Plenary Session II.
Kami Ahmad (Harvard Med School) Nucleosomes.
- Histone replacement (H3.3). Targeted to active regions. Xnp part of replacement complex. H3 strongly expressed in S phase, H3.3 is constituitive.
- Constitutive H3 rescues all H3.3 phenotypes (sterility, lethality, etc) Process of exchange more important than what’s added.
- XNP follows H3.3 tightly on polytene chromosomes.
- XNP tracks with polII arrival at heat-shock genes—detect at 5′, lots at 20′, leaves when recovering, uninduced.
- Induce genes without H3.3 available. Measure with Mnase. Go from protected to unprotected and stay unprotected. What happens to transcription when there’s no H3.3 availalble? Max level of transcription is reduced. Transcription still terminates after induction (nucleosomes not required for termination). XNP is still recruited to puffs without H3.3. It persists at the gene following induction, unlike wildtype.
- Model: Xnp recognizes nucleosome free regions. Assembly of new nucleosomes displaces xnp. H3.3 knockdown → global increase of Xnp associated with chromatin.
- TAGA anti-nucleosomal satellite – continually add and remove H3.3, region expands in H3.3 knockdown. Hira also recognizes gaps. ASF1 et al associate with shuttling H3.3.
- Pulse H3.3-GFP, accumulates in a replication independent way, throughout chromosome in xnp mutants (viable) despite moderate reduction in H3.3 chromosome association. Xnp and hira are redundant, double mutant lethal.
Therese Markow (UCSD) ‘what nature means for the lab’
- species variation in duration of copulation 30s-2hr.
- In wild, melanogaster often found ing community of 4-6 drosophilids. Biased sex ratio in wild communities. Flies are preyed on by ants, paresitized by mites,
- males can mate with newly emergent virgin females. 99% of wild-collected females are inseminated. Most matings seen are re-matings. 150-400 progeny per female. Wild-captured females ~150 progeny (how do you know you caught the beginning?) male from wild cross to lab virgin only 100 progeny. Field copulations are 2x as long. Wild caught flies males moved to vials still 20min.
- Claim wild caught mated females live longer than virgins.
Vivian Budnik (U Mass) Synaptic plasticity
- using larvae nerve muscle junctions. Glutamate neurons 1b each neuron 1 muscle ennervation. Glutamate 1s each neuron ennervates all ventral or all dorsal neurons.
- Use starvation to increase locomotive behavior. Correlates with increased synaptic efficacy. Image GFP neurons before and after starvation, show increase in number of synaptopods. Kill neurons move less. Stimulate with channelrhodopsin, sufficient to increase locomotion speed.
Eric Lai (Sloan-Kettering) miRNAS. prev. Rubin lab post-doc
- dominant Espl and brd alleles are 3’UTR mutations. All have lots of miR target loci.
- Ago2 dicer independent miRNA pathway. Individual mRNAs have 100s of targets, many targets are conserved. Are all targets equally relevant. Not phenotypcially required in lab?
- Overexpression of mir-iab-8 represses hox genes (ubx Abd-B ?). Deletion has little phenotype. Iab-4 can quench spotty, early, posterior ubx expression. Derepression of ubx in terminal part of brain, see co-expression of hox genes not normally expressed together.
- Heterozygosity of target genes rescues null miRNA expression ‘phenotypes’.
- Many targets, some of are more ‘important’ than others.
Anna Dornhaus (U of Arizona)
- Evolution of social behavior in bees
- honey bees communicate socially food location, bumblebees don’t.
- Ineffective dance floor for honey-bees reduces foraging efficiency, effect depends dramatically based on habitat. By modeling (and intuition) relevance of communication has nothing to do with colony size. Does correlate with habitat (matters most in India/tropics, where honeybees originated).
- Artificial ‘flower’ schemes, multiple information channels (color scent pattern) improves certainty, reduces decision time. Nectar guides bring bees to front door (for polination) instead of knocking in the backdoor and stealing the goods without polinating.
- Bees learn flower patterns. Bees choose when to learn patterns (based on rate of environmental change).
- Q: How do you distinguish ‘choosing not to learn’ and ‘failing to learn’?
Wieschaus (Princeton): Mechanisms of shape change
- shape change dynamics: it’s a gel not a waterballon.
- slam and grandslam double mutants = no membrane invagination.