Sexual dimorphism Flashcards
what is the main determinant of sexual determination/dimorphism in Drosophilia
the X autosome ratio - triggers alternative gender dependent slicing cascades of both dosage compensation and somatic and neural sex determination
describe the gender-dependent splicing cascade that leads to male CNS dependent gender dimorphism in drosophila
The SEX LETHAL (SXL) protein is not expressed during early male development (due to the 1X:2A ratio).
As a result, it does not initiate sustained functional Sxl or transformer (tra) mRNA and protein expression.
In the absence of functional TRA protein, TRANSFORMER 2 (TRA2) regulates male-specific splicing of the fruitless (fru) gene in a subset of CNS neurons, which leads to the production of BTB-zinc finger FRUM protein isoforms.
FRU^M initiates a transcriptional programme responsible for almost all CNS-dependent gender dimorphism including courtship behaviour.
what are the crucial sexual dimorphisms in the Manduca sexta (tobacco hawk moth)
the macula cellular cortex is only in the male (senses female pheromones with its antennae)
males have thicker antennae and larger olfactory glomeruli in the brains antennal lobe (specialised for odorant mediated sex specific behaviours)
female invest a lot of energy in their gametes and only let the most evolutionary impressive males to fertilise them
what is (sex chromosome) dosage compensation
the process by which organisms equalize the expression of genes between members of different biological sexes.
eg In fruit flies the males boost the expression from the single x chromosome
in fruit flies what contributes to male soma and behaviour and female soma
Double sex DSX and fruitless FRU contribute to males soma an behaviour
only double sex contributes to female soma
what sexually dimorphic courtship behaviours are shown by male Drosophila melanogaster (the innate mating behaviour)
a | The male fruit fly orientates towards the female, then follows her,
b | taps her,
c | sings a species-specific courtship song by vibrating one wing.
d | Finally, he licks the genitalia of the female,
e | curls his abdomen in an attempt to copulate with her.
what is the purpose of male Drosophila tapping/licking in the innate mating behaviour
detecting taste smell and somatosensory cues (whether it is a female, whether they recently mated)
what do fru3 mutant phenotypes affect?
courtship song, transfer of sperm and seminal fluid
optogenetic stimulation of neurons expressing the fruitless FRU gene produces what (in male drosophila)
causes fly to produce male specific behaviour in a random pattern
fruitless free genotypes of drosophila exhibit what behaviour
the flies will court each other – forming conga lines of courting males (fruitless behaviour)
what is the binary Gal4-UAS system
a biochemical method to study gene expression to get transgene expression in a pattern of your choice
targetted reporter gene expression is created by two transgenes:
P-Gal4, expressing the foreign transcription factor GAL4 in the pattern of promotor P
UAS-Transgene, which uses GAL4 binding sites (UAS) to produce transgene expression
where are Fru M neurons found
in the brain projecting through the ventral nerve cord, the muscle required for copulation, some for external genitalia (penis and clasper), sensory neurons that are specific in the leg antenna, proposis.
what structures in drosophila brain is larger in males than in females
da1 glomerulus bigger in male (receiving input from olfactory sensory neurons in antennae) + VAlv, VL2a
the antenna lobe senses phenylacetic acid and other food odours that act as aphrodisiac.
upon detection of males pheromones what happens in the male drosophila brain
suppression of coutship behaviours by pathway from olfactory sensers -> DA1 ORN -> DA1 PN -> DCI -> DNI -> VNC
how can drosophila differentiate between males and females
Two fru sensory neurons in front leg, one sense female hydrocarbons the other male by tapping off the
how to allow females to express fru gene (drosophila melongaster)
Create female fluy that expressed male fruitless protein – via correcting female specifics splicing by removing the exon that adds a stop codon.
why dont female drosophila express the Fru protein
the female-specific splicing caused by binding of Tra/Tra2 yields a transcript that includes a second exon, which has a stop codon and does not produce a functional protein
what are P1 cells (drosophila)
the group of Fru cells responsible for most of mating behaviours in males
how do we know the female fruit fly brain is equipped with latent circuitry underlying male like behaviour
Temperature-induced stimulation of pC1 cells in ♀triggers ♂-like courtship of both ♀ & ♂ - this function maps to dsx-pC1 neurons (equivalent to fru P1 neurons)
what does the P1 cluster of neurons do (in male fruit fly)
central control of ♂ courtship
Integrates sensory and dopaminergic (motivational) input)
Controls output via Descending Neurons > Ventral Nerve Cord
Courtship song
Copulation
how do Fru^M neurons participate in different aspects of courtship
Sensory Input
Auditory (courtship song)
Olfactory (pheromones, food-associated aphrodisiacs)
Gustatory (pheromones)
Visual
P1 cluster: central control of ♂ courtship
Is the male brain dispensable for male copulation?
yes
Fruit flies - decapitation of male during copulation leads to successful copulation. The brain is not required the ventral nerve cord is.
There was an increased duration for matings in which wild-type Drosophila melanogaster males were decapitated shortly after copulation initiation
what directs the musculature of male copulation in fruit flies
Circuit of doublesex-expressing neurons in the equivalent of the spinal cord controls copulation itself:
Glutamatergic motor neurons that coordinate the joining of genitals
GABA-ergic inhibitory interneurons that promote release of genitals by opposing the motor neurons
mechanosensory neurons that connect to brain and abdominal ganglion
what control female mating receptivity in fruit flies
In virgin females, pC1 neurons integrate auditory, olfactory, and somatosensory inputs and in turn activate vpoDNs (vaginal plate opening descending neurons, which also receive auditory input more directly).
vpoDNs project axons to the ventral nerve cord to promote vaginal plate opening, which is essential for copulation.
pC1 neurons receive tonic excitation from SAG neurons of the ventral nerve cord, which are activated by sex peptide sensory neurons (SPSNs)
what happens in the chemistry of virgin female fruit flies after they mate
They receive sperm and seminal fluid - fluid has signalling molecule sex peptide sensed by sensory neurons in female reproductive tract inhibits female receptivity for a period of time including vaginal plate opening.
- After mating, the sex peptide inhibits SPSNs, thereby reducing the excitatory drive onto SAG neurons and pC1 neurons
what structure has the sex-specific memories of being rejected in male drosophila
FruM mushroom body g neurons
what does the male birdsong signal
Signal to females: Species Individual identity Location Readiness to mate Compete with rivals Territory Neighbour vs stranger
what happens in the stages after hatching in the learning process of birdsong (in zebra finches)
in days after hatching. During the sensory stage, a young bird listens to and memorizes a tutor song. During the sensorimotor stage (25-90 days), he sings an immature song and compares it to the tutor song he memorizes. The song takes its mature form at the crystallized stage (90 days)
what do the song pathways consist of in zebra finches
consisting of HVC, RA, and the brainstem motor nuclei that regulate muscle contraction in the vocal and respiratory systems, is responsible for song production. The anterior forebrain pathway, consisting of LMAN, area X, and DLM, is essential for song learning. Dopamine neurons project to and modulate neurons in area X.
what animal experiences seasonal neurogenesis
songbirds – adult neurogenesis does occur in seasonal patterns, (possibilities for neurodegenerative diseases)
what sexual dimorphism is shown in the bird brain
Volumes of nuclei making up the song circuits (area X, HVC, and RA) are larger in males than in females in both canaries and zebra finches (bottom). Area X is unrecognizable in zebra finch females.
what is unique about the sexual characteristics of the Aspidoscelis uniparens (whiptail lizard)
they are all female and the sexually dimorphic behaviour is related to the hormone cycle
what gender specific activity is associated with each part of the hormonal cycle in the whiptail lizard
- Progesterone associates with male-like behaviour, acts in MPOA-equivalent area of hypothalamus, displays a displaying a male-like mounting behaviour
- Oestrogen associates with female-like behaviour, acts in VMH-equivalent area of hypothalamus, assuming a female-like mating position
what causes the masculinisation of the human genitalia between weeks 9-12 of gestation
The SRY gene, located on the short arm of the Y chromosome, initiates a cascade of gene expression and hormonal signaling that results in masculinization of human genitalia. (including tgfbeta mullarian inhibiting substance)
which brain regions are deactivated upon seeing a picture of a loved one
Cortical areas in the occipital/parietal junction (OP), medial temporal (MT), temporal pole (TP), lateral prefrontal (LPF), posterior cingulate (PC), medial prefrontal/paracingulate (MP), and the amygdala (A) are all sites of diminished activation
what brain regions are activated in response to seeing a picture of ones beloved
the ventral tegmental area and the caudate nucleus
what can induce partner preference (without mating) in voles
Vasopressin infusion (or oxytocin)
up until what stage in the early human embryo are the genitalia sexually indifferent in humans
weeks 4–7 of gestation
what is testosterone derived from
indirectly from cholesterol and progesterone
name 6 genetic disorders resulting in intersexuality in humans
Klinefelters - XXY - male secondary sex characteristics
Turner - XO - incomplete female development
47-XYY - XYY - male secondary sex characteristics
congenital adrenal hyperplasia - 21hydroxylase mutation -hypermasculinisation of XY and masculinisation of XX ppl
androgen insensitivity - testosterone receptor or Mullerian inhibiting substance mutations - hypotrophic testicular tissue, female secondary sex characteristics in XY
testes-at-12 - 5-alpha-reductase mutation - incomplete male genital development prior to puberty; brain and behavioiur remain masculinarised
what is the mechanism of action of testosterone
Testosterone diffuses across the plasma membrane, binds to the androgen receptor, and causes nuclear translocation of the complex. The complex binds to promoters of target genes to regulate their transcription (androgen receptor responsive gene)
what is the mechanism of action of estradiol
Intracellular estradiol can derive either from circulating estradiol or from circulating testosterone converted to estradiol by the enzyme aromatase.
Binding to the estrogen receptor the complex allow entry into the nucleus and where it binds to target promoters of the estrogen receptor responsive genes
what are the actions of steroid sex hormones in the brain
direct: estrogen is known to alter membrane permeability and neurotransmitter synthesis release and reuptake
indirect: estrogen binds to its receptor and promotes or inhibits transcription
in the rat brain where were the most estradiol sensitive neurons
most estradiol-sensitive neurons are located in the basal diencephalon and telencephalon, with a high concentrated in the preoptic area, hypothalamus, and more laterally in the amygdala,
androgen receptors in the brains hypothalamic nuclei do what sexually specific function
control gonadal function, sexual behavior, and parenting behavior
other than the hypothalamus, in which structures are androgen receptors located and what potentially sexually dimorphic behaviors do they control
cognition (cortex),
learning and memory (cortex, hippocampus, amygdala),
aggression and stress (hippocampus, amygdala),
pain sensation (thalamus, brainstem),
and motor control (substantia nigra, cerebellum)
what stops the mothers estrogen from entering the fetal brain and effecting sex determination (shown in rodents)
alpha-fetoprotein AFP - binds estrogen with high affinity extracellularly
what causes the male configuration of the (rat) brain
circulating testosterone enters brain cells, aromatase converts it to estradiol, intracellular estradiol promotes the male configuration of the brain (binds to receptor and enters the nucleus to alter gene expression)
when treated with testosterone or estradiol what behaviour is shown in female rats
When treated with testosterone or estradiol, female exhibit some male typical behaviours and abnormal female typical behaviours
what signalling pathway allows puberty begin
- Puberty is marked by activation of gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus.
Kisspeptins released from Kiss1 neurons in the arcuate nucleus (ARC) and anteroventral periventricular nucleus (AVPV) stimulate GnRH release from GnRH neurons, which express the Kiss1R.
GnRH circulates to the anterior pituitary, where it stimulates endocrine cells to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
The bloodstream transports LH and FSH to the gonads (testes or ovaries), which respond by producing steroid sex hormones that regulate the differentiation of secondary sex characteristics during puberty.
Sex hormones also circulate to the brain to affect further sexual differentiation during puberty and activate sexual behavior in adults
what do high levels of progesterone and estrogen do to the morphology of the brain
increase in dendritic spines in the hippocampus
what does estrogen do to nervous transmission in the (rat) brain
increases the amplitude of excitatory postsynaptic potentials in individual hippocampal neurons - high frequency stimulation further enhances these effects of estrogen suggesting a role in synaptic and circuit plasticity in the hippocampus
what was the impact of testosterone on the rat pelvic ganglion (in culture)
processes become thicker and more highly branched, and the cell body (soma) grows in size
what is sexually dimorphic about the spinal nucleus of the bulbocavernosus (onuf’s nucleus in human). what is this structure responsible for
A location that controls genital muscles - Muscle develops in both sexes, presence of testosterone allow it to be maintained, absence leads to degeneration of the muscles and neurons (females)
what does aromatase do
converts Testosterone > 17-b-estradiol (acts on ER in both ♂ & ♀)
what does 5-a-reductase do
Testosterone > 5-a-dihydrotestosterone (↑active on AR)
what does 21 hydrovylase do
Progesterone >Deoxy-corticosterone (T↑DHT↑)
what are the impacts of steroid hormones on the vertebrate brain
Important enyzymatic steps
Aromatase: Testosterone > 17-b-estradiol (acts on ER in both ♂ & ♀)
5-a-reductase: Testosterone > 5-a-dihydrotestosterone (↑active on AR)
21 hydroxylase: Progesterone >Deoxy-corticosterone (T↑DHT↑)
Effectors of sex determination
Perinatal period (organization)
(post-)puberty (activation via Hypothalamic-Pituitary-Gonadal Axis)
Widespread impact on brain
Directly (membranes) & via receptors (transcriptional response)
Local impact: dendritic spines, growth, programmed cell death, postsynaptic excitation, LTP
what sexually dimorphic hypothalamic nuceli are associated with sexual behaviours
The anteroventral paraventricular nucleus (AVPV) (a collection of dopaminergic neurons ) is larger in females than males
The sexually dimorphic nucleus of the preoptic area (SDN-POA) is larger in male rats than in female
give features of sexual differentiation in the spotted hyena
- ♀ larger, more aggressive than ♂
- ♀ socially dominant
- ♀ clitoris (as large as ♂ penis) for: urination, receiving semen, giving birth
- Deficiency in placental aromatase
- Mother makes androstenedione (fetal exposure)
- ♀ pups fight siblings from birth
- ♀ have feminine SDN-POA and SNB
what are the aromatase differentials in the male and female brains
More aromatase expressing neurons in the amygdala and ventromedial hypothalamus of the male brain
which sex has a larger volume and number of neurons in the anteroventral periventricular nucleus
female
which sex has a larger volume and number of neurons in the sexually dimorphic nucleus (SDN-POA)
male
which sex has a larger volume and number of neurons in bed nucleus of the stria terminalis
males
which sex has a larger volume and number of neurons in the ventral part of the principal BNST nucleus
females
what is the major pathway linking the accessory olfactory system to the hypothalamus in the rodent brain
The accessory olfactory system innervates sexually dimorphic nuclei such as the MeA (medial amygdala) and BNST (bed nucleus of the stria terminalis), which both project axons to the hypothalamic MPOA (medial preoptic area) and VMH (ventromedial hypothalamic nucleus)
what is the major pathway that links the main olfactory systems to the hypothalamus in the rodent brain
axons from the main olfactory bulb send projections to the anterior olfactory nucleus, piriform cortex, VMH and ACN that send input to the thalamus
(GnRH neurons form reciprocal connections with VMH neurons)
what is TRPC2 (vomeronasal organ) needed for
male sex specific courting, ultrasonic vocalisation and suppression of male male courting
what is CNGA2 (olfactory epithelium) needed for
male mating behavior
male territorial aggression
female maternal pup retrieval
what structures are involved in pheromone perception (rodents)
MeA and (aromatase neurons) BNST
what structures are needed for sexual behaviour (rodent)
MPOA and VMH
what is lordosis and how is it facilitated in the female rat
a Reflex that makes genetalia available (arched back) - The ventromedial hypothalamic nucleus (VMH) facilitates lordosis in female rats
what regulates female and male mating behaviours in rats
Progesterone receptor– expressing (PR+) VMH neurons regulate female and male mating behaviors as well as male aggression
how does sexual experience regulate sexually dimorphic behaviours in rats
Sexual experience alters encoding by estrogen receptor–expressing (Esr1+) VMH neurons
what is the neural circuit for sexual behaviour in male rodents
pheromones from receptive female are detected by vomeronasal organ sending projections to the Medial amygdala
circulating testosterone is converted to estrogens and acts on the MeA and mPOA to send projections to the ventral midbrain and then brainstem and through to the spinal cord (L5) to affect erection and ejaculation.
androgens act on spinal nerves to augment reflexes
describe the neural circuit for sexual behaviour in female rats
estrogens induce production of progesterone receptors to respond to that hormone in the ventromedial hypothalamus
estrogens affect neurons at the VMH and periaqueductal gray to send signals to the medullary reticular formation and to the spinal cord (L1-L6) via the reticulospinal tract to stimulate lordosis
what regulates parental behaviour in rodents
medial preoptic area (MPOA) galanin-expressing neurons.
what behavioural changes occur with ablation of MPOA gal neurons in rodents
decreased pup retrieval behavior of fathers
reduced pup-retrieval behavior in mothers.
caused virgin females to attack pups
what are the sexually dimorphic nuclei in mammalian circuits for sexual and parental behaviour
BNST Aromatase+ (♂ sex discrimination)
VMH PR+ (♀ receptiveness, ♂ sexual vs aggressive behaviour)
MPOA Galanin+ (parental behaviour)
neuropeptides can be found as far back in evolution as in _________
nematodes
what is nematocin required for (in c elegans)
for optimal execution of multiple steps of male mating
eg response to contact, backing, turning, vulva search and sperm transfer
what is the difference between the brain structure of prairie voles and promiscuous montane voles
Prairie voles (form lifelong mating pair bonds), have a high density of oxytocin receptors in the nucleus accumbens (NAcc), caudate putamen (CP), and prefrontal cortex (PFC), all associated with reward and reinforcement. males have enhanced density of vasopressin receptors in the ventral pallidum and lateral septal nuclei.
Promiscuous montane voles lack a high density of receptors in the NAcc and CP. Have high density vasopressin receptors in the LS but diminished in the VP
