Gamete Biology

Factors Maintaining Normal Sperm Tail Structure During Epididymal Maturation Studied in Gopc^-/- Mice

Abstract
Gopc (Golgi-associated PDZ- and coiled-coil motif-containing protein)^-/- mice are infertile, showing globozoospermia, coiled tails and a stratified mitochondrial sheath. Transmission electron microscope (TEM) images of the spermatozoa were studied quantitatively to analyze disorganization processes during epididymal passage. Factors maintaining straight tail and normal mitochondrial sheath were also studied by TEM and immunoflorescent microscopy. Sperm tails retained a normal appearance in the proximal caput epididymidis. Tail disorganization started between the proximal and the middle caput epididymidis, and the latter is the major site for it. The tail moved up through the defective posterior ring and coiled around the nucleus to various degrees. Tail coiling occurred in the caput epididymidis suggesting it was triggered by cytoplasmic droplet migration. SPATA19/spergen-1, a candidate mitochondrial adhesion protein, remained on the stratified mitochondria, while GPX4/ PHGPx, a major element of the mitochondrial capsule, was unevenly distributed on them. From these findings, we speculate GPX4 is necessary to maintain normal sheath structure, and SPATA19 prevents dispersal of mitochondria, resulting in a stratified mitochondrial sheath formation in Gopc^-/- spermatozoa. The epididymal epithelium was normal in structure and LRP8/apoER2 expression suggesting that tail abnormality is due to intrinsic sperm factors. Three cell-structures are discussed as requisite factors for maintaining a straight tail during epididymal maturation: 1) a complete posterior ring to prevent invasion of the tail into the head compartment, 2) stable attachment of the connecting piece to the implantation fossa, 3) a normal mitochondrial sheath supported by SPATA19 and supplied with sufficient and normally distributed GPX4.

Key words: Epididymis • Sperm maturation