BIOL 303 Lecture Notes - Lecture 12: Pronephros, Gonadal Ridge, Sertoli Cell
14 May 2018
School
Department
Course
Professor
General
• This lecture will be shorter than others
• This is Prof Dufort’s last lecture
Chromosomal Sex Determination
• There are many different ways that chromosomes determine sex in an individual
• Humans: The sex of an individual is determined by the 2 sex chromosomes (X/Y)
• Grasshoppers: you either have one X chromosome (male) or 2 X chromosomes (female)
• In a lot of birds: The Z/W system → ZZ = male, ZW = female
• Bees: haploid individual = male, diploid = female
Environmental Sex Determination – not relevant for exams
• Temperature may determine sex
• Environment may determine sex Ex. how many other males/females are in the area
Sex Determination in Mammals
Kidney differentiation
• Sex determination occurs in mice on day 10 after
fertilization and in humans during week 14 → takes
over the differentiating kidney AKA the kidney
differentiates first
• Pronephros act like primitive kidneys and are linked
to the nephric duct
• The nephric duct has many names Ex. Mullerian duct
• Anterior end is by the pronephros where your
shoulders would be
• As you go down, you get the mesonephros which are
similar to the pronephros but these are not the
definitive kidney
• The definitive kidney comes from a third region
called the metanephrogenic mesenchyme AKA
Metanephrose (the above three phases shown in
figure 1)
• As gestation continues, the pronephros
degenerates, the mesonephrose is taken over by the
reproductive system – the Wolffian duct (the
green region in figure 2), and the metanehprose
becomes the kidney
• As the testes develop you maintain the Wolffian
duct (XY)
• If you’re an XX individual, you are left with the
Mullerian duct
• The genital ridge → this is where the gonad forms
Figure 1
Figure 2
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Biol 303 March 13th, 2018
2
• At the genital ridge (week 4), there is a mixture of somatic and germ cells that develop
differently in males and females
• At 8 weeks, either testis cords develop (male) or germ cells embed in a surface
epithelium (female)
• At 16 and 20 weeks respectively, there are testis and ovary structures being formed
Specification and Migration of Mouse Primordial Germ Cells
• PGC = Primordial Germ Cell
• The developing gonads have to start migrating down into the ovary or the testes
• There is a bi-potential gonad at week 6 (bi-potential = could become male or female)
• At week 8, you have male or female determination = testis or ovary
• Granulosa cells are very important for gonad support → in the male you have tubules
with germ cells at the exterior with supporting Leydig and Sertoli cells around them
(these produce hormones)
How does the indifferent gonad determine if it will become an ovary or testis?
• In the bipotential gonad, the genes you are expressing determine if you will be male or
female
• 1950s experiments: looking at patients whose sex did not match their chromosomes →
they found out that it is the small arm of the Y chromosome that contains the genes
specifying male-ness → there is a gene in this area that is very important (SRY)
SRY Gene
• SRY = Sex Regulatory Region (on the Y
chromosome)
• SRY is a DNA binding factor (sort of a
transcription factor)
• This is the gene that is important for
specifying male sex
• Experiment to determine that it is the correct
gene for specifying male sex: express the
SRY gene in an XX embryo → if it grows
into a male then you know you have the
right gene
• See figure 3 for Sex outcomes with SRY
• SRY is important in humans but not all
species, some species don’t have SRY at all
Sox9 Gene
• Located on the autosomes
• First identified from female patients that had problems conceiving and turned out to have
genetic mutations (XY with 1 copy of Sox9)
• In XY individuals, you have 2 copies of Sox9 and become male
• In XX individuals, you also have 2 copies of Sox9 but become female
• In XX individuals with 3 copies of Sox9, you get a male → No SRY
Figure 3
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
General: this lecture will be shorter than others, this is prof dufort"s last lecture. In a lot of birds: the z/w system zz = male, zw = female. Environmental sex determination not relevant for exams: temperature may determine sex, environment may determine sex ex. how many other males/females are in the area. If you"re an xx individual, you are left with the. Mullerian duct: the genital ridge this is where the gonad forms. Figure 3 gene for specifying male sex: express the. Sox9 gene: located on the autosomes, first identified from female patients that had problems conceiving and turned out to have genetic mutations (xy with 1 copy of sox9) In xy individuals, you have 2 copies of sox9 and become male. In xx individuals, you also have 2 copies of sox9 but become female. In xx individuals with 3 copies of sox9, you get a male no sry.
