1. Animal Science 434 Lecture 13: Spermatogenesis

2. Production of Fertile Sperm hormonal regulation of the testis mitotic division of spermatogonia meiotic divisions of spermatocytes morphologic transformation of spermatids into spermatozoa hormonal regulation of the testis mitotic division of spermatogonia meiotic divisions of spermatocytes morphologic transformation of spermatids into spermatozoa

3. Hormonal Regulation of the Testis

4. LH GnRH FSH

5. Time of Day (24 hr) Pulses are important !

6. Hypothalamus GnRH E2E2 E2E2 Inhibin ABP Sertoli Cells Sertoli Cells Leydig Cells Leydig Cells Seminiferous Tubule Seminiferous Tubule Ant. Pituitary FSH on Sertoli Cells estradiol inhibin ABP tight junctions FSH on Sertoli Cells estradiol inhibin ABP tight junctions FSH LH Negative Feedback of Estradiol and Inhibin Germ Cells Germ Cells T T ABP + T ABP + T To Epid. Negative Feedback of Androgens TJ

7. Spermatogenesis

8. Myoid Cells Sertoli Cell

10. Every 13.5 Days a new group of cells initiate the cycle Every 13.5 Days sperm are released from this point Spermatozoa Secondary Spermatocyte Primary Spermatocyte Round Spermatid Spermatogonia

11. (A, intermediate, B) Spermatogonia (A, intermediate, B) Primary Spermatocyte Primary Spermatocyte Secondary Spermatocyte Round Spermatid Spermatozoa A A A II BB PP SS RS SP Spermato- cytogenesis Spermio- genesis Mitosis Meiosis Rete Testis Spermiation Typical Sequence of Spermatogenesis

12. A A A A A A I I I I B B B B P P P P S S S S RS SP 1 1 2 2 4 4 8 8 16 32 64 Potential Sperm Produced Many Sperm are Produced

13. Mitotic Divisions species dependent –between 2 and 6 divisions (4 to 64 potential daughter cells produced) classifications vary among species and investigators –A 1, A 2, A 3, A 4, B 1, B 2, P –A d, A p, B, P –A s, A 0, A 1, A 2, I, B, P cytoplasmic bridges form between daughter cells species dependent –between 2 and 6 divisions (4 to 64 potential daughter cells produced) classifications vary among species and investigators –A 1, A 2, A 3, A 4, B 1, B 2, P –A d, A p, B, P –A s, A 0, A 1, A 2, I, B, P cytoplasmic bridges form between daughter cells

14. Degenerating Spermatogonia (Apoptosis, as high as 75%) Cytoplasmic Bridges Present Among Daughter Cells All develop surrounded by 1 Sertoli cell !

15. Germ Cells / Sertoli Cell SpeciesPrimaryRoundMax. Potential SpermatocytesSpermatidsSpermatids Equine3.0 ± 0.210.9 ± 0.964 Bovine1.2 ± 0.15.2 ± 0.664 Human1.3 ± 0.14.2 ± 0.216

16. Apoptosis of Germ Cells Season Disease Trauma or heat Hormone levels Normal part of spermatogenesis Season Disease Trauma or heat Hormone levels Normal part of spermatogenesis

17. Stem Cell Renewal To keep spermatogenesis going indefinitely Replenish testis incase of injury, trauma, or high heat To keep spermatogenesis going indefinitely Replenish testis incase of injury, trauma, or high heat

18. FSH A4A4 A4A4 A3A3 A3A3 A2A2 A2A2 In B B P P A1A1 A1A1 Spermatogonial Renewal in the Rat and Bull Spermatogonial Renewal in the Rat and Bull Periodic Entry of Cells into Mitosis Periodic Entry of Cells into Mitosis Stem Cell Pool Stem Cell Pool

19. FSH ApAp ApAp AdAd AdAd B B P P Spermatogonial Renewal in the Primate Spermatogonial Renewal in the Primate Stem Cell Pool Stem Cell Pool

20. Stem Cell

21. Spermiogenesis

22. Golgi Phase Development of Acrosome Migration of Centrioles Development of Acrosome Migration of Centrioles

23. Cap Phase Acrosome Development Continues Flagellum Elongates Acrosome Development Continues Flagellum Elongates

24. Acrosomal Phase Acrosome Manchette Elongation Acrosome Manchette Elongation

25. Maturation Phase Manchette disapears Mitochondria migrate Dense fibers form Manchette disapears Mitochondria migrate Dense fibers form

26. Spermiation

28. Temporal Relationships of Spermatogenesis

29. Spermatogenesis 57 days Stallion

30. Multiple Generations of Germ Cells

31. Bull Spermatogenesis

33. Stages Specific cellular associations within a small segment of a seminiferous tubule stages are not the same length in time Specific cellular associations within a small segment of a seminiferous tubule stages are not the same length in time

34. Bull Spermatogenesis - Stages

35. Stages Specific cellular associations within a small segment of a seminiferous tubule stages are not the same length in time Specific cellular associations within a small segment of a seminiferous tubule stages are not the same length in time

36. Bull Spermatogenesis - Stages

37. Cycle progression through sequence of all stages

38. Bull Spermatogenesis - Cycles

39. Cycle progression through sequence of all stages 4.5 cycles to form spermatozoa –some species variation progression through sequence of all stages 4.5 cycles to form spermatozoa –some species variation

40. Duration of Spermatogenesis BullRamBoarStallionMan cycle (days)13.510.48.312.216 Spermatogenesis6147395775 BullRamBoarStallionMan cycle (days)13.510.48.312.216 Spermatogenesis6147395775

41. Coordination of Stages Form Waves some portion of seminiferous tubule is always releasing sperm

42. Compartmentalization of Spermatogenesis and the Blood Testis Barrier

43. Seminiferous Tubule and Interstitial Tissue

44. Interstitial Tissue Vascular System Provides Nutrients Oxygen Growth Factors Hormones Vascular System Provides Nutrients Oxygen Growth Factors Hormones Blood Vessel

46. Tight Junctions Myoid Cells Luminal Adluminal Basal Compartments

47. Cycles and Stages

48. Compartmentalization Basal –mitosis spermatogonia (A, I, B) primary spermatocytes Adluminal –meiosis primary spermatocytes secondary spermatocytes spermatids –spermiogenesis Lumen –spermiation Basal –mitosis spermatogonia (A, I, B) primary spermatocytes Adluminal –meiosis primary spermatocytes secondary spermatocytes spermatids –spermiogenesis Lumen –spermiation

49. Blood Testis Barrier Sertoli cells and associated tight junctions first appears at puberty induced by FSH after puberty can be maintained by FSH and/or testosterone essential for meiosis Sertoli cells and associated tight junctions first appears at puberty induced by FSH after puberty can be maintained by FSH and/or testosterone essential for meiosis !!!!!

50. Tight Junction Role in Meiosis Sertoli cells can manipulate environment around 1° spermatocyte –Enters meiosis –Completes meiosis Destruction of TJ causes impairment of meiosis –Heat, heavy metals, pesticides, lack of FSH or Testosterone Sertoli cells can manipulate environment around 1° spermatocyte –Enters meiosis –Completes meiosis Destruction of TJ causes impairment of meiosis –Heat, heavy metals, pesticides, lack of FSH or Testosterone

51. Capacity for Sperm Production SpeciesTestisSperm/gmDSP Weight (gm)(X 10 6 )(X 10 9 ) Dairy Bull6501810 Beef Bull500188 Ram5502614 Boar7503025 Stallion165183 Man404.045 -.2 SpeciesTestisSperm/gmDSP Weight (gm)(X 10 6 )(X 10 9 ) Dairy Bull6501810 Beef Bull500188 Ram5502614 Boar7503025 Stallion165183 Man404.045 -.2

52. Duration of Spermatogenesis BullRamBoarStallionMan cycle (days)13.510.48.312.216 Spermatogenesis6147395775 BullRamBoarStallionMan cycle (days)13.510.48.312.216 Spermatogenesis6147395775

53. FSH ApAp ApAp AdAd AdAd B B P P Spermatogonial Renewal in the Primate Spermatogonial Renewal in the Primate Stem Cell Pool Stem Cell Pool

54. Capacity for Sperm Production SpeciesTestisSperm/gmDSP Weight (gm)(X 10 6 )(X 10 9 ) Dairy Bull6501810 Beef Bull500188 Ram5502614 Boar7503025 Stallion165183 Man404.045 -.2 SpeciesTestisSperm/gmDSP Weight (gm)(X 10 6 )(X 10 9 ) Dairy Bull6501810 Beef Bull500188 Ram5502614 Boar7503025 Stallion165183 Man404.045 -.2

55. Variation in Sperm Production Testis Size Efficiency of spermatogenesis –mitotic division –degeneration of germ cells Length of spermatogenesis Testis Size Efficiency of spermatogenesis –mitotic division –degeneration of germ cells Length of spermatogenesis

56. Apoptosis of Germ Cells Season Disease Trauma or heat Hormone levels Normal part of spermatogenesis Season Disease Trauma or heat Hormone levels Normal part of spermatogenesis

57. Over Population of Spermatogonia SG Basement Membrane Sertoli Tight Junction PS SG Basement Membrane Sertoli AP Normal Apoptosis Inhibited SG Basement Membrane Sertoli SG

58. Animation of Spermatogenesis View the Animation of Spermatogenesis Using the Link at the Bottom of the Screen The objective is to see how the process of spermatogenesis takes place over time and involves both stages and cycles. In the animation, the timing of events is correct but we have taken liberties in moving groups of cells from side to side to make room for development of other cells. The animation begins with primordial germ cell migration into the primary sex chord and replication of gonocytes to form stem cell A-Type spermatogonia. The objective is to see how the process of spermatogenesis takes place over time and involves both stages and cycles. In the animation, the timing of events is correct but we have taken liberties in moving groups of cells from side to side to make room for development of other cells. The animation begins with primordial germ cell migration into the primary sex chord and replication of gonocytes to form stem cell A-Type spermatogonia.