The chromosome 4 workshop report

In the concluding session the compilation and availability of available resources on chromosome 4 were discussed. A listing of these resources is available from Jeff Murray at the University of Iowa for anyone with an interest in human chromosome 4. Rick Myers stressed the commitment of the UCSF Genome Center to make resources available to the mapping community as a whole as soon as they have been identified and characterized. There was general agreement that such a philosophy will facilitate the rapid generation and integration of the maps from several groups currently working in this area. The chromosome 4 committee for the Human Gene Mapping workshops was scheduled to meet in August of 1991, and a second chromosome 4-specific meeting is to be held in Leiden on June 13 and 14, 1992 (contact Gert-Jan van Ommen for information). Future venues for the meeting are planned to alternate between countries with groups participating in mapping projects on this chromosome and initially will focus particularly on groups with chromosome wide mapping interests such as EUROGEM and the Human Genome Center.     

The IFR process: beyond the specialist workshop

The process of determining Instream Flow Requirements (IFRs) has been well developed to the point at which an IFR table which quantifies the temporal distribution of discharge, upon which the modified flow regime is based, is produced. During the last three years, the process has been further developed by linking the IFRs (using the IFR model) to an historical time series and a natural flow trigger. It has become imperative that the liaison between IFR specialists and developers of the methodology should not end here, as some of the most important requirements for supplying the IFR include the determination of the yield of a system as well as the design and ultimate operation of storage structures. On the basis of some case studies this paper considers how the liaison should take place after the specialist workshop and summarises the areas where further development is required.     

The Arabidopsis deetiolated2 mutant is blocked early in brassinosteroid biosynthesis.

The Arabidopsis DEETIOLATED2 (DET2) gene has been cloned and shown to encode a protein that shares significant sequence identity with mammalian steroid 5 alpha-reductases. Loss of DET2 function causes many defects in Arabidopsis development that can be rescued by the application of brassinolide; therefore, we propose that DET2 encodes a reductase that acts at the first step of the proposed biosynthetic pathway--in the conversion of campesterol to campestanol. Here, we used biochemical measurements and biological assays to determine the precise biochemical defect in det2 mutants. We show that DET2 actually acts at the second step in brassinolide biosynthesis in the 5 alpha-reduction of (24R)-24-methylcholest-4-en-3-one, which is further modified to form campestanol. In feeding experiments using 2H6-labeled campesterol, no significant level of 2H6-labeled campestanol was detected in det2, whereas the wild type accumulated substantial levels. Using gas chromatography-selected ion monitoring analysis, we show that several presumed null alleles of det2 accumulated only 8 to 15% of the wild-type levels of campestanol. Moreover, in det2 mutants, the endogenous levels of (24R)-24-methylcholest-4-en-3-one increased by threefold, whereas the levels of all other measured brassinosteroids accumulated to < 10% of wild-type levels. Exogenously applied biosynthetic intermediates of brassinolide were found to rescue both the dark- and light-grown defects of det2 mutants. Together, these results refine the original proposed pathway for brassinolide and indicate that mutations in DET2 block the second step in brassinosteroid biosynthesis. These results reinforce the utility of combining genetic and biochemical analyses to studies of biosynthetic pathways and strengthen the argument that brassinosteroids play an essential role in Arabidopsis development.     

The actual biochemical block in the arg-2 mutant of Chlamydomonas reinhardi

Arg-2, one of the first arginine-requiring mutants isolated in Chlamydomonas reinhardi, has long been regarded as lacking the enzyme argininosuccinate synthetase. In view of various discrepancies found in the literature, the position of this mutant has been reviewed. The results show that arg-2 has a normal argininosuccinate synthetase activity but lacks argininosuccinate lyase. This finding is in agreement with the results of recombination and complementation analysis, which indicate that arg-2 is included in the arg-7 cistron.Chercheur qualifié du Fonds National Belge de la Recherche Scientifique.     

The Arabidopsis mutant eer2 has enhanced ethylene responses in the light

By screening for ethylene response mutants in Arabidopsis, a novel mutant, eer2, was isolated which displays enhanced ethylene responses. On a low nutrient medium (LNM) light-grown eer2 seedlings showed a significant hypocotyl elongation in response to low levels of 1-amino-cyclopropane-1-carboxylate (ACC), the precursor of ethylene, compared with the wild type, indicating that eer2 is hypersensitive to ethylene. Treatment with 1-MCP (1-methylcyclopropene), a competitive inhibitor of ethylene signalling, suppressed this hypersensitive response, demonstrating that it is a bona fide ethylene effect. By contrast, roots of eer2 were less sensitive than the wild type to low concentrations of ACC. The ethylene levels in eer2 did not differ from the wild type, indicating that ethylene overproduction is not the primary cause of the eer2 phenotype. In addition to its enhanced ethylene response of hypocotyls, eer2 is also affected in the pattern of senescence and its phenotype depends on the nutritional status of the growth medium. Furthermore, linkage analysis of eer2 suggests that this mutant defines a new locus in ethylene signalling.     

Studies ofH-2K b mutant mice

Three newH-2 ^b mutant strains, B6.C-H-2 ^bm9 , B6.C-H-2 ^bm10 and B6.C-H–2 ^bm11 , are described. The three mutant strains are of the gain and loss type as they reject skin grafts reciprocally with the parental C57BL/6Kh. The mutations, which arose independently, are all allelic at the same locus as 11 other mutant strains already described. By complementation and other studies the mutated gene has been shown to beH-2K ^b . The strains were typed directly and by absorption with antisera specific for H-2K^b and H-2D^b private and public specificities and for Ia^b specificities. Each strain typed differently with these sera. The strain B6.C-H-2 ^bm9 was found to be serologically identical with C57BL/6. The strains B6.C-H-2 ^bm10 and B6.C-H-2 ^bm11 were found to have alterations in the private H-2K^b specificity, H-2.33, and in the public specificity, H-2.5, but to a different extent. B6.C-H- 2^bm10 had a marked decrease in the amount of H-2.33 expressed on the splenic cell surface as compared to C57BL/6 and also has a marked decrease in the expression of H-2.5 on both spleen and red blood cells. In comparison, B6.C-H-2 ^bm11 has a decrease in the expression of H-2.33 but an increase in the expression of H-2.5 on both splenic and red blood cells. The other H-2^b specificities appeared to be unaltered as compared with C57BL/6.