THE CENTRAL REGION OF THE SYNAPTONEMAL COMPLEX IN BLAPS CRIBROSA STUDIED BY ELECTRON-MICROSCOPE TOMOGRAPHY

The synaptonemal complex (SC) in the beetle Blaps cribrosa contains a highly organized central element (CE), two flanking lateral elements ( LEs), and a number of regularly spaced transverse filaments (TFs) cros sing the central region. The CE is built like a ladder with two longit udinal components running in parallel and a number of regularly spaced transverse CE components, bridging the two longitudinal components. T he CE is multi-layered with the ladders of the individual layers more or less in register. Essentially every TF originates in one of the LEs , crosses the CE through a transverse CE component and reaches the opp osite LE; every transverse CE component in a given layer corresponds t o one, and only one, TF. In a CE layer, short irregular pillars form t he junctions between the transverse and longitudinal CE components. Ad jacent pillars are connected to each other by fine fibrous bridges: th e two pillars in the same transverse CE component are linked, and so a re the pillars along each longitudinal component, and also more occasi onally adjacent pillars in separate CE layers. It is proposed that a T F with the two associated short pillars represents the structural unit in the central region. The ordered structure of the CE is accomplishe d by linking adjacent pillars to each other into the well-defined thre e-dimensional organization of the CE.