PGC

• Primordial Germ cells


  Any biological cell that gives rise to the gametes of an organism that reproduces sexually
• Germ cells that still have to reach the gonads are primordial germ cells, precursor germ cells, or gonocytes
• Introduction


  In mammals generally, a few cells in the pre-embryonic stage are induced by signal transduction of neighbouring cells to become primordial germ cells
• Primordium


  The beginning or first discernible indication of an organ or structure
• Primordial Germ Cells


  • They divide repeatedly on their migratory route through the gut and into the developing gonads
  • During gastrulation these group of cells are set aside to form oocyte or spermatozoa, they migrate through the posterior endoderm, which forms the hind gut from there to genital ridge which is the site of developing gonads
• Preformation (segregation)


  Germ cells determinants (germplasm) are set aside before or at fertilization and remain segregated throughout the lifespan of the organism
• Epigenesis (recreation)


  Primordial germ cells are generated during development. Seen in all mammals and, many other species, germ cells are "set aside" before other cell types
• Descendants and Migration

  1. The pgc are the common origins of spermatozoa and oocytes and thus represent the germline ancestors, they are diploid and can be recognised in the epiblast in the 2nd week

  2. In the 3rd week, the pgc wander amoebically from epiblast into the yolk sac wall and collect near the exit of the allantois, to become extraembryonal lying in the endoderm and mesoderm of the yolk sac wall

  3. During the fourth week they begin to migrate from the yolk sac towards the developing gonads, where they arrive by the end of the fifth week

  4. Mitotic divisions increase their number during their migration and also when they arrive in the genital ridge
• Differentiation


  1. Differentiation of primordial germ cells into oogonia begins shortly after their arrival in the Ovary. By the third month of development, some oogonia give rise to primary oocytes that enter prophase of the first meiotic division

  2. In the male and female, primordial germ cells form spermatogonia and oogonia respectively. After repeated mitotic divisions in the latter, some of these are arrested in prophase of meiosis I to form primary oocytes
• Gametes are derived from primordial germ cells that are formed in the epiblast during the second week which later moved to the wall of the yolk sac
• Maintenance of pluripotency within this cell population may arise through epigenetic modifications that suppress somatic differentiation programs
• Transformation of these population of cells lead to germ cell tumour
• Primordial Germ Cells


  The progenitors and ancestors of the sex cells
• Types of cells


  • Unipotent cell
  • Multipotent cell
  • Pluripotent cell
  • Totipotent cell
  • Embryonic Stem cell
  • Embryonic Germ cell