Abstract
In the chicken, sex determination relies on a ZZ (male)/ZW (female) chromosomal system, but underlying mechanisms are still not fully understood. The Z-dosage and the dominant W-chromosome hypotheses have been proposed to underlie primary sex determination. We present a modelling approach, which assembles the current knowledge and permits exploration of the regulation of this process in chickens. Relying on published experimental data, we assembled a gene network, which led to a logical model that integrates both the Z-dosage and dominant W hypotheses. This model showed that the sexual fate of chicken gonads results from the resolution of the mutual inhibition between DMRT1 and FOXL2, where the initial amount of DMRT1 product determines the development of the gonads. In this respect, at the initiation step, a W-factor would function as a secondary device, by reducing the amount of DMRT1 in ZW gonads when the sexual fate of the gonad is settled, that is when the SOX9 functional level is established. Developmental constraints that are instrumental in this resolution were identified. These constraints establish qualitative restrictions regarding the relative transcription rates of the genes DMRT1, FOXL2 and HEMGN. Our model further clarified the role of OESTROGEN in maintaining FOXL2 function during ovary development.
Highlights
In chickens, a reference experimental model, sex determination is genetically determined, that is individual sex results from the chromosomal constitution established in the zygote at fertilization
This model showed that the sexual fate of chicken gonads results from the resolution of the mutual inhibition between DMRT1 and FOXL2, where the initial amount of DMRT1 product determines the development of the gonads
We relied on experimental data and made a few assumptions to define a logical model with the following features: (1) The model integrates current hypotheses for chicken sex determination; namely the Z-dosage and the dominant W hypotheses
Summary
A reference experimental model, sex determination is genetically determined, that is individual sex results from the chromosomal constitution established in the zygote at fertilization. Chicken sex chromosomes, constituted by a ZZ (male) or a ZW (female) system, are unrelated to the XX/XY mammalian chromosomes [1]. This work focuses on the sexual development of the chicken bi-potential gonad into either testis or ovary. Molecular genetic technologies have permitted the cloning and characterization of genes controlling primary sex determination. These genes can be categorized into two classes, male- and female-promoting genes, depending on their role in controlling the development of bi-potential gonads (see electronic supplementary material, figure S1)
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