Mammalian Protein SCP1 Forms Synaptonemal Complex-like Structures in the Absence of Meiotic Chromosomes

Rupert Öllinger, Manfred Alsheimer, and Ricardo Benavente*

Department of Cell and Developmental Biology, Biocenter, University of Würzburg, D-97074 Würzburg, Germany

Monitoring Editor: Joseph Gall

Synaptonemal complexes (SCs)are evolutionary conserved, meiosis-specific structures thatplay a central role in synapsis of homologous chromosomes, chiasmatadistribution and chromosome segregation. However, it is stillfor the most part unclear how SCs do assemble during meioticprophase. Major components of mammalian SCs are the meiosis-specificproteins SCP1, 2 and 3. To investigate the role of SCP1 in SCassembly, we expressed SCP1 in a heterologous system, i.e.,in COS-7 cells which normally do not express SC proteins. Notably,under these experimental conditions SCP1 is able to form structuresthat closely resemble SCs (i.e., polycomplexes). Moreover, weshow that mutations which modify the length of the central ${alpha}$ -helicaldomain of SCP1 influence the width of polycomplexes. Finally,we demonstrate that deletions of the nonhelical N- or C-terminiboth affect polycomplex assembly, although in a different manner.We conclude that SCP1 is a primary determinant of SC assemblythat plays a key role in synapsis of homologous chromosomes.

^*Corresponding author. E-mail: benavente{at}biozentrum.uni-wuerzburg.de