Conformational flexibility in a small globular hormone: X-ray analysis of avian pancreatic polypeptide at 0.98-Å resolution

The 36-amino acid avian pancreatic polypeptide has been studied by x-ray analysis at 0.98-Å resolution and refined using a restrained least-squares technique to an agreement factor of 15.6%. The polypeptide, which has a compact globular structure with a hydrophobic core, comprises a polyproline–like helix (residues 2–8) and an α-helix (residues 14–32). The molecule forms symmetrical dimers linked through zinc atoms in the crystal lattice. The high-resolution analysis defines sequence-dependent distortions in the α-helical parameters due to hydrogen bonding of water molecules and side chains. The thermal parameters indicate an increased flexibility of the main chain at the turn between the helices and in the C-terminal residues. For the first time, six-parameter anisotropic thermal ellipsoids have been refined for each atom; these define the directions of the molecular motions in the polypeptide, indicating concerted vibrations. The physiological roles of conformation, flexibility, and dynamics of this polypeptide hormone are discussed.     

Multihormone regulation of MMTV-LTR in transfected T-47-D human breast cancer cells

Multihormonal regulation on the long terminal repeat (LTR) region of mouse mammary tumour virus (MMTV) has been studied using T-47-D human breast cancer cells stably transfected with the steroid sensitive LTR-C3 chimaeric gene. The specificity of steroid action on transfected LTR sequences has been compared with regulation of endogenous cellular markers. We conclude that the hormone response element of the LTR can be induced by physiological concentrations of androgen, progestin and glucocorticoid. 17 beta-Oestradiol did not regulate the LTR at physiological levels but an effect was found at 10(-6) M. This effect was not inhibited by antioestrogen nor was it reproduced by the synthetic oestrogen diethylstilboestrol suggesting such effects do not occur via the oestrogen receptor. The antioestrogens tamoxifen and transhydroxytamoxifen do not induce the LTR. No significant steroid competition was found in LTR regulation: whilst oestradiol did not act at physiological concentration it did not interfere with induction by androgen, progestin or glucocorticoid. Such gene regulation did not simply follow receptor status of the cells nor was it reflected in patterns of growth regulation by steroids. The implications of these findings on the mechanism of steroid hormone action are discussed.     

Involvement of the rolled/MAP kinase gene in Drosophila mitosis: interaction between genes for the MAP kinase cascade and abnormal spindle

We have found that mutations that lead to loss of rolled/MAP kinase function result in a reduced mitotic index in the larval central nervous system, consistent with an interphase block to cell cycle progression, associated with a low frequency of cells showing chromosome over-condensation in mitosis and abnormal anaphase figures. In contrast to wild-type tissue, such rolled mutants do not show a significant increase in accumulation of mitotic cells when treated with colchicine. We have studied double mutant combinations between mutations affecting the activity of rolled/MAP kinase and several genes that are essential to the establishment of a bipolar spindle during progression through mitosis, and find no interactions with mutations in polo, mgr,or aurora. However, partial loss-of-function mutations in rolled enhance the abnormal spindle (asp) phenotype, whereas gain-of function mutations in rolled or in the gene encoding its activating kinase Dsor1, act as suppressors. We discuss these findings in relation to the proposed role of MAP kinase in mediating the spindle integrity checkpoint.     

Observations on variability in LH release and fertility during oestrus in the domestic cat (Felis catus)

Hormonal changes, behaviour, ovulation and fertility were examined in response to coitus at two different times during oestrus in the female domestic cat housed in conditions of natural light (N = 13). On Day 2 or Day 4/5 of oestrus females were allowed 1 copulation in 15 min (single matings) or 2-3 copulations in 30 min (multiple matings). Plasma LH, oestradiol-17 beta and progesterone concentrations during the 24-h period after coitus were measured by radioimmunoassay; ovulation was assumed to have occurred if progesterone values were elevated 7-30 days after coitus. With the exception of 2 out of 3 animals receiving single matings on Day 2 of oestrus, all animals showed subsequent elevated progesterone values. Females receiving multiple matings had significantly greater releases of LH as measured by the area under the curve than those receiving single matings. There was significantly greater variability in the LH response of queens on Day 2 of oestrus compared to those on Day 4/5 for peak values and area under the curve; the only failure in release of LH was in queens on Day 2. Oestradiol levels did not differ significantly between Day 2 and Day 4/5 of oestrus. Progesterone values remained less than 1 ng/ml for 24 h after coitus. Both LH peak values and area under the curve were significantly greater for animals that became pregnant. There were also significant differences in coital behaviour between queens on Day 2 and those on Day 4/5 of oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

ULTRASTRUCTURE OF CONIDIOGENESIS IN SPHAEROSTILBE OCHRACEA

Conidium development in Sphaerostilbe ochracea is phialogenous. Mature synnemata are cup-shaped at the apex. The hyphal tips inside the apex are cut off by a septum to form elongated phialides that initially are not distinguishable from other hyphae. Numerous small vesicles aggregate in the tips of the incipient phialides, after which a second wall layer is deposited inside the original wall of the young phialides. As the conidium forms, the outer wall layer breaks, leaving a minute collarette at the apex of the phialide. Some wall material adheres to the first conidium as it matures. Subsequent conidia push out of the mouth of the phialide; as they do so they separate and are held together in a mucoid droplet. Conidia are one-celled when formed but soon become two-celled through formation of a median septum.     

The secretion of LH and testosterone in the rabbit.

In the male rabbit, LH and testosterone are secreted as 4–6 discrete pulses per day. The testosterone response to LH is rapid. The testosterone data did not show a normal distribution, but the same data expressed logarithmically were more nearly so. There was no evidence of a 24 h cycle in plasma testosterone levels.