Cell Nucleus Chen Li Department of Cellular and Genetic Medicine 13 223 chenli2008@fudan.edu.cn
Outline A. Historical background B. Structure of the nucleus: nuclear pore complex (NPC), lamina, nucleolus, chromatin C. Function of the nucleus: passive diffusion and active transport through the NPC, breakdown and re-formation of nuclear lamina, chromatin assembly, chromatin modifications
A. Historical background
Discovery of the nucleus Robert Hooke (British), 1665 Antonie van Leeuwenhoek (Dutch), 1674 Robert Brown (Scottish),1831
Characteristics of the nucleus Largest cellular organelle in animals Mammalian red blood cells do not have nucleus Appear in interphase, disappear in mitosis
Size of nuclei in different cells Type Animal cell nucleus Plant cell nucleus Eukaryote cell Prokaryote cell (no nucleus) Diameter 5-10 μm 5-20 μm 20-30 μm 5-10 μm
B. Structure of the nucleus C. Function of the nucleus
Structure of the nucleus
Detailed structure of the nucleus Nuclear envelope inner nuclear membrane outer nuclear membrane Perinuclear space Nuclear pore complex (NPC) Lamina (envelope) nucleus Nuclear skeleton nuclear matrix chromosome scaffold fibrillar component nucleolus Granular component chromatin Perinucleolar heterochromatin euchromatin
Structure of the nuclear envelope
Function of the nuclear envelope Separate DNA, RNA and protein Transport RNA, RNP, nuclear protein through nuclear pore
The nuclear pore complex (NPC)
Structure of the NPC (top view) Octagon structure Ring, spoke, plug Wheel with 8 spokes
Structure of the NPC (side view) Nuclear ring, cytoplasmic ring Sandwich, basket
Function of the NPC Provide aqueous channels Allow small molecules freely permeable Block large molecules transported selectively. Bidirectional transportation Transport RNA, RNP, nuclear protein through nuclear pores.
Passive diffusion through the NPC Allows free entry/exit of many small molecule (< 10 nm) and proteins (< 60 kd) Exceptions: some small molecules are actively transported or blocked
Active transport through the NPC Regulates the entry/exit of molecules based on the recognition of nuclear localization sequence (NLS) or nuclear export signal (NES) Requires energy: RAN cycle (Ras-related nuclear protein) [Ran-GTP Ran-GDP] nuclear import receptor (importin), export receptor(exportin)
Nuclear localization sequence (NLS) nuclear resident protein, NLS-protein basic amino acid No conservation in sequence NLS not be cut after transport. PKKKRKV SV40 Exception
Receptor-mediated entry/exit Nuclear import receptor: importin export receptor: exportin Energy source: Ras-related nuclear protein (RAN) cycle [Ran-GTP Ran-GDP]
NLS-protein import (binding)
NLS-protein import (translocation)
NES-protein export
Nuclear lamina
Structure of nuclear lamina
Function of Nuclear lamina Provides stability Anchors the NPC Binds the inner nuclear membrane Transduces signals Anchors perinuclear chromatin
Function of Nuclear lamina Lamina breakdown take place in interphase prophase Lamin phosphorylated by lamin kinase p34/cdc2 Lamin A/C depolymerized Nuclear membrane breakdown into vesicles attach with Lamin B
Breakdown and re-formation of nuclear lamina
No membrane organelle Fibrillar & granular components NORs rrna + Ribonucleoprotein (RNP) = ribosome Nucleolus
Chromatin Chromatin contains DNA and proteins. Histone /nonhistone proteins
DNA: deoxyribonucleic acid Watson & Crick, 1953
Histones DNA is bound to the histones through electrostatic forces between the negatively charged phosphate groups in the DNA backbone and positively charged amino acids. Found only in eukaryotic cells
Non-histone proteins Sequence specific DNA binding proteins (e.g., transcription factors) Enzymes (DNA polymerase, RNA polymerase), structural proteins (e.g., high mobility group protein: HMG), additional regulatory proteins
Chromatin structure Nucleosome, H1, H2A, H2B, H3, and H4 and DNA. Octamer (H3) 2 (H4) 2 (H2A H2B) 2, 146 bp DNA, 1.75 round H1, 20 bp DNA Linker DNA, 60bp, beads-on-astring
Chromatin assembly 2 m dsdna in nucleus of 10 μm diameter = 2 Km thread in a tennis ball! Condenses about 10,000-fold during cell division
Chromatin assembly Step 1: 2 nm dsdna 10 nm nucleosome (7-fold) Step 2: 10 nm nucleosome 30 nm solenoid (6-fold)
Chromatin assembly
Chromatin assembly Step 3: 30 nm solenoid 300 nm supersolenoid (10 fold) Scaffold-radial loop structure model Step 4: 300 nm super-solenoid 700 nm chromatin fiber miniband (4 fold) Miniband Step 5: 700 nm chromatin fiber 1.4 μm chromatid (5 fold)
Chromatin assembly
Multiple coiling model From DNA to chromosome
Euchromatin & Heterchromatin Type Euchromatin Heterchromatin Phase interphase interphase Form Extend form Condense form Fold <2000 fold condensation >2000 fold condensation Condensation solenoid super-solenoid,chromatin fiber Dye Basic dye light Basic dye dark Activity Transcriptionallyactive transcriptionallyinactive Subtype H1 less more Histone acetylation high low Constitutive & facultative
Clinical implications Barr bodies One of the female X chromosome is randomly inactive. Chimera Fragile X syndrome
Chromatin modifications DNA methylation Histone acetylation Phosphorylation
Chromatin modifications DNase I hypersensitive sites Chromatin accessibility
ENCODE Encyclopedia of DNA Elements (ENCODE) Consortium research progress: Nature 9/2012 A landmark in the understanding of the human genome after Human Genome Project. Catalogs regulatory events that act at DNA, RNA, and protein levels
Chromosomes during cell division Appear in metaphase Sister chromatids
Human chromosome karyotype
Chromosome structure 3 functional elements: origin, Centromere (primary constriction), Telomere Four types: Metacentric, Submetacentric, Acrocentric, Telocentric chromosome
Chromosome structure 3 10 9 bp, ~21,000 protein coding genes Non-repetitive DNA: protein coding sequences Moderately Repetitive DNA: SINEs, LINEs, regulatory sequences, rrna, trna, histone Highly Repetitive DNA: satellite DNA, mini-satellite DNA, micro-satellite DNA
Functions of the nucleus Houses chromosomes Provides an isolated environment for DNA replication and gene expression Provides an isolated environment for the processing of mrna and rrna Regulates the entrance and exit of proteins and nucleic acids from/to the cytoplasm How cell nucleus functions
Thanks!