Cytologic evidence for three human X-chromosomal segments escaping inactivation

Summary Early replication of prometaphasic human sex chromosomes was studied with the bromodeoxyuridine (BrdU)-replication technique. The studies reveal that two distal segments of Xp, including bands Xp 22.13 and Xp 22.3, replicate early in S-phase and therefore may not be subject to random inactivation. Furthermore, the replication of these distal segments of Xp occurs synchronously with those of the short arm of the Y chromosome including bands Yp 11.2 and Yp 11.32. These segments of Xp and Yp correspond well to the pairing segment of the X and Y chromosomes where a synaptonemal complex forms at early pachytene of human spermatogenesis. The homologous early replication of Yp and the distal portion of Xp may be interpreted as a remnant left untouched by the differentiation of heteromorphic sex chromosomes from originally homomorphic autosomes. A third early replicating segment is situated on the long arm of the X chromosome and corresponds to band Xq 13.1. This segment may be correlated with the X-inactivation center postulated by Therman et al. (1979).     

The nature and construction of skeletal spines inPocillopora damicornis (Linnaeus)

Extreme variability in the size, shape and spacing of skeletal spines ofPocillopora damicornis has been demonstrated both within single colonies and also between colonies from different environments. Preliminary studies indicated that the majority of spines from branch tips at the apex of the colony display a ‘fasciculate’ growth surface in contrast to partly fasciculate or ‘smooth’ growth surfaces exhibited by spines from branch tips at the base of the colony. No significant differences in the height and width of costal spines from apical and basal branch tips within a single colony were observed, although spines from colonies exposed to strong wave action tended to be significantly shorter and narrower than those from more sheltered environments. Both costal and coenosteal spines from wave-exposed colonies displayed branching and divided extremities while those from sheltered environments consisted of simple cones. Spines develop as an outgrowing of the calicoblastic ectoderm which secretes the skeleton. Growing costal and coenosteal spines are enveloped by a layer of calicoblastic ectoderm which penetrates through mesogloea, aboral gastroderm, coelenteron, oral gastroderm, mesogloea and finally oral ectoderm. Spines within the corallite are surrounded by calicoblastic ectoderm, mesogloea and aboral gastroderm only. A scheme for the growth of the spines is discussed.     

Reproductive studies of the Oryx

The genus Oryx comprises one species already extinct in the wild and others that are rapidly disappearing. It is important to understand the reproductive physiology of these species in order to ensure their successful captive propagation. It was determined behaviorally and hormonally that the scimitar-horned oryx's 21–22 d estrous cycle very closely resembled that of the domestic cow. Four females of three species (Arabian, scimitar-horned, and fringe-eared oryx) were treated with prostaglandin (PG) and pregnant mares serum gonadotropin (PMSG) or follicle-stimulating hormone (FSH). All animals responded to prostaglandin treatment with shortened cycles and behavioral estrus. Ovulation occurred in all females but only one responded to gonadotrophin treatment with a mild superovulation. An embryo recovered from an Arabian oryx was frozen in liquid nitrogen for 6 months. Upon thawing, the normal-appearing morula was surgically transferred to a scimitar-horned oryx. The recipient failed to carry the embryo and returned to estrus within three weeks of the transfer. It was demonstrated that induction of ovulation and synchronization of estrus can be achieved in the three Oryx species with PMSG or FSH combined with prostaglandin treatment.     

On the interaction of tritiated 2-ketobutyrate with 2-keto-3-deoxygluconate-6P aldolase ofPseudomonas putida. Evidence suggesting enzyme-mediated,uncatalyzed tritium exchange

2-Keto-3-deoxygluconate-6P aldolase ofPseudomonas putida mediates exchange between hydrogen isotope at the methylene carbon of 2-ketobutyrate and water. This occurs with aK _m of 20 mM, 100 times the corresponding value for pyruvate, and a V_max approximating 1/710 that of KDPG cleavage. Ketobutyrate is competitive with both pyruvate and 2-keto-3-deoxygluconate-6P for the enzyme. In addition, there is no evidence for C-C synthesis between ketobutyrate andd-glyceraldehyde-3P. A comparison of relativeV/K values for hydrogen exchange shows pyruvate to be 17,600 times better as a substrate than ketobutyrate. The detritiation of [3-³H]ketobutyrate is stereochemically random. In addition, the reaction proceeds with ak _H/k _T isotope effect of 15.3, consistent with C-H bond turnover being rate-determining. The E-ketobutyrate complex is reductively trapped, inactivating the enzyme. Reductive inactivation kinetics of E-ketobutyrate compared to E-pyruvate suggests more of the complex may be partitioned to ketimine in the ketobutyrate case than in the pyruvate case. A mechanism is considered in which ketobutyrate is bound as a ketimine in an orientation such that the active site acid/basic group cannot mediate catalytic ketimine/eneamine interconversion. Thus, exchange would result from hydrogen ionization at C-3′ of the ketimine, a slow spontaneous step compared to overall complex turnover. This noncatalyzed deprotonation would explain dissymmetry in exchange, the poorV/K compared to pyruvate, and a large tritium isotope effect.     

Stratigraphy of the fossil Chironomidae (Diptera) from Lake Grasmere,South Island,New Zealand,during the last 6000 years

The fossil chironomid fauna of a 3.26 m long sediment core from Lake Grasmere has been analysed. The fossil chironomid taxa belong mainly to the subgroups Tanytarsini, Orthocladiinae, Chironomini, and Tanyphodinae. Heptagyini and Podonominae were not common. Tanytarsini were the dominant component of the fauna with Corynocera sp. as the most abundant species during pre-Polynesian times (before 1000 yr BP). The abundance and the composition of the fossil chironomid taxa have fluctuated markedly over the last 6000 years. These fluctuations could be partly correlated with changes in the stratigraphy of the sediments in the core. Layers of highly minerogenic sediment contained the lowest numbers of remains whereas high abundances were found in the sections of the core with the greatest proportion of organic matter. It is suggested that major shifts in the structure of the chironomid community have been mainly caused by changes in the hydrology and inflows of the lake, and the rate and type of sedimentation, in addition to variations in lake productivity.     

Silver Enhancement of Nickel-Diaminobenzidine as Applied to Single and Double Immunoperoxidase Staining

A reliable and practical method is proposed for increasing sensitivity and detection efficiency of immunocytochemical techniques, based on silver enhancement of the nickel-diaminobenzidine product of the peroxidase reaction. The procedure produces a strong signal at the site of the end product of the peroxidase reaction which is visible as black grains at the light microscopic level. The method has been used to detect peroxidase labeled probes in immunocytochemical tissue preparations and blotting assays and is ideal for the purposes of double staining and photographic documentation.     

Hepatozoon in grey squirrels (Sciurus carolinensis) trapped near Reading, Berkshire

Hepatozoon infections of Sciurus carolinensis were investigated by a 30-month capture/recapture trapping programme. Details of trapping methods, squirrel husbandry and blood sampling techniques are discussed.
Hepatozoon gametocytes infected blood monocytes and could be detected in blood smears or by concentration of leucocytes. From blood smears, 71% (154/218) of the squirrels were infected. Prevalence appeared to be influenced by host hormonal and breeding patterns. Significantly more adult males than adult females were infected (P<0.025). Infections were significantly more prevalent in adults overall and in adult males than in juvenile males (P< 0.001 in both cases), but not significantly different between female adults and juveniles (P>0.05). Prevalence rates were generally higher: (i) in summer and winter, when animals mate, compared to spring and autumn; and (ii) in 1984 than in 1983, possibly relating to differences of squirrel breeding success and juvenile recruitment in the two years. Parasitaemias were overdispersed in the sampled host population and significantly lower in females (38%) than in males (48%) (P<0.05), although there was no significant difference between the age classes. Animals, either recaptured or laboratory-maintained, showed chronic fluctuating parasitaemias with no obvious pattern. Squirrels with overt parasitaemias showed trophozoites and schizogonic stages of Hepatozoon in the lung and rarely in liver and spleen. Three out of 16 animals with no obvious parasitaemias had lung tissue stages of the parasite. Results suggest that Hepatozoon is more prevalent in grey squirrel populations than blood smears suggest.