Sexual differentiation in cats and dogs

Question 1

Sexual differentiation and development of female and male reproductive tract.

3 processes happens in the following order:

Answer 1

1. Chromosomal or genotypic sex programming (establishment of chromosomal sex)
2. Gonadal sex development (development of gonadal sex)
3. Phenotypic sex development (development of phenotypic sex)

Question 2

Sexual differentiation and development of female and male reproductive tract.

3 processes that happen in a certain order. What is the first process?

Answer 2

1. Chromosomal or genotypic sex programming (establishment of chromosomal sex)

Question 3

3 processes that happen in a certain order. What is the 2nd process?

Answer 3

2. Gonadal sex development (development of gonadal sex)

Question 4

3 processes that happen in a certain order. What is the 3rd process?

Answer 4

3. Phenotypic sex development (development of phenotypic sex)

Question 5

The dog has ? chromosomes and the cat has ?

Answer 5

The dog has 78 chromosome numbers and the cat has 38 chromosome numbers.

Question 6

Miniature schnauzer pseudohermafrodism.

Answer 6

is a rare genetic condition in which a dog has ambiguous genitalia or a mismatch between chromosomal sex and physical sexual characteristics.

Affected dogs may show a mix of male and female reproductive structures. This condition is relatively uncommon but has been documented in Miniature Schnauzers due to breed-specific genetic predispositions.

Question 7

Genotypic sex development determined by

Answer 7

Sex is determined by sex chromosomes:
Female: XX
Male: XY

In absence of masculinizing signals, the female pathway is the default program.

Question 8

Two genes are important in testis determination:

Answer 8

1. SRY (sex determining region on the Y chromosome) encodes for the SRY protein or the testis development factor (Tdf)
2. Sox9, also known as SRY-Box Transcription Factor 9, is an important gene is sex determination. The SOX family of genes are all transcription factors for the Y chromosomal sex-determining factor SRY.

Question 9

Describe Pre-attachment development of the embryo.

Answer 9

It begins with fertilization, forming a zygote, followed by cleavage (rapid cell divisions) to create a morula.

The morula develops into a blastocyst, a hollow structure with an inner cell mass (future embryo) and outer trophoblast layer (future placenta)

Question 10

The primary embryonic germ layers. (3)

Answer 10

endoderm
mesoderm
ectoderm

Germ layers, responsible for the gonads and external genitals.

Question 11

endoderm gives rise to? (3)

Answer 11

GI tract
lungs
endocrine system

Question 12

mesoderm responsible for the development of (4)

Answer 12

muscle
skeleton
cardiovascular

and repro system: gonads, uterus, cervix, part of vagina, epididymis, ductus deferens, accessory glands

Question 13

ectoderm responsible for the development of (5)

Answer 13

nervous system (NB hypothalamus and both lobes of the pituitary gland)
skin
hair

so, portions of the vagina and vestibule, penis and clitoris (cause of the skin portion).

Question 14

Development of the embryo.
What embryonic germ layer eventually envelopes the fetus, yolk sac and allantois?

Answer 14

the mesoderm

It forms part of the extraembryonic membranes, such as the chorion and amnion.

Question 15

The undifferentiated gonad is made of two cell types:

Answer 15

1. Primordial germ cells from the yolk sac endoderm
2. Supporting cells of mesothelial origin

Question 16

The gonads originate at

Answer 16

the Gonadal ridge that develops on the dorsal wall of the body cavity.

Question 17

Gonadal sex differentiation.

The reproductive system develops in close relation to and at the same time as the

Answer 17

renal system.

Question 18

Gonadal sex differentiation.

The mesonephros gives rise to the

Answer 18

urogenital ridge, containing the
mesonephros, indifferent gonad and wolffian (mesonephric) and Mullerian (paramesonephric) ducts.

Question 19

The early embryo utilizes 3 morphologically distinct systems:

Answer 19

1. Pronephros
2. Mesonephros
3. Metanephros

Question 20

Phenotypic sex development.

The organization of the genitalia and the
brain depends on

Answer 20

the presence, or absence of testosterone/ androgen.

Alfa-fetoprotein is the factor that diverts female and male brain developmental paths.

Alfa-FP prevents estradiol from entering the brain thus, the hypothalamus is feminized and the surge center develops.

In males, testosterone freely enters the brain, alfa-FP doesn’t bind it up and thus, the brain is “defeminized”.

Question 21

Events leading to formation of the male and female reproductive system.

Answer 21

whether the testes determining factor is present or not, so it depends on the chromosomes.

And then whether alfa-fetoprotein blocks stuff and feminizes the brain or not.

Question 22

How male genitalia is developed.

Answer 22

testes determining factor,
testes develop
sertoli cells secrete anti-mullerian hormone.
AMH causes leydig cells to differentiate as well as, degeneration of the paramesonephric ducts (also known as mullerian ducts).

leydig cells then produce testosterone and dihydrotestosterone.
testosterone causes development of the male duct system.
dihydrotestosterone causes the development of the penis, scrotum and accessory sex glands.

Question 23

Steps on the descent of the testes.

Answer 23

gubernaculum grows
gubernaculum end is fused to peritoneum in the inguinal ring
visceral growth occurs
then gubernaculum does some regressing
and finally becomes fully regressed leaving the testes in the scotum

Question 24

The development of the female reproductive tract takes place because of

Answer 24

the absence of TDF.

Question 25

Development of the testes and ovaries - schematics.

Answer 25

Question 26

Forming of the uterus, cervix and vagina.

Answer 26

Question 27

Review theses schematics in sex differentiation.

Answer 27

mullerian ducts become female repro parts, in males they regress. wolffian ducts become male repro parts, in females they regress. the urogenital sinus stays open in females, closes in males forming urethra, prostate. fetal genital swellings remain open, form vulva in females, form scrotum in males.

Question 28

PMDS = ? What breed is overrepresented?

Answer 28

Persistent Müllerian Duct Syndrome (PMDS) is a reproductive disorder in which the uterus and other parts of the female reproductive tract develop in male dogs making them intersex. Possess testes that are frequently retained. e.g. Miniature Schnauzers Clinical signs of hyperestrogenism (alopecia, gynecomastia) when functional sertoli cell tumor present (which is more common in PMDS).

Question 29

What effect does AMH have on development in male dogs?

Answer 29

Anti-Müllerian Hormone (AMH) is a glycoprotein hormone produced by the Sertoli cells in the testes of male mammals. During embryonic development, AMH causes the regression of the Müllerian ducts, which would otherwise develop into female reproductive structures such as the uterus, fallopian tubes, and upper part of the vagina. This process occurs in male embryos to ensure the development of the male reproductive tract from the Wolffian ducts.

Question 30

Which diagnostic steps could confirm PMDS in suspected cases?

Answer 30

Persistent Müllerian Duct Syndrome (PMDS) is a reproductive disorder in which the uterus and other parts of the female reproductive tract develop in male dogs making them intersex. U/S to look for uterus

Question 31

Would you remove the uterine/testicular structures in PMDS?

Answer 31

Yes, the uteruses are prone to pyometra and the undescended testes are prone to sertoli cell tumors.