P-600 Loss of nucleoporin NUP210L and chromatin protein BAF-L together, but not separately cause male infertility in the mouse revealing their redundant roles in nuclear integrity

Abstract

Study question Could colocalised spermatid-specific genes Banf2 and Nup210l, whose individual loss has no effect on male fertility, have redundant functions at the caudal nuclear envelope? Summary answer Banf2 and Nup210l are required together for nuclear integrity and male fertility by organising microtubules into the manchette and preventing nuclear invagination. What is known already Nup210l encodes a transmembrane nucleoporin and Banf2 encodes BAF-L a paralogue and binding partner of the chromatin protein BAF. NUP210L and BAF-L localise to the caudal nuclear pole in human elongating spermatids. Nuclear pores are also reorganised into a dense array at the caudal pole during spermatid elongation. The inactivation of either of these genes in the mouse has no effect on male fertility. In human, the biallelic loss of NUP210L has been described in a single case of an infertile man producing mainly spermatozoa with a descondensed nucleus and histone retention. Study design, size, duration We created double knockout mice lacking NUP210L and BAF-L based on their colocalisation to the caudal nuclear pole of elongating spermatids in human. We compared the fertility and spermatogenesis of these double knockout mice (n = 10) to control littermates (n = 10) Participants/materials, setting, methods Double mutants were compared to controls by defining sperm parameters and testicular histology. We also used immunofluoresence to study the nuclear lamina, the manchette and the nuclear pore complex array throughout spermiogenesis. Nuclear structure was also studied by transmission electron microscopy. Main results and the role of chance In the mouse, loss of both NUP210L and BAF-L causes a catastrophic failure of spermiogenesis as the spermatids begin elongation (step 10-11), with most elongating spermatids entering apoptosis (determined by TUNEL). Deformation of the nucleus is seen in 90% of round spermatids while a destabilisation of the manchette and the nuclear pore complex array is observed in elongating spermatids. Electron microscopy shows that microtubules invaginate the spermatid nucleus. Our results show that BAF-L and NUP210L are involved in redundant processes that are important for nuclear integrity during spermatid elongation. We conclude that there may be a critical nexus of nuclear pore complex and the chromatin at the caudal nuclear pole during spermatid elongation. Limitations, reasons for caution We present solid data for a functional roles of NUP210L and BAF-L and their redundancy in the mouse, but we do not provide mechanistic information. We cannot be sure that the same redundancy exists in the human. Wider implications of the findings Our study is relevant to infertility and all genetic diseases, presenting an illustration of functional redundancy and non-homologous digenic inheritance. We reveal a critical function for BAF-L and NUP210L in the positioning of manchette microtubules. We show that function can be hidden from genetic approaches based on single gene inactivation. Trial registration number No