Tubulin posttranslational modifications modify the atypical spermatozoon centriole

Abstract

Sperm cells are transcriptionally and translationally silent. Therefore, they may use one of the remaining mechanisms to respond to stimuli in their environment, the post-translational modification of their proteins. Here we examined three post-translational modifications, acetylation, glutamylation, and glycylation of the protein tubulin in human and cattle sperm. Tubulin is the monomer that makes up microtubules, and microtubules constitute the core component of both the sperm centrioles and the axoneme. We found that the sperm of both species were labeled by antibodies against acetylated tubulin and glutamylated tubulin.

Figure 1. Acetylated tubulin and glutamylated tubulin are observed in both cattle and human sperm centrioles, while glycylated tubulin staining is variable

A ) The three main parts of cattle and human sperm are the head (H), neck (N), and tail (T). The head contains the nucleus (Nu), the proximal centriole (PC) and distal centriole (DC) are within the neck, and the tail consists of the axoneme (Ax), which extends through the midpiece (M), the principal piece (P), and end piece (E). B ) The proximal centriole is barrel-shaped, comprised of nine microtubule triplets, and is nearly perpendicular to the anterior side of the distal centriole. The distal centriole has an atypical structure with two protein rods (Ro), has nine splayed doublet microtubules, and is directly connected to the axoneme. C-H ) Immunofluorescence staining was used to observe different proteins and posttranslational modifications in cattle ( C , E , G ) and human ( D , F , H ) sperm. POC1B (magenta) is observed almost exclusively in the proximal and distal centrioles. Tubulin (red) labels the PC, DC, and axoneme. C-D ) The antibody (Thermo Fisher Scientific, MA533079) against acetylated tubulin (Ace Tub, green) was primarily detected in the PC, DC, and especially in the axoneme of cattle ( C ) and human ( D ) sperm. E-F ) The antibody (Adipogen, AG-20B-0020-C100) against glutamylated tubulin (Glu Tub, green) labeled the PC and DC of cattle ( E ) and human ( F ) sperm. G ) The antibody (EMD Millipore, MABS277) against glycylated tubulin (Gly Tub, green) was not detected in any centriolar components of cattle. H ) The antibody (Adipogen, rabbit ab, AG-25B-0034-C100) against monoglycylated tubulin (Gly Tub, green) was not detected in the PC of human sperm, but there is some signal in the midpiece and DC. Note that only the tail structures labeled by the anti-posttranslational modification antibody are annotated in the low magnification panels.