AZFa protein DDX3Y is differentially expressed in human male germ cells during development and in testicular tumours: new evidence for phenotypic plasticity of germ cells.

BACKGROUND: DDX3Y (DBY), located within AZoospermia Factor a (AZFa) region of the human Y chromosome (Yq11), encodes a conserved DEAD-box RNA helicase expressed only in germ cells and with a putative function at G1-S phase of the cell cycle. Deletion of AZFa results most often in germ cell aplasia, i.e. Sertoli-cell-only syndrome. To investigate the function of DDX3Y during human spermatogenesis, we examined its expression during development and maturation of the testis and in several types of testicular germ cell tumours (TGCTs), including the pre-invasive carcinoma in situ (CIS) precursor cells which are believed to originate from fetal gonocytes. METHODS: DDX3Y protein expression was analysed during development in different tissues by western blotting. The localization of DDX3Y in normal fetal and prepubertal testis tissue of different ages as well as in a series of distinct TGCT tissue samples (CIS, classical seminoma, spermatocytic seminoma, teratoma and embryonal carcinoma) was performed by immunohistochemistry. RESULTS: Germ cell-specific expression of DDX3Y protein was revealed in fetal prospermatogonia but not in gonocytes and not before the 17th gestational week. After birth, DDX3Y was expressed at first only in the nuclei of Ap spermatogonia, then also in the cytoplasm similarly to that seen after puberty. In CIS cells, DDX3Y was highly expressed and located predominantly in the nuclei. In invasive TGCT, significant DDX3Y expression was found in seminomas of the classical and spermatocytic type, but not in somatically differentiated non-seminomas, consistent with its germ-cell specific function. CONCLUSIONS: The fetal germ cell DDX3Y expression suggests a role in early spermatogonial proliferation and implies that, in men with AZFa deletion, germ cell depletion may begin prenatally. The strong expression of DDX3Y in CIS cells, but not in gonocytes, indicates phenotypic plasticity of CIS cells and suggests partial maturation to spermatogonia, likely due to their postpubertal microenvironment.

Analysis of gene expression in normal and neoplastic human testis: new roles of RNA.

Large-scale methods for analysing gene expression, such as microarrays, have yielded a wealth of information about gene expression at the mRNA level. However, expression of alternative transcripts, together with the presence of a wide range of largely undescribed RNA transcripts combined with regulation from the RNA interference pathway, may cause misinterpretations when trying to base conclusions from expression data derived from studies at the mRNA level. With HLXB9, PRM1, DICER and E2F1 as examples, we here show a range of situations that can occur when investigating gene expression, and give recommendations for the complementary methods that can verify gene expression data from large-scale studies, as well as give new information regarding the regulation of specific genes. Especially, we show that the absence of a protein despite high expression of the corresponding mRNA can be caused by expression of miRNAs targeting the mRNA. Additionally, we show through cloning the presence of both known and new miRNAs in the testis emphasizing the necessity for following up mRNA expression data by investigating expression at the protein level.

Do environmental factors play a role in the aetiology of carcinoma in situ testis and the testicular dysgenesis syndrome?

The hypothesis of the Testicular Dysgenesis Syndrome (TDS), first suggested in 2001, propose that several disorders of the male reproductive system such as infertility, hypospadias, cryptorchidism and testicular cancer are all symptoms of TDS, which is most likely initiated during early foetal development, and may be provoked by external factors such as endocrine disruptors in addition to genetic predisposition. Testicular germ cell tumours (TGCTs), considered the most severe symptom of TDS, have increased in incidence during the last 60 years, to become the most common malignancy in young Caucasian men aged 17-45 years. TGCTs of young men originate from carcinoma in situ (CIS) cells. In the last few years, progress has been made identifying candidate genes involved in the neoplastic development of CIS, which may elucidate the timing of the initiation of CIS, currently thought to originate in foetal life from primordial germ cells or early gonocytes. Histological dysgenetic features are frequently seen in testes affected with the TDS components testis cancer or cryptorchidism. A TDS-like phenotype can be induced in male rats by in utero exposure to high concentrations of dibutyl phthalate (DBP) suggesting that ubiquitously present environmental endocrine disruptors may play a role in the aetiology of human TDS. So far, no animal model has been able to mimick all the symptoms of TDS including TGCTs although CIS-like cells have been found in a spontaneous testicular neoplasm in a rabbit.