Case report of apoptosis in testis of four AZFc-deleted patients: increased DNA fragmentation during meiosis, but decreased apoptotic markers in post-meiotic germ cells.

AZFc deletions of the Y chromosome are the major known genetic cause of spermatogenetic failure. Meiotic studies have shown a prevalence of synaptonemal complex fragmentation and an excess of early-stage sperm cells, suggesting that the maturation block could involve apoptosis. We present a prospective and observational study of apoptotic markers in the sperm of four AZFc-deleted patients and two non-obstructive azoospermic controls without an AZFc deletion. Polycaspases assays and terminal deoxynucleotidyl transferase dUDP nick-end labelling (TUNEL) assays were combined to evaluate the incidence of apoptosis in pre-meiotic, meiotic and post-meiotic germs cells identified, respectively, using anti-melanoma-associated antigen A4 (MAGE-A4), anti-synaptonemal complex protein 3 (SCP3) and anti-sperm acrosome membrane-associated protein 1 (SPACA1) antibodies. We detected apoptosis at all stages of AZFc-deletion spermatogenesis. Using the caspase assay, the incidence of positive cells was found to be heterogeneous for pre-meiotic (from 4.8 to 84.5%) and meiotic stages (from 7.9 to 57.6%), while for post-meiotic cells, the mean incidence was 6% in AZFc-deleted patients compared with 26.5% in controls (P < 0.05). Using the TUNEL assay, the mean percentage with DNA fragmentation for meiotic cells was 54.0% in AZFc-deleted patients compared with 20.3% in controls (P < 0.05), while the percentage of TUNEL-positive post-meiotic cells ranged from 5.3 to 44.7%. Spermatocyte loss in AZFc-deleted patients occurs via the apoptotic pathway. In post-meiotic cells, the lower incidence of apoptosis in testis from three of the four AZFc-deleted patients, compared with controls, is consistent with AZFc deletions having little negative impact on sperm quality.

Human and mouse ZFY genes produce a conserved testis-specific transcript encoding a zinc finger protein with a short acidic domain and modified transactivation potential.

Mammalian ZFY genes are located on the Y chromosome, and code putative transcription factors with 12-13 zinc fingers preceded by a large acidic (activating) domain. In mice, there are two genes, Zfy1 and Zfy2, which are expressed mainly in the testis. Their transcription increases in germ cells as they enter meiosis, both are silenced by meiotic sex chromosome inactivation (MSCI) during pachytene, and Zfy2 is strongly reactivated later in spermatids. Recently, we have shown that mouse Zfy2, but not Zfy1, is involved in triggering the apoptotic elimination of specific types of sex chromosomally aberrant spermatocytes. In humans, there is a single widely transcribed ZFY gene, and there is no evidence for a specific role in the testis. Here, we characterize ZFY transcription during spermatogenesis in mice and humans. In mice, we define a variety of Zfy transcripts, among which is a Zfy2 transcript that predominates in spermatids, and a Zfy1 transcript, lacking an exon encoding approximately half of the acidic domain, which predominates prior to MSCI. In humans, we have identified a major testis-specific ZFY transcript that encodes a protein with the same short acidic domain. This represents the first evidence that ZFY has a conserved function during human spermatogenesis. We further show that, in contrast to the full acidic domain, the short domain does not activate transcription in yeast, and we hypothesize that this explains the functional difference observed between Zfy1 and Zfy2 during mouse meiosis.

HSFY genes and the P4 palindrome in the AZFb interval of the human Y chromosome are not required for spermatocyte maturation.

BACKGROUND: Recurrent AZFb deletions on the human Y chromosome are associated with an absence of ejaculated spermatozoa consequent to a meiotic maturation arrest that prevents the progression of germ cells to haploid stages. The extreme rarity of partial deletions has hampered the identification of the AZFb genes required for normal meiotic stages. The critical interval, refined by two overlapping deletions associated with full spermatogenesis (AZFc and b1/b3), measures over 4 Mb and contains 13 coding genes: CDY2, XKRY, HSFY1, HSFY2, CYORF15A, CYORF15B, KDM5D, EIF1AY, RPS4Y2 and four copies of RBMY. METHODS AND RESULTS: We screened 1186 men from infertile couples for Y chromosome deletions, and identified three unrelated oligozoospermic men and one azoospermic man who carry an identical 768 kb deletion resulting in loss of the entire P4 palindrome, including both HSFY genes, the only coding genes within the deletion interval. This 768 kb deletion was not found in 1179 control men. The deletion breakpoints share only 4 bp of nucleotide identity, revealing that the deletions are not recurrent, but are descendants of a founding deletion. Confirming this, we find that all four men carry a Y chromosome of the same highly defined haplogroup (R1b1b1a1b) (incidence 30% in Southern France), although further haplotype analyses showed that they were not closely related. CONCLUSIONS: Although the HSFY deletion is restricted to our infertile group, it has been transmitted naturally over many generations, indicating that HSFY genes make only a slight contribution to male fertility. Importantly, our study formally excludes HSFY genes as the AZFb factor required for progression through meiosis.