatory sequences B A Same genetic information but different environment B A Gene expression A + B A Different proteins Different functions B + B A 27

28 Isolate new transcription factors and determine in which cells they are = one step to understand that phenomenon 28

29 One transcription factor is caracterized by : +/- 1 1 Its effect on transcription 2 2 Its affinity for one specific regulatory sequence CAGGTG These properties can be used to isolate novel transcription factors 29

30 Aim of my PhD work : isolate novel transcription factors involved in the development of the nervous system CAGGTG = a regulatory sequence important for the development of the nervous system Search for all the transcription factors able to bind to this regulatory sequence in the brain Strategy = one-hybrid screening in the yeast Identification of ZENON, a novel transcription factor 30

31 One-hybrid screening in yeast His- mutant his3 his- medium 31

32 One-hybrid screening in yeast Gal4 ADNc his3 his- medium 32

33 One-hybrid screening in yeast Gal4 ADNc his3 his- medium 33

34 ZENON expression is restricted to old neurons in the nervous system Function in protection? 34

35 ZENON = Zinc finger protein Expressed in NeurONs ZENON? 35

36 Why a post-doc? 36

37 Research is international Available data Publications by the scientific community Hypothesis Experiment Result Report 37

38 Research is expensive Available data Publications by the scientific community Hypothesis Experiment Money!!! Public and private sources Result Report 38

39 And competition is high! Available data Publications by the scientific community Hypothesis Competition Experiment Money!!! Public and private sources Result Report 39

40 So we have to work hard and accumulate many papers! PhD (3-5 years) Not enough papers Post-doc 2 years or more Enough papers More stable position Money for experiments Etc 40

41 It is nice to go abroad for a post-doc Personal reasons : good opportunity to live in a foreign country Learn a new language Discover a strong and original culture Career reasons : Research is international, so it is nice to have an international experience English Financial reasons : easier to find money to go abroad than to stay at home. Thank you to JSPS! 41

42 But of course There are many excellent researchers that did not go abroad for a post-doc Going abroad is not a guarantee to have a better situation after coming back in the home country So it is better to go abroad not only for career! 42

43 Regulation of protein synthesis by cytoplasmic mrna polyadenylation 43

44 What is gene expression? DNA sequence = INFORMATION Protein synthesis = FUNCTION Genes TRANSCRIPTION TRANSLATION mrna Nucleus Cytoplasm 44

45 Sometimes extracellular signals directly regulate translation Stimulus (ex : progesterone) Quicker In some situations, regulation of transcription is not possible 45

46 Cytoplasmic mrna polyadenylation Polyadenylation = add a lot of adenine (A) at the end of mrna Necessary for stability and translation of mrna Occurs in the nucleus of all cells and sometimes also observed in the cytoplasm regulation of translation Nucleus Cytoplasm mrna PA (A) (A) 250 (A) 250 Translation Stimulus PA DA PA mrna (A) (A) 250 (A) 250 (A) (A) 250 Storage Translation 46

47 Meiotic maturation of Xenopus laevis oocytes : a model to study cytoplasmic mrna polyadenylation Model = Simple system A lot of information available Transposition to more complicated systems 47

48 Meiotic maturation of Xenopus laevis oocytes : a model to study cytoplasmic mrna polyadenylation Immature oocytes 1 mm Lay-out Fertilization 1 mm Mature oocytes Very small cells 48

49 Meiotic maturation of Xenopus laevis oocytes is cytoplasmic polyadenylation-dependent * * Trancription and storage of mrna Polyadenylation and translation of stored mrna 49

50 Meiotic maturation of Xenopus laevis oocytes : a model to study cytoplasmic mrna polyadenylation Meiotic maturation is cytoplasmic polyadenylation-dependent Meiotic maturation can occur in vitro (progesterone addition in the culture medium) Meiotic maturation is very easy to detect Frog oocytes are very big and easy to manipulate 50

51 Isolation of Xenopus laevis oocytes by surgery (I) Anesthesy of a Xenopus laevis female 51

52 Isolation of Xenopus laevis oocytes by surgery (II) A piece of ovary is pulled out 52

53 Isolation of Xenopus laevis oocytes by surgery (III) Culture of the oocytes 53

54 Isolation of Xenopus laevis oocytes by surgery (IV) Rescue of the frog 54

55 Isolation of Xenopus laevis oocytes by surgery (V) 6 weeks after the frog can be re-used! 55

56 Aim of my post-doc work in Japan : to determine if IRBIT regulates mrna polyadenylation or not IRBIT = a novel protein Potential function in the regulation of mrna polyadenylation IRBIT protein IRBIT antisense Over-expression Down-expression? 1 mm 1 mm 56

57 Over-expression and down-expression by injection 57

58 Conclusion : I am very happy to be in Japan! Powerfull and high-tech research, systematic approach For the moment, amount of money devoted to research is too limited Good synergy inside a team French are very individualistic poeple Data is more important than theory Theory is more important than data 58

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