FIRST PERSON

First person – James FabrizioFirst Person is a series of interviews with the first authors of aselection of papers published in Biology Open (BiO). James Fabriziois first author on ‘Tubulin-binding cofactor E-like (TBCEL), theprotein product of the mulet gene, is required in the germline for theregulation of inter-flagellar microtubule dynamics during spermatidindividualization’, published in BiO. James is a Professor of Biology/Jean Ames-DeNunzio Endowed Chair of Faculty Excellence at theCollege of Mount Saint Vincent, USA, investigating the genetics ofspermatid individualization in Drosophila melanogaster.

What is your scientific background and the general focus ofyour lab?I have always studied sperm development in Drosophila! I was firstintroduced to this amazing process as a graduate student at St John’sUniversity, where I used genetics and cell biology to studyspermatid individualization. Later, as a post-doctoral fellow at theUniversity of Pennsylvania, I became more of a DevelopmentalBiologist, studying the role of soma-to-germline communicationduring spermatocyte development. Since I joined the faculty at theCollege of Mount Saint Vincent, I have returned to spermatidindividualization. While I no longer study spermatocytes, I stilldraw upon the wealth of knowledge and new ways of thinkingprovided to me by my post-doctoral training to study post-meioticspermatogenesis. Currently, my lab is trying to understand the rolethat cytoplasmic microtubules play in spermatid individualization.Moreover, since the College of Mount Saint Vincent is a teachingcollege dedicated primarily to undergraduate education, my lab alsoseeks to expose undergraduates to original research. The thrill ofresearch and discovery combined with the joy of learning, teachingand mentorship has always made our lab, the ‘FabLab’, a veryspecial place on campus.

How would you explain the main findings of your paper tonon-scientific family and friends?Sperm development in all animals, including flies and mammals,occurs within a syncytium, or common cytoplasm. In other words,as sperm multiply and mature, they remain connected to each otherby cytoplasmic bridges so that resources may be shared in acommon ‘sac’. Only at the very end of spermatogenesis areindividual sperm cells resolved, or ‘shrink-wrapped’, from thissyncytium in a process known as sperm individualization. We firstrealized the mulet gene was important for the individualizationprocess when we looked at testes dissected from flies that weremutant for mulet; the males were sterile, the spermatids were notindividualized, and the individualization machinery was severelydiscoordinated. In this paper, we show that we can also cause thismulet defect by knocking down expression of the mulet genespecifically in the developing sperm, showing that mulet is required

in the male sex cells themselves for individualization. In addition,when we drive expression of the normal mulet gene in the mutanttestes, sort of like gene therapy for flies, spermatid individualizationis fixed along with male fertility, showing that it is indeedmulet thatis required for sperm development. That said, we are beginning torealize that the sperm defect in mulet mutant males is probably notthe result of a problem with the individualization machinery itself.Indeed, the mulet gene encodes a protein that remodels the spermsac before individualization so that the shrink-wrapping process canoccur in a coordinated fashion. Specifically, mulet is needed for theremoval of a set of cellular cables, or microtubules, from betweenthe sperm tails; we know this because electron microscopy revealsthe presence of excess microtubules around each sperm tail inmuletmutant testes. Normally, the individualization machinery assemblesat the sperm heads and travels down the sperm tails, shrink-wrapping each spermatid into a membrane as it moves along thesperm tails. In mulet mutant testes, excess microtubules remainbetween the sperm tails and appear to ‘derail’ the individualizationmachinery, thus producing a discoordinated individualizationmachine that is characteristic of the mulet mutation.

What are the potential implications of these results for yourfield of research?A failure to individualize sperm results in sperm cells with excesscytoplasm attached to their tails, which makes it very difficult forthe sperm to swim. These ‘cytoplasmic droplet’ sperm are found inmost infertile men. Indeed, a failure of individualization isresponsible for the majority of human male infertility cases.Given the genetic similarity between flies and humans, we hope touncover genes responsible for sperm individualization inDrosophila so that our results may be applied to the human

James Fabrizio

James Fabrizio’s contact details: Department of Biology/Division of NaturalSciences, College of Mount Saint Vincent, 6301 Riverdale Avenue, Riverdale,NY 10471, USA.E-mail: James.Fabrizio@mountsaintvincent.edu

This is an Open Access article distributed under the terms of the Creative Commons AttributionLicense (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use,distribution and reproduction in any medium provided that the original work is properly attributed.

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system. Our lab studies sperm development and male infertility. Theleading cause of male infertility is a failure at the very end ofspermatogenesis. Drosophila is an exceptional organism forbiological research; it is easy to maintain in the laboratory,possesses strong mutational genetics, a sequenced genome, and∼65% genetic homology to human beings. Drosophila alsopossesses gigantic sperm cells – almost 2 mm long! Thus, we caneasily use Drosophila to study spermatogenesis, and due to thegenetic similarity to humans, the results we obtain will applydirectly to human spermatogenesis and fertility.

“Failure of individualization isresponsible for the majority of humanmale infertility cases.”

What has surprised you the most while conducting yourresearch?The most interesting (and puzzling) aspect of the work has been theinverse correlation between the severity of both the mulet mutantalleles and RNAi-mediatedmulet knockdown and the severity of theindividualization phenotype. In other words, we see a weakindividualization phenotype when mulet expression is knockeddown severely but a severe individualization phenotype whenmuletis knocked down modestly! We believe the explanation for thisresides in the role of the mulet gene product, Tubulin-bindingcofactor E-like (TBCEL) in removing a population of cytoplasmicmicrotubules from between the sperm tails prior to individualization

so that the individualization complex can move unimpeded along theflagella. Thus, in cases of moderate TBCEL knockdown, we believethat these cytoplasmic microtubules are not completely degraded,resulting in microtubules fragments between the flagella that derailthe individualization machinery, causing a severe disruption in thestructure of the individualization complex. In contrast, in the case ofsevere TBCEL knockdown, cytoplasmic microtubules may be leftintact, providing the individualization complex with a continuous,alternate route to the tips of the sperm tails.

What, in youropinion, are someof the greatest achievementsin your field and how has this influenced your research?I suppose for me it all began with thework of Tokuyasu, Peacock andHardy in 1972, who first beautifully characterized Drosophilaspermatid individualization in Drosophila using the electronmicroscope. Many years later, Steve Wasserman and SteveDiNardo published a paper (Castrillon et al., 1993) that essentiallyprovided a gold mine of genes that affect spermatid individualization;mulet came from that screen! These two papers together set the stagefor my PhD thesis and my first paper on spermatid individualization(Fabrizio et al., 1998), where we characterized the process byanalyzing spermatid individualization mutants using a fluorescenceassay for the individualization complex. Certainly, the work fromKathryn Miller’s lab, which revealed the molecular components ofthe investment cones of the IC, and Eli Arama’s lab, which revealedmuch of the mechanism behind spermatid individualization, havebeen a constant source of inspiration for me. Finally, the use of theGal4/UAS system in Drosophila, first for overexpression and rescueand more recently for driving RNAi, has been a critical technicaladvancement that made our work possible.

What changes do you think could improve the professionallives of early-career scientists?I have been running a small undergraduate research lab for the past17 years, so that world of big labs with big grants, graduate studentsand post-docs is far away for me. However, as a professor at a smallliberal arts college who spends most of his time teaching andmentoring undergraduates, perhaps I can offer a unique perspective.Would a career in undergraduate education be an improvement inthe professional lives of early-career scientists? For many, I thinkabsolutely, yes. We in undergraduate education need the talents andpassions of early-career scientists! Colleges are full of raw talent inthe form of undergraduate students, who are just waiting to beinspired by passionate and dedicated scientists with a zeal forteaching and mentorship. We have the pleasure of ‘planting theseeds’ in these eager young minds, a pleasure that is very often lostin the education of graduate students. Moreover, while our careerdoes require productive and engaged scholarship, our livelihood isnot solely dependent on grant money and publications. This leavesroom for the joys of teaching, learning and science without theenormous pressures of a high-powered research environment. Soto return to the original question, I think it is important that early-career scientists get some teaching experience if they think theymight one day consider a career in undergraduate education. And Ibelieve a career in undergraduate education can itself be animprovement in a scientist’s professional life.

“We in undergraduate education need thetalents and passions of early-careerscientists!”

This is a rare section through the membrane portion of theindividualization complex, taken by my co-author Janet Rollins, viewedby transmission electron microscopy. Notice the whorls of membranespiralling around each axoneme as individualization proceeds.

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What’s next for you?My next group of undergraduate scientists and I will begin toexamine how the various components of the individualizationcomplex are affected by the mulet mutation. Are the investmentcones of these individualization complexes really normal? Is themassive machine that these cones are pushing along the sperm tailsnormal? We will examine the localization of various markersin the mulet mutant background to address these questions.If possible, we would also love to capture movies of theindividualization process using spinning disk confocalmicroscopy, and perhaps use the technique to compareindividualization dynamics between wild-type and mulet mutanttestes. I also look forward to finding ways of integrating this

research into the laboratory component of my DevelopmentalBiology course in the fall!

ReferencesCastrillon, D. H., Gonczy, P., Alexander, S.,Rawson, R., Eberhart, C. G.,

Viswanathan, S., DiNardo, S. and Wasserman S. A. (1993). Toward aMolecular Genetic Analysis of Spermatogenesis in Drosophila Melanogaster:Characterization of Male-Sterile Mutants Generated by Single P ElementMutagenesis. Genetics 135, 489–505.

Fabrizio, J. J., Hime, G., Lemmon, S. K., and Bazinet, C. (1998). Genetic dissectionof sperm individualization in Drosophila melanogaster. Development 125, 1833-43.

Fabrizio, J. J., Rollins, J., Bazinet, C. W., Wegener, S., Koziy, I., Daniel, R.,Lombardo, V., Pryce, D., Bharrat, K., Innabi, E., et al. (2020). Tubulin-bindingcofactor E-like (TBCEL), the protein product of the mulet gene, is required in thegermline for the regulation of inter-flagellar microtubule dynamics duringspermatid individualization. Biology Open 9, bio049080. doi:10.1242/bio.049080

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