Organelles of Sperm

BY SHAHROKH PAKTINAT

Introduction

Differentiation of germ cells

Oocyte

Spermatozoon

Structure of Mammalian Spermatozoon

Sperm head & Sperm tail or flagellum

Rodent → hook-shaped or falciform

Ungulate, carnivore & primate → spatula-shaped or spatulate

Major distinction: centrosomes

Sperm Head

Nucleus (DNA & Protamines)

Reduced nuclear envelope (removed NPC)

Perinuclear theca or perinuclear matrix:

Subacrosomal layer

Equatorial segment (folded-over complex of PT, IAM & OAM)

Postacrosomal sheath (harbor SOAF)

Sperm Head

Sperm Flagellum

9+2 arrangement of microtubules

9 Outer dense fibers

4 major Segments (innermost and external structures):

Connecting piece: 9 segmented columns, capitulum, basal plate

Midpiece: mitochondrial sheath, mtDNA

Principal piece: annulus, fibrous sheath

End piece: axonemal doublets, outer dense fibers

Spermiogenesis

Extensive remodeling process

Biogenesis of accessory structures:

Acrosome

Amalgamation of cytosol

PT

Axoneme

Head shaping and hypercondensation

Centrosome reduction

Mitochondria rejection

NE reduction

Spermiogenesis

Recycle of organelles and proteins

Ubiquitin-dependent proteolysis (26 S proteasome)

E1, E2, E3 & E4

Monoubiquitin regeneration

Known substrates:

H2A & H3

Mitochondrial membrane protein prohibitin

Nucleolar ribonucleoproteins, NPC proteins, nucleoporins

Spermiogenesis

Transient structures & molecules:

Transitional proteins (TP1 & TP2)

Pro-acrosomal granules

Caudal manchette

Chromatid body

Residual body & Cytoplasmic droplet (CD)

Sperm Transport

Liquefaction

Chemotaxis (guanylate cyclase, ANP, P91& formylated N-peptides) → granulosa cell

Capacitation (2-4h in vitro): hyperactivation & acrosome reaction

Cholesterol removal

Expression of mannose binding site & progesterone receptor

Phosphorylation of tyrosine residues

Calcium influx

ROS

Changes of Sperm Head During Fertilization

ZP glycoproteins → ZP1, ZP2 & ZP3

ZP3 → before AR

ZP2 → after AR

Acrosome reaction (proacrosin)

P hormone & P-binding protein

Receptors of P: PR1 (Ca), PR2 (PTk) & PR3 (Cl & GABA) → infertility

Zona penetration → ubiquitin-proteasome system

Equatorial acrosome → equatorin

Changes of Organelles During Fertilization

Surface membranes → lost

PT → dissolved for oocyte activation

Smooth NE → replaced by maternally derived NE

Protamines → degraded & replaced by oocyte-derived histones

Zygotic centrosome → maternal centrosomal proteins + sperm-contributed centriole

Mitochondria, axoneme, accessory structures → degraded

Sperm Incorporation in Ooplasm, Oocyte Activation & Zygotic Development

Incorporation of plasma membranes → adhesion molecules & receptors

In mouse: α6β1 integrin receptors & ADAM proteins (fertilin β & cyritestin) & CD9

Direct contact of equatorial & postacrosomal segments with ooplasm

Transmission of SOAF into ooplasm → oocyte activation

PLC-zeta → calcium oscillation-inducing component of SOAF

Other PT proteins → oocyte activation & early stages of pronuclear development

Candidate Molecules Involved in the Sperm-Oocyte Fusion

Sperm Incorporation in Ooplasm, Oocyte Activation & Zygotic Development

Reversal of histone-protamine exchange

Replacement of NPC-free NE by de novo formed NE

Sperm contributed mRNAs → translated or maternal mRNA silencing

Sperm proximal centriole + oocyte pericentriolar material → zygotic centrosome

Sperm mitochondria → degraded by ooplasmic proteasomes

Ubiquitin label → spermatogenesis

Oocyte glutathione

Other sperm accessory structures

Importance of Centrosome in Fertilization

Incomplete centrosomes → arrest in fertilization → infertility

Absence or anomaly → Immotile or non-progressive sperms

vasectomy → anti-centriole antibodies

Ultrastructure & Pathology of Human Spermatozoa

Thanks for Your Attention