Abstract
In vertebrate embryos, Müllerian ducts give rise to the female reproductive tract. Here, we present a comprehensive analysis of Müllerian duct differentiation using single cell transcriptomics in the chicken embryo, a unique model for duct development. The data reveal greater cellular complexity of Müllerian duct differentiation than previously understood. Transcriptomic profiling of early formed Müllerian ducts identifies molecular signatures for the Müllerian duct Epithelium (MDE) and the Müllerian Duct Mesenchyme (MDM), the two principle compartments of the Müllerian duct. The MDE expresses
PAX2, LHX1, WNT7, LGR5, PDGFA/D
, and
CDH1/2
. The MDM is marked by
WNT4, EMX2, POSTN, OSR1, VIM,DMRT
and the EMT markers
ZEB1/2
. In the male, the regressing mesenchyme (MDM) has a unique molecular signature, expressing the transcription factors
MSX1, MSX2, RUNX2, GATA5, DLX3
and
DLX5
, and the signaling regulators
DKK4
and
NRG1
(Neuregulin). Single cell transcript profiling of the regressing male mesenchyme identifies new genes implicated in duct regression, including the WNT antagonist, DKK4. DKK4, responds to Anti-Mullerian Hormone induction and can induce duct regression when ectopically expressed in females. The duct mesenchyme in the female follows a different fate, with a molecular signature comprising
SMARCA2/ HMGA2/ZEB1/2/TWIST1/2/DMRT2
and persistent expression of
FOXE1, OSR2
and
HGF
(Hepatocyte Growth Factor). Cell clusters in the developing female ducts reflects spatial pre-patterning of the duct prior to later regionalisation. In contrast to AMH-mediated bilateral Müllerian duct regression in males, female chicken embryos show an unusual pattern of left duct differentiation and contralateral right duct regression. We find that right female duct does not regress in the same manner as in males, being transcriptionally distinct and lacking a population of regressing mesenchyme, despite presumably being mediated by AMH, as in males.