Module 6

Question 1

What does the HPG axis refer to and what is it crucial in?

5pt

Answer 1

HPG axis refers to the concerted action individual glands, i.e. the hypothalamus, the pituitary, and the gonadal glands (testes/ovaries)
Crucial in:
Development of gonads
Sexual differentiation
Reproduction
Mating behaviors

Question 2

What are the 2 major functions of the gonads in the adult animal?

2pt

Answer 2

Make gametes and make sex steroid hormones

Question 3

What is Gonadotropin-releasing hormone (GnRH) from the HPG axis in animals

5pt

Answer 3

• GnRH is a peptide hormone that binds to its own receptor in the pituitary
• GnRH is very low during childhood, and activated at puberty
• Later pulse activity is critical for successful reproductive function
• In males, GnRH is secreted in pulses at a constant frequency
• In females, the frequency varies during the menstrual cycle

Question 4

What is Luteinizing hormone (LH) and follicle
stimulating hormone (FSH) from the HPG axis in animals

3pt

Answer 4

• LH and FSH are peptide hormones
• In males, LH induces synthesis of testosterone, FSH stimulates meiosis in primary spermatocytes
• In females, “LH surge“ triggers ovulation and development of corpus luteum, FSH induces growth and recruitment of immature ovarian follicles

Question 5

What is Progesterone (P4) from the HPG axis in animals

5pt

Answer 5

• P4 is a progestogen steroid hormone produced by the corpus luteum
• If no fertilization occurs, drop in P4 will lead to menstruation
• It is essential for implantation and gestation, and reduces contractility of uterus
• Inhibits lactation during pregnancy
• Drop of P4 after pregnancy marks the onset of labor

Question 6

What are Estrogens from the HPG axis in animals

2pt

Answer 6

• Estrogens are the primary female sex hormones, which promote formation of female secondary sex characteristics and reproductive system
• It increases fat stores, stimulates endometrial and uterine growth

Question 7

What are Androgens from the HPG axis in animals

3pt

Answer 7

• Androgens are the primary male sex hormones and promote development of the male reproductive system and secondary sexual characteristics (muscle growth and body hair)
• Testosterone
• Dihydro-testosterone

Question 8

Waht is the HPGL axis in oviparous (egg laying) vertebrates?

1pt

Answer 8

GTH I and GTH II are structurally homologous to
the tetrapod FSH and LH hormones.

Question 9

What are the characteristics of LH and FSH

5pt

Answer 9

Both:
* 32 kD dimeric glycoprotein

LH:
* t1/2 = 20-30 min
* Acts on steroid hormone producing cells
* Leydig cells of the testes
* Thecal cells of the ovary

FSH:
* t1/2 = 2-3 hours
* Acts on specific follicular cells
* Sertoli cells of the testes
* Granulosa cells of the ovary

Question 10

What are glycoprotein hormones?

7pt

Answer 10

• LH and FSH are glycoprotein hormones
• Glycoprotein hormones contain two glycosylated polypeptide chains held by non-covalent links. These are called subunits.
• FSH and LH share a common α subunit withTSH and hCG
• Each hormone has a distinct β subunit
• Within a species the α subunits of LH and FSH are similar and essential to the formation of the final hormone while the β subunits are different
• The β subunits provide the biological activity of the hormone. Independent units are biologically inactive.
• The subunits are coded by different genes.

Human chorionic gonadotropin (hCG) is a hormone produced by the placenta during pregnancy.

Question 11

Which unit would bind to the FSH or LH receptor and what kind of receptor is it?

2pt

Answer 11

β subunit
Cell surface receptor

Question 12

What are examples of sex steroid hormones and how are they synthesized?

6pt

Answer 12

Progesterone
* Synthesis: theca and granulosa cells (luteal phase –> corpus luteum), placenta, adrenal cortex

Testosterone
* Synthesis: testes (Leydig cells), adrenal cortex

Estradiol
* Synthesis: ovarian follicle (thecal cells), corpus luteum

Question 13

What is steroidogenesis and where are the principal sites for it?

2pt

Answer 13

Many cells and tissues (e.g., liver) can metabolize one steroid to another, but a cell is said to be ‘steroidogenic’ only if it can initiate the process by expressing P450scc/CYP11A1, which initiates steroidogenesis
Principal sites of steroidogenesis are:
* adrenal cortex
* ovaries
* testes
* placenta
* skin, liver and kidney

Question 14

Where does cholesterol come from and how do you name steroid hormones?

3pt

Answer 14

Cholesterol precursor comes from cholesterol synthesized within the cell from acetate
* cholesterol ester stores in intracellular lipid droplets or from uptake of cholesterol-containing low density lipoproteins

Basic cyclopentanoperhydrophenanthrene ring structure and carbon numbering system of all steroid hormones (Pregnenolone is C21, Testosterone is C19)

Question 15

What does biosynthesis of steroid hormones require and what are the rate limiting steps?

3pt

Answer 15

Requires MANY oxidative enzymes located in
both mitochondria and endoplasmic reticulum

Two main rate-limiting steps in this process:
1. The transport of free cholesterol from the cytoplasm into mitochondria
2. Within mitochondria, cholesterol is converted to pregnenolone by an enzyme in the inner membrane called CYP11A1 (aka P450scc)

• This is the immediate precursor for the synthesis of all of the steroid hormones

Question 16

What happens to lipid droplets rich in cholesteryl esters?

1pt

Answer 16

Lipid droplets rich in cholesteryl esters normally accumulate in steroidogenic cells and their mobilization is the preferred initial source of cholesterol for steroidogenesis

Question 17

What is Steroidogenic Acute Regulatory Protein (StAR) and how is it activated?

4pt

Answer 17

• A rapidly induced, short-lived, 37 kDa protein that acts OMM to stimulate the flow of cholesterol from the OMM to the IMM. At the IMM, cholesterol is taken up by P450scc and converted to pregnenolone
• Activate intracellular kinases that, in turn, phosphorylate transcription factors that upregulate StAR expression
• StAR is activated by phosphorylationand this facilitates transfer of cholesterol from the outer to inner mitochondrial membrane
• Allows entry of cholesterol into the steroid biosynthetic pathway, beginning with pregnenolone.

Question 18

What are the groups of steroid hormones?

5pt

Answer 18

• Glucocorticoids: cortisol is the major representative in most mammals
• Mineralocorticoids: aldosterone being most prominent
• Androgens: such as testosterone
• Estrogens: including estradiol and estrone
• Progestogens (also known a progestins): such as progesterone

Question 19

What is boar taint?

3pt

Answer 19

Off-odours/off-flavours found predominantly in
the meat of some intact male pigs
* 2 chemicals that males pigs develop naturally as they become reproductively mature
* Consumers who experience Boar Taint are put off eating pork
* Boar taint is prohibited by food quality regulations in most countries

Physical castration of male piglets is the most common practice to avoid boar taint used worldwide
* driven mostly by economic forces

In research from the European Union, more than 25% of intact males exhibited off-odor compounds, with androstenone and/or skatole in fat tissue above sensory thresholds

Question 20

What are the advantages & disadvantages to raising castrated males?

4pt

Answer 20

Advantages:
* Less aggression in casterated males
* Removes chance of getting boar taint

Disadvantages:
* Lower feed efficiency in casterated males
* Public perception of casteration

Question 21

What are the compounds associated with boar taint?

2pt

Answer 21

16-androstene steroids (primarily androstenone)
* Leydig cells in the testis

Skatole and other indoles
* Metabolism of tryptophan by the gut microflora

Occur naturally in male pigs as they mature

Question 22

How is Androstenone Synthesized and how does it cause boar taint?

4pt

Answer 22

• Synthesis increases as the pig nears maturity (testes)
• Synthesized from pregnenolone in reaction catalysed with CYP17A1 and CYB5 followed by reductases
• CYB5 may be potential target for specific inhibition of androstenone synthesis
• Enters the blood stream to be transported to peripheral tissues (primarily adipose) where it accumulates to cause boar taint

Question 23

How is Skatole synthesized and how does it cause boar taint?

4pt

Answer 23

• Skatole is produced by the bacterial breakdown of tryptophan in the hind gut
• Production affected by diet as well as the composition of the gut microflora
• Metabolism and clearance is regulated by the activity of the Phase I and Phase II enzymes in the liver that degrade skatole
• The balance between production and clearance of skatole determines how much skatole accumulates in fat.

Question 24

How do you control boar taint?

3pt

Answer 24

Immunocastration using a commercially available vaccine (Improvest® from Zoetis)
* stimulates the production of antibodies against gonadotropin releasing hormone (GnRH)

Vaccine induces the production of antibodies that inactivate GnRH

Shut down testicular development to the same extent as surgical castration and eliminate the production of both androstenone and the sex steroids

Question 25

What does immunocasteration do? | 3pt

Answer 25

* Growth rate, feed conversion and lean yield of immunocastrates are closer to that of intact males than to barrows (surgically castrated animals) * Also reduces aggressive and sexual behaviours with head knocking, fighting and mounting behaviours as compared to intact males * What about skatole? * Levels of skatole are also low in immunocastrated pigs, and this is most likely due to enhanced metabolic clearance by the liver after steroid production is suppressed!

Question 26

What are the 2 main functions of the testes? | 2pt

Answer 26

Steroidogenesis Spermatogenesis

Question 27

What is the anatomy of the testes? | 2pt

Answer 27

The testis comprises two structurally and functionally distinct compartments: 1. seminiferous tubule compartment: composed of Sertoli cells and developing germ cells at various stages of spermatogenesis, accounts for 80% to 90% of the volume of the testis 2. interstitial compartment: composed of Leydig cells that secrete testosterone + other cell types (fibroblasts and macrophages)

Question 28

What are the phases spermatogenesis can be divided into? | 3pt

Answer 28

1. proliferation and differentiation of spermatogonia 2. meiosis 3. spermiogenesis, a complex process that transforms round spermatids after meiosis into a complex structure called the spermatozoa. ## Footnote In the seminiferous tubule compartment

Question 29

What are the main functions of sertoli cells? | 6pt

Answer 29

1. Delivery of nutrients and growth factors for spermatogenic cells 2. Physical support of germ cells 3. Release of the spermatids towards the tubular lumen (spermiation) 4. Secretion of tubular fluid (within sperm are made) 5. Phagocytosis of apoptotic germ cells 6. Produce androgen-binding protein (ABP)

Question 30

What is the interstitial compartment comprised of and what is its job? | 2pt

Answer 30

Comprised primarily of Leydig cells (which bind luteinizing hormones, LH) Main job is to production of testosterone * Used in sperm development * Development of secondary male sex characters (tubercles in fish, lion’s mane, facial hair men) at puberty * Production of dihydrotestosterone via 5α-reductase

Question 31

What is the hypothalamic-pituitary-testicular axis | 2pt

Answer 31

Major positive regulators of testis function are LH and FSH In androgen target tissues, T and DHT in the circulation diffuse through the plasma membrane and bind to androgen receptors

Question 32

What are the specific FSH/LH action in the testes | 4pt

Answer 32

FSH makes androgen-binding protein (ABP) * Binds testosterone * Maintains high T levels in seminiferous tubule -> how does it do this and why is this important? * Testosterone sustains sperm production

Question 33

How does testosterone support sperm production/development? | 4pt

Answer 33

In concert with FSH, testosterone acts locally (paracrine signalling) on Sertoli cells within the seminiferous tubules of the testes to initiate and maintain spermatogenesis. 1. Maintain the blood–testis barrier 2. Sertoli-spermatid adhesion 3. Release of mature sperm

Question 34

What is the anatomy of the ovary? | 3pt

Answer 34

The ovary consists of three structurally distinct regions: * An outer cortex containing the surface germinal epithelium and the follicles * A central medulla consisting of stroma * A hilum around the area of attachment of the ovary to the mesovarium

Question 35

What is oogenesis? | 4pt

Answer 35

Starts with developing oogonia into primary oocytes Making of oocytes (2nàn) starts (meiosis) but stops either before or shortly after birth in mammals. During the menstrual/estrus cycle, primary oocytes complete maturation through further meiotic divisions. This first meiotic division is coordinated by hormones: * Follicle stimulating hormone (FSH), estrogen, luteinizing hormone (LH), and progesterone!! The oocyte is arrested in cell division prior to the second meiotic division, which only occurs after fertilization.

Question 36

What are the endocrine cells of the ovarian follicle? | 4pt

Answer 36

Granulosa cells and Thecal cells Development of an antrum marks gonadotropin dependency. Multiple layers of granulosa and theca cells are present The follicle destined to ovulate distinguishes itself from the rest of the cohort through accumulation of large quantities of antral fluid The mural granulosa cells in the periphery primarily serve as steroidogenic cells

Question 37

In the luteal phase what does increased activity of 3βHSD2 do? | 1pt

Answer 37

In the luteal phase, increased activity of 3βHSD2 in the corpus luteum metabolizes pregnenolone to progesterone.

Question 38

What does Aromatase do? | 4pt

Answer 38

* Enzyme that is responsible for a key step in the biosynthesis of estrogens (transforms testosterone to estradiol) * Located in the endoplasmic reticulum of the cell * Found in many tissues including gonads, brain, adipose tissue, placenta, blood vessels, skin, bone, endometrium * Tissues of endometriosis, uterine fibroids, breast cancer, and endometrial cancer * Aromatase inhibitors are frequently used to treat those diseases

Question 39

What is the Corpus Luteum? | 4pt

Answer 39

* Develops from an ovarian follicle during the luteal phase (after ovulation) of the menstrual cycle or estrous cycle * Essential for establishing and maintaining pregnancy in females * Secretes primarily estrogens and progesterone, which are steroid hormones responsible for the thickening of the endometrium (uterine lining) * The granulosa cells become granulosa-lutein cells (large cells), and the theca cells are transformed into theca-lutein cells (small cells)