Cytoplasmic polyadenylation | The RNA Underworld

Cytoplasmic polyadenylation | The RNA Underworld

While in Lexington … | The RNA Underworld

Dr. Hunt:

Some interesting parallels between male gametes in plants (pollen is male, right?) and in mammals. CstF-64 is greatly overexpressed (250-fold) in mammalian male germ cells compared to other tissues (Dass et al. Biol Reprod 64, 1722–1729, 2001) as it is in pollen. Unlike pollen though, CPSF-160 is also overexpressed in mammalian germ cells.

Along with your observations that lots of seemingly important polyadenylation genes are absent or underexpressed in different species, I wonder if there is an interesting, though highly speculative review article in here somewhere? What does it mean for a gene to be genetically essential (knock it out and the organism dies) versus important-but-optional (some tissues or some organisms get along without them)? What do you think?

Best wishes,
Clint

Pollen seems to be a special case unto itself. In addition to the behavior of CstF64 and a few other genes, the expression of CPSF160 and CstF77 genes in pollen was less than 10% than what is seen in most other tissues. Most remarkably, plants have a distinctive PAP gene expressed almost exclusively in pollen. We really don’t know what may be going on in pollen. (The near-absence of CPSF160 in pollen intrigues me – maybe pollen is more like the apicomplexans than I could ever have imagined….)

Interesting stuff, as always.

I will add that we have found that CstF-64 is dispensable in several mammalian systems, albeit with an asterisk in each case. When we knocked out tauCstF-64 (Cstf2t, the Cstf2 paralog) in mice, the mice were fine. Males were infertile, since germ cells have the highest expression of tauCstF-64. But otherwise the mice were fine. Of interest, polyadenylation continued in the germ cells, although spermatogenesis was messed up severely.

Similarly, we knocked out CstF-64 (Cstf2) in mouse embryonic stem cells, the cells were fine, too. They grew more slowly and had a partially differentiated phenotype, but we were surprised that they even survived. In this case, tauCstF-64 probably compensated for the absence of CstF-64. But CstF-64 is not genetically necessary for stem cells.

Although it pains me to say this, I think that CstF-64 is “optional” for polyadenylation in most organisms. The role it plays is in fine-tuning polyadenylation site choice, but is not strictly necessary for the overall process.

But please don’t tell anybody. My career has been based on trying to prove that CstF-64 is important. 😀

Best wishes,
Clint

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