High-frequency conversion to a "fluffy" developmental phenotype in Aspergillus spp. by 5-azacytidine treatment: evidence for involvement of a single nuclear gene.

Transient exposure of mycelia from Aspergillus niger and Aspergillus nidulans to the cytidine analog 5-azacytidine, leading to no more than 0.3 to 0.5% substitution for cytosine by 5-azacytosine in A. nidulans DNA, resulted in the conversion of a high fraction of the cell population (more than 20%) to a mitotically and meiotically stable "fluffy" developmental phenotype. The phenotypic variants are characterized by the developmentally timed production of a profuse fluffy network of undifferentiated aerial hyphae that seem to escape signals governing vegetative growth. Genetic analysis with six different fluffy clones reveals that this trait is not cytoplasmically coded, is recessive in heterozygous diploids but codominant in heterokaryons, and exhibits a 1:1 Mendelian segregation pattern upon sexual sporulation of heterozygous diploids. Complementation and mitotic haploidization studies indicated that all variants are affected in the same gene, which can be tentatively located on chromosome VIII of A. nidulans. Molecular analysis to search for modified bases showed that DNA methylation is negligible in in both A. niger and A. nidulans and that no differences could be detected among DNAs from wild-type cells, fluffy clones, or mycelia exposed to 5-azacytidine. It thus appears that high-frequency conversion of fungal mycelia to a stable, variant developmental phenotype by 5-azacytidine is the result of some kind of target action on a single nuclear gene and that this conversion can occur in organisms virtually devoid of DNA methylation.     

Structural studies of an Inv (1, −2) kappa light chain

A Bence Jones protein with phenotype Inv (1, –2) was isolated from the urine of a patient with multiple myeloma. Inv typing of the patient's relatives established the presence of anInv ¹ allele in the kindred, and that the patient's genotype wasInv ¹/Inv ³. Hence, the absence of Inv (2) in the Bence Jones protein was shown to be genetic and not an artifact caused by the disease. The tryptic peptide-containing residues 191 through 194 were isolated and shown to be composed of Leu, Tyr, Ala, Cys, with Leu at the amino end. Hence, the residue at 191 is the same as that present in Inv (1, 2) Bence Jones proteins. More detailed study of the tryptic peptides established that residue 153 is Val rather than Ala as in all other K chains thus far studied. The primary sequence: Ala¹⁵³, Leu¹⁹¹ determines Inv (1, 2); Ala¹⁵³, Val¹⁹¹ determines Inv (3); and Val¹⁵³, Leu¹⁹¹ determines Inv (1). The Val¹⁵³, Val¹⁹¹ sequence has not been observed. It may correspond to Inv (–). These data are strikingly similar to the data for the Kern and Oz isotypes (changes at 154 and 191, respectively) in the chain. As in the case of theK chain, only three of the four possible combinations have been observed. The implications of this parallelism and of crystallographic findings on chains, reported by others, are discussed.     

The Organically Handicapped Child—How Can the Family Physician Help?

The better his understanding of some of the ways in which an organic deficit might affect normal development of the handicapped child, the more able the family physician will be to offer guidance to the family aimed at preventing the development of secondary problems. He can thus be instrumental in helping a child achieve his maximal potential.First, it is important to take into account how the parents'' emotional and intellectual responses to having a defective child may interfere markedly in normal parent-child relationship. Second, ways in which each deficit will limit a child''s exposure to stimuli must not be over-looked. Third, one must consider how a deficit may indirectly distort the normal learning patterns when parents do not make age appropriate demands. Fourth, it is important to understand how specific interference in the area of language skills may cause further developmental retardation. Fifth, one must be aware of special problems that an organically handicapped child must face in the society outside of the family. Last of all, in an older child, one must consider the need for a full scale evaluation to sort out primary and secondary factors in the picture.     

Endogenous polyamine content during in vivo maturation and in vitro culture of maize pollen

Changes in polyamine content during in vivo maturation and in vitro culture of maize (Zea mays L.) pollen were studied. The endogenous content of free, conjugated and bound polyamines was analyzed during 30 days of pollen evolution, in both developmental pathways (microsporogenesis and androgenesis). The induction of androgenesis from cold-pretreated uninucleate pollen results, in most of cases, in a lower total polyamine content than that of the in vivo uninucleate pollen. These differences indicate that polyamine metabolism is altered during the induction of androgenesis, and this could be a consequence of increased polyamine assimilation. In general, pollen stages that involve cell division (tetrades, pre-anthesis pollen and four-day cultured pollen) are characterized by a predominance of free Spd. The increase of Spd and Spm in 15-day cultured pollen, when the first embryoids are formed, outline the possible implication of these polyamines in embryogenetic processes. Furthermore, these findings may contribute to the improvement of maize androgenesis yield, especially in recalcitrant genotypes, by the exogenous application of polyamines or polyamine-inhibitors to the culture medium.Abbreviations PAs polyamines - Put putrescine - Spd spermidine - Spm spermine - S free polyamine fraction - SH conjugated polyamine fraction - PH bound polyamine fraction