Autoradiographic Evidence of Synthesis of an Arginine-rich Histone during Spermiogenesis in Drosophila melanogaster

The relationship of the "sphere chromatophile" to the fate of displaced histones following histone transition in rat spermiogenesis

Cytochemical, radioautographic, and microspectrophotometric studies bearing on the relationship of histone transition to the origin and development of the protein and RNA components of the "sphère chromatophile" in the developing spermatogenic cells of the albino rat are presented. These studies show that the sphère chromatophile has many features in common with somatic nuclei: it contains histonelike basic proteins rich in lysine, with lesser amounts of arginine. No evidence is found for the presence of a protamine in this granule. The sphère chromatophile is rich in RNA, but contains no DNA. The failure of a positive reaction with basic protein stains, unless the RNA is first removed, indicates either a chemical bonding or a very close association between the RNA and basic protein. The basic protein and RNA components of the sphère chromatophile appear to have different origins in the cell. A sequence of stages in the development of the lysine-rich basic protein component of this structure commences with the appearance of tiny grains in those spermatid nuclei which are beginning to replace lysine-rich histones with arginine-rich histones. Subsequently, similar-staining cytoplasmic grains appear, which coalesce to form the sphère chromatophile in the cytoplasm. Labeling studies show that the basic protein component is synthesized at about the time of the last premeiotic DNA (and histone) synthesis. The results of the microspectrophotometric measurements support the idea that the basic protein lost from the spermatid nucleus is the source of the basic protein in the sphère chromatophile.

Megaloblastosis: from morphos to molecules

OBJECTIVE

Megaloblastosis (i.e., megaloblastic transformation of erythroid precursor cells in the bone marrow) is the cytomorphological hallmark of megaloblastic anemia resulting from vitamin B12 and folate deficiency. It is characterized by a finely stippled lacy pattern of nuclear chromatin, which is believed to be an expression of deranged cellular DNA synthesis. However, the molecular basis of these cytomorphological aberrations still remains obscure. The current presentation describes the results of our studies on some molecular events associated with the development of megaloblastosis.

METHODS

Transmission electron microscopy was used to study megaloblasts as well as DNA fibers extracted from megaloblastic and normoblastic bone marrows with and without treatment with proteinase K during the extraction procedure; cellular DNA synthesis in bone marrow cultures was studied by incorporation of 3H-thymidine and deoxyuridine suppression test, while histone biosynthesis in bone marrow cells was studied by in vitro incorporation of 3H-tryptophan, 3H-lysine and 3H-arginine into histones.

RESULTS

Derangement of DNA synthesis occurred due to an impaired de novo pathway of thymidylate synthesis in both vitamin-B12- and folate-deficient human megaloblastic bone marrows as well as in the bone marrows of rhesus monkeys and rats with experimentally induced folate deficiency. Interestingly, folate-deficient monkeys developed frank megaloblastic bone marrows, but folate-deficient rats did not. On the other hand, megaloblastic changes in the bone marrow of human patients with myelodysplastic syndrome and erythroleukemia were not associated with this DNA synthetic abnormality. Biosynthesis of predominantly arginine-rich histones in megaloblastic bone marrows was markedly reduced as compared to normoblastic bone marrows, which was consistently associated with elongation and despiralization of chromosomes and finely stippled nuclear chromatin in megaloblasts.

CONCLUSION

The impaired biosynthesis of predominantly arginine-rich nuclear histones appeared to be a common molecular event (a denominator) underlying the development of megaloblastosis with or without abnormal DNA synthesis.

Ultrastructure of the spermatozoon of Megaselia scalaris Loew (Diptera:Brachycera:Cyclorrhapha:Phoridea:Phoridae)

When viewed by scanning electron microscopy (SEM), the spermatozoon of the phorid dipteran Megaselia scalaris appears threadlike, lacking distinct head and tail areas. These areas can be observed, however, in appropriately stained material. Measurements of Feulgen-stained material reveal average lengths of the head, tail, and total cell of 18.7, 128.7, and 147.4 μm, respectively. When tested for sulfhydryl and disulfide groups, the head displays only disulfide groups. Transmission electron microscopy (TEM) reveals 12 different regions: three (1-3) in the head, four (9-12) in the tail, and five (4-8) in a short zone of overlap between the head and tail. Most of the cell lies in regions 9 and 11 of the tail and 3 of the head, accounting for, respectively, 37.3%, 45.7%, and 11.2% of the total length. A tubelike acrosome indents the anterior end of the nucleus. The tail originates asymmetrically in relation to the long axis of the cell as a peglike structure associated with the dorsolateral region of the nucleus. No centriole is visible, and the nucleus has a notched appearance in longitudinal sections. Two mitochondrial derivatives and an axoneme displaying a 9+9+2 microtubule configuration and ATPase activity extend throughout most of the tail. In regions 9 and 10, an asymmetrically arranged accessory body is also present. Features having possible taxonomic utility include the asymmetrically arranged accessory body, the size and shape of the acrosome, and the notched appearance of the nucleus. The present report is apparently the first to describe the spermatozoon of a cyclorrhaphous dipteran which is not a member of the Schizophora.

A gene necessary for late sperm function in Drosophila melanogaster

A male-sterile mutant, ms(1)7, of Drosophila melanogaster is defective in post-ejaculatory sperm function. The mutant gene is located at one of at least five male fertility loci in 18F through section 20 of the polytene X-chromosome. It is proposed that the ms(1)7+ gene product modifies a component of the sperm head. A nearby gene may be functionally related to ms(1)7+.