LATERAL ELEMENT CROSS CONNECTIONS OF THE SYNAPTONEMAL COMPLEX AND THEIR RELATIONSHIP TO CHIASMATA IN RAT SPERMATOCYTES

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Abstract
Observations are presented in support of the hypothesis that at meiotic prophase a reciprocal crossover is accompanied by a crossover of the lateral elements of the synaptonemal complex, (SC) (Moens, 1974). Rat spermatocyte nuclei in developmental stage VII (Clermont, 1972) of the seminiferous epithelium cycle, but not pachytene nuclei in stages I to VI, had SC modifications in the form of a cross connection between the lateral elements. In structure these crossover (CO) elements, resemble the lateral element. The CO element was found in a variety of positions, usually more or less perpendicular to the SC but also slanted or parallel along the central element or detached from the SC. Reconstructions of entire nuclei indicate an average of 1 such CO element/SC and a nonrandom distribution of CO elements among the SC. Because the crossing-over of lateral elements produces a 180.degree. twist or removes a 180.degree. twist, the pattern of SC coiling was examined. Coiling starts in early pachytene prior to CO element formation. At stage VII one nucleus had 78 coils, all counter clockwise, and another nucleus had 97 such 180.degree. coils. If SC coils are associated with the process of crossing-over, then the regulation of crossover distribution such as chiasma position interference has an explanation in the structure and behavior of the SC.