L2 pt 1: Sperm transport, Gamete interaction

Question 1

How and where do sperm mature?

Answer 1

• During transport through epididymis -> sperm acquire motility
• This process is androgen-dependent
• Transfer of proteins is mediated by epidiymosomes and molecular chaperones (e.g. EPPIN which coats the surface and prevents proteolytic attack and thus premature capacitation)
• They may be stored in cauda epididymis and/or vas deferens depending on species

Question 2

What functions does seminal plasma serve?

Answer 2

• Buffering (acidic RT conditions important for mucus structure)
• Oxidation protection (reducing agents like ascorbic acid) against atmospheric oxygen
• Metabolic support (fructose, sorbitol)
• Preparation for RT; considerable change to surface proteome and glycocalyx structure upon exposure to seminal plasma observed in many species
• Note: Seminal plasma is produced by accessory sex glands

Question 3

Where do sperm wait before ovulation in humans?

Answer 3

• In oviducal isthmus (maintained by OEC attachment)
• Move to ampulla (possibly by chemotaxis involving odorant receptors in flagellum) upon ovulation

Question 4

In some species, there are reservoirs of sperm attached to uterine ECs as well as OECs. How does the process of release differ in these two reservoirs?

Answer 4

• UECs: No changes to membrane; sialidase secreted by ovary upon ovulation, cleaving sialyl links between sperm and UEC
• OECs: Capacitation is a necessary condition for release, with remodelling of sperm PM taking place
• In both cases, binding of the sperm to the epithelial cells stimulate secretion of maintenance factors, allowing prolonged survival in the reproductive tract

Question 5

What is the function of EPPIN?

Answer 5

• Coats surface of sperm
• Type of protein inhibitor which protects from proteolytic attack and thus prevents premature capacitation

Question 6

How does the UTJ act as a physical barrier to sperm entry?

Answer 6

• Transient sphincter action

Question 7

What is the key physiological difference that sets species apart in terms of sperm surface proteome?

Answer 7

• Whether sperm are deposited into vagina (e.g. cow) or directly into uterus (e.g. sheep)
• Likely due to differences in accessory sex gland anatomy

Question 8

What function do cumulus cells on oocyte serve during ovulation? What happens after they break down?

Answer 8

• Allow oocyte to adhere to epithelium in oviducal ampulla once release ovary via fimbriated ostium
• As CCs break down, oocyte is swept towards isthmus and waiting sperm by contractions and cilia beats

Question 9

Components of oviduct:

Answer 9

• Isthmus
• Ampulla
• Fimbriae

Question 10

At what point is capacitation of sperm generally thought to occur?

Answer 10

• At point of deposition into tract

Question 11

What 2 key structural changes takes place in sperm during capacitation?

Answer 11

• Formation of lipid rafts in membrane -> sets stage for acrosome reaction
• Hyperactivated tail movements

Question 12

List signals that modulate periconception environment in female RT:

Answer 12

• Short range (local responses to gametes and embryo)
• Long range (environmental factors, nutrition, hormonal status)

Question 13

What are the three types of selective mechanisms on sperm in the reproductive tract?

Answer 13

• Physical barriers (interactions with cervical mucus, sphincter action of UTJ)
• Biochemical (e.g. BSP preventing premature capacitation, beta-defensin) -> Molecular passport concept
• Immunological (e.g. NETS, post-breeding endometritis)

Question 14

List some key members of the sperm glycocalyx with suggested roles on sperm survival and transport:

Answer 14

• Sialic acid: sequestration of sperm, allowing immune targeting by NETs -> phagocytosis
• Note that sialic acid expressed by UECs may be useful in binding sperm in some species
• Beta-defensin 126: conferring negative charge allowing ease of progression through electronegative mucus
• Beta-defensins may also have a general role in avoiding immunorecognition

Question 15

What are two types of sperm behaviour though to be important for sperm transport in the ewe RT? (Link to human ART techniques)

Mike tyson sigma male

Answer 15

• Thigmotaxis: interactions with physical barrier of membranes -> orientation etc
• Rheotaxis: Fluid-flow behaviour (i.e. in viscoelastic mucus) -> largely elucidated using microfluidic chips -> relevant to the use of Zymot chip in human IVF

Question 16

What are the 2 broad functions of reproductive mucus?

Answer 16

• Trap defective sperm
• Trap pathogens

Question 17

What are the 3 key effects biochemical interactions have on sperm survival and transport?

Answer 17

• Stabilisation of sperm membrane
• Delay of capacitation
• Establishment of sperm reservoirs in UECs/OECs

Question 18

What biochemical factors are important in the capacitation process? (Various species; 5x)

Answer 18

• Calcium
• Bicarbonate
• Albumin
• High density lipoproteins
• Heparin

Question 19

List the different features of the maternal immune response (x5):

Answer 19

• Antibodies
• Complements
• Macrophages
• Leukocytes
• Neutrophils

Question 20

What are NETs? Give an example of a sperm surface marker which may protect against NETs:

Answer 20

• Neutrophilic extracellular traps
• Can trap sperm and initiate phagocytosis via PMNs
• PMN: Polymorphonuclear granulocytes (some sperm surface proteins may be able to prevent PMN binding -> e.g. CRISP3 in horses)