spermatogenesis

overview and terminology

• gametogenesis

  • development of gametes

• spermatogenesis

  • development and production of spermatozoa

  • spermiogenesis: final stage of sperm maturation; spermatids to spermatozoa

• oogenesis

  • development and production of oocytes

• primordial germ cells (PGCs)

  • stem cell that will differentiate into gametes

meiosis overview

• meiosis: process involving 2 specialized cell divisions in germ cells that generate haploid gametes

bull reproductive tract

testes anatomical structure

• Leydig cells produce testosterone

• 2 Cell Theory for steroid production

  • Leydig = theca cell

  • Sertoli cell = granulosa

• controlled by hormones from the pituitary gland

• in males: important for testosterone production

testes anatomical structure (cont)

spermatogenesis: overview

• cytoplasmic bridges are important for transporting nutrients and gene products

primordial germ cells (PGCs)

post-blastocyst development

PGC migration

• why do PGCs migrate?

  1. to reach the gonadal ridge, the site of their development and differentiation

  2. to escape the differentiation signals occurring during gastrulation in the embryo proper

testes/ovary development

PGC proliferation

donor-derived spermatogenesis following stem cell transplantation in sterile NANOS2 knockout males

• how is this technology applicable to beef and dairy industries?

  • opportunities:

    • restoring fertility — human implications, chemo/radiation therapy

    • increase sperm production of elite sires — collection of bulls happens so often — produce more straws/quantities

    • beef x dairy implications

    • clean up bulls on farm — better genetic potential

    • older bulls may die; transport them

    • sub for AI

  • limitations:

    • low fertility

    • genetic modification concerns

    • expensive

    • issue with sperm quality — or the sperm that you want

    • can’t sex the semen

    • animal welfare

    • time consuming

    • more research

    • not available everywhere/geographical limitations

    • fertility efficiency issue — fertility not truly restored