Study Questions 9

Question 1

What is the difference between mammalian and bird sex determination? (What is the similarity?)

Answer 1

Difference Similarity Mammal Bird
Sex Chromosomes Both sexes have 1 sex chromosome in common (X, Z) XX (female), XY (male) e) ZZ (Male), ZW(Female) -sex chromosome autosomal in mammal

Male Determination Sry gene Dmrt1 gene

Question 2

List and briefly explain 2 female and two male sex chromosome abnormalities

Answer 2

Male
Klinefelter Syndrome Inherit 1+ X = XX+Y = tall, sterile, feminine body, may not show symptoms if ratio of XY: XXY low
XYY Inherit extra Y = XYY = high testosterone, tall, acne, fertile

Female
Turner Syndrome Inherit only 1 X = X0 = sterile, mental
Metafemale Inherit extra X = XXX+ = fertile, tall, mental

Question 3

Define primary and secondary sex determination in mammals.

Answer 3

● Primary sex determination = determination of gonads
○ Only chromosomal, no environmental
■ Y always makes male
■ Carries SRY gene that encodes testis-determining factor
○ Development of egg vs sperm
● Secondary sex determination – sexual phenotype development outside gonads through hormones
○ External genitalia
○ Duct system (Wolffian vs Mullerian)

Question 4

Where do the mammalian genitalia originate from? (remember there are two “places” of origin, one for external and one for internal genitalia)

Answer 4

● External Genitalia – genital tubercle and urogenital sinus
○ Male – Penis, Prostate, Scrotum
○ Female – labia, clitoris, lower vagina
● Internal Genitalia – potential genital ducts
○ Male – Wolffian Duct – epididymis, vas deferens, seminal vesicle
○ Female – Mullerian Duct – uterus, oviduct, cervix, upper vagina

Question 5

5. From what part of what germ layer do the gonads develop? Is this the same in both sexes?

Answer 5

Intermediate mesoderm develop into germ layer (bipotential gonads), same for both sexes

Question 6

From what cells do the sperm and oocytes develop? Is this the same in both sexes?

Answer 6

● Sperm and oocytes develop from germ cells and this is the same in both sexes
● Germ cells put through different conditions to specify spermatogenesis and oogenesis

Question 7

Where is the gene for “maleness” located in mammals? What is this gene called (full name)? Where is it located (what chromosome)?

Answer 7

● Located in the Y chromosome on the short arm

Question 8

What is truly unique feature of mammalian gonads at the beginning of embryonic development and how are they called?

Answer 8

● Bipotential Gonads are indifferent in beginning and can develop into ovaries or testes (usually gonads cannot make both)
● Unique feature of mammal gonads – go through bipotential (indifferent) stage

Question 9

What is the origin of Sertoli and Leydig cells and what do they secrete? What are their (cells’) homologs in female gonads and what do they secrete?

Answer 9

Sertoli
Origin Epithelial cells from genital ridge
Secrete Anti-mullerian factor, GDNP

Leydig
Interstitial mesenchyme cells,Testosterone Granulosa Cells-Epithelial cells of genital ridge, Estrogen
Thecal Cells-Mesenchyme cells of ovary, Androgen

Question 10

10. What is the major signaling pathway responsible for the formation of testis vs. ovary from the bipotential gonad? How does this signaling work (what other proteins are involved)

Answer 10

● Ovary
○ B-catenin Pathway – Wnt4 and Rspo1 activated by genital ridge factors
■ Rspo1 further stimulate Wnt pathway > make B-catenin
■ B-catenin further activate Rspo1 and Wnt4, initiate ovarian pathway (positive feedback loop), inhibit Sox9 accumulation
● Testis
○ Testis-determining pathway – genital ridge factor activate SRY gene
■ Sry activate sox9 and fgf9
■ Fgf9, repress B-catenin, prevent ovary forming pathway
■ Testis form

Question 11

11. Briefly describe the ovary pathway

Answer 11

● Genital Ridge activate Wnt4, Rspo1
● Wnt4 activate Wnt pathway, Rspo1 improves pathway
● Wnt pathway cause b-catenin to accumulate
● B-catenin
○ induce transcription of ovary producing genes
■ activate ovary-specific transcription factors (Tatabox activating factors)
○ blocks testosterone pathway (inhibit Sox9, Sry)
● Positive loop of Wnt4/b-catenin
● Non-functional rspo1 = male development

Question 12

12. Briefly describe the testis pathway

Answer 12

● Presence of SRY gene > block b-catenin
● SRY work with Sf1 to activate sox9
● Sox9 activate fgf9 = stimulate testis development
● Sox9 prevent b-catenin from activate ovary-producing genes
● Sox9/fgf9 loop specifies testis

Question 13

Which protein is coded by what is considered to be an autosomal testis-determining gene? What type of morphogen is it (i.e. what does it do - how it regulates male sex)? How many copies of this gene are present in a normal male cell? Could this protein be expressed from a normal (un-modified) female genome? Why or why not? What happens if XX individual has an extra copy of this gene?

Answer 13

● Sox9 is autosomal testis-determining gene (high mobility group box protein?)
○ Transcription factor morphogen that binds to DNA to induce testis formation
○ 2 copies are present in normal male cell because autosomal
○ This protein cannot be expressed in normal female genome
■ Repressed by b-catenin, need sry and sf1 to activate sox9
○ If XX has extra copy, will develop testis but will not have sperm development
■ Has sox9 gene expression and anti-mullerian factor
■ Seminiferous tubules lack sperm b/c 2 X chromosomes in sertoli cells

Question 14

14. What is the role of Fgf9 in normal testis development?

Answer 14

Migration of mesonephric cells into XY Gonad and induction of sertoli cells

Question 15

15. What is the role of SF1 in testis development?

Answer 15

● Formation of bipotential gland
● Downregulated in females, high in males
● Induce testosterone-related genes
● Regulate AMH expression (Anti-mullerian hormone)
● Convert wolffian duct to epididymis, vas deferens

Question 16

16. What is the role of Dax1 in gonadal development?

Answer 16

● Initially expressed in genital ridge of both sex
● Downregulates Sf1 expression = no induction of testosterone genes
● Antagonizes function of Sry and Sox9
● Development of ovaries from gonads

Question 17

Briefly explain regulatory cascade involved in Drosophila sex determination. Wnt signaling testis
(what step in gene expression does it regulate)?

Answer 17

● Females determinants on X, male determinants on autosomes
● Transcription factors from x chromosome and secreted factor compete to activate or repress Sxl gene promoter
○ Sxl active = female
■ Sxl activates transformer (tra) genes
■ Tra splice doublesex (DsxF) in female way, fruitless pre-mRNA in female-specific way
■ DsxF protein repress male differentiation gene
■ Make transcription factor for female specific traits
○ Sxl inactive = male
■ Absence = no Tra proteins
■ DsxM splice in male way and fruitless pre-mRNA processed in male-specific way
■ DsxM transcription factor repress female differentiation genes, direct male-specific traits

Question 18

18. Define secondary sex determination.

Answer 18

● Response to hormones secreted by ovaries or testes (AMH testosterone for males)
● 2 phases
○ During organogenesis within embryo
○ During Puberty

Question 19

Which signaling pathway is involved in secondary sex determination? What is the difference between signaling through this pathway in formation of internal vs. external genitalia?

Answer 19

● Wnt signalling pathway involved w/ secondary sex determination
● Pathway acts in genital ridge to activate female path > wnt inhibitor prevent b-catenin production, estrogen + receptor help form clitoris and labia majora
○ Mesenchyme make wnt pathway inhibitor that lead to feminization of genital tubercle > clitoris, labia majora (external genitalia)
● Pathway acts in genital tubercle to activate male path > activate b-catenin to make penis, scrotum
○ Testosterone bind to testosterone receptor in mesenchyme to prevent expression of wnt inhibitor (inhibition of inhibitor) = Wnt expression in mesenchyme > penis, scrotum (external genitalia)
● Internal genitalia – wnt pathway block sox9 and activate b-catenin for females, opposite for males

Question 20

What will be the outcome if an individual has a mutation in the gene for testosterone receptor?

Answer 20

Lack of testosterone receptor result in androgen insensitivity syndrome (complete and incomplete) = no masculinisation (require both receptor and Sry, AMH expression) = undescended testis

Question 21

. Briefly explain the term “brain sex”.

Answer 21

● Female and male monkeys chose to play with human children’s “sex-typed” toys
○ Female chose to play with doll, male play with toy car
■ NO SOCIAL INFLUENCE =something in the brain different between sexes
● Genes on X, Y chromosome regulate brain development – different gene expression in M/F before gonad differentiation (Sry expression in male, more epinephrine secreting neuron in F)
○ Change in structure of brain due to sex

Question 22

. Where do the gametes arise from? What is the difference between frogs and mammals in respect to specification of the cells which will form gametes?

Answer 22

● Gametes arise from primordial germ cells through
○ Autonomous specification with cytoplasmic determinants (germplasm) in frogs
○ Conditional Specification with neighbour cells in mammals

Question 23

What is the role of ring canals during oocyte formation in Drosophila?

Answer 23

● Ring canals are cytoplasmic bridges that connect cytocytes (cluster of 16 cells) during oocyte formation
○ Cells with 4 interconnections (2) can become oocyte, only one of two actually does
○ Canal allow intercellular material to pass from 15 nurse cells to oocyte
● Process of oocyte formation
○ Germ cell form germline stem cell
○ Stem cell divide to form itself and differentiated daughter cell (cystoblast)
○ Cystoblast do mitosis 4 times w/ incomplete cytokinesis to form 16 cells of cystocytes that are connected by ring canals
○ 1 of the 2 cells with 4 interconnections become oocyte, rest become nurse

Question 24

Where do the germ cells form in mammals? What is their origin and where do they first migrate? Which signaling pathway is involved and which tissue is producing the initiating morphogene? What is the germ cells’ final destination?

Answer 24

● Mammalian germ cells form at posterior epiblast at the junction of the extraembryonic ectoderm, allantois and primitive streak (Posterior proximal epiblast)
● Germ cells originate from epiblast cells
● Germ cells first migrate to the endoderm from the primitive streak
● Wnt signalling pathway is involved (high wnt, BMP in area where germ cells made)
● The extraembryonic ectoderm produces in the initiating morphogen (BMP)
● Germ cells final destination is gonads

Question 25

What is AVE? (Give the full name.) What is its role in formation of PGCs? When did we mention it before?

Answer 25

● Anterior visceral endoderm (AVE) originates from the visceral endoderm (hypoblast) together with Node (organizer – equivalent to Hensen’s node in birds) is involved in A-P axis determination AVE inhibits Wnts, nodal etc. – causes anterior development
● Recognizes epiblast in respect to where PGC precursors can emergy

Question 26

What are the major differences between male and female mammalian gametogenesis (there is a table on one of the slides, but I want you to use your own words to describe the differences)

Answer 26

● Meiosis occurs indefinitely in males but is finite in females
● Only one gamete made per meiosis in females but four in males
● Meiosis does not complete until fertilization in female (months, years), completes periodically (Days, weeks) in males
● Diploid gamete undergoes differentiation in female whereas male gamete differentiation at haploid stage
○ Meiosis arrested at 1st prophase and reinitiated in females, males complete meiosis
● Female chromosome have equal transcription and recombination but male sex chromosome does not during prophase I
● Males degrade retinoic acid as a result of embryo testes enzyme, does not occur in females

Question 27

27. What is the major difference between primary and secondary spermatocyte?

Answer 27

Primary spermatocyte is diploid, secondary is haploid

Question 28

28. What is unusual about communication between spermatogonia?

Answer 28

● Receptors for both Wnt and BMP
● Incomplete cytokinesis – to form synctium for communication via cytoplasmic bridges
○ Result in divisions that make interconnected cells = synchronized maturity

Question 29

. Describe the role(s) of galactosyltransferase molecules on spermatogenic cells.

Answer 29

● Galactosyltransferase on spermatogenic cell bind to carbohydrate on sertoli cell for nutrients
● *Also a sperm surface protein that recognize carbohydrate on ZP3 initiating acrosomal reaction

Question 30

What is the role of Sertoli cells in respect to developing sperm cells? (Remember their role in the developing testis)

Answer 30

Developing Sperm Cells - Secrete AMF to support sperm production through nourishment and protection Secrete GDNF which determine if spermatogonia stay as stem cells or differentiate into spermatocytes

Developing Testis - Surround germ cells and organize them around testis cords

Question 31

31. What are the two types of ovulation in mammals?

Answer 31

● Stimulation of ovulation by copulation (mating) (rabbits, minks)
● Periodic ovulation