Biology subjects

Major, A. T.

Publications and source records attributed to Major, A. T..

3 recordsLinked to original sources

bioRxiv2022

DMRT1 regulation of TOX3 modulates expansion of the gonadal steroidogenic cell lineage

Vertebrate gonads comprise three primary cell types, germ cells, steroidogenic cells, and supporting cells. The latter are the first cell type to differentiate in the embryonic gonad and direct the formation of other somatic lineages. During gonadal sex determination, the supporting cell lineage differentiates into Sertoli cells in males and pre-granulosa cells in females. In the chicken embryo, the molecular trigger for Sertoli cell differentiation is the Z-linked gene DMRT1. Recently, single cell RNA-seq data indicate that that chicken steroidogenic cells, derive from differentiated supporting cells. This differentiation process is achieved by a sequential upregulation of steroidogenic genes and down-regulation of supporting cell markers. The exact mechanism regulating this differentiation process remains unknown. We identified the gene TOX3 as a novel transcription factor expressed in embryonic Sertoli cells of the chicken testis. TOX3 knockdown in males resulted in increased CYP17A1 positive Leydig cells. TOX3 over-expression in male and female gonads resulted in a significant decline in CYP17A1 positive steroidogenic cells. TOX3 expression is negatively regulated by estrogens in vivo, but not induced during masculinization induced by estrogen inhibition. In ovo knock-down of the testis determinant, DMRT1, in male gonads resulted in a down-regulation of TOX3 expression. Conversely, DMRT1 over-expression caused an increase in TOX3 expression. Taken together, this data indicates that DMRT1 regulation of TOX3 modulates expansion of the steroidogenic lineage, either directly, via cell lineage allocation, or indirectly via signaling from the supporting to steroidogenic cell populations.

developmental biology↗

bioRxiv2022

Cell lineage specification during development of the anterior lateral plate mesoderm and forelimb field

The lateral plate mesoderm (LPM) is a transient embryonic tissue that gives rise to a diverse range of mature cell types, including the cardiovascular system, the urogenital system, endoskeleton of the limbs, and mesenchyme of the gut. While the genetic processes that drive development of these tissues are well defined, the early cell fate choices underlying LPM development and specification are poorly understood. In this study, we utilize single-cell transcriptomics to define cell lineage specification during development of the anterior LPM and the forelimb field in the chicken embryo. We identify the molecular pathways directing differentiation of the aLPM towards a somatic or splanchnic cell fate, and subsequent emergence of the forelimb mesenchyme. We establish the first transcriptional atlas of progenitor, transitional and mature cell types throughout the early forelimb field and uncover the global signalling pathways which are active during LPM differentiation and forelimb initiation. Specification of the somatic and splanchnic LPM from undifferentiated mesoderm utilizes distinct signalling pathways and involves shared repression of early mesodermal markers, followed by activation of lineage-specific gene modules. We identify rapid activation of the transcription factor TWIST1 in the somatic LPM preceding activation of known limb initiation genes, such as TBX5, which plays a likely role in epithelial-to-mesenchyme transition of the limb bud mesenchyme. Furthermore, development of the somatic LPM and limb is dependent on ectodermal BMP signalling, where BMP antagonism reduces expression of key somatic LPM and limb genes to inhibit formation of the limb bud mesenchyme. Together, these findings provide new insights into molecular mechanisms that drive fate cell choices during specification of the aLPM and forelimb initiation.

developmental biology↗

bioRxiv2021

TGIF1 is required for chicken ovarian cortical development and generation of the juxtacortical medulla

During early embryogenesis in amniotic vertebrates, the gonads differentiate into either ovaries or testes. The first cell lineage to differentiate gives rise to the supporting cells; Sertoli cells in males and pre-granulosa cells in females. These key cell types direct the differentiation of the other cell types in the gonad, including steroidogenic cells. The gonadal surface epithelium and the interstitial cell populations are less well studied, and little is known about their sexual differentiation programs. Here, we show the requirement of the transcription factor gene TGIF1 for ovarian development in the chicken embryo. TGIF1 is expressed in the two principal ovarian somatic cell populations, the cortex and the pre-granulosa cells of the medulla. TGIF1 expression is associated with an ovarian phenotype in sex reversal experiments. In addition, targeted over-expression and gene knockdown experiments indicate that TGIF1 is required for proper ovarian cortical formation. TGIF1 is identified as the first known regulator of juxtacortical medulla formation. These findings provide new insights into chicken ovarian differentiation and development, specifically in the process of cortical and juxtacortical medulla formation, a poorly understood area. SUMMARY STATEMENTThe transcription factor TGIF1 is required for proper ovarian sex differentiation in chicken embryos, regulating development of the cortical and juxtacortical medulla, independently of the supporting cell sex lineage.

developmental biology↗