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SUPER EXCITED TO FINALLY SHARE THIS FULL STORY! 
A 4 years journey to understand the rules of transgenerational small RNA inheritance in worms
https://twitter.com/OdedRechavi/status/1297907153836158977?s=20
A 4 years journey to understand the rules of transgenerational small RNA inheritance in worms
https://twitter.com/OdedRechavi/status/1297907153836158977?s=20
Thanks @OdedRechavi! Here are more details 
SUPER THREAD!
4 years ago we found that small RNA inheritance is regulated across generations (Cell 2016). We wondered: what are the rules of this inheritance? And why do heritable responses vary between isogenic progeny?
(1/19)
SUPER THREAD! 4 years ago we found that small RNA inheritance is regulated across generations (Cell 2016). We wondered: what are the rules of this inheritance? And why do heritable responses vary between isogenic progeny?
(1/19)
We started, quite naively, to examine inheritance patterns in lineages of thousands of worms. We dreamed of a hidden pattern (like Mendelâs 3:1 ratio
) that will teach us something new about the epigenetic inheritance process itself. But, VERY surprisingly, we foundâŠ
(2/19)
) that will teach us something new about the epigenetic inheritance process itself. But, VERY surprisingly, we foundâŠ(2/19)
Zero variability in lineages that derive from the same mother⊠All showing the same inheritance patterns at each generation (RULE #1).
That was REALLY confusing.
(Leah:
Oded: âthis is your challenge, Leah. This is what youâve been trained for all these yearsâ)
(3/19)
RULE #1).That was REALLY confusing.
(Leah:
Oded: âthis is your challenge, Leah. This is what youâve been trained for all these yearsâ)
(3/19)
Still, lineages derived from different mothers exhibited VERY different inheritance patterns. Even when these mothers were in fact isogenic sisters which were hatched together, grown together, etc.
(4/19)
(4/19)
Variability between different lineages could of course stem from differences in exposure to the original heritable signal. We took endless efforts to minimize such exposure variability, but still observed very dramatic differences in inheritance in different lineages.
(5/19)
(5/19)
So, what if itâs not a bug, but a feature?
What if these different inheritance patterns stem from internal differences in the way isogenic individuals process heritable signals â and transmit them to the next generations?
(6/19)
What if these different inheritance patterns stem from internal differences in the way isogenic individuals process heritable signals â and transmit them to the next generations?
(6/19)
We needed a way to examine inter-individual differences in small RNAs processing which is not triggered by external stimuli.
In C. elegans, some transgenes get spontaneously silenced by small RNAs, especially in the germline. It can be a real pain, but for us it was perfect!
In C. elegans, some transgenes get spontaneously silenced by small RNAs, especially in the germline. It can be a real pain, but for us it was perfect!
We used such transgene to examine whether the spontaneous â and variable â silencing of the transgene at the parental generation could predict the fate of the variable heritable response that is initiated at each generation.
(8/19)
(8/19)
Turned out it did!
(I was literally dancing in the lab when seeing this for the first time)
RULE #2: different isogenic mothers stochastically assume different inheritance states that determines the fate of inheritance.
(9/19)
(I was literally dancing in the lab when seeing this for the first time)
RULE #2: different isogenic mothers stochastically assume different inheritance states that determines the fate of inheritance. (9/19)
Calculation of the transgenerational âtransition rulesâ across the many different lineages revealed the third and final rule:
RULE #3: the longer a silencing response lasts in a lineage, the more likely it is that it would continue to the next generation too.
(10/19)
RULE #3: the longer a silencing response lasts in a lineage, the more likely it is that it would continue to the next generation too. (10/19)
We found 3 simple rules that together can predict the segregation of heritable small RNA responses in the population.
But,
Whatâs the mechanism?
(11/19)
But,
Whatâs the mechanism?
(11/19)
What is the source of these different inheritance states, what makes them, and how can they be manipulated?
Among other things, we examined differences in gene expression and small RNA levels in sister worms that show different inheritance states.
(12/19)
Among other things, we examined differences in gene expression and small RNA levels in sister worms that show different inheritance states.
(12/19)
*** Pause: Parental leave! ***
I finished cloning the small RNA and mRNA libraries a couple of days before giving birth and planned to analyze the data while on a leave.
Ha. Haha. Hahahaha.
(13/19)
I finished cloning the small RNA and mRNA libraries a couple of days before giving birth and planned to analyze the data while on a leave.
Ha. Haha. Hahahaha.
(13/19)
We found 349 genes which typify the different states of inheritance in isogenic worms and were surprised to learn that many of them are in fact stress and immunity related genes.
But who is really responsible for generating these coordinated differences?
(14/19)
But who is really responsible for generating these coordinated differences?
(14/19)
A few leads in the data, and a little leap of faith, eventually led us to Heat Shock Factor-1 (HSF-1); a super conserved transcription factor, important both in stress and through development.
(15/19)
(15/19)
We found that HSF-1 varies in different individuals, its control over gene expression remarkably resembles the states-related gene expression changes, it regulates many small RNA factors, and its manipulation CANCELS the silencing variability.
(16/19)
(16/19)
And I know what youâre thinking now⊠WHATâS THE PHYSIOLOGICAL RELEVANCE?
Well the very final experiment reveals this unicorn. But Iâll leave some mystery, read the paper!
(17/19)
Well the very final experiment reveals this unicorn. But Iâll leave some mystery, read the paper!
(17/19)
Full details (less gifs though) can be found in the paper.
We really enjoyed working on this project and hope you would enjoy reading it!
(18/19)
We really enjoyed working on this project and hope you would enjoy reading it!
(18/19)
I am so grateful to everyone that was involved in this journey: colleagues, family, mentors, the reviewers (great suggestions!) and especially to Oded â who is famous for being funny but should be even more famous for being the incredible mentor and scientists he is!!!
(19/19)
(19/19)
