A MEIG1/PACRG complex in the manchette is essential for building the sperm flagella

Abstract

A key event in the process of spermiogenesis is the formation of the flagella, which enables sperm to reach eggs for fertilization. Yeast two-hybrid studies revealed that meiosis-expressed gene 1 (MEIG1) and Parkin co-regulated gene (PACRG) interact, and that sperm-associated antigen 16, which encodes an axoneme central apparatus protein, is also a binding partner of MEIG1. In spermatocytes of wild-type mice, MEIG1 is expressed in the whole germ cell bodies, but the protein migrates to the manchette, a unique structure at the base of elongating spermatid that directs formation of the flagella. In the elongating spermatids of wild-type mice, PACRG colocalizes with α-tubulin, a marker for the manchette, whereas this localization was not changed in the few remaining elongating spermatids of Meig1-deficient mice. In addition, MEIG1 no longer localizes to the manchette in the remaining elongating spermatids of Pacrg-deficient mice, indicating that PACRG recruits MEIG1 to the manchette. PACRG is not stable in mammalian cells, but can be stabilized by MEIG1 or by inhibition of proteasome function. SPAG16L is present in the spermatocyte cytoplasm of wild-type mice, and in the manchette of elongating spermatids, but in the Meig1 or Pacrg-deficient mice, SPAG16L no longer localizes to the manchette. By contrast, MEIG1 and PACRG are still present in the manchette of Spag16L-deficient mice, indicating that SPAG16L is a downstream partner of these two proteins. Together, our studies demonstrate that MEIG1/PACRG forms a complex in the manchette and that this complex is necessary to transport cargos, such as SPAG16L, to build the sperm flagella.

Formation and function of the manchette and flagellum during spermatogenesis

“…However, studies of transport complexes localized only in the manchette underline the crucial importance of IMT for sperm tail development. Meiosis-expressed gene 1 (MEIG1) and Parkin-co-regulated gene (PACRG) form a complex in the manchette, which appears to be required for transport of cargos to the sperm tail (Li et al 2015). PACRG depletion affects the localization of MEIG1 in the manchette indicating that it is an upstream protein in the pathway.…”

Crystal structure of human PACRG in complex with MEIG1

“…In the 9+2 axoneme structure, this would position MEIG1 towards the interior of the axoneme, facing the central doublet. According to Li et al [27], MEIG1 would act as an adaptor protein for cargo protein SPAG16, which is itself interacting with central pair proteins [41].…”

“…MEIG1 KO mice display male sterility, but don't have other phenotypic traits found in PACRG KO mice, suggesting a more specific role in sperm maturation. PACRG and MEIG1 colocalize to the manchette of elongating spermatids, and both are required for the manchette localization of the cargo protein SPAG16, a sperm central apparatus protein [27]. Furthermore, the manchette localization of MEIG1 requires PACRG, whereas the localization of PACRG is unaffected by the loss of MEIG1.…”

Sperm dysfunction and ciliopathy

“…MEIG1-knockout mice show male infertility, but no other phenotypes for ciliopathy are observed [176][177][178]. Further studies suggest that MEIG1/PACRG plays a critical role in the control of the structure called ''manchette'' [179], a microtubule-based structure transiently formed during spermiogenesis. This structure is thought to play roles in the significant morphological changes of the nucleus and in flagellar formation.…”