John J. Biesele

Cilia in cardiac differentiation

In a study of chick heart development, approximately 700 cilia were observed in random and serial sections from differentiating myoblasts, myocytes, fibroblasts and fibrocytes following glutaraldehyde-osmium fixation. Additional cilia were observed in hearts of embryonic and adult lizards, mice, and rabbits. The diplosomal “9+0” cilia, often observed completely enclosed in the cytoplasm, were revealed to be present in most nonmitotic cells but were never observed in mitotic cells (P=0.001). Because the number of cells increases greatly during early cardiogenesis and because most of the cells were revealed to possess a single abbreviated cilium each, the deposition of cilia presumably occurs. Therefore, we suggest that the blockage of mitosis usually associated with the initiation of cytodifferentiation can be correlated with the formation of cilia and maybe mediated by the transformation of the mitotic centrioles into ciliary basal bodies.

Urea extraction of Z bands, intercalated disks, and desmosomes

Specific extraction of Z bands, intercalated disks and desmosomes was accomplished with molar concentrations of urea. Thick and thin filaments and M line material were undisturbed, demonstrating that the Z band protein is not similar to actin, myosin, or the M-line protein. The literature indicates that the tropomyosins are the only other structural proteins present in sufficient amounts to account for the extracted Z bands. However, the evidence for a lipid-protein association in the Z bands is considered and is further supported by the close association of the dense material of the Z bands, intercalated disks, and desmosomes with the lipoprotein cell membranes.

Preliminary biochemical investigations of the intermediate filaments

Preliminary biochemical investigations of differentiating cardiac muscle first revealed the occurrence of a third class of filaments, differing in appearance and reactivities from the thick and thin filaments of the sarcomere. These intermediate filaments were more resistant to extraction with neutral salts, β-mer-captoethanol, and urea than were the thick filaments, thin filaments, or Z material. Combined with the data from the accompanying report, sufficient evidence is presented to discount virtually all previous models of myofibrillogenesis.

TRISOMY 18 IN A HYDROCEPHALIC FETUS.

Autosomal trisomies may be responsible for intrauterine death of the fetus. The present report described a female hydrocephalic fetus aborted at 25 weeks gestation; leukocyte and skin cultures as well as autoradiography revealed trisomy 18. Further case histories may indicate whether the association of hydrocephalus with trisomy 18 is incidental or significant.

Some morphological effects of alkylating agents

Abstract The hypothesis that cytotoxic effects of alkylating agents result from attack on the 7-position of guanine moieties, with cross-linking of deoxyribonucleic acid strands, is considered in light of evidence for alkylation of ribonucleic acid and protein in vivo and for some cross-linking of deoxyribonucleic acid molecules with the other two. Preferential breakage sites in chromosomes and certain similarities in cytological effects of alkylating agents and of nitrogenous base analogues are also discussed.

Nuclear and Chromosomal Changes During Sperm Formation in the Scorpion, Centruroides Vittatus (Say)

SUMMARYThe pattern of chromatin condensation in the developing sperm nucleus of the scorpion, Centruroides vittatus, is described. The chromatin fibrils become especially distinct and remain well defined until quite late in spermiogenesis. The fibrils that compose the chromosomes are arranged in groups. The chromosomes in this species have diffuse kinetochores. The sperm head is helical in the swimming sperm and acquires this shape without the influence of microtubules, which are not present. Also absent is the centriole adjunct, though this organelle is found in other scorpions.

A Possible Mechanism of Chromosomal Movement in the Scorpion,Centruroides Vittatus(Say)

SUMMARYThe proposal presented indicates that anaphasic chromosomal movement in the scorpion, C vittatus, is associated with enlargement of vesicles some of which apparently are connected to or closely associated with the chromosomal microtubules. Filling of vesicles attached to the centriole end of the tubules could greatly enhance the pulling of the chromosomes toward the centriole region. It is suggested that this mechanism could work in combination with other known phenomena associated with cell division.