DMRT1 Is Upregulated in the Gonads During Female-to-Male Sex Reversal in ZW Chicken Embryos1

Abstract

Sex in birds is chomosomally based (ZZ male, ZW female), but the mechanism underlying sex determination remains unknown. An unresolved question is whether Z gene dosage plays a role in avian sex determination. DMRT1 is an avian Z-linked gene that shows higher expression in male gonads during embryogenesis and has been proposed as a putative testis-determining gene in birds. The Z-linkage of this gene makes it an ideal candidate for testing the question of gene dosage in avian testis determination. A higher level of DMRT1 expression in male (ZZ) versus female (ZW) embryonic gonads may reflect the presence of two Z-linked copies in the male, or it may be due to specific and active upregulation of DMRT1 during testis formation. A functional interventionist strategy was used to distinguish between these two possibilities. DMRT1 expression was analyzed in chicken embryos during experimentally induced female-to-male sex reversal, using the aromatase enzyme inhibitor fadrozole. DMRT1 expression was analyzed by whole mount in situ hybridization and reverse transcription polymerase chain reaction (for mRNA) and indirect immunofluorescence (for protein). Female-to-male sex-reversed embryos (genetically ZW) showed elevated levels of DMRT1 expression similar to those of normal males (with two copies of the Z chromosome). Elevated levels of DMRT1 are therefore associated with testis development, both in normal males (ZZ) and in sex-reversed females (ZW). SOX9 expression was also activated during female-to-male sex reversal but appeared delayed relative to DMRT1 upregulation. These results show that testis development does not require two Z-linked copies of DMRT1, but it does involve active upregulation of the gene. Higher levels of DMRT1 expression during testis differentiation therefore do not simply reflect a gene dosage difference between the two sexes but imply active involvement in male development.

Isolation of chicken homolog of the FOXL2 gene and comparison of its expression patterns with those of aromatase during ovarian development

“…These investigations revealed that cFoxL2 protein distribution was restricted to the medullar part of the ovary during early development. The same region of expression has been reported for aromatase transcripts Nakabayashi et al, 1998;Nishikimi et al, 2000;Oreal et al, 2002) and for the aromatase protein (Smith et al, 2003). The double immunolocalization of cFoxL2 and aromatase proteins to the sections of the left female gonad at E14 in our study demonstrated that cFoxL2 and aromatase proteins are expressed in the same cells.…”

Sexual dimorphic expression of DMRT1 and Sox9a during gonadal differentiation and hormone‐induced sex reversal in the teleost fish Nile tilapia (Oreochromis niloticus)

“…The present study indicates clearly, for the first time in fish, that tDMRT1 is expressed in the germcell-surrounding cells and medullarycell-mass cells, which differentiate into the efferent duct during testicular differentiation, irrespective of the genetic sex. A recent report on a study using chickens showed that ZW sex reversal from female to male was accompanied by DMRT1 expression in medullary cells, which developed into Sertoli cells (Smith et al, 2003). Furthermore, our recent study indicates that medaka DMRT1 is expressed in the germ-cell-surrounding cells and the intratesticular efferent duct, al- though medaka DMRT1 is expressed after testicular differentiation, unlike in tilapia (Kobayashi et al, 2004).…”

“…These studies have all shown that DMRT1 is dominantly expressed in the testis. During gonadal sex differentiation in the chicken, in particular, DMRT1 was found by in situ hybridization to be expressed almost exclusively in the testis, and the signals were localized in the Sertoli cells (Smith et al, 1999(Smith et al, , 2003. Evidence of the male-specific expression of DMRT1 was also obtained in humans, a reptile species and a frog species (Raymond et al, 1999;Smith et al, 1999;Kettlewell et al, 2000;Moniot et al, 2000;Shibata et al, 2002).…”

“…However, information on the distribution of DMRT1 within the gonads is limited to the mouse (Raymond et al, 1999) and the chicken (Smith et al, 2003). Although the distribution of DMRT1 in the gonads in medaka (Kobayashi et al, 2004) and zebrafish (Guo et al, 2005) was reported, these reports were not as thoroughly described.…”

“…DMRT1 appears to be involved in a certain type of XY sex reversal in humans (Bennet et al, 1993;Flejter et al, 1998;Yi et al, 2000;Veitia et al, 2001). In chickens, aromatase inhibitor-treated ZW embryos showed sex reversal, accompanied by DMRT1 expression (Smith et al, 2003). In teleost fish also, DMRT1 has been linked to both natural sex change from female to male, and to sex hormone-dependent sex reversal (He et al, 2003;Guan et al, 2000;Marchand et al, 2000).…”