The nuclear envelope consists of two parallel membranes separated by 10-50 nm. It serves as a barrier between the nucleus and cytoplasm. Nuclear pores are circular complexes of proteins that form openings in the nuclear envelope, allowing transport of molecules between the nucleus and cytoplasm. The nuclear envelope forms through the recruitment of membrane vesicles to chromatin, fusion of these vesicles, and assembly of nuclear pore complexes. Key proteins like POM121 and NDC1 are essential for nuclear pore complex assembly after the formation of the double nuclear membrane.

1. NUCLEAR ENVELOPE and
NUCLEAR LAMINA
Dr.Sujit Ghosh

2. NUCLEAR ENVELOPE and
NUCLEAR LAMINA
1.NUCLEAR MEMBRANE
2. Nuclear Pore Complex
3. Nuclear Lamina

3. 1a.
Nuclear Envelope• The nuclear envelope has two membranes,
each with the typical unit membrane
structure. They enclose a flattened sac and
are connected at the nuclear pore sites. The
outermost membrane is continuous with
the rough endoplasmic reticulum (ER) and
has ribosome’s attached (see figure to the
left). The space between the outer and inner
membranes is also continuous with rough
endoplasmic reticulum space. It can fill with
newly synthesized proteins just as the rough
endoplasmic reticulum does. The nuclear
envelope is enmeshed in a network of
filaments for stability.
The nuclear envelope is shown
in an electron micrograph

4. 1b.
Nuclear Envelope
• The formation of the eukaryotic nuclear envelope (NE)
also requires membrane fusion events. The nuclear
membranes are separated by a lumen and joined by nuclear
pore complexes
• The nuclear envelope both populated with a variety of
transmembrane proteins
• Made up of
– outer nuclear membrane
– inner nuclear membrane,
• connecting
– nuclear membrane to cytoskeleton,
– nuclear lamina
– chromatin

5. 1c.
Formation of nuclear envelope
– Mechanism of vertebrate nuclear envelope
assembly has been studied from cell free system of
Xenopus egg extracts This has allowed the in vitro
dissection of NE formation into distinct steps:
• recruitment of membrane vesicles or tubules to the chromatin
surface,
• fusion of these vesicles/tubules ,vesicle fusion,
– promoted by the small GTPase Ran, p97, and αSNAP,
– regulated by importin β and transportin
– These will form double nuclear membranes, nuclear pore complex
(NPC) assembly,
– A recent study showed that the vesicle–vesicle fusion event required for
forming the double nuclear membranes in Xenopus egg extracts is
dependent on SNARE proteins

7. The nuclear envelope consists of two cellular
membranes arranged parallel to one another and separated
by 10 to 50 nm
The membranes of the nuclear envelope serve as a barrier
that keeps ions, solutes, and macromolecules from passing
freely between the nucleus and cytoplasm.
The two membranes are fused at sites forming circular pores
that contain complex assemblies of proteins.
The nuclear envelope is the barrier between the nucleus and
cytoplasm, and nuclear pores are the gateways across that
barrier. Unlike the plasma membrane, which prevents
passage of macromolecules between the cytoplasm and the
extracellular space, the nuclear envelope is a hub of activity
for the movement of RNAs and proteins in both directions
between the nucleus and cytoplasm.

10. 2. NPC

12. FORMATION OF NPC
• Formation of Nuclear pore complexes form at two times in the
vertebrate cell cycle:
– NPCs double in number in G1-S phase,
– disassemble in prophase and reform at the end of mitosis.
• There are two school of thought regarding the assembly of NPC
WITH NUCLEAR MEMBRANE – ONE DURING FORMATION OF
NUCLEAR MEMBRANE OTHER AFTER THE FORMATION OF
NUCLEAR MEMBRANE
• The most current model of postmitotic NPC assembly argues that
only the initial steps of NPC assembly occur on chromatin, followed
by double nuclear membrane assembly and concurrent nuclear pore
assembly in these nuclear membranes.
• Indeed, cell-free experiments using the NPC assembly inhibitor
BAPTA or an NPC insertion assay show that NPCs can form in vitro
in completely closed nuclear membranes, presumably through
opposing bilayer fusion. POM121 and NDC1 are essential for nuclear pore
complex assembly FOR NUCLEAR PORECOMPLEX ASSEMBLY POM121 and
NDC1 are essential

14. FG are the direct mediators of
nucleocytoplasmic transport