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R J Huskey

Publications and source records attributed to R J Huskey.

10 recordsLinked to original sources
PubMed1987

Stage-specific hypermutability of the regA locus of Volvox, a gene regulating the germ-soma dichotomy.

Mutation at the regA locus confers on somatic cells of Volvox (which otherwise undergo programmed death) ability to redifferentiate as reproductive cells. Stable mutations at the regA locus, but not at other loci, were induced at high frequency when embryos at one particular stage were exposed to either UV irradiation, novobiocin, nalidixic acid, bleomycin, 4-hydroxyaminoquinoline-1-oxide, 5-bromodeoxyuridine, or 5-fluorouracil. All treatments led to some mutations that were not expressed until the second generation after treatment. The sensitive period was after somatic and reproductive cells of the next generation had been set apart, but before they had undergone cytodifferentiation. Hypermutability occurs in presumptive reproductive cells (in which regA is normally not expressed) somewhat before regA normally acts in somatic cells. We postulate that hypermutability of regA in the reproductive cells at this time reflects a change of state that the locus undergoes as it is inactivated.

Bleomycin↗
PubMed1986

Developmental changes in the sensitivity of Volvox to ultraviolet light.

The response of Volvox to ultraviolet irradiation was analyzed. Young individuals isolated from a synchronous culture were exposed to UV light (120 J/m2) and subjected to variable length periods of dark following irradiation. The major effect of the UV treatment was the inability of the gonidia present in the colonies at the time of irradiation to continue and complete the developmental program. Individuals show a heightened sensitivity to UV for a limited period immediately following inversion and are insensitive at other stages of development. The cytotoxic effect of UV during this interval is completely reversed by the immediate exposure to white light and is increased with longer periods of dark treatment prior to exposure to white light. The temporal profile of the sensitivity defines a smooth curve in which the maximal sensitivity occurs three hours after inversion. The response to higher doses of UV (up to 500 J/m2) is a nonlinear increase in cytotoxicity and is disproportionately greater in those individuals just prior to the period of maximal sensitivity than those later in development. The results suggest that Volvox has at least two pathways for the repair of UV damage and that one of these, the principal dark repair pathway, is temporarily deficient in the gonidia of young individuals.

Animals↗
PubMed1974

Partial exclusion between T-even bacteriophages: an incipient genetic isolation mechanism.

Conditional lethal mutant systems developed in T-even bacteriophages T2, T4 and T6 have been used to study the partial exclusion which characterizes mixed infections of these phages. In bacteria mixedly infected with T2 and T4, the dominant phage (T4) acts against localized exclusion sensitivity determinants in the genome of the excluded phage (T2). These determinants are clustered near genes controlling early functions; the determinants themselves do not appear among the progeny, but markers located close to them appear infrequently, by recombination. The excluding action of T4 does not depend on the action of any gene so far identified by conditional lethal mutations, nor does it depend on differences in DNA glucosylation between infecting phages. Regardless of mechanism, the genetic consequence of this partial exclusion is to limit genetic exchange between T2 and T4 in the region of the genome controlling early functions, while retaining the capacity for extensive exchange in other regions; in short, partial exclusion constitutes a localized genetic isolating mechanism. Related forms of partial exclusion characterize mixed infections of other T-even phages, including those of some phages newly isolated from nature.

Chromosome Mapping↗
PubMed1973

Genetic control of development in Volvox: isolation and characterization of morphogenetic mutants.

Morphogenetic mutants of the colonial green alga, Volvox carteri f. nagariensis, were induced by chemical mutagenesis. The 68 independent mutants are classified into 12 readily identifiable phenotypes affecting various stages of asexual development. Nine of the mutants are temperature sensitive with normal development at 25 degrees and mutant development occurring at 35 degrees . Some mutant genes appear to be involved in the regulation of differentiation or the stability of the differentiated state. Other mutations occur in genes apparently responsible for structural components of dividing cells or adult colonies. Two mutants affect different aspects of the posterior-anterior polarization of the mature colony. One mutation affects a gene which acts very early in colonial development, but affects the appearance of the mature colony. The mutants isolated demonstrate the feasibility of using Volvox to study the genetic control of early steps in embryogenesis.

Alkanesulfonates↗
PubMed1969

Multiplicity reactivation as a test for recombination function.

Multiplicity reactivation of bacteriophage inactivated by ultraviolet light is dependent on the recombination function of either the host bacterial cell or the infecting bacteriophage. Absence of both recombination systems leads to a loss of multiplicity reactivation.

Coliphages↗