Transmission of genetic information Genetics and genomics for 3 rd year Dentistry students...

Transmission of genetic information

Genetics and genomics for 3rd year Dentistry students 13.02.2015.

Genetic informations (DNA) is passed

- within cells of an organism

- from one generation to next

generation

Multicellular cell cycle

GoG2

G1

S

M-phase

Restriction point

G2

M

- Growth factors- anchorange

mitosis cytokinesis

Interphase

Checkpoints:

Restriction pointG2M (spindle)

Regulators of cell cycle

cyclin dependent kinases (Cdk-s) cyclins phosphatases

other kinase regulatory proteins: activating and inhibitory kinases, kinase inhibitors, Aurora and polo like kinases (Plk) ubiquitin ligases

universal and conservative

Due to the activity of cell cycle and checkpoint machinary

DNA and centrosome are duplicated (interphase – S-phase)

and halved in M-phase (mitosis) with high fidelity

Genetically identical cells

Intact DNA is replicated in then is precisely halvedsemiconservative way (for this centrosome is(only once), needed)

G1 S meta-anaphase

Structure of centrioles and

centrosome (MTOC)

PCM = pericentriolar matrixTuRCs = tubulin ring

Distal appendages

Subdistal appendages

Different kinases regulate the duplication and separation of centrosome

M phase (events and

regulation)

Dramatic changes in M-phase (initiated by MPF)

DNA microtubules nuclear envelope marker

Interphase metaphase

telophase

anaphase

Initiation of M-phase: activation of MPF (M-phase promoting complex=Cdk1-B

cyclin)

Cdk1

B cyclin

Activating kinase

Inhibitory kinase

MPFiMPFi

phosphatase

MPFa

Main substrates of MPF

• lamins of nuclear lamina nuclear envelope breaks down

• condensin complex chromosome condensation

• MAP-s (microtubule associating proteins) mitotic spindle formation

• phosphatase (+ feedback) activation

• GM130 (Golgi matrix protein) disruption of Golgi

• myosin II

• activation (indirectly) of APC (anaphase promoting complex)There are much more substrates of MPF

from DNA to chromosome

Phosphorylation of condensin

induces the condensation of DNA

Cohesin Condensin

Cornelia de Lange syndrome (SMC = structural maintance of chromosomes = ATP-ases + other proteins)

Cohesin Condensin

Cornelia de Lange syndrome (SMC = structural maintance of chromosomes = ATP-ases + other proteins)

Centromere and kinetochore are not the same structures

telomere Chromosomal passenger complex

Kinetochore

Scleroderma

Autoimmune disease – autoantibodies produced againts kinetochore proteins

Mitotic phases

Mitotic spindle in metaphase

polar

Types of kinetochore–microtubule attachments

Normal in mitosis

not normal in mitosis

Kinetochors are

Bioriented

Monooriented

Monooriented

bioriented

Mitotic phases

If kinetochor MT-s are attached to all kinetochors ensuring precise segregation of duplicated DNA, checkpoint machinary allows the cell to step over M checkpoint and it enters anaphase and M-phase is completed.

In anaphase sister chromatids separate.

Anaphase

(Kinetochore MT depolymerisation)

(Polar MT polymeriation)

Anaphase is promoted by Anaphase Promoting Complex (APC)

MPF indirectly activates APC (needed to complete mitosis and to start cytokinesis) APC is a ubiquitin ligase induction of protein degradation in proteasome

(Securin and B cyclin, protein binding the centrioles)

Different kinases regulate the duplication and separation of centrosome

APC

Cohesin Condensin

(SMC = structural maintance of chromosomes = ATP-ases + other proteins)

Separase (activated by APC) and Plk are needed for the separation of

cohesin

Nature Reviews Molecular Cell Biology

Kinetochores are bioriented Amphitelic attachment

1.

2.

Activity of APC

Separation of cohesin

Activation of phosphatases (completion of mitosis an d cytokinesis)

APC ubiqutination of B cyclin

degradation of B cyclin

MPFi activation of phosphatase dephosphorylation of lamins reformation of nuclear envelope condensin chromosome decondensation MAP-s disappearance of mitotic spindle (MPF effects are reversed) cytokinesis

Activity of APC

M-(spindle) checkpoint

APCAPC

APCAPC

Cdc20

Van szabad kinetochor

Cdh1

APCAPC

Cdc20

No free kinetochors

APC, stops in metaphaseAPC, stops in metaphase

M-(spindle) checkpoint

Free kinetochore

Types of kinetochore–microtubule attachments

Normal in mitosis

not normal in mitosis

Kinetochors are

Bioriented

Monooriented

Monooriented

bioriented

Activated M (spindle) checkpoint

Aurora B activates M-checkpoint machinary

Inactive M (spindle) checkpoint, enters anaphase

Cytokinesis is usually symmetric

(actin és myosin II)

Contractile ring

Asymmetric cytokinesis

Ontogenesis, gametogenesis (couse – asymmetric mitotic spindle)

There are several forms of atypical mitosis (M-phase)

• Have been listed and shown in practice

• They result genetically different cell populations

in an organism mosaicism

which can be the cause of genetic diseases (see later)

Type Description Consequence

Typical   Genetically identical cells.

Atypical  Genetically not identical cells

(In the organism: mosaicism)

Endomitosis (Endoreduplication)

DNA is duplicated, but during M-phase the nuclear envelope remains intact. - No separation of chromatids- Separation of chromatids

Giant cell, giant nucleus

Polythene chromosomesMore chromosome (polyploid cell)

No cytokinesis Mitosis is not followed by cytokinesis.

Multinucleated (giant ) cells.

Multipolar division Due to atypical duplication and division of centrosome chromosomes are pulled to more than two poles

Different chromosome number.

Bridge formation (anaphase lag)

A chromatid is pulled from two poles.

Breakage of chromosome (structural chromosomal aberration)

Non-disjunction Lacking of kinetochor microtubules of a chromatid.

Change of chromosome number.

Strebhardt et al. Nature Reviews Cancer 6, 321–330 (April 2006) | doi:10.1038/nrc1841

Transmission of genetic information from generation to generation

- asexual reproduction – offsprings are genetically identical with the parent (clones)

- sexual reproduction – offsprings differs from the parents and from each other (genetic variability)

Genetically identical cells in an organism

Genetically different cellsGenetically different individuals

Genetic variability

- significance

- is increased by – mutations

– sexual reproduction

meiosis (generation of gametes)

- homologous recombination (crossing over) - independent assortment of homologous chromosomes

fertilisation

Genetic variability is important in prokaryotes,too

Provided by horizontal gene transfer

Significance of meiosis

- genetic variability (genetically different cells)

- chromosome number is halved (2n n)

Meiosis

DNA replication (S) - Meiosis I – prophase metaphase anaphase telophase DNA replication

- Meiosis II – prophase metaphase anaphase telophase

Meiosis I. Prophase

Leptotene

Bouquet arrangement = by their telomeres chromosomes bind to nuclear envelope later gather at one site - possible role of cytoskeleton - significance: chromosomes are closer to each other

telomeres

MTOC

Zygotene

Synapsis (pairing) of homologous chromosomes by the help of synaptonemal complex Bivalent chromosomes - tetrads formation,pseudoreduction

Paternal chromosome maternal chromosome2 sister chromatids 2 sister chromatids

By Chung-Ju Rachel Wang, Department of Molecular and Cell Biology, University of California, Berkeley, USA. 2nd Prize.Olympus BioScapes Digital Imaging Contest

Zygotene

Pairs of chromosomes

Homologous chromosomes

similarity – same shape, size and genes

differences – different origin, (maybe) different allele of a gene

In a diploid human cell:22 pairs autosomes1 pair sex chromosomes XX or XY

Pachytene

Homologous recombination = crossing over

Crossing over is obligatory (between non sister chromatids) Number of crossing overs: 13/chromosome pair

Pachytene Homologous recombination = crossing over

paternal maternal

Recombination of paternal and maternal DNA sequences (genes)

Centromere–blueRecombination -yellow

Pairing and recombination even between X an Y

Diplotene

Kiazmákchiasmata

Separation of chromosomes (detachment of synaptonemal complex)

Sites of crossing overs = chiasmatabecome visible

Meiosis I prophase

Több száz DSB DBS-ek axiálisan DBS-ek többsége kijavítódik szinapszis megszűnik(hot spot-ok, SPO11 szinapszis néhány crossing over crossing over maradIndukálja) kialakul kiazma

DNAs are bound by cohesin

DBS= double stranded DNA break

Kohezin csak a centromer regióban marad a karokról leválik

Meiosis I prophase

Several hundreds DSB DBS-ek axiálisan DBS-ek többsége kijavítódik szinapszis megszűnik(hot spots, induced by SPO11) kiazma

DNAs are bound by cohesin

DSB= double stranded DNA break

Kohezin csak a centromer regióban marad a karokról leválik

Synaptonemal complex

Appears

Meiosis I prophase

Several hundreds DSB DSB-s are axial DSB-ek többsége kijavítódik szinapszis megszűnik(hot spots, induced by SPO11) kiazma

DNAs are bound by cohesin

DSB= double stranded DNA break

Kohezin csak a centromer regióban marad a karokról leválik

Synaptonemal complex Synaptonemal complex

Appears

Meiosis I prophase

Several hundreds DSB DSB-s are axial DSB-s are repaired szinapszis megszűnik(hot spots, induced by some become CO SPO11)

DNAs are bound by cohesin

DBS= double stranded DNA break

Kohezin csak a centromer regióban marad a karokról leválik

Appears

Synaptonemal complex

Meiosis I prophase

Several hundreds DSB DSB-s are axial DSB-s are repaired(hot spots, induced by some become CO SPO11)

DNAs are bound by cohesin

DBS= double stranded DNA break

Kohezin csak a centromer regióban marad a karokról leválik

Appears diappears

Synaptonemal complex

Meiosis I prophase

Several hundreds DSB DSB-s are axial DSB-s are repaired(hot spots, induced by some become CO SPO11) chiasmata are visible

DNAs are bound by cohesin

DBS= double stranded DNA break

cohesin detaches from arms, remains only at centromere

Appears diappears

Synaptonemal complex

Meiosis I. Meta-, ana-, telophase

Metaphase

sister chromatids are bound by cohesin (at centromer) homologous chromosomes are bound by chiasmata

homologous chromosomes are arranged in the equatorial plane

Anaphase

Independent alignment of

homologous pairs

independent (random) assortment of

homologous chromosomes

or

Number of variations in human 223= 8 x 106, Increased by homologous recombination (not shown in the figure)

Kinetochore orientation and separase activity in meiosis I

Meiosis I

shugosin

shugosin

Cooriented sister chromatids of a chromosome (bioriented bivalents)

Telophase and cytokinesis

2 haploid (2 sister chromatids) (halving of chromosome number =

reduction division)

What does ensure chromosome number reduction (in meiosis I)?

• Synapsis (- recombination – chiasma) connecting

homologous chromosomes

• Cooriented sister chromatids of a chromosome (bioriented bivalents)

• Cohesin is separated only from arms

Significance of synapsis

A spermatocyte from an infertile man immunostained with antibodies against SCP1 and SCP3 (red) to observe synapsis, MLH1 (green) to visualize sites of recombination, and CREST antiserum (blue) to identify centromeres. Meiotic defects, such as abnormal recombination and an increase in unpaired regions (arrows) were observed in some members of the infertile population.

No synapsis,

no segregation

Abnormal chromosome number

Meiosis II.

- before it there is NO DNA replication

- Meiosis II. is like mitosis

4 haploid (1 sister chromatids), genetically different cells

Kinetochore orientation and separase activity in meiosis II

Meiosis I Meiosis II

shugosin

shugosin

Homologous recombination and independent assortment of homologous chromosomes

Segregation of sister chromatids

Significance of meiosis

- genetic variability (genetically different cells)

- chromosome number is halved (2n n)

Atypical meiotic processes

• May cause chromosome abnormalities in gametes

• Which in turn may cause genetic diseases

Meiosis II

Non-disjunction

Meiotic non-disjunction and its consequence

Aneuploid genom mutation

If non-disjunction occurs in spermatogenezis

Meiosis I meiosis II

Meiosis is part of gametogenesis

-gonium (46)

Primary gonocyte (46)

Spermium (23)

In embryo

From Puberty

Zygote (46)

polocytes

Secondary gonocyte (23)

polocyte

spermatid

Spermatocyte Oocyte

synapsis starts

At the end of chromosomes

Inside the chromosomes

Synaptonemal complex

compact Less compact

shorter longer

Sites of chiasmata

(green in figures)At the end of chromosomes

Inside the chromosomes

Number of chiasmata

less more

Primary spermatocyte

Primary oocyte

Sex specific differences in meiosis I prophase

Sex differences differences in non-disjunction

Meiotic (I and II) non-disjunction may occur both in oogenesis and spermatogenesis

BUT

More frequent in oogenesis

Sex chromosome non-disjunction is more frequent in spermatogenesis

Regulation

Regulation of meiosis in oogenesis

main regulator is MPF (maturation promoting factor)

Causes of major specificities of

female meiosis

Retinoic acid (RA) induces meiosis in female embryo

Meiosis inhibiting factor

Inaktív MPF

Arrest in prophase I diplotene (in embryo) cAMP

Inhibitory kinasez phospatase

InactiveMPF

Unknown ligand or constituvily active receptor

Adenylylcyclase (active)

meiosis stops

Primary oocyte

cAMP may enter the cells throug gap junctions from neighboring cells

phosphodiesterase (inactive)

Green – activered - inactive

Release from meiosis I prophase (from puberty) Effect of LH (from granulosa cells):

Inhibitory kinase phosphatase

Aktive MPF

Meiosis continues

cAMP

Green – activered - inactive

Adenylylcyclase (inactive)

Primary oocyte

phosphodiesterase (active)

C mos protein synthesis

MAPK activation

APC inhibitor

APC inhibition

Stop in metaphase II

Arrest in metaphase II(secondary oocyte)

caused by CSF-cytostatic factor (?)

Regulation of meiosis in oogenesis

Regulation of meiosis in oogenesis

Release from metaphase II(secondary oocyte) arrest

due to fertilisation

Ca ion inactivation of APC inhibitor APC activation completion of meiosis

Genetically identical cells in an organism

Genetically different cellsGenetically different individuals