The SRY-related SOX9 gene is involved in both chondrogenesis and the early steps of mammalian sex determination. Mutations in the human SOX9 gene cause campomelic dysplasia, a severe skeletal malformation syndrome associated with male-to-female sex reversal in most, but not all, XY individuals. Here we show that SOX9 contains a dimerization domain, and binds co-operatively as a dimer in the presence of the DNA enhancer element in genes involved in chondrocyte differentiation, such as Col11a2 and Col9a2, but binds as a monomer to the regulatory region of the sex-determining gene SF1. Frameshift SOX9 mutations truncate its two activation domains, while all missense mutations reported to date lie in the high mobility group (HMG) DNA-binding domain. We identify a missense mutation (A76E), the first outside the HMG domain, in an XY patient presenting with campomelic dysplasia but without sex reversal. This mutation disrupts the dimerization capability of SOX9, interfering with both the DNA binding and consequent transactivation of both the Col11a2 and Col9a2 enhancers. Consistent with the patient's phenotype, the A76E mutation does not affect DNA binding and activation of the SF1 enhancer. DNA-dependent cooperative dimerization could represent a novel mechanism to achieve tissue-specific regulation of gene expression by a SOX transcription factor. These results establish that SOX9 cooperative dimerization is required for chondrogenesis but not for sex determination and may explain why campomelic dysplasia need not be associated with XY sex reversal.

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Abstract. Mutations in ATRX (alpha-thalassaemia and mental retardation on the X-chromosome) can give rise to ambiguous or female genitalia in XY males, implying a role for ATRX in testicular development. Studies on ATRX have mainly focused on its crucial role in brain development and α-globin regulation; however, little is known about its function in sexual differentiation and its expression in the adult testis. Here we show that the ATRX protein is present in adult human and rat testis and is expressed in the somatic cells; Sertoli, Leydig, and peritubular myoid cells, and also in germ cells; spermatogonia and early meiotic spermatocytes. The granular pattern of ATRX staining is consistent with that observed in other cell-types and suggests a role in chromatin regulation. The findings suggest that ATRX in humans may play a role in adult spermatogenesis as well as in testicular development. Key words: ATR-X syndrome, Germ cells, Spermatogenesis, Testis development (J. Reprod. Dev. 57: [317][318][319][320][321] 2011) he ATR-X (alpha thalassemia, mental retardation, X-linked) syndrome is a rare X-linked recessive developmental disorder affecting male children and young adults [1]. Affected individuals display a variable array of clinical features including severe mental retardation, a variety of facial and skeletal abnormalities, mild α-thalassemia, genital abnormalities, microcephaly and short stature [1].The ATRX gene comprises 36 exons and encodes a modular protein of 280 kDa it contains two highly conserved domains, a PHDlike finger which interacts with chromatin, and a SWI//SNF-like ATPase domain [2]. A naturally occurring isoform that arises due to a failure to splice intron 11 from the primary transcript is also present, this isoform has been characterized as ATRXt and encodes a protein of roughly 150 kDa [3]. It shares a similar expression profile to ATRX, its function is unknown [3].ATRX is a nuclear protein showing intense punctate staining associated with the DAPI-bright regions of the nucleus and interacts with the heterochromatin protein HP1 [4]. The protein is widely expressed throughout development is strongly associated with pericentromeric heterochromatin, ribosomal DNA repeats but also shows diffuse nuclear staining [4]. The ATRX protein is also found in promyelocytic leukemia nuclear bodies via an interaction with the Daxx protein and shows displays robust nucleosome remodeling activity, implying that ATRX functions as a chromatin remodeling protein [4,5]. The down regulation of alpha globin expression in ATR-X patients indicates that ATRX plays a role in gene expression [6]. Its specific cellular function is unknown.In humans, 80% of mutations in ATRX cause genital abnormalities. These may be very mild (undescended testes or deficient prepuce), but the abnormalities extend through to hypospadia, micropenis and ambiguous or female genitalia (Table 1) [1,7,8]. The most severely affected children, who are clinically defined as male pseudohermaphrodites are most commonly associated with truncati...

Lymphedema distichiasis syndrome (LDS) is a rare autosomal dominant condition characterized by lower limb lymphedema, distichiasis, and variable additional features. LDS is usually caused by heterozygous sequence variants in the FOXC2 gene located at 16q24, but in one previous instance LDS has resulted from a balanced reciprocal translocation with a breakpoint at 16q24, 120 kb distal to the FOXC2 gene suggesting a position effect. Here, we describe a second family with LDS caused by a translocation involving 16q24. The family were ascertained after detection of a paternally inherited balanced reciprocal translocation t(16;22)(q24;q13.1) in a pregnancy complicated by severe fetal hydrops. There was a past history of multiple miscarriages in the father's family, and a personal and family history of lymphedema and distichiasis, consistent with the diagnosis of LDS. Using whole genome amplified DNA from single sperm of the male proband, bead array analysis demonstrated that the FOXC2 gene was intact and the chromosome 16 breakpoint mapped to the same region 120Kb distal to the FOXC2 gene. This case highlights the clinical consequences that can arise from a translocation of genomic material without dosage imbalance, and that it is increasingly feasible to predict and characterize possible effects with improved access to molecular techniques.