Lecture Last - April 5.docx

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University of Toronto St. George
Cell and Systems Biology
Dorothea Godt

Lecture Last – April 5th CSB429 Drosophila Courtship Behaviour Complex, many different elements Starts with a male and female coming together (see each other) - Results in male orienting himself towards female The female then usually walks away at this point Male then begins to tap at the female with its forelegs It then switches it orientation (infront of female) and flaps the wing closest to her (wing vibration) Note: these elements can repeat over and over again Usually the female continues to walk away Male follows it and gets very intiminate wit hit (touching female at gential location) Male then curls its abdomen And if the female is perceptive, it will let the male mate with it; and it takes 20 minutes for sperm to be transferred from male to female Looks like the female is not doing much and mostly the male who is actively engaged in courtship behaviour, however, its not true that the female is doing nothing and the female ahs a repertoire of elements What is actually happening? Why does the male undergo all these strange things? I mean it makes sense to follow her but why must it tap female with forelegs and flap wings? Well it turns out, during process the flies communicate with each other with all senses (visual sesnse = look at each other) recognize if the opposite is male or female Talk to each other with pheromones (both male and female produce pheromones that can be attractive or repulsive) All flies have tastebuds on their legs, so when male taps females with its forelegs it is tasting the female There are 2 phermones: volatile pheromones (carried in the air) and received by the olfactory system, and non-volatile pheromones which are perceived through direct contact (taste) Male basically is interested in visual cues and pheromones, if the other fly produces the right pheromones, the male continues with its courtship behaviour (spread out wing and vibrate), and this is actually the love song of male to female Does the female like the love song of the male? If so, then she slows down and becomes perceptive to male advances During process: visual cues, olfactory cues, gasatory/taste cues, and we have sound How do they perceive these different stimuli? Flies are well equipped for this Large eyes: easy visualAntenna = ear and nose of the fly - Part of antenna is important for olfactory and other part is important for sound perception Taste buds = located on the feet - Also found in proboscis Maximillary palp – olfactory Female - Rejects male, moves away, pushes him away with hind and middle legs Love Song Sine Song Pulse Song If the female is perceptive to the male’s love song, the male will mount her and reach over with sex combs to hold on to female and inject seminal fluid and sperm into female where it is stored Summary Start with communication of 2 flies with each other, and communication involves all senses - Pheromones as stimulus, antenna responds to – signal sent to brain and is processed and brain will activate neurons that lead to a particular behaviour In case of males, this behaviour consists of a bunch of stereotypical patterns (tapping, touching, flapping wings, following , and eventually mounting) In case of female, we have perceptive female (slows down, spreads wing) or the female rejects the male (runs away, protrudes ovipositor, kicks, etc.) Question is, why does the process have to be so complicated? Fitness control? If female produces good pheromones or male produces good love song = sign of healthy flies and will produce healthy off spring Correct species? To make sure you’re mating with the correct species - We are a single species, no other humanoid species that we don’t have to worry about accidently mating with - So we don’t have that problem but for flies, there are many different fly species that look similar to each other and htey all produce love songs and pheromones and often different species of flies aggregate at food sources they all like (rotten apple) so it becomes important to recognize fly of same species Many of theses stimuli ensure that only the same species begin courtship behaviour Very few flies that produce hybrid offspring and they are usually infertile What causes different behaviour of females and males? Males produce a love song, why? Females are capable of doing so but they don’t Females can run around and what not, but male always follows female What causes this difference in behaviour between 2 sexes? What regions in the brain of a male control male courtship behaviour? Females never show a male calling behaviour, we can use that to figure out which parts of brain the male useSo Antenna lobe responsible for respond to sound and olfactory stimuli and the antenna lobe might be an important part of the brain for courtship behaviour, so if we feminize this part of the brain, we can ask how it affects the male - When we do this, it blocks malecourtship behaviour – so this antenna lobe plays a role in triggering courtship behaviour Feminization, how? - Transformer protein – if we can get male cells to express this, we can feminize those cells This experiment shows that there are parts of brain that are associated with male courtship behaviour Breakthrough: fruitless (fru) mutant, which leads to a complete block of courtship behaviour - Produce no progeny because not interested - If we put a bunch of these mutant males together, they begin trying to court each other (form lines or mating circles where they try to mate each other) Fruitless Gene with a number of promoters and spliced alternatively to produce different isoforms and only one promoter produces the transcript that shows a sex-specific splice - So only in males is this spliced Fru-M RNA > Fru-M protein In females, we have transformer around (and Tra2) and it will binf to the splice site and induce a splice at exon 2, so we have a different splice transcript that is not translated Tra is not only involved in splicing of transcript, but it blocks the translation of the transcript all together - So we get a Fru-F RNA that is not translated Sexually dimorphic Male and female splices are different (see slide) So to test the function of fruitless, we want to induce expression of Fru in females (normally don’t have it because of transformer) and remove Fru expression in males (normally expressing Fru) To do this use knock in mutations Fru-F – mutate the splice site at exon 1 (GT to CT) and it will not produce a transcript that will not give rise to functional protein because splicing is not set up properly (no Fru in males and females) Fru-M – delete the Tra1 binding site – constitutive male specific splice because Tra can not bind – will have successful production of Fru protein in males and females What happens when you do this? Fru-F females – no functional Fru protein, behave like normal females (expected because females don’t have Fru normally)) - Result? Normal mating behaviour, fertileFru-F Males – no functional Fru protein, almost like a knockout of Fru, and there should be no courtship behaviour and produce no progeny (sterile do to not interested in reproducing), should produce normal sperm but not tested (cause this is dependent on double sex which is not affected by fruitless) Aside: there is a muscle that depends on fruitless, and it is required for curling of abdomen during courtship behaviour. If fruitless is not involved in producing this muscle, it is involved in neuronal receptors which are important for stimulating production of this muscle. So this muscle depends on presence of fruitless (no courtship behaviour including no abdomen curling) - Muscle of Lawrence Fru-M Males – normal courtship behaviour, fertile Fru-M Females – male courtship behaviour, try to court females (no interest in mating with males though) - They court other females, chase them around – kind of like fruitless mutant males that form lines, these fru-M females form lines too - The Fru-M female will
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