Transcript Animal Science 434 Reproductive Physiology

Animal Science 434
Reproductive Physiology
Lec 5: Embryogenesis of the Pituitary
and Sexual Development
Development of the Pituitary
Gland
Germ Cell Migration
Migration begins by the 4 week of gestation in cow and human.
Migration from endoderm
through mesoderm.
In birds the migration is via the blood stream.
Fetal Kidneys
• Pronephros
– regresses
• Mesonephros
– portions of reproductive tract
• Metenephros
– Adult kindney and urinary ducts
Development of Mesenephros and Metenephros
Jost Experiments
Sex Determination: The Jost Paradigm
Chromosomal Sex
Chromosomal Sex
Gonadal Sex
Gonadal Sex
Hormonal Sex
Phenotypic Sex
Phenotypic Sex
Brain and/or Behavioral Sex
Chromosomal Sex
• Sex is environmentally determined
– sea worms, fish
• Single Pair of sex chromosomes
– mammals, some but not all vertebrates
• Multiple sex chromosomes
– invertebrates, insects, reptiles
• Haplodiploidy
– bees, spiders
Chromosomal Sex
A. Drosophila
• Sex depends on the number of X chromosomes
– X or XY or XO  Male
– XX or XXX or XXY  Female
B. Human (mammals)
• XY or XXY or XXYY or XXXY or XXXXY  Male
(testis)
• XX or XXX  Female (ovary)
• XO  Female with incomplete ovarian development
• XXY or XXYY or XXXY or XXXXY  testis but
impaired sperm production
C. Conclusion
• The primary gene that controls testicular differentiation is
on the Y chromosome in mammals.
The Y Chromosome
A. Region coding for testicular development
• Short arm of Y chromosome
–H-Y Antigen
« no longer believed to be involved
–SRY
« Codes for a DNA binding protein
« acts as a transcription factor or assists other
transcription factors
« the gene products which are transcribed regulate
primary sex chord differentiation (formation of
seminiferous tubules), androgen production and AntiMullerian Hormone (AMH) production
« in the absence of the SRY protein, primary sex chord
regress and secondary sex chords (egg nests) develop
The Y Chromosome Cont.
B. Other genes on the Y chromosome
– Spermatogenesis
– androgen production
– long bone growth
SRY and Birds
• Birds
» females ZW, males ZZ
» W chromosome determines sex
» SRY is found on the Z chromosome !
• SRY is not the only sex determining
gene in animals
Gonadal Sex
XY Male
Testis Determining Factor
(SRY gene product)
Testes develop
Testicular Development
Mesonephric Duct
(Wolffian Duct)
Mesonephric Tubules
Rete Tubules
Mullerian Duct
Tunica
Albuginea
Undifferentiated
Sex Chords
Mesonephric
Tubules
Rete Tubules
Wolffian
Duct
Mullerian Duct
Primary, Epithelial or
Medullary Sex Chords
Tunica
• Primordial germ cells
Albuginea • Sertoli Cells
Hormonal Sex
XY Male
Testis Determining Factor
(SRY gene product)
Testes develop
Sertoli cells secrete
anti-mullerian hormone (AMH)
AMH causes leydig
cells to differentiate
Testosterone
Development of male
duct system
Wolffian Duct Cells
Nucleus
Testis
T
T
TR
Efferent Ducts
Rete Tubules
(Vas Efferentia)
Epididymis
Ductus
Deferens
Seminiferous
Tubules
Tunica
Albuginea
XY Male
Testis Determining Factor
(SRY gene product)
Testes develop
Sertoli cells secrete
anti-mullerian hormone (AMH)
AMH causes leydig
cells to differentiate
Testosterone
Development of male
duct system
Degeneration of
Mullerian duct
Vas efferentia
Female Development
XX Female
No TDF
Testes Determining Factor
Ovaries Develop
No
Testosterone
Wolffian Ducts
Regress
No AMH
Mullerian ducts become
the oviducts, uterus, cervix
and part of the vagina
Ovarian
Development
Regressing
Tubules
Mullerian
Duct
Epithelial
Sex Chords
Future Ovarian
Cortex
Wolffian
Duct
Regressing
Tubules
Mullerian
Duct
Regressing
Epithelial
Sex Chords
Future Ovarian
Cortex
Regressing
Wolffian
Duct
Regressing
Tubules
Primordial
Follicles
Mullerian
Duct
Regressing
Epithelial
Sex Chords
Future Ovarian
Cortex
Regressing
Wolffian
Duct
Secondary or
Cortical Sex
Chords
(egg nests)
Primordial
Follicles
Mullerian
Duct
Ovarian
Medulla
Regressing
Wolffian
Duct
Ovarian
Cortex
Development
of the Uterus, Cervix
and Vagina
Mullerian Duct
Fused Mullerian
Duct
Hymen
Reproductive tract develops outside the
peritoneum!
Broad Ligament Development
(transverse anterior section)
Ovary
Regressing
Wolffian Duct
Mullerian
Duct
Ovary
Regressing
Wolffian
Duct
Mullerian
Duct
(Posterior Transverse Section)
Genital Fold
(Future Broad Ligament)
Regressing
Wolffian
Duct
Mullerian
Duct
Testis Determining Factor
(SRY gene product)
XX Female
XY Male
Testes develop
Sertoli cells secrete
anti-mullerian hormone (AMH)
AMH causes leydig
cells to differentiate
Testosterone
Development of male
duct system
No TDF
Degeneration of
Mullerian duct
Ovaries Develop
No
Testosterone
Degeneration of
Wolffian duct
No AMH
Mullerian ducts
become
the oviducts,
uterus, cervix
and part of the
vagina
Phenotypic Sex
XY Male
Testis Determining Factor
(SRY gene product)
Testes develop
Sertoli cells secrete
anti-mullerian hormone (AMH)
AMH causes leydig
cells to differentiate
Degeneration of
Mullerian Duct
Testosterone
Dihydrotestosterone
Development of male
duct system
Development of penis
scrotum and accessory
sex glands
Wolffian Duct Cells
Nucleus
Testis
T
T
TR
Accessory Sex Glands* and External
Genitalia Cells
Nucleus
Testis
T
T
D
5Reductase
DR
*Prostate, Cowper’s Gland
Significance of DHT
• Androgen receptor has a higher
affinity for DHT
• Can get effects with low levels of
circulating testosterone
• Secondary sex characteristic tissue
in the male expresses 5-reductase
External Genitalia
Differentiation
Testis Determining Factor
(SRY gene product)
No TDF
XX Female
XY Male
Testes develop
Ovaries Develop
No
Testosterone
Sertoli cells secrete
anti-mullerian hormone (AMH)
AMH causes leydig
cells to differentiate
Degeneration of
Mullerian duct
Degeneration of
Wolffian duct
Testosterone
Dihydrotestosterone
Development of male
duct system
Development of penis
scrotum and accessory
sex glands
No AMH
Mullerian ducts
become
the oviducts,
uterus, cervix
and part of the
vagina
Brain or Behavioral Sex
Brain and Behavioral Sex Differentiation
Genetics
Gonadal
Steroid
Hormones
Brain
Structure
Experience
Sexual
Behavior
Brain Sexual Differentiation
• Rat female
– Give testosterone shortly after birth
• fail to copulate or cycle like female as adult
• Sexually dimorphic nucleus
• Human male and female differences in
behaviors
– aggression
– childhood play
– 3D visual rotation
Decent of the Testis
into the Scrotum
Testicular Descent
Growth of testis
Fusion of the
tunica
albuginea and
peritoneum
to form the
visceral tunica
vaginalis
Front View
Rapid growth
of
gubernaculum
Testis is
pulled down
to the inguinal
ring.
Gubernaculum
regresses
Testis pulled into
scrotum
Continued regression of
Gubernaculum
Testis pulled deeper
into Sscrotum
Vaginal Process
attaches to Scrotum
Space between
Visceral and Parietal T.V.
is continuous with
Peritoneum
Failure or Problems With
Testicular Descent
• Cryptorchid
– unilateral
– bilateral
• Inguinal Hernia
Inguinal Hernia
Loop of
Intestine
Abnormalities in
Development
The Freemartin in Cattle
• Female born twin to a bull
• Extra embryonic membranes fuse to form
a common chorion
• Comon blood supply
• Both fetuses share a common hormone
milieu
– testosterone
– anti-mullerian hormone
• Animals are chimeric
– both express TDF
Testicular Feminization in
an XY Individual
• No androgen receptor
• Testis
• No testosterone response so no Wolffian
duct development
• AMH present so mullerian ducts regress
• External genitalia is female due to lack of
androgen
5  Reductase Deficiency in
an XY Individual
• testis
• AMH present so Mullerian ducts
regress
• some Wolffian ducts
• psuedovagina and female external
genitalia
• at puberty may differentiate into
phenotypic male
Describe the development of the
reproductive tract and/or gonad
in an undifferentiated
• embryo that is castrated.
• female embryo (XX) that has a testis
transplated next to the right gonad.
• female embryo (XX) that has a
testosterone implant placed next to
each gonad.