SUMO mediates the coordinate regulation of meiotic chromosome length and crossover rate.

Meiotic prophase-I chromosomes are organized into linear arrays of chromatin loops anchored to proteinaceous axes that define the interaction interfaces for the pairing and synapsis of homologous chromosomes. Chromatin loop size and axial chromosome length are inversely correlated and vary widely both between and within species, including between the sexes. The molecular basis of this variation remains unclear. Here, we provide evidence that the small ubiquitin-like modifier, SUMO, regulates loop-axis organization in mouse meiosis. Our analysis shows that the longer axes of oocyte chromosomes contain more SUMO per unit length than the shorter axes of spermatocyte chromosomes. In mouse models, the loss of SUMO1 results in shorter axes and longer chromatin loops. Conversely, increased SUMO1 conjugation, caused by mutation of the SENP1 isopeptidase, produces longer axes with shorter loops. Axis length positively correlates with meiotic recombination. Accordingly, Sumo1 and Senp1 mutations respectively decrease and increase crossover frequency. These findings identify SUMO as a key regulator of meiotic chromosome architecture and suggest a molecular basis for the physiological variation in chromosome length and recombination rates seen among species, sexes, individuals, and individual meiocytes.