ALBERT

Notes: Summary 1. In the loops of primary spermatocyte nuclei actinomycin causes characteristic and reproducible disintegrations of the structural elements composing the loops. The alterations become visible for the first time about 6 hours after injection of actinomycin and reach a maximum after about 24–30 hours. 2. The structure of the nucleolus is also changed by actinomycin. It looses its cortical “ribosomal” layer and detaches from the nuclear membrane to which it is normally attached. 3. All structural damage of the loops and the nucleolus caused by actinomycin is reversible. The regeneration of the loops starts approximately 40 hours after injection and is completed after about 100–120 hours. 4. In males with two Y chromosomes which form loops of different morphology because of genetical differences the actinomycin effects similar alterations as in normal males. During the regeneration each Y chromosome autonomously determines its specific type of loops. 5. The results are in good agreement with our hypothesis that the loops are modifications of the chromosome structure at sites of active genes.

Notes: Abstract Examination of living spermatid nuclei of Gryllus domesticus has revealed the presence of the same structures, the X chromosome, the round body and the axial core structures, which have been described from electron microscopic observations. The outer ribbons of the axial core structures and the round body are composed of 100 Å fibres indiscernible from and often continuous with the fibres composing the X chromosome. That the outer ribbons of the axial core structures and the round body are chromosomal is further substantiated by the results of cytochemical examinations of formaldehyde fixed material which show that the axial core structures and the round body contain RNA, DNA and basic protein. Neither acetic acid-ethanol nor cold ethanol fixation preserve the round body and the axial core structures suggesting that a protein may be responsible for maintenance of the central core structure. The central core structures are always found in close association with condensed chromatin in regions where the chromosome elements are about 1000 Å apart, suggesting that the relative state of condensation of the chromatin and the spacial relationship between condensed regions may be two of the chief factors concerned in central core formation. Maintainance of the condensed state of the chromatin, however, may in turn depend upon central core integrity.

Notes: Summary Spermiogenesis of X/Y males in Drosophila has been reinvestigated by light and electron microscopy. A description of normal spermiogenesis in both D. melanogaster and D. hydei, as well as spermatogenesis in Y deficient males of both species is provided. In D. hydei, spermatogenesis of X/O males does not proceed beyond meiosis. In D. melanogaster, the number of sperm in cysts of X/O testes may be reduced to less than half the normal number. Two different developmental patterns can be distinguished in X/O testes: In most cases early spermatid differentiation is severely disturbed so that the nebenkern disintegrates into many mitochondrial derivatives, each of them being incompletely transformed into paracrystalline material. Cysts with these deviations do not develop further than elongated spermatid stage. Less frequently, differentiation of the spermatid is relatively normal with almost complete transformation of the nebenkern derivatives into paracrystalline bodies. Even in such sperm, the geometrical relations in sperm tail organelles appear disturbed and development does usually not reach the stage of isolated sperm. In addition, many structural malformations in the axial complex are found. It seems that X/O spermatids in D. melanogaster contain all the structural components of normal sperm but fail to organize them properly. Morphogenetic processes in the developing spermatid of Drosophila hydei have been shown to be dependant upon the presence of regions of the Y chromosome which form specific lampbrush loops during growth stage of spermatocytes. In contrast to X/O males where spermatogenesis does not proceed beyond meiotic prophase, males with Y fragments produce aberrant spermatids and/or immotile, aberrant sperm. In one case, however, the production of slightly motile sperm in males deficient for a certain loop forming locus has been observed. Different Y segments (loops) differ in their morphogenetic capacity, but in general the effect of the loops seems to be additive and all five Y chromosomal factors must act together for the production of motile sperm. Developmental aberrations appearing during spermiogenesis in partially Y deficient males were classified into early and late effects and analysed. It appears that all structural components of sperm organelles (flagellum, nebenkern derivatives etc.) are present in the spermatids of all such males. The components, however, frequently fail to be organized into ordered complexes of typical architecture. The degree of order attained varies between cysts and also between sperm in the same cyst. It ranges from severe disorganization to near normality in a variable number of sperm. In addition there is a pronounced general effect of the Y, and of Y fragments on the length of sperm. It is concluded that the Y chromosomal factors control the coordination of the various synthetic and morphogenetic processes leading to the formation of functional sperm without themselves contributing structural information on the molecular level.