Martin Estermann expands the avian sex determination field with the emu


By Azelle Hawdon

Martin Estermann, a former graduate student from Monash University, Australia was the recipient of the 2020 Society for Developmental Biology Emerging Research Organisms Grant. Estermann received the grant to fund his research on avian sex determination during his Ph.D. studies in Craig Smith’s laboratory at Monash University’s Biomedicine Discovery Institute. More recently, Estermann has transitioned to be a postdoctoral fellow at the National Institute of Environmental Health Sciences in Durham, North Carolina in Humphrey Yao’s lab, where he studies gonadal sex determination and differentiation in mouse models.

I met with Estermann to discuss his background and career while gaining insight to how the emu broadens our understanding of avian sex determination.

Estermann was born in General Roca, in the northern Patagonian region of Argentina, then relocated to Pergamino, Buenos Aires, to study genetics at the National University of Northwestern Buenos Aires (UNNOBA). Whilst always being fascinated by the fact that a single cell has all the information required to form a whole functional living being, it was not until his undergraduate studies that Estermann discovered his interest in embryology and developmental genetics.

His first research experience in developmental biology took place in Argentina at the Instituto Tecnológico de Chascomús (INTECH) under the direction of Gustavo Manuel Somoza and Juan Ignacio Fernandino. There, Estermann worked on the influence of temperature in sex determination and the brain-pituitary-gonadal axis in the medaka fish. During this time, Estermann learned lab techniques which would prove critical in the next stages of his early scientific career. Subsequently, Estermann returned to UNNOBA in Junín, Argentina, to complete a two-year fellowship at the Centro de Investigaciones Básicas (CIBA), where he studied the genetic and epigenetic regulation of immunity against tuberculosis under the guidance of Virginia Pasquinelli.

“It sounds like a career swap, but I learned new concepts and techniques that changed the way to tackle science. I am currently applying some of those concepts to the developmental biology field,” Estermann said.

Estermann became interested in avian sex determination at the Latin American Genetics Conference, when he was introduced to the concept that the same primordial organ can differentiate into an ovary or testis depending on the signals it receives. He was particularly fascinated by the chicken as a model for developmental biology. Specifically, by how the accessibility of the embryo enables its exposure to different chemicals or manipulation of gene expression whilst simultaneously monitoring developmental progression.

When Estermann found out Craig Smith at Monash University was studying the genetic regulation of sex determination in birds using the techniques he was interested in, he contacted Smith about doing a Ph.D. in his lab, starting his journey in avian sex determination. During his Ph.D., Estermann was able to apply his previous research experiences and learn new techniques specific to chicken development. Here, he made his first foray into ‘omics analyses, performing the first whole-gonad single-cell RNA-sequencing study.

Estermann was especially interested in studying how sex is determined in emus, which are flightless birds endemic to Australia. Estermann’s interest in the emu lies in its sex chromosomes. Mammals have an XY sex-determination system, where males are hemizygous for X-linked genes (i.e. they possess an XY sex chromosome pair), in contrast, birds have the ZW system, where males are ZZ and females are hemizygous ZW.

“There are two main theories on how the sex is determined in birds. The first one involves a W-linked gene driving female sex differentiation. The other one involves a Z-linked gene that acts in a dose dependent manner (double dose in males, one in females) to induce gonadal masculinization. Until now, no W-linked gene was found to induce ovarian differentiation,” Estermann said.

In most birds, the W chromosome is much smaller than the Z chromosome, bearing only a handful of genes. However, in emus, both Z and W chromosomes are of similar size. As such, if there is any W-linked gene that could act as a female sex determination gene, it could be hidden in the large W chromosome.

In Australia, there are currently few grant schemes or funding opportunities that allow Ph.D. students, especially international students, to explore their own research ideas. While Estermann was interested in exploring emu gonadal development and differentiation, his lab funding was primarily allocated for work in the chicken model. When Estermann heard about the SDB Emerging Research Organism grant, he saw it as an excellent opportunity to kick-start his gonadal research with emu embryos. Indeed, securing external funding from the SDB made the emu gonadal project possible. With this project Estermann was able to apply all the techniques he had learned to work with the chicken model to a novel research organism. He described how rewarding it was to expand on the avian gonadal field, which is mostly based on research in chickens, by researching the emu and other non-traditional avian models. Prior to receiving the SDB grant, Estermann compared the expression pattern of different sex specific genes and determined that gonadal morphogenesis is conserved among different bird species.

“I believe each species has a different story to tell, and emus are no exception,” Estermann said.

Large blue emu egg next to small brown chicken eggHowever, studying the emu did not come without its challenges. Estermann explained that the large size of the emu egg and the hardness of the shell made it practically impossible to use scissors to cut a window for experimental manipulation, as is done with chicken embryos.

“I had to hit the eggs with the handle of a spatula to crack a small window and then proceed to open it with forceps!” Estermann said.

Additionally, as emus are seasonal breeders their eggs are available for only a few months per year, unlike the year-round supply of chicken eggs. This made working with the emu system more challenging, especially in the middle of the COVID-19 pandemic.

This experience also made Estermann aware of the pros and cons of working with a non-model organism and gave him a greater appreciation for people working with non-traditional organisms. Research-wise, Estermann was able to improve his data analysis skills and is now not afraid to try new techniques or new animal models. Estermann is extremely grateful to have been awarded the SDB Emerging Research Organisms grant, as without the financial aid he wouldn’t have been able to perform this research project, which fell outside the scope of his planned Ph.D. studies.

I asked Estermann about his experiences in applying for the SDB Emerging Research Organism grant. He said, “This was my first time applying [for] a grant and I have to say it was a whole learning process. I applied twice to the program, being unsuccessful the first time. Fortunately, the reviewers gave me feedback about my application, which was really helpful and improved the proposal a lot, to the point of getting awarded in the following year application rounds.”

Estermann shared that he believes the avian sex determination field is at a point where it needs to move away from comparative studies with mammals. He hopes to see data about different species from the three different bird clades, especially the most diverse one, the neoaves. Estermann envisions that in the future the field will move away from the classical histology-based examinations of tissue and towards a new era of transcriptomics.

“There was a big effort to sequence several birds’ genomes over the last decade so the next step would be to see how gene expression is conserved (or not) during gonadal sex determination and differentiation in birds,” Estermann said. “We still have a lot to learn!”

Estermann shared that some of his favorite moments as a developmental biologist are when he collects embryos, whether they are from a fish, bird or mouse. Estermann said he finds them fascinating and admits that his phone is full of photos of embryos. He also enjoys attending developmental biology conferences.

Estermann said, “You never know who you would meet or what you will learn from them. Could be a new animal model or a new technique or even a research field you didn’t think existed. I think developmental biology conferences are so diverse that it forces you to think outside the box.”

Finally, Estermann ended by commenting that he considers the community of developmental biologists on Twitter to be one of the best. Twitter is one of his favorite ways to interact with other scientists, find freshly published papers, and also see amazing videos of developing organisms.

If anyone is interested in sex differentiation, gonad development or limb formation and is interested in the chicken embryo as a model (and some other birds), Estermann endorses his Ph.D. supervisor Craig Smith, who is currently looking for Ph.D. students.

Last Updated 02/02/2023