Research – TezakLab

Overview

Unlike most organs whose fate is pre-determined, the gonad arises as a bipotential primordium with the ability to develop into either an ovary or a testis, each with a distinct function and morphology. This makes the gonad an ideal system to study both cell fate decisions and organogenesis. Interestingly, in many reptile species, incubation temperature controls gonadal sex determination through a process known as temperature-dependent sex determination (TSD). A major goal of our research is to understand the molecular mechanisms underlying this fascinating phenomenon. Ultimately, we hope our work can reshape established paradigms in the field of sex determination, expand our knowledge of key processes in developmental biology and evolutionary ecology, and highlight the broader implications of environmental disruptions on fundamental biological processes.

Current research projects in the Tezak lab generally fall within the following three categories:

Understanding the relationship between temperature and germ cell biology.

Germ cells (GCs) are a critical group of cells which give rise to eggs (in the ovary) or sperm (in the testis). In other words, these are the cells responsible for the continuation of the species! Our work recently established that, in the red-eared slider turtle (T.scripta), incubation temperature directly impacts GC number and gene expression during early embryonic development. We now aim to unravel the mechanism by which temperature influences germ cell ‘behavior’. We also hope to understand how natural incubation conditions (outside of the lab) and rising temperatures will impact germ cell biology.

Establishing the role of germ cells in sex determination.

Recent evidence from our lab and others show that GCs can have a feminizing effect on the bipotential gonad, essentially pushing the gonad towards an ovarian fate. However, the mechanisms that drive this phenomenon remain unexplored. Our lab is currently testing the hypothesis that GCs promote the ovarian fate via density dependent signal(s) that repress the male pathway. We are tackling this hypothesis from different angles spanning live imaging approaches, single-cell omics, and functional egg incubation experiments.

Exploring temperature-dependent sex determination in a broader evolutionary context.

It remains unclear whether the number of GCs present in the gonads at the time of hatching determines the reproductive potential in T. scripta or other oviparous reptiles. However, if true, the discovery that incubation temperature directly influences GC number could have important implications for understanding the impacts of climate change on reproductive potential. A number of projects in the lab now seek to define the effects of incubation temperature on GC biology in other reptile species with different sex determination strategies and explore whether high GC number is consistently associated with ovary development.

Tezak, Boris, Barbora Straková, Dhanawn J. Fullard, Shannon Dupont, Jennifer McKey, Ceri Weber, and Blanche Capel. “Higher temperatures directly increase germ cell number, promoting feminization of red-eared slider turtles.” Current Biology (2023).

Tezak, Boris, Blair Bentley, Mikaela Arena, Samantha Mueller, Taylor Snyder, and Itzel Sifuentes-Romero. “Incubation environment and parental identity affect sea turtle development and hatchling phenotype.” Oecologia 192, no. 4 (2020): 939-951.

Tezak, Boris, Itzel Sifuentes-Romero, Sarah Milton, and Jeanette Wyneken. “Identifying sex of neonate turtles with temperature-dependent sex determination via small blood samples.” Scientific reports 10, no. 1 (2020): 1-8.

Tezak, Boris M., Itzel Sifuentes-Romero, and Jeanette Wyneken. “A new approach for measuring temperature inside turtle eggs.” Journal of Experimental Biology 221, no. 20 (2018): jeb188698.

Sifuentes-Romero, Itzel, Boris M. Tezak, Sarah L. Milton, and Jeanette Wyneken. “Hydric environmental effects on turtle development and sex ratio.” Zoology 126 (2018): 89-97.

Tezak, Boris M., Kathleen Guthrie, and Jeanette Wyneken. “An immunohistochemical approach to identify the sex of young marine turtles.” The Anatomical Record 300, no. 8 (2017): 1512-1518.