Evidence that the multifunctional polypeptides of vertebrate and fungal fatty acid synthases have arisen by independent gene fusion events

The enoyl reductase (NADPH binding site) of rabbit mammary fatty acid synthase has been radioactively labelled using pyridoxal phosphate and sodium [3H]borohydride. Using this method we have been able to add this site to the four sites whose location has already been mapped within the multifunctional polypeptide chain of the protein. The results show that the enoyl reductase lies between the 3-oxoacylsynthase and the acyl carrier. This confirms that the active sites occur in a different order on the single multifunctional polypeptide of vertebrate fatty acid synthase and the two multifunctional polypeptides of fungal fatty acid synthase, and suggests that these two systems have arisen by independent gene fusion events.     

Duplicated phosphoglucose isomerase genes in avocado

Summary Avocado (Persea americana) cultivars were assayed for phosphoglucose isomerase (PGI) isozymes using starch gel electrophoresis. Three PGI genes were identified: one monomorphic locus, Pgi-I, coding for the plastid isozyme and two independently assorting loci, Pgi-2 and Pgi-3, coding for the cytosolic isozymes. The genetic analysis was based on comparisons of PGI zymograms from somatic and pollen tissue and on Mendelian analysis of progeny from selfed trees. The isozymic variability for PGI can be used for cultivar identification and for differentiating between hybrid and selfed progeny in avocado breeding.     

Human articular chondrocytes acquire 1,25-(OH)2 vitamin D-3 receptors in culture

The vitamin D endocrine system is crucial in calcium homeostasis in mammalian species. Central to this role 1,25-dihydroxyvitamin D-3 (1,25-(OH)2D3) receptors have been detected in freshly isolated osteoblast-like bone cells and it has been shown that the active metabolite of vitamin D-3 1,25-(OH)2D3, increases bone resorption in vitro and in vivo. The requirement of 1,25-(OH)2D3 for the normal development of growth plate cartilage can be seen in vitamin D deficient rickets. However, there is still considerable controversy regarding the presence of 1,25-(OH)2D3 receptors in chondrocytes. In this paper, we report the presence of a 3.5-S 1,25-(OH)2D3-binding macromolecule in freshly isolated human costal but not articular chondrocytes. After subculture, both articular and costal chondrocytes have receptors. Saturation binding analysis revealed a single class of binding sites with an apparent Kd of 0.09 nM and approx. 2700 receptor molecules per cell for articular chondrocytes and a Kd of 0.1 nM and approx. 2000 receptor molecules per cell for costal chondrocytes. The presence of 1,25-(OH)2D3 receptors did not correlate with the switch from synthesis of cartilage-specific type II collagen to types I and III collagens. The acquisition of 1,25-(OH)2D3 receptors by articular chondrocytes may, therefore, be another phenotypic characteristic of cultured cells or may appear in vivo when chondrocytes are exposed to vascular or inflammatory cell products.     

Differential effects of parathyroid hormone responsive cultured human cells on biological activity of parathyroid hormone and parathyroid hormone inhibitory analogues

We have employed parathyroid hormone (PTH) responsive human cells cultured from dermis or giant cell tumors of bone (GT) to evaluate the biological properties of a newly developed in vivo PTH inhibitor, [Tyr34]bPTH-(7-34)-amide (PTH-Inh). Short periods of incubation of cells from dermis or GT with maximal stimulatory concentrations of PTH in the presence of increasing concentrations of PTH-Inh resulted in a dose-dependent inhibition of the adenosine cyclic 3',5'-phosphate (cAMP) response (Ki = 3 X 10(-7) M and 4.2 X 10(-7) M for GT and dermal cells, respectively). In both cell cultures, PTH-Inh alone did not increase cAMP levels, and in desensitization experiments, preincubation with PTH-Inh alone did not desensitize cells to PTH. Hence, the analogue displayed no agonist properties. Unexpectedly, when PTH-Inh was incubated with dermal cells in the presence of PTH, the PTH-Inh failed to block desensitization, suggesting a loss of biological effectiveness of the inhibitor. When medium containing PTH-Inh alone was removed from dermal cells and tested for inhibition of the acute PTH response in untreated cells, there was apparent loss of inhibitory efficacy (t1/2 = 20 h). In contrast, incubation of native PTH or bPTH-(1-34) with cells did not affect the biological activity of these ligands. Unlike the dermal cells, the PTH-Inh did block desensitization to PTH in GT, and there was no loss of inhibitor efficacy when medium containing PTH-Inh was incubated with GT (48 h) and then tested in untreated cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

A NIMA-related protein kinase is essential for completion of the sexual cycle of malaria parasites

The molecular mechanisms regulating the sexual development of malaria parasites from gametocytes to oocysts in their mosquito vector are still largely unexplored. In other eukaryotes, NIMA-related kinases (Neks) regulate cell cycle progression and have been implicated in the regulation of meiosis. Here, we demonstrate that Nek-4, a new Plasmodium member of the Nek family, is essential for completion of the sexual cycle of the parasite. Recombinant Plasmodium falciparum Nek-4 possesses protein kinase activity and displays substrate preferences similar to those of other Neks. Nek-4 is highly expressed in gametocytes, yet disruption of the nek-4 gene in the rodent malaria parasite P. berghei has no effect on gamete formation and subsequent fertilization. However, further differentiation of zygotes into ookinetes is abolished. Measurements of nuclear DNA content indicate that zygotes lacking Nek-4 fail to undergo the genome replication to the tetraploid level that precedes meiosis. Cell cycle progression in the zygote is identified as a likely precondition for its morphological transition to the ookinete and for the successful establishment of a malaria infection in the mosquito.     

The involvement of galectin-1 in skeletal muscle determination, differentiation and regeneration

The dogma that a cell is rigidly committed to one tissue type has been heavily challenged over the past few years with numerous reports of transdifferentiation of cells between different lineages. Cells capable of entering lineages other than that of their tissue of origin have been identified in several diverse tissues. Recently we have focussed on a non-committed myogenic cell within the dermis that is capable, under certain conditions, of expressing muscle specific markers and even fusing to the terminally differentiated stage of muscle cell development. We have identified galectin-1 as being a potent factor implicated in this process. In this review we discuss our findings and consider the involvement of galectin-1 in muscle determination, differentiation and regeneration.