Stem cell biology

1. PRIMORDIAL GERM CELLS
P.PARANI SANKAR | 3rd B.sc Biotechnology | A8UBT028

2. INTRODUCTION
• Primordial germ cells (PGCs) are the precursors of the gametes.
• They are unipotent and differentiate into sperm and gametes.
• PGCs in culture give rise to Pluripotent embryonic stem cells.
• PGCs in are extensively studied in models like drosophila , zebra fish , mice
but human are not studied well due to ethical issues .

3. SEX DIFFERENTATION
a) The sex chromosomes in the somatic cells of the genital ridges determine which type of
gonad the ridge becomes.
b) In females:
Differentiates
PGCs Oogonia
9th week
 Oogonia gets arrested at diplotene stage in meiosis 1.
 In the male , after reaching the developing the testis , PGCs are usually termed
Gonocytes.
 Gonocytes enter mitotic arrest and stay quiescent till birth.

4. DIFFERENTIATION OF PGCs

5. MORPHOLOGY
PGCs are generally
 Spherical and larger in size ,
 Large nucleus with marked
nuclear membrane.
 Diameter .10 to 20µm.
 Morphological modifications of
PGCs depending on the 2
phases:
 Separation and migration phase
 Colonization phase .

6. ORIGIN
In mammals the primordial germ cells have extra gonadal origin.
Alkaline phosphate enzyme is used as a Marker to determine the location
and migration of these cells.
In human embryo, PGCs originate in the endodermal epithelium of the yolk
sac in the vicinity of the allantoic stalk.
Germplasm
PGC recognised
Sperm Ovum
Embryo Gametes Early embryonic stage
PGC Inside embryo

7. TRANSPORTATION OF PGCs
 PGC originate outside , they move to reach gonads.
 They transported into two types ,
o By Blood stream in chick embryo
o By Amoeboid movement in human embryo

8. MIGRATON
Separation
• PGCs leave
the hindgut
epithelium and
enter the
mesenchymal
cells of the
dorsal
mesentry.
Migration
• PGCs use
amoeboid
movement to
move between
mesenchymal
cells of dorsal
mesentry to
travel to
genital ridges.
Colonization
• PGCs reach
and populate
the genital
ridges.
 Begins to migrate from yolk sac in the 4th week and reach gonads by 5th week in
mammals.
 Controlled through two separate ligand receptor , chemo attractant signalling
interactions.

9. PGCs IN
DIFFERENT
ANIMALS
FISHES:
PGC
ENDODERM

10. BIRDS AND
REPTILES
PGC ENDODERM
Extra embryonic part of the
blastoderm
Anterior to the head region of
the embryo

11. “THINK GLOBALLY , ACT LOCALLY”