Synaptonemal Complex und Chromosomenstruktur in der achiasmatischen Spermatogenese vonPanorpa communis (Mecoptera)

Abstract

Abstract. Meiotic prophase in the spermatocytes of Panorpa communis was studied. There is a proper sequence of meiotic stages in the testes. Therefore the temporal development of chromosome structure and the synaptonemal complex (SC) could be studied exactly. The structure and function of the SC are interpreted in a new model.--The chromosomes have a lambrush form from leptotene to diakinesis. At leptotene each chromatid produces an additional axis of basic protein and RNA. The axis becomes one of the lateral elements of the SC. At pachytene the DNA of the bivalents is separated into three regions: 1. Most of the DNA forms long loops outside the SC. 2. Smaller portions of the ])NA filaments are twisted around the lateral elements of the SC. 3. Short DNA loops (called pairing loops) extend into the pairing space. In Panorpa the SC is composed of two lateral elements (chromosome axes), which are connected by equally spaced transverse filaments, a ladder-like central element in the middle of the pairing space and, on each side of the pairing space parallel to the lateral elements, two tCNA containing strands. These are regarded as connected RNA copies of the pairing loops and are responsible for the exact pairing of homologous chromosome segments. At diplotene the axes of the sister chromatids separate to form "double complexes" with four lateral elements. The double complexes of the oocytes contain only transverse filaments between the axes of the homologous chromatids. After a short time they disappear again and the homologues separate to form the chiasmatic bivalents. In the spermatocytes all four chromatid axes are connected by transverse filaments. The pairing complex persists until diakinesis, thereby causing the suppression of the diplotene stage in the light microscope. This may be the only reason for the achiasmatic meiosis in the spermatocytes of Panorpa.(Zusammenfassung see p. 68.) A. EinleitungSeit der Entdeckung des ,,synaptonemal complex" (SC) durch M. J. Moses im Jahre 1956 ist diese Paarungsstruktnr, die zwischen homologen Chromosomen w/~hrend der meiotischen Prophase ausgebildet wird, yon verschiedenen Autoren in fast allen daraufhin untersuchten Organismen gefunden worden (Literatur bei Moses, 1968). 2*

Achiasmatic male meiosis of collochore type in the heteropteran family Miridae

“…In the families Saldidae and Nabidae (NOK- KALA andNOKKALA 1983,1984), the alignment of homologous chromosomes attained early in meiosis is retained externally unchanged until the beginning of anaphase, whereas in Miridae, after synapsis, tenacious collochores are formed to maintain the bivalent condition. When analyzing the evolutionary relationship between these two types of achiasmatic meiosis, it should be noted in the first place that in those meioses, where the alignment of homologous chromosomes is preserved as such during meiotic prophase, the alignment is based on the behaviour of synaptonemal complex (GASSNER 1969;WELSCH 1973;RASMUSSEN 1976RASMUSSEN , 1977. In the second place, collochores obviously represent structures formed independently of the synaptonemal complex as evidenced by their presence in male meiosis of Drosophila melanogaster lacking synaptonemal complexes (MAYER 1964).…”

A study of recombination, formation of chiasmata and synaptonemal complexes in female and male meiosis of Ephestia kuehniella (Lepidoptera)

“…Thus the statement is supported, that synaptonemal complexes may be a necessary prerequisite for crossing-over, but this presence is not a sufficient condition for crossing-over. The absence of synaptonemal complexes coincides with the absence of a normal pachytene stage in the achiasmatic Drosophila male (Cooper 1950, Darlington 1934) while both, pachytene and synaptonemal complexes, are present in the achiasmatic females of Ephestia and Bombyx and the achiasmatic males of Panorpa (UIlerich 1961, Welsch 1973). This indicates a closer relationship between formation of synaptonemal complexes and the formation of the pachytene.…”

Three-dimensional reconstruction of chromosome pairing during the zygotene stage of meiosis in Lilium longiflorum (thunb.)

“…The constant somatic pairing in Drosophila may account for this special finding. Several investigations have described the lepto-tene chromosome as lampbrush-like (7,9,60), but the molecular nature of the attachment of the chromatin from the two sister chromatids to the lateral component is not understood. A meiosis-unique histone with some similarities to the H 1 histone is synthesized during the preleptotene-leptotene interval in Lilium longiflorum (50) and total histone synthesis has been reported to be uncoupled from the premeiotic DNA replication and to extend into zygotene (3,56).…”