Biomedical subjects

M H Leibowitz

Publications and source records attributed to M H Leibowitz.

3 recordsLinked to original sources

PubMed1995

Mutations in aurora prevent centrosome separation leading to the formation of monopolar spindles.

We show that female sterile mutations of aurora (aur) are allelic to mutations in the lethal complementation group ck10. This lies in a cytogenetic interval, 87A7-A9, that contains eight transcription units. A 250 bp region upstream of both aur and a divergent transcription unit corresponds to the site of a specific chromatin structure (scs') previously proposed to be a barrier to insulate enhancers of the major hsp70 gene at 87A7. Syncytial embryos derived from aur mothers display closely paired centrosomes at inappropriate mitotic stages and develop interconnected spindles in which the poles are shared. Amorphic alleles result in pupal lethality and in mitotic arrest in which condensed chromosomes are arranged on circular monopolar spindles. The size of the single centrosomal body in these circular figures suggests that loss of function of the serine-threonine protein kinase encoded by aur leads to a failure of the centrosomes to separate and form a bipolar spindle.

Alleles↗

PubMed1989

Mitosis in Drosophila development.

Many aspects of the mitotic cycle can take place independently in syncytial Drosophila embryos. Embryos from females homozygous for the mutation gnu undergo rounds of DNA synthesis without nuclear division to produce giant nuclei, and at the same time show many cycles of centrosome replication (Freeman et al. 1986). S phase can be inhibited in wild-type Drosophila embryos by injecting aphidicolin, in which case not only do centrosomes replicate, but chromosomes continue to condense and decondense, the nuclear envelope undergoes cycles of breakdown and reformation, and cycles of budding activity continue at the cortex of the embryo (Raff and Glover, 1988). If aphidicolin is injected when nuclei are in the interior of the embryo, centrosomes dissociate from the nuclei and can migrate to the cortex. Pole cells without nuclei then form around those centrosomes that reach the posterior pole (Raff and Glover, 1989); the centrosomes presumably must interact with polar granules, the maternally-provided determinants for pole cell formation. The pole cells form the germ-line of the developing organism, and as such may have specific requirements for mitotic cell division. This is suggested by our finding that a specific class of cyclin mRNAs, the products of the cyclin B gene, accumulate in pole cells during embryogenesis (Whitfield et al. 1989). Other genes that are essential for mitosis in early embryogenesis and in later development are discussed.

Animals↗

PubMed1982

The effect of ascorbate, hydroperoxides, and bradykinin on prostaglandin production by corneal and lens cells.

Epithelial cells from the rabbit cornea, fibroblasts from the rabbit and calf cornea, and calf lens epithelial cells were placed in individual cultures. Prostaglandin (PG) synthesis by these cell types was determined. Lens epithelial cells produced no detectable PGs under basal conditions. Corneal fibroblasts primarily produced PGE2, while epithelial cells primarily produced thromboxane A2. PG production by corneal fibroblasts was highly responsive to bradykinin, ascorbic acid, hydrogen peroxide, and t-butyl hydroperoxide, an organic peroxide. Quantitative differences in PG production between the rabbit and calf corneal fibroblasts were observed. Our results suggest that the reported therapeutic actions of ascorbic acid in the eye may, at least in part, be mediated through the PGs. Our results also support the proposed role for hydroperoxides in the control of PG synthesis.

Animals↗