A seminal study: Dr. Paula Cohen and colleagues embark on multi-institutional NIH grant to analyze sperm development
Male infertility is on the rise, with significant declines in sperm quantity and quality occurring across the human population worldwide in the past two decades. The reason for this is poorly understood, and scientists suspect spermatogenesis, the process of how sperm develops, is a crucial piece in this puzzle.
Dr. Paula Cohen, professor of genetics at the College of Veterinary Medicine (CVM) and associate vice provost for life sciences at Cornell, is leading the effort to solve this puzzle. Thanks to a multi-center, $8M+ grant from the NIH National Institute of Child Health & Human Development, Cohen and her collaborators will untangle the complex genetic rulebook for making sperm, while also looking for hidden causes of infertility related to spermatogenesis. Cohen is uniquely positioned to tackle these questions — as director of the Cornell Reproductive Sciences Center (formerly the Center for Reproductive Genomics), she unites Cornell’s scientific experts on reproductive health and fertility and emphasizes the genetic and epigenetic mechanisms that lead to healthy egg and sperm cell production. Together with her colleagues at Cornell and beyond, this grant will tackle the questions of spermatogenesis in three phases, plus involves an educational outreach portion.
“This prestigious new NIH Center grant is a tremendous accomplishment for Dr. Cohen and the entire interdisciplinary research team she has assembled,” says Dr. Robert Weiss, associate dean for research and graduate education. “The newly funded research builds on decades of cutting-edge reproductive science at Cornell as well as Dr. Cohen's leadership of the highly successful Center for Reproductive Genomics on campus. The new award from the NIH will support several exciting basic and clinical research projects that hold tremendous promise for advancing human reproductive health and powerfully synergize with Cornell's radical collaboration initiative in genome biology."
Cohen and Dr. Charles Danko, Robert N. Noyce Associate Professor in Life Science and Technology, head up the first portion of the grant, which is aimed at understanding how RNA is regulated during spermatogenesis — how certain RNAs are made at certain times, and what might happen if they aren’t created in the right order, or at all.
“Spermatogenesis is an amazing process,” says Cohen. “There are so many steps the cell needs to go through, and each step has a very different genetic program.”
Because sperm cells have so much genetic action happening in such a short period of time, they make the perfect test subject to better understand how RNA is regulated in general. “In terms of regulation, what a sperm cell goes through is phenomenal,” says Cohen. “If we want to understand these processes better, the sperm is a really fascinating system to use.”
Specifically, Cohen and Danko will look at bromodomain-containing proteins which regulate gene expression by controlling the rate that DNA is transcribed into RNA. This is done by either compacting or loosening chromatin, the protein strands that form up the double helix structure of DNA. When chromatin is compact, genes are prevented from getting translated into protein. When it’s loose, those genes become open to transcription.
“My lab studies transcriptional regulation and genomics,” says Danko. “Both disciplines are necessary to understand what happens during the tremendous amount of chromatin compaction that occurs in sperm — how this process is coordinated provides a fascinating window into transcriptional control.”
Investigating “junk” RNA
Once RNAs are made in the sperm cell, there’s still the matter of how they behave and where they go. For this part of the mystery, Dr. John Schimenti, professor of genetics, and Dr. Andrew Grimson, associate professor of molecular biology and genetics at the College of Agriculture and Life Sciences, will be collaborating to unravel these questions.
Specifically, they’ll be looking at a mysterious portion of messenger RNA (mRNA) known as the three-prime untranslated region, or 3’-UTR in science speak — a ‘tail’ at the end of the mRNA strand that was long considered to be ‘junk’ RNA. Studies have now established this to be far from the truth — with the 3’-UTR suspected to be the mRNA’s instruction manual. Scientists have already found that sperm cells have a lot of variation in the length of their 3’-UTR tails, but no one knows exactly why this variation exists. “There is some evidence that 3’-UTR length can affect infertility, says Cohen.
Schimenti is an expert in reproductive genetics and using genetically engineered mice to determine effects of human DNA variants upon fertility, while Grimson is an expert on post-transcriptional gene regulation. Dr. Kathleen Hwang, the urologist at the University of Pittsburgh, will provide samples from fertile and infertile men. These sperm will be sequenced and examined by Schimenti and Grimson to determine if there are any patterns within the 3’-UTR tails that might be associated with infertility.
“We know that untranslated sequences of mRNAs have important roles, but nobody has ever addressed relationship of variants in these sequences to infertility before,” says Schimenti. “I am excited about working with my colleagues that together, provide complementary expertise to tackle the problem.”
Monitoring RNA modifications
With Schimenti, Grimson, and Hwang helping to identify possible 3’-UTR defects, an additional branch of the grant will look at what might be cause of those defects. This project is headed up by Dr. Samie Jaffrey, Greenberg-Starr Professor of pharmacology at Weill Cornell Medicine. Jaffrey is an expert in the very new field of epitranscriptomics, a branch of epigenetics that looks at the modifications that can impact RNA and how it functions. Different proteins monitor these modifications — “readers, writers and erasers,” Cohen calls them. “This opens up a massive can of worms,” she says. “If you alter these reader, writer and eraser proteins in the RNA, they can all result in infertility in mice — and are really important for spermatogenesis. In the future, if we knew there were certain RNA modifications that caused infertility in men, we could screen for them.”
With this goal in mind, Jaffrey will be looking at epitranscriptomic modifications of mRNA to see how they impact the mRNA’s 3’-UTR tails.
Ultimately, when the grant concludes, Cohen and her colleagues will have uncovered new insights to sperm development — which will in turn shed light on many crucial problems, including infertility and IVF. “Everything we do here adds to our arsenal to help patients trying to have a baby,” says Cohen.
Written by Lauren Cahoon Roberts