Speedy A-Cdk2 binding mediates initial telomere-nuclear envelope attachment during meiotic prophase I independent of Cdk2 activation

Telomere attachment to the nuclear envelope (NE) is a prerequisite for chromosome movement during meiotic prophase I that is required for pairing of homologous chromosomes, synapsis, and homologous recombination. Here we show that Speedy A, a noncanonical activator of cyclin-dependent kinases (Cdks), is specifically localized to telomeres in prophase I male and female germ cells in mice, and plays an essential role in the telomere-NE attachment. Deletion of Spdya in mice disrupts telomere-NE attachment, and this impairs homologous pairing and synapsis and leads to zygotene arrest in male and female germ cells. In addition, we have identified a telomere localization domain on Speedy A covering the distal N terminus and the Cdk2-binding Ringo domain, and this domain is essential for the localization of Speedy A to telomeres. Furthermore, we found that the binding of CDK2 to Speedy A is indispensable for Cdk2's localization on telomeres, suggesting that Speedy A and CDK2 might be the initial components that are recruited to the NE for forming the meiotic telomere complex. However, Speedy A-Cdk2-mediated telomere-NE attachment is independent of CDK2 activation. Our results thus indicate that Speedy A and CDK2 might mediate the initial telomere-NE attachment for the efficient assembly of the telomere complex that is essential for meiotic prophase I progression.