The cytosolic chaperonin CCT associates to cytoplasmic microtubular structures during mammalian spermiogenesis and to heterochromatin in germline and somatic cells.
Spermiogenesis, the haploid phase of spermatogenesis, is characterised by a dramatic cytodifferentiation of spermatids. The two major steps, nuclear shaping and cytoplasmic reorganisation of the organelles, rely on an extensive remodelling of the microtubule cytoskeleton. Folding of alpha- and beta-tubulin is mediated by the cytoplasmic chaperonin containing TCP-1 (CCT), highly expressed in testis. We studied CCT cellular distribution throughout spermatogenesis by immunofluorescence and immunoelectron microscopy. We unveil two main cytoplasmic localisations for CCT: at the centrosome and at the microtubules of the manchette, a structure unique to male germ cells. Both structures are essential for spermatid differentiation and may require CCT function. Although CCT is essentially cytoplasmic, a few reports suggest that a subset may have a nuclear localisation. We demonstrate that in the nucleus of germline and somatic cells, part of CCT associates to heterochromatin. In interphase cells, CCT seems generally confined to constitutive heterochromatin. Nevertheless, in condensing nucleus of future spermatozoon, it is also associated with chromatin undergoing compaction. Finally, in fully-condensed mitotic chromosomes, CCT is located all along the chromosomes. Our finding that CCT is associated with constitutive heterochromatin and to compacting chromatin raises the possibility that it may be implicated in maintenance and remodelling of heterochromatin.
Souès
Sylvie
S
Laboratoire de Biologie Cellulaire, Centre Universitaire des Saints-Pères, Université René Descartes--Paris V, 45 rue des Saints-Pères, 75270 Paris cedex 06, France. Sylvie.Soues@biomedicale.univ-paris5.fr
Kann
Marie-Louise
ML
Fouquet
Jean-Pierre
JP
Melki
Ronald
R
D000818:Animals; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D006570:Heterochromatin / Q000378:metabolism*; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008870:Microtubules / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013087:Spermatids / Q000378:metabolism / Q000648:ultrastructure; D013091:Spermatogenesis / Q000502:physiology*; D013234:Stem Cells / Q000378:metabolism / Q000648:ultrastructure
D006570:Heterochromatin; C533315:Tcp1 protein, mouse; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins