Lack of Spem1 causes aberrant cytoplasm removal, sperm deformation, and male infertility

Abstract

We identified a previously uncharacterized gene, spermatid maturation 1 (Spem1), encoding a protein exclusively expressed in the cytoplasm of steps 14 -16 elongated spermatids in the mouse testis. This protein contains no known functional domains and is highly conserved across mammalian species. Male mice deficient in Spem1 were completely infertile because of deformed sperm characterized by a bent head wrapped around by the neck and the middle piece of the tail. We show that lack of Spem1 causes failure of the cytoplasm to become loose and detach from the head and the neck region of the developing spermatozoa. Retained cytoplasmic components mechanically obstruct the straightening of the sperm head and the stretching of the growing tail, leading to the bending of the head in the neck, followed by the wrapping of the head by the neck or the middle piece of the sperm tail. Our study reveals that proper cytoplasm removal is a genetically regulated process requiring the participation of Spem1 and that lack of Spem1 causes sperm deformation and male infertility. cytoplasmic droplets ͉ gene knockout ͉ spermatogenesis ͉ spermiation ͉ spermiogenesis

The E2 Ubiquitin-conjugating Enzyme UBE2J1 Is Required for Spermiogenesis in Mice

“…Akin to Ube2j1 Ϫ/Ϫ mice, SPEM1 Ϫ/Ϫ males (but not females) are sterile and their sperm are ϳ85% immotile because of severe deformations in the head/neck region, caused by retention of cytoplasmic remnants. The ultrastructural characteristics are strikingly similar to our observations in Ube2j1 Ϫ/Ϫ sperm (38). SPEM1 interacts with UBQLN1 (ubiquilin 1) at the manchette of elongating spermatids (39).…”

“…An intriguing case is SPEM1 (spermatid maturation 1), a protein of unknown molecular function, which is expressed exclusively in elongating spermatids between steps 14 and 16, implying a function in cytoplasm removal and/or spermiation (38). Akin to Ube2j1 Ϫ/Ϫ mice, SPEM1 Ϫ/Ϫ males (but not females) are sterile and their sperm are ϳ85% immotile because of severe deformations in the head/neck region, caused by retention of cytoplasmic remnants.…”

Atg7 is required for acrosome biogenesis during spermatogenesis in mice

“…However, we observed a slightly increased level of phosphorylated p70S6 kinase ( Figure 4A), suggesting enhanced protein synthesis in TNAP-Atg7 −/− mouse testes. Similar to Spem1-knockout mice [16], we found that the polyubiquitinated protein level increased by 1.5-fold in Atg7-deficient testes compared with Atg7 Flox/ Flox ones ( Figure 4B and 4C), indicating the inhibition of protein degradation. Consistent with findings from Atg7 knockout in other tissues [9,17,18], LC3-I but not the membrane-associated form LC3-II was accumulated in Atg7-deficient testes ( Figure 4D).…”

Conditional inactivation of Miwi2 reveals that MIWI2 is only essential for prospermatogonial development in mice

“…A floxed Miwi2 allele (Miwi2 lox ) was generated by conventional ES cell targeting through homologous recombination. 51 A conditional Miwi2-targeting vector was constructed using Quick & Easy Red/ET Conditional Knock Out Kit-loxP kit (GeneBridge, Cat#: K005) according to the manufacturer's protocol. Briefly, two loxp site-containing PGK donor cassettes (loxP-pgk-Neo r -loxP) were inserted into introns 8 and 12 of Miwi2 gene contained in a BAC clone (BAC#:RP23-340G24, Children's Hospital Oakland Research Institute, Oakland, CA, USA), and the first PGK cassette was deleted by a Cre-expressing vector fragment (706-Cre) to retain a 34-bp loxp site sequence in the targeting vector (Figure 1a).…”