Rafael D. Acemel
@rdacemel.bsky.social
RyC researcher at Centro Andaluz de Biología del Desarrollo (Sevilla/Spain). Trying to apply genomics to understand things about gene regulation and Evo-Devo.
In depth analysis and more nuanced discussions can be found in the paper. Thanks again to all the authors. We are eager to receive feedback!
February 2, 2026 at 11:19 AM
In depth analysis and more nuanced discussions can be found in the paper. Thanks again to all the authors. We are eager to receive feedback!
Based on this, we propose that supporting cells from Pax2-positive cells is an ancestral feature of Archelosauria, and those cells might be more prone to become steroidogenic. In contrast, in mammals supporting cells derive mostly from cells from the coelomic epithelium.
February 2, 2026 at 11:19 AM
Based on this, we propose that supporting cells from Pax2-positive cells is an ancestral feature of Archelosauria, and those cells might be more prone to become steroidogenic. In contrast, in mammals supporting cells derive mostly from cells from the coelomic epithelium.
In fact, #BorisTezak immunos on T. scripta confirmed the coexpression of Pax2 and Sox9.
February 2, 2026 at 11:19 AM
In fact, #BorisTezak immunos on T. scripta confirmed the coexpression of Pax2 and Sox9.
We performed PAGA trajectory analysis, which are consistent with the idea that supporting cells in turtles (granulosa and Sertoli) derive mostly from Pax2-positive mesenchymal cells.
February 2, 2026 at 11:19 AM
We performed PAGA trajectory analysis, which are consistent with the idea that supporting cells in turtles (granulosa and Sertoli) derive mostly from Pax2-positive mesenchymal cells.
Indeed, supporting cells in mice and chickens are thought to come from different progenitors. In mouse they mostly derive from coelomic epithelium cells, while in chicken mainly from a Pax2-positive mesenchymal population.
February 2, 2026 at 11:19 AM
Indeed, supporting cells in mice and chickens are thought to come from different progenitors. In mouse they mostly derive from coelomic epithelium cells, while in chicken mainly from a Pax2-positive mesenchymal population.
But if non-mammalian supporting cells are steroidogenic, then are they really homologous to mammalian supporting cells? And where do they come from?
February 2, 2026 at 11:19 AM
But if non-mammalian supporting cells are steroidogenic, then are they really homologous to mammalian supporting cells? And where do they come from?
Our data supports a model in which fetal Leydig cells (interstitially derived) could be a mammalian innovation. In fact, in mammals, androgens are dispensable for sex determination and only required to fully masculinize the embryo. Outside mammals, androgens are produced by supporting lineage cells!
February 2, 2026 at 11:19 AM
Our data supports a model in which fetal Leydig cells (interstitially derived) could be a mammalian innovation. In fact, in mammals, androgens are dispensable for sex determination and only required to fully masculinize the embryo. Outside mammals, androgens are produced by supporting lineage cells!
Again, #BorisTezak performed some nice immunos validating the colocalization of the steroidogenic gene Cyp11a1 with supporting cells that are also Sox9 positive.
February 2, 2026 at 11:19 AM
Again, #BorisTezak performed some nice immunos validating the colocalization of the steroidogenic gene Cyp11a1 with supporting cells that are also Sox9 positive.
We checked in turtles, and bingo! Androgen producing enzymes such as Cyp11a1 are produced by cells of the supporting lineage in T. scripta. Then, exclusively in ovaries, as in chicken, the aromatase Cyp19a1 converts androgens into estrogens in granulosa cells.
February 2, 2026 at 11:19 AM
We checked in turtles, and bingo! Androgen producing enzymes such as Cyp11a1 are produced by cells of the supporting lineage in T. scripta. Then, exclusively in ovaries, as in chicken, the aromatase Cyp19a1 converts androgens into estrogens in granulosa cells.
While fetal Leydig cells and theca cells have been identified in chicken, these steroidogenic populations derive from supporting cells, not interstitial cells!
February 2, 2026 at 11:19 AM
While fetal Leydig cells and theca cells have been identified in chicken, these steroidogenic populations derive from supporting cells, not interstitial cells!
However, we could not find interstitial cells expressing steroidogenic enzymes in T. scripta. This was puzzling: androgens and estrogens are critical for sex determination in turtles. However we think there is a catch!
February 2, 2026 at 11:19 AM
However, we could not find interstitial cells expressing steroidogenic enzymes in T. scripta. This was puzzling: androgens and estrogens are critical for sex determination in turtles. However we think there is a catch!
But this was not the only surprise. Given the conservation of main gonadal lineages, we expected to find the equivalent of fetal Leydig cells in mammals: a population mainly derived from interstitial cells and in charge of producing androgens.
February 2, 2026 at 11:19 AM
But this was not the only surprise. Given the conservation of main gonadal lineages, we expected to find the equivalent of fetal Leydig cells in mammals: a population mainly derived from interstitial cells and in charge of producing androgens.
To explore this relationship closer #BorisTezak did some beautiful immunos showing the transient coexpression of Twist1 and Sox9 followed by the downregulation of the latter in female gonads of T. scripta.
February 2, 2026 at 11:19 AM
To explore this relationship closer #BorisTezak did some beautiful immunos showing the transient coexpression of Twist1 and Sox9 followed by the downregulation of the latter in female gonads of T. scripta.
Twist1 is the first transcription factor differentially expressed in female cells. It is not expressed there either in mouse or chicken and has never been implicated in sex determination before! However, Twist1 has been shown to antagonize Sox9, a pro-testicular gene, but in mouse chondrogenesis 👀.
February 2, 2026 at 11:19 AM
Twist1 is the first transcription factor differentially expressed in female cells. It is not expressed there either in mouse or chicken and has never been implicated in sex determination before! However, Twist1 has been shown to antagonize Sox9, a pro-testicular gene, but in mouse chondrogenesis 👀.
Thus, to identify new factors involved in sex determination in turtles we looked for genes differentially expressed in supporting cell progenitors at either MPT and FPT. We did not find many, but one of them caught our attention: Twist1.
February 2, 2026 at 11:19 AM
Thus, to identify new factors involved in sex determination in turtles we looked for genes differentially expressed in supporting cell progenitors at either MPT and FPT. We did not find many, but one of them caught our attention: Twist1.
After data integration we found that all main gonadal lineages are conserved: germinal, interstitial and supporting cells. Supporting cells are often first to read sex determining inputs, differentiating into either Sertoli cells in males or granulosa cells in females and guiding other cell types.
February 2, 2026 at 11:19 AM
After data integration we found that all main gonadal lineages are conserved: germinal, interstitial and supporting cells. Supporting cells are often first to read sex determining inputs, differentiating into either Sertoli cells in males or granulosa cells in females and guiding other cell types.
Importantly, we could rely on previous single-cell data in chicken from the #Smith lab (www.cell.com/cell-reports...) and in mouse from the #Nef lab (www.science.org/doi/10.1126/...) to aid in the annotation and perform evolutionary comparisons!
Insights into Gonadal Sex Differentiation Provided by Single-Cell Transcriptomics in the Chicken Embryo
Gonadal cell-lineage specification during embryogenesis has long been thought to be
similar among vertebrates. In this chicken study, Estermann et al. show that this
is not the case, finding major dif...
www.cell.com
February 2, 2026 at 11:19 AM
Importantly, we could rely on previous single-cell data in chicken from the #Smith lab (www.cell.com/cell-reports...) and in mouse from the #Nef lab (www.science.org/doi/10.1126/...) to aid in the annotation and perform evolutionary comparisons!
To uncover cell types and genetic programs involved in sex determination in T. scripta we performed single-cell RNA-seq experiments at either MPT or FPT in three different timepoints: before (Yntema Stg.15), during (Stg. 18) and after (Stg. 23) sex determination.
February 2, 2026 at 11:19 AM
To uncover cell types and genetic programs involved in sex determination in T. scripta we performed single-cell RNA-seq experiments at either MPT or FPT in three different timepoints: before (Yntema Stg.15), during (Stg. 18) and after (Stg. 23) sex determination.
To answer this question we studied the sex determination process of the turtle Trachemys scripta. In this species, embryos incubated at 26ºC (the male producing temperature, MPT) develop as males while embryos incubated at 31ºC (FPT) develop as females.
February 2, 2026 at 11:19 AM
To answer this question we studied the sex determination process of the turtle Trachemys scripta. In this species, embryos incubated at 26ºC (the male producing temperature, MPT) develop as males while embryos incubated at 31ºC (FPT) develop as females.
From a more Evo Devo perspective, we were fascinated on how cell types and sex determining networks may evolve to integrate genetic (like mammals and birds) or environmental (turtles) sex-determining inputs.
February 2, 2026 at 11:19 AM
From a more Evo Devo perspective, we were fascinated on how cell types and sex determining networks may evolve to integrate genetic (like mammals and birds) or environmental (turtles) sex-determining inputs.