Rainbow trout Sox24, a novel member of the Sox family, is a transcriptional regulator during oogenesis
Introduction
The SRY (sex-determining region of the Y chromosome) gene has been identified as a testis determining factor in mammals (Gubbay et al., 1990; Sinclair et al., 1990). This gene encodes a DNA binding domain known as the HMG (high mobility group) box. The discovery of SRY/Sry in mouse and human rapidly led to the isolation of Sox genes, encoding a protein with an SRY-type HMG box in a wide variety of organisms (Denny et al., 1992a). The SRY-type HMG boxes bind to the minor groove of the (A/T)(A/T)CAAG motif (Denny et al., 1992b; Harley et al., 1992, Harley et al., 1994; van de Wetering et al., 1992), and induce a sharp bend in the DNA helix (Ferrari et al., 1992; Giese et al., 1992; Connor et al., 1994). The Sox genes are expressed during the embryonic development and also in some adult tissues, and are considered to play diverse roles in development as a transcription factor. In chicken, the Sox2 gene is expressed in the early developing lens and is implicated in the regulation of crystallin genes (Kamachi et al., 1995). The mouse Sox4 gene is involved in cardiac development as well as lymphocyte differentiation (Schilham et al., 1996), and human SOX4 can transactivate the CD2 gene (Wotton et al., 1995). The human SOX9 gene was identified as a causal gene for autosomal sex reversal and campomelic dysplasia (Foster et al., 1994; Wagner et al., 1994), and human SOX9 is likely to be a regulator of the type II collagen gene, COL2A1 (Lefebvre et al., 1997; Ng et al., 1997).
In salmonid ovaries, the follicles develop with a degree of synchrony, and large numbers of follicles at approximately the same stage of development can be obtained from a single animal, which is an enormous advantage for biochemical studies. Since in fish, as in other vertebrates, oogenesis can be divided into two parts, the growth phase and the maturation phase, the studies in fish could contribute to an understanding of oogenesis in vertebrates. However, in contrast to the understanding of endocrine regulation of oocyte growth and maturation in fish (Nagahama et al., 1995), the underlying gene regulation remains to be elucidated. The observation that between fish and mammals, the SOX-LZ (SOX6) and SOX9 genes show high degrees of conservation of gene structure and expression in spite of the evolutionary distance (Takamatsu et al., 1995Takamatsu et al., 1997) led us to seek for Sox genes expressed in rainbow trout ovary to understand their roles in oogenesis in fish. Here, we describe the isolation of a novel Sox cDNA from a rainbow trout ovary cDNA library and the characterization of its expression and transactivation activity.
Section snippets
Isolation of rainbow trout Sox24 cDNA clones
SRY-type HMG box sequences were amplified by PCR from rainbow trout ovary cDNA as described by Takamatsu et al. (1995), and one of the obtained sequences, Sox24, was used to screen a rainbow trout ovary cDNA library constructed with λZAPII vector (Stratagene). Positive clones were isolated, and rescued as pBluescript plasmids by in-vivo excision. The nt sequence was determined by using ssDNA by the dideoxy method (Sanger et al., 1997) with T7 DNA polymerase.
Northern (RNA) blot analysis
Total RNA was prepared by the
Isolation of rainbow trout Sox24 cDNA
By a PCR-based strategy with degenerate oligos corresponding to highly conserved aa sequences within the SRY-type HMG boxes, we obtained three kinds of Sox sequences from rainbow trout ovary cDNA as described by Takamatsu et al. (1995). Using one of the Sox sequences, designated Sox24, as a probe, we isolated a full-length cDNA clone (pRTSox24) from a rainbow trout ovary cDNA library. Sequence analysis revealed that the rainbow trout Sox24 is 367 aa and has an acidic region (66%) (aa 188–211) in
Acknowledgements
This work was supported in part by a grant pioneering research project in biotechnology from the Ministry of Agriculture, Forestry and Fisheries, Japan, and by a grant from the Kitasato Research Foundation.
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2008, General and Comparative EndocrinologyCitation Excerpt :Accordingly, these two genes are also strongly inhibited in our experiment. Additionally, various markers of previtellogenic oocytes, namely sox23, sox24, nup62 and vtgr (Yamashita et al., 1998; Kanda et al., 1998; Perazzolo et al., 1999) are barely expressed, reinforcing the fact that there are still not growing oocyte and differentiated granulosa cell in these trans-differentiating gonads. If the androgen treatment does inhibit ovarian-specific genes, this masculinization does not induce similar gene expressions like what is observed in the control male population.