Once we discuss reminiscences in biology, we are likely to give attention to the mind and the storage of data in neurons. However there are many different reminiscences that persist inside our cells. Cells bear in mind their developmental historical past, whether or not they’ve been uncovered to pathogens, and so forth. And that raises a query that has been difficult to reply: How does one thing as basic as a cell maintain on to info throughout a number of divisions?
There isn’t any one reply, and the small print are actually tough to work out in lots of circumstances. However scientists have now labored out one reminiscence system intimately. Cells are in a position to bear in mind when their mum or dad had a tough time dividing—an issue that is typically related to DNA harm and most cancers. And, if the issues are substantial sufficient, the 2 cells that end result from a division will cease dividing themselves.
Setting a timer
In multicellular organisms, cell division may be very fastidiously regulated. Uncontrolled division is the hallmark of cancers. However issues with the person segments of division—issues like copying DNA, repairing any harm, ensuring every daughter cell will get the proper variety of chromosomes—can result in mutations. So, the cell division course of contains a number of checkpoints the place the cell makes certain every thing has labored correctly.
But when a cell makes it by way of all of the checkpoints, it is presumably all good, proper? Not totally, because it seems.
Mitosis is the portion of cell division the place the duplicated chromosomes get separated out to every of the daughter cells. Spending numerous time in mitosis can imply that the chromosomes have picked up harm, which can trigger issues sooner or later. And prior analysis discovered that some cells derived from the retina will register when mitosis takes too lengthy, and the daughter cells will cease dividing.
The brand new work, finished by a crew of researchers in Okinawa, Japan, and San Diego, began by exhibiting that this habits wasn’t restricted to retinal cells—it appears to be a basic response to a gradual mitosis. Cautious timing experiments confirmed that the longer cells spent making an attempt to endure mitosis, the extra seemingly the daughter cells could be to cease dividing. The researchers time period this technique a “mitotic stopwatch.”
So, how does a cell function a stopwatch? It is not like it might probably ask Siri to set a timer—it is largely caught working with nucleic acids and proteins.
It seems that, like many issues relayed to cell division, the reply comes all the way down to a protein named p53. It is a protein that is key to many pathways that detect harm to cells and cease them from dividing if there are issues. (You might recollect it from our current protection of the growth of elephant stem cells.)
A stopwatch product of proteins
The researchers discovered that, whereas mitosis was occurring, p53 began exhibiting up in a fancy with two different proteins (ubiquitin-specific protease 28 and the creatively named p53-binding protein 1). If you happen to made mutations in one of many proteins that blocked this advanced from forming, the mitotic stopwatch stopped ticking. This three-protein advanced solely began constructing as much as vital ranges if mitosis took longer than regular, and it remained secure as soon as it shaped in order that it might get handed on to the daughter cells as soon as cell division was accomplished.
So, why does this advanced kind solely when mitosis takes longer than regular? The important thing turned out to be a protein referred to as a kinase, which attaches a phosphate to different proteins. The researchers screened chemical compounds that inhibit particular kinases which might be lively throughout mitosis and DNA restore, and located a selected one which was wanted for the mitotic stopwatch. Within the absence of this kinase (PLK1, for the curious), the three-protein advanced does not kind.
So, the researchers suppose that the stopwatch seems to be like this: throughout mitosis, the kinase slowly attaches a phosphate to one of many proteins, permitting it to kind the three-protein advanced. If mitosis will get finished rapidly sufficient, the degrees of this advanced do not get very excessive, and it has no impact on the cell. But when mitosis goes extra slowly, then the advanced begins build up, and it is secure sufficient that it is nonetheless round in each daughter cells. The existence of the advanced helps stabilize the p53 protein, permitting it to cease future cell divisions as soon as it is current at excessive sufficient ranges.
Per this concept, all three of the proteins within the advanced are tumor suppressors, that means that mutations in them make tumor formation extra seemingly. The researchers confirmed that the mitotic stopwatch was continuously faulty in tumor samples.
So, that is how particular person cells handle to retailer certainly one of their reminiscences—the reminiscence of issues with cell division. The mitotic stopwatch, nevertheless, is simply one of many reminiscence storage methods, with fully separate methods dealing with totally different reminiscences. And, on the identical time that is taking place, a lot of different pathways additionally feed into the exercise of p53. So, whereas the mitotic stopwatch might effectively deal with one particular kind of downside, it is built-in into numerous extra, advanced methods working within the cell.
Science, 2024. DOI: 10.1126/science.add9528 (About DOIs).