Dynamic CENH3 centromere associations in male meiosis of hexaploid wheat in line with the progression of ASY1 and ZYP1 synaptonemal complex proteins

Abstract

Long before the initiation of chromosome synapsis at meiosis, centromeres in some plant species undergo associations, but the processes and progression to homologous pairing is still a matter of debate. The present study used immunolabelling with CENH3 that stains centromeres during meiosis, ASY1 associated with the lateral elements and ZYP1 of the central element of the synaptonemal complex (SC) in hexaploid wheat (2n=42). We correlated meiotic centromere movement and early telomere behaviour to the progression of the SC. We show that centromeres form single or multiple associations in meiotic interphase. During leptotene, we observed progressive clustering of the centromeres at the nuclear periphery and then formation of the telomere bouquet at the opposite pole of the nucleus. Critically the dynamics of the presynaptic centromere associations coincide with key events of synapsis initiation starting from the subtelomeric regions. Once distal synapsis emerges at zygotene, centromere clusters gradually resolve individually, indicated by more than 21 CENH3 foci that are associated with ASY1, but not ZYP1. Homologous chromosome arms are connected by ZYP1 foci that elongate, and the centromeres subsequently synapse during late zygotene. Changes in the frequency of centromere associations and CENH3 area implied significant expansion of the centromeric regions, which differed from the contraction-expansion state of the global chromatin. From metaphase I to telophase II, the number of CENH3 foci reflects the transition from homologous pairing, through segregation of bivalents and then sister chromatid separation.
AS thanks EU Marie Curie FP7-PEOPLE-2013-IEF grant agreement 625835

Full text

Dynamic CENH3 centromere associations in male meiosis
of hexaploid wheat in line with the progression of ASY1 and
ZYP1 synaptonemal complex proteins
Adel Sepsi, James Higgins, Pat Heslop-Harrison, Trude Schwarzacher
Introduction
Before the initiation of chromosome synapsis in hexaploid bread wheat (Triticum
aestivum, 2n=6x=42) centromeres undergo a series of associations, which lead
to the formation of homologous centromere pairs at pachytene. The role of
presynaptic associations and their progression to homologous pairing at meiosis
is still a matter of debate.
ais7@le.ac.uk
AS#thanks#EU#Marie#Curie#FP7-PEOPLE-2013-IEF#grant#agreement#625835#
Centromere associations during meiotic
interphase and early prophase. Bar=5µm
CENH3 TRS DAPI CENH3 ASY1 CENH3 ASY1
Interphase Leptotene Early Zygotene
Centromere dynamics from zygotene, through pachytene
to diplotene of meiotic prophase I. Bar=5µm
Results
• Centromeres formed single or multiple associations in meiotic
interphase. At early leptotene they underwent progressive
polarisation (clustering) at the nuclear periphery that was
followed by the formation of the telomere bouquet
• The resolution of centromere clusters and a structural
reorganisation of the centromeric chromatin coincided with
synapsis initiation starting from the subtelomeric regions.
Centromere clusters gradually resolved individually, indicated by
more than 21 CENH3 foci, associated with ASY1 but not ZYP1.
• Homologous chromosome arms were then connected by the
alignment and fusion of interstitial ZYP1 loci that started to
elongate at zygotene, and centromeres synapsed as a
continuation of this interstitial synapsis.
Conclusion
Our results suggest that centromere associations are
involved in the timing of chromosome synapsis and
allow structural reorganisation of the centromeric
chromatin. The gradual release of individual
centromeres from the clusters imply elongation of
interstitial synapsis between corresponding
homologues.
Mid Zygotene Late Zygotene Pachytene Diplotene
ZYP1 ASY1 CENH3 MERGED
Homologous
chromosomes Centromeres ASY1 ZYP1
Mid Zygotene Pachytene Diplotene
Early Zygotene
Here, we aimed to correlate centromere and chromosome arm
pairing, providing accurate timing for centromere dynamics in meiotic
prophase I. We performed dual immunolocalisation of CENH3 protein
and the Synaptonemal Complex (SC) proteins ASY1 and ZYP1.
Department of Genetics, University Road, Leicester, LE1 7RH, UK
Heslop-Harrison J. S. and Schwarzacher T. (2011) Plant J.#
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Higgins J. D. et al. (2012) Plant Cell, 24, 4096–4109.
Schwarzacher T (1997) Sex Plant Reprod, 10, 324–331.
ASY1 ZYP1 CENH3