Search

To investigate the role of SOX9 gene in amphibian gonadogenesis, we analyzed its expression during male and female gonadogenesis in Xenopus tropicalis. The results showed that in both sexes SOX9 mRNA and protein were first detectable after metamorphosis when the gonads were well differentiated and remained present until the adult stage. In the testis, SOX9 expression was restricted to the nucleus of Sertoli-like cells, similarly to what has been observed in other vertebrates suggesting a conserved role in vertebrate testicular differentiation. In the ovary, in sharp contrast with what has been observed in all vertebrates examined so far, the SOX9 protein was localized in the cytoplasm of previtellogenic oocytes before being translocated into the nucleus of vitellogenic oocytes suggesting an unexpected role during oogenesis. These results suggest that the SOX9 gene may not be a sex-determining gene in X. tropicalis and may play different functions in testicular and ovarian differentiation., (Copyright (c) 2008 Wiley-Liss, Inc.)

In mammals, the gene Sry initiates signaling pathways triggering the differentiation of a testis from a sexually indifferent gonad. Assuming that these morphogenetic events may alter the proteolytic balance, the expression of matrix metalloproteinases (MMPs) and inhibitors (TIMPs) was investigated in gonads from 11.5 days postcoitum (dpc) onward, when testicular organogenesis occurs. Whereas selective MMPs and TIMPs (1-3) were detected in undifferentiated gonads (11.5 dpc) and in neonatal testes, a single TIMP (TIMP-1) was expressed in a sexually dimorphic manner from 12.5 dpc onward (i.e., after overt male gonad differentiation), demonstrated by using a semiquantitative reverse transcriptase-polymerase chain reaction and a Western blot analysis. To gain insight into the role of TIMP-1, the expression of gelatinases (mRNA levels and enzyme activity) was monitored. However, no sex differences could be evidenced, indicating that TIMP-1 was not inhibiting this class of MMPs during testis organogenesis. Apart from being an inhibitor of MMPs, TIMP-1 is known to display growth promoting activities. Of interest, testicular TIMP-1 (but not TIMP-2) levels were further enhanced up to 2 weeks of age, consistent with a role in the early postnatal testicular growth. We, therefore, established an organotypic culture system in which seminiferous cords may differentiate de novo and grow, depending on culture conditions. In that system and mimicking the in vivo situation, TIMP-1 immunolocalized strongly within the male gonadal territory and weakly in female gonads, in which no organization was evident. Experiments are now under way to determine to what extent TIMP-1 is a morphogenic gene involved in seminiferous cord formation and development., (Copyright 2003 Wiley-Liss, Inc.)

The acidic keratins K18 and K19 have been shown to display a sex-specific expression during gonadal differentiation in the rat. To extend these findings, we have undertaken a study of the expression of genes encoding for K18 and K19 and their basic partner K8 in the mouse from 10.5 days of gestation until adulthood, using immunofluorescence, in situ hybridization, and reverse transcriptase polymerase chain reaction (RT-PCR). In the urogenital ridge at 10.5 days of gestation, K18, K19, and K8 are present, in both sexes, in coelomic epithelium in the area of the prospective gonad. At 11 days and 10 h of gestation, they are detected in differentiating gonadal blastema. In male gonads at 11 days and 16 h of gestation the first Sertoli cells differentiate. They are stained for anti-Müllerian hormone by immunofluorescence and appear as dispersed cells throughout the blastema. Progressively, they adhere to each other and form differentiating seminiferous cords. K19 disappears as Sertoli cells differentiate. K18 and K8 continue to be detected in Sertoli cells during fetal life and after birth until 14 days postpartum. In the adult testis, no keratin is observed. In differentiating ovaries, the three keratins are present in somatic cells of the ovigerous cords during fetal life and in primordial follicles differentiating from 1-2 days postpartum. In the course of follicular development, K19 is no longer detected as primordial follicles differentiate into growing follicles. K18 and K18 are present in all stages of follicular development. These results show both differences and similarities with the results previously obtained in the rat. In the mouse, in contrast to the rat, keratins are detected in adult ovaries, and K18 is found in undifferentiated gonads and in ovaries. K18 is, thus, not specific to the testis in the mouse, as it is in the rat. In both species, K19 ceases to be expressed in male gonads as Sertoli cells differentiate and form seminiferous cords. The present observations confirm that downregulation of K19 gene expression in the fetal testis is one of the earliest molecular events attesting the commitment of the undifferentiated gonad to the male differentiative pathway.

In mammals, anti-Müllerian hormone (AMH) is produced by Sertoli cells from the onset of testicular differentiation and by granulosa cells only after birth. SOX9, a transcription factor related to the testis-determining factor SRY, is expressed in mouse testis 1 day before AMH. To determine the relationship between AMH and SOX9 in birds, we cloned the AMH promoter in search of SOX9 response elements, and we compared the expression of AMH and SOX9 in the gonads of chick embryos using in situ hybridization. Potential SOX response elements were found in the AMH promoter; however, AMH is expressed in both sexes at stage 25, 1 day before the first SOX9 transcripts appear in the male gonads. SOX9 is never expressed in the female. These results do not support the hypothesis that SOX9 could trigger the expression of testicular AMH in the chick but does not exclude a later role in testis development.

Morphological differentiation of gonads results within successive morphogenetic steps beginning with the formation of the undifferentiated gonad, identical in both sexes, through the differentiation of the characteristic gonadal structures, seminiferous tubes in the testis and follicles in the ovary. In this paper, we report recent data on each of these steps and particularly on the origin of somatic gonadal cells. Results from our laboratory are summarized with special emphasis on the relationships between cellular differentiation and morphogenetic processes.

Lhx9 (LIM/Homeobox gene 9) encodes a transcription factor implicated in various developmental processes, including gonadogenesis. Our observations in the rat show that Lhx9 expression present in undifferentiated gonads disappears as epithelial cells differentiate into Sertoli cells and begin to express AMH. In rat and in chick testes, Lhx9 expression present in interstitial cells decreases progressively to become undetectable after birth. In the female rat, Lhx9 is highly expressed in epithelial ovigerous cords of the fetal ovary. Its expression is down-regulated as epithelial cells differentiate into granulosa cells during the process of folliculogenesis occurring at birth. If this process is impaired by the lack of oocytes, ovigerous cord organization is maintained together with Lhx9 expression. In conclusion, Lhx9 expression can be inversely correlated with the commitment into a differentiation pathway of the different categories of mesothelium-derived cells of the gonad. [Copyright &y& Elsevier]