Absence of annulus in human asthenozoospermia: Case Report†

Abstract

The annulus is a septin-based ring structure located at the junction of the midpiece (MP) and the principal piece (PP) of spermatozoa flagellum. In the mouse, deletion of Septin 4, a structural component of the sperm annulus, prevents annulus formation and leads to MP-PP disjunction, flagellar bending, asthenozoospermia and male sterility. Testis anion transporter 1 (Tat1) is a germ cell-specific member of the SLC26 anion transporter family and is co-expressed with Septin 4 at the sperm annulus. Interestingly, Tat1 null sperm bear an atrophic annulus, causing a phenotype similar to that of Sept4 null sperm. We searched for Tat1 misexpression and/or mislocalization in spermatozoa from asthenozoospermic subjects (n = 75) and controls by performing an immunofluorescence detection assay on sperm smear preparations. We found one patient showing moderate asthenozoospermia, with 97% of sperm lacking Tat1, Septin 4 and Septin 7 proteins at the annulus. We confirmed the absence of the annulus structure by transmission electron microscopy and observed that spermatozoa from the patient displayed MP-PP disjunction and abnormal mitochondrial organization. We show that the structural defects in sperm are not caused by abnormal transcription or point mutations of the TAT1 and SEPT4 genes; however, although both proteins are expressed, they are not properly localized at sperm annulus. The case we studied, so far unreported in human, confirms the involvement of Tat1 and Septin proteins in the constitution of the annulus, but also raises questions about the function of this structure in human sperm motility.

Relationship between absence of annulus and asthenozoospermia in Iranian men

“…Therefore, they introduced the septins as appropriate diagnostic markers for a subset of asthenozoospermia. In France, Lhuillier and colleagues [10] in a similar study analyzed 75 cases of asthenozoospermia including 28 cases of isolated asthenozoospermia, 13 cases of oligo-asthenozoospermia and 34 cases of teratoasthenozoospermia, but they found only one case of loss of annulus that is in accordance with our finding on a population with the same ethnicity. This discrepancy may be attributed to the origin of the populations screened (Japanese versus Caucasian), to the small sizes of the cohort studies or to other causes remains to be determined.…”

“…The annulus structure was completely absent in all spermatozoa analyzed. c Western blot analysis for septin 4 which was not detected in the gel; PC positive control Septin proteins belong to the GTPase superclass of P loop NTPases [10][11][12]. Sept4 null mice show the reproductive phenotypes similar to a subset of asthenozoospermic patients [7,8].…”

The expression pattern of SEPT7 correlates with sperm morphology

“…In the mouse, gene targeting of Septin4, Septin12, and Tat1 lead to abnormal mitochondrial organization and tail defects [6,7,11,25]. In humans, absence of the annulus is associated with abnormal mitochondrial organization in poor-motility sperm [9]. A recent study showed that DNAJB13, which is a type II HSP40, attaches itself to the annular anlage and then recruits septins via direct interaction with SEPT4 or a SEPT4-containing septin complex for the formation of an authentic annulus in the early stage of sperm flagellum morphogenesis.…”

“…Septin4 null mice are viable; however, males are sterile because they produce immotile sperm with a defective annulus [7,8]. In humans, disorganized annulus/SEPTIN rings were identified in a subset of patients with asthenozoospermia [9,10]. SEPT12 is also a component of the sperm annulus [6].…”

“…A terato-asthenozoospermic patient exhibited the absence of an annulus in 97% of his ejaculated spermatozoa, in which normal SEPT4/7 signals at the annulus were also lacking. Although both proteins are expressed, they are not properly localized in these sperm cells [9]. Another study revealed the presence of a defective annulus/SEPT4/7 phenotype in some patients with asthenozoospermia.…”