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Developmental biology - Sperm

Dazl Controls Thousands of Sperm Genes

Dazl protein essential in regulating male infertility...

Germ cells are extraordinary - they become sperm and eggs and ultimately an organism's offspring. Male germ cells are unique in particular as they can replicate themselves again and again over the course of a male's life. "This specialized cell requires unique regulation and control of gene expression [function]," explains the study's first author, Leah Zagore, a graduate student at Case Western Reserve University.

A single protein regulates a battery of key genes inside developing sperm, according to this new study out of Case Western Reserve University School of Medicine. Scientists discovered a protein - Dazl - controls a network of genes essential for developing sperm to replicate and survive. Their findings, published in Cell Reports, could lay the groundwork for future research into therapies for infertile men.
Leah Zagore's research shows how Dazl physically attaches to 2,290 RNAs inside germ cells, the progenitor cells that ultimately grow into sperm.

"Dazl binds a very simple sequence in RNA, a string of three RNA bases (G-U-U), which occurs all over RNA fragments. But we found G-U-Us that are directly bound by Dazl are highly concentrated in a specific spot on RNAs. This spot occurs right before the 'polyA tail' found at the end of nearly all messenger RNAs which act as templates to make proteins," expains Zagore's advisor Donny Licatalosi PhD, assistant professor in the Center for RNA Science and Therapeutics at Case Western Reserve University School of Medicine.

This highly restricted pattern indicates Dazl's polyA tail determines where it binds. The polyA tail mechanism loads Dazl onto thousands of different mRNAs. However, only a subset of RNAs with Dazl binding (~22%) seem to be regulated by it. Although many RNAs are loaded with Dazl, only a small proportion generate a positive gene regulation response.
"You could think about it as a mass marketing campaign with only a handful of responders whose opinions really count." Many RNAs in the subset of regulated genes encode cell cycle proteins - placing Dazl in a central role regulating cell proliferation in developing sperm.

Donny D. Licatalosi PhD, Center for RNA Science and Therapeutics, Case Western Reserve University, Cleveland, Ohio, USA.

Transcriptome-wide maps reveal broad DAZL binding to thousands of mRNAs near polyA tails
DAZL binding to GUU sites requires local polyA sequences
DAZL positively regulates a subset of its directly bound RNA targets
DAZL controls an mRNA regulatory program necessary for germ cell survival

The RNA binding protein DAZL is essential for gametogenesis, but its direct in vivo functions, RNA targets, and the molecular basis for germ cell loss in Dazl-null mice are unknown. Here, we mapped transcriptome-wide DAZL-RNA interactions in vivo, revealing DAZL binding to thousands of mRNAs via polyA-proximal 3? UTR interactions. In parallel, fluorescence-activated cell sorting and RNA-seq identified mRNAs sensitive to DAZL deletion in male germ cells. Despite binding a broad set of mRNAs, integrative analyses indicate that DAZL post-transcriptionally controls only a subset of its mRNA targets, namely those corresponding to a network of genes that are critical for germ cell proliferation and survival. In addition, we provide evidence that polyA sequences have key roles in specifying DAZL-RNA interactions across the transcriptome. Our results reveal a mechanism for DAZL-RNA binding and illustrate that DAZL functions as a master regulator of a post-transcriptional mRNA program essential for germ cell survival.

Leah L. Zagore, Thomas J. Sweet, Molly M. Hannigan, Sebastien M. Weyn-Vanhentenryck, Raul Jobava, Maria Hatzoglou, Chaolin Zhang and Donny D. Licatalosi.

This work was supported by funds from the National Institutes of Health to L.L.Z. (T32 GM08056) and D.D.L. (R01 GM107331).

The work was a collaborative effort involving Columbia University and selected Case Western Reserve core facilities, including the Cytometry and Microscopy Core, Genomics Core, and Transgenic and Targeting Facility. Zagore L, et al. "Dazl regulates germ cell survival through a network of polyA-proximal mRNA interactions." Cell Reports.

For more information about Case Western Reserve University School of Medicine, please visit: case.edu/medicine.

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The PolyA Tail has an important role in DAZL-RNA binding and regulation. WILD TYPE refers to the typical form of a species as it occurs in nature. Credit: Zagore et al.

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