LEM-domain proteins are lost during human spermiogenesis but BAF and BAF-L persist

Reproduction. 2017 Oct;154(4):387-401. doi: 10.1530/REP-17-0358. Epub 2017 Jul 6.

Abstract

During spermiogenesis the spermatid nucleus is elongated, and dramatically reduced in size with protamines replacing histones to produce a highly compacted chromatin. After fertilisation, this process is reversed in the oocyte to form the male pronucleus. Emerging evidence, including the coordinated loss of the nuclear lamina (NL) and the histones, supports the involvement of the NL in spermatid nuclear remodelling, but how the NL links to the chromatin is not known. In somatic cells, interactions between the NL and the chromatin have been demonstrated: LEM-domain proteins and LBR interact with the NL and respectively, the chromatin proteins BAF and HP1. We therefore sought to characterise the lamina-chromatin interface during spermiogenesis, by investigating the localisation of six LEM-domain proteins, two BAF proteins and LBR, in human spermatids and spermatozoa. Using RT-PCR, IF and western blotting, we show that six of the proteins tested are present in spermatids: LEMD1, LEMD2 (a short isoform), ANKLE2, LAP2β, BAF and BAF-L, and three absent: Emerin, LBR and LEMD3. The full-length LEMD2 isoform, required for nuclear integrity in somatic cells, is absent. In spermatids, no protein localised to the nuclear periphery, but five were nucleoplasmic, receding towards the posterior nuclear pole as spermatids matured. Our study therefore establishes that the lamina-chromatin interface in human spermatids is radically distinct from that defined in somatic cells. In ejaculated spermatozoa, we detected only BAF and BAF-L, suggesting that they might contribute to the shaping of the spermatozoon nucleus and, after fertilisation, its transition to the male pronucleus.

MeSH terms

  • Adult
  • Aged
  • Animals
  • Chromatin Assembly and Disassembly
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Gene Expression Regulation, Developmental
  • HeLa Cells
  • Humans
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Male
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Mice
  • Middle Aged
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / metabolism
  • Nuclear Lamina / metabolism
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Receptors, Cytoplasmic and Nuclear / genetics
  • Receptors, Cytoplasmic and Nuclear / metabolism
  • Signal Transduction
  • Spermatids / metabolism*
  • Spermatogenesis*
  • Spermatozoa / metabolism*
  • Young Adult

Substances

  • ANKLE2 protein, human
  • BANF1 protein, human
  • BANF2 protein, human
  • DNA-Binding Proteins
  • Intracellular Signaling Peptides and Proteins
  • LEMD1 protein, human
  • LEMD2 protein, human
  • LEMD3 protein, human
  • Membrane Proteins
  • Neoplasm Proteins
  • Nuclear Proteins
  • Receptors, Cytoplasmic and Nuclear
  • emerin
  • lamin B receptor
  • lamina-associated polypeptide 2