Development of the reproductive tract and Spermatogenesis

Question 1

What are the four levels for organization of the development of the reproductive tract? What is the stimulus for development of the M or F repro tracts at the four levels?

Answer 1

1.) Chromosomal/Genotype
2.) Gonadal development
3.) Internal Genitalia
4.) External Genitalia/Phenotype

mullerian develops into female reproductive tracts
wolffian develops into male reproductive tracts

Question 2

Define spermatogenesis, spermatocytogenesis, and spermiogenesis

Answer 2

Spermatogenesis: Process of
spermatozoa development from
Spermatogonia to mature Sperm

Spermatocytogenesis: Cellular
division phase of spermatogenesis

Spermiogenesis: Process of
Maturation from Spermatid to
Sperm

spermatogonia undergo meitosis, spermatocytes undergo meiosis.

Question 3

Understand the germinal cell lines in reference to cell division and spermatogenesis

Answer 3

Spermatocyte= Diploid (2N)
Spermatids = Haploid (1N)

Question 4

Be able to describe the “spermatogenic wave of development within the seminiferous
tubules”

Answer 4

• Referred to as testicular wave
• Different regions of same
  seminiferous tubule will be in
  different stages of spermatogenesis
• Continuous sperm output

Question 5

Understand the function and development of the Blood testis barrier.

Answer 5

Tight Cell Junctions (TCJ) of Sertoli Cells form beneath
Spermatocyte during Meiosis 1 while the TCJ above the
spermatocyte is degrading.

Small transitional zone is formed and upper area opens for cell to
migrate then lower layer closes behind. (I think of this like a lock
on a river)

Immunologic barrier (Sperm cells express different surface
proteins and will be recognized as non-self)

Development encouraged by androgen and retinoic acid

Development Inhibited by Activin and TGF-Beta-3

Question 6

Length of spermatogenesis and stages vary per species. Know the average is 60 days for
spermatogenesis with additional 10 days for maturation within the epididymis

Answer 6

great, thanks.

• Average time for Spermatogenesis is 60 days
  Time from germ cell development to release into Seminiferous tubule
• Average time of maturation within epididymis: 10 days
• Most sensitive stages of development (Meiotic prophase) is 30 days
  prior to ejaculation.

Question 7

What are the general phases of spermatogenesis?

Answer 7

1.) Proliferation: Mitosis of Spermatogonia to make
renewable supply of spermatogonia stem cells as well as
Spermatogonia that will undergo meiosis and become
gametes. (Spermatogonia A1-A4, I and B)
(More to note about proliferation: Spermatogonia replicate via mitotic division, The cohort of cells remain connected via cytoplasmic intracellular bridges, A few cells will not have bridges and remain as stem cells, A few cells will degenerate)

3.2.) Meiotic Phase:
Primary Spermatocytesà Meiosis 1 &2 = Spermatids

3.) Differentiation phase: “Spermiogenesis” Spermatid
differentiates into a functional Spermatozoa

Question 8

What is the stimulus for development of the genetic sex? testes? regression of mullerian ducts? wolffian ducts?

Answer 8

Egg contributes X chromosome, Sperm contribution determines fetal
genotype: Y= Male, X=Female

Gonadal development is determined by presence of absence of the Y chromosome SRY region (Sox9 gene)

Testes Produce Anti-Mullerian Hormone (AMH) which causes regression of the Mullerian ducts

Testes Produce Testosterone the causes development of Wolffian Ducts which makes the vas deferens and and epididymides.

Testosterone –> DHT for development of the urogenital sinus (urethra, prostate), genital tubercle (penis), and genital swellings (scrotum).

Question 9

What is the embryological origin of seminiferous tubules? The epididymes and vas deferens? Mullerian ducts? Urethra and prostate? Penis? Scrotum? spermatazoa?

Answer 9

primordial germ cells fom the yolk sak, to the genital ridge for the sex cords which elongate to seminiferous tubules. the interstitial cells of the corsd become sertoli cells and the mesenchymal cells between the sex cords become leydig cells.

The Wolffian Duct system develops into Vas Deferens and epididymides if there is testosterone

The Mullerian Duct system develops into oviduct, uterus, cervix and cranial vagina, unless there is Mullerian
inhibiting hormone from a testis, then this duct system regresses.

Urogenital Sinus will become a closed urethra and prostate in the presence of DHT. The genital tubercle will become the penis in the presence of DHT. Genital swelling will become the scrotum in the presence of DHT.

Primordial germ cells > Spermatozoa
Sex Cords > Seminiferous tubules
Interstitial Cells of cords > Sertoli cells
Mesenchymal cells between cords > Leydig cells

Question 10

What could cause a discrepancy between
Genotype and Phenotype?

Answer 10

Chromosomal abnormality such as XXY, XO, XY with SRY deletion

Androgen receptor defect
5 alpha Reductase defect

Androgen Exposure How would this happen?

Question 11

Be able to define Hermaphrodite vs. Pseudohermaphrodite

Answer 11

Hermaphrodite:
* Both Testicular and Ovarian Tissue
present
* Rare
* Most common in swine

Pseudohermaphrodite:
* Ovaries Present with Male external Genitalia
* Female Pseudohermaphrodite
* Very Rare

• Testes with Female External Genitalia
• Male Pseudohermaphrodite
• uncommon

Question 12

Demonstrate an understanding of Androgen Resistance Syndromes, Freemartinism, Cryptorchidism.

Answer 12

Androgen Resistance Syndromes: Incomplete masculinization of XY individual. Bilateral Testes. Normal regression of Mullerian Ducts. Normal testosterone secretion. Female external genitalia.

Two forms of this syndrome
1.) 5 Alpha reductase deficiency > inadequate DHT production
2.) Androgen Receptor dysfunction:
Testosterone and DHT may fail to have normal effect.

Freemartin Characterisitics:
Early fusion of placental blood vessels
between twins may facilitate transfer
of hematopoietic precursor cells,
Testosterone, and AMH from the Bull
twin to the Heifer.
Female Calf
* Hypoplastic ovaries which may contain Seminiferous tubules
* Variable Development of Mullerian Ducts
* Wolffian duct derivatives present
* Shortened Vaginal vault
* +/-Enlarged clitoris,
* +/- Tuft of fur at ventral vulva
* May have abnormal anal to vulvar distance

Statistics:
85-95% of Heifers that are born with a Bull co-twin will be affected
First 30 days of pregnancy, consider if reabsorbed bull co-twin

Diagnosis:
* Check length of vaginal vault (clinically easy)
* Karyotype to document chimera (historical)
* PCR of lymphocytes (whole blood sample)

Cryptorchidism
* Genetic condition in some species
* Normal Migration of Testes into scrotum is due to widening and shortening of the
Gubernaculum
* Androgen responsive phase in Migration of testes

• Retained Testis:
• normal hormone production
• abnormal sperm production
• Increased risk for neoplasia