Does DAX1A (NR0B1A) Play a Role in Gonadal Function?

Abstract

The orphan nuclear receptor DAX1 (dosage-sensitive sex reversal-AHC critical region on the X chromosome gene 1; NR0B1) is known to play important roles in development, steroidogenesis, as well as in sex determination. Recently, an alternatively spliced form of DAX1, called DAX1A(NR0B1A) was described. DAX1A is encoded by DAX1 exons 1 and 2A, which is located within the intron between DAX1 exons 1 and 2. Its expression was observed in several tissues including ovary and testis. Cell culture expression studies further showed that DAX1A had an inhibitory effect on DAX1, thus suggesting a role for DAX1A in the regulation of gonadal differentiation/function. However, the relative level of DAX1 vs. DAX1A transcripts has not been studied using quantitative analyses. Herein, we developed and performed quantitative real-time RT-PCR (qPCR) with standard curves for both DAX1 and DAX1A and mRNA expression levels for both transcripts were compared in human testis, whole ovary, isolated follicles and corpora lutea (n=3 for each tissue). DAX1 mRNA was detected in all samples of human testes (0.85 amoles/μg 18S), ovaries (0.97 amoles/μg 18S), ovarian follicles (0.31 amoles/μg 18S), and corpus luteum (0.32 amole/μg 18S). DAX1A mRNA was detectable in all samples of testes (0.02 amole/μg 18S), and ovaries (0.06 amoles/μg 18S), but was detectable in only one ovarian follicle (n=3) and one corpus luteum sample (n=3). DAX1 mRNA levels were significantly higher (>40 -fold) than seen for DAX1A in the testis and ovary samples (P<0.01), while the low level of DAX1A in follicular and luteal samples prevented quantification. These results suggest DAX1 is clearly the predominant isoform found in human testis and ovary. In addition, the low abundance of the DAX1A transcript questions its role in ovarian or testicular physiology.