Hex-1, a gene unique to filamentous fungi, encodes the major protein of the Woronin body and functions as a plug for septal pores.

We have identified a gene, named hex-1, that encodes the major protein in the hexagonal crystals, or Woronin bodies, of Neurospora crassa. Analysis of a strain with a null mutation in the hex-1 gene showed that the septal pores in this organism were not plugged when hyphae were damaged, leading to extensive loss of cytoplasm. When grown on agar plates containing sorbose, the hex-1(-) strain showed extensive lysis of hyphal tips. The HEX-1 protein was predicted to be 19,125 Da. Analysis of the N-terminus of the purified protein indicated that 16 residues are cleaved, yielding a protein of 17,377 Da. A polyclonal antibody raised to the HEX-1 protein recognized multiple forms of the protein, apparently dimers and tetramers that were resistant to solubilization by sodium dodecyl sulfate and reducing reagents. Treatment of the protein with phosphatase caused dissociation of these oligomers. Preparations enriched in Woronin bodies contained catalase activity, which was not detected in comparable fractions from the hex-1(-) mutant strain. These results support the hypothesis that the Woronin body is a specialized peroxisome that functions as a plug for septal pores.

A recombinant inbred strain analysis of sleep-time responses to several sedative-hypnotics.

The results of previous studies suggested that the sleep-time differential between long-sleep (LS) and short-sleep (SS) mice decreases for a series of sedative-hypnotic drugs as lipid solubility increases. Using the LS x SS recombinant inbred (RI) strains, we have tested whether this relationship arises because of common genetic influences on the sleep-time responses or was simply a fortuitous difference between LS and SS mice. Mice were sleep-time tested after intraperitoneal injections of a variety of sedative-hypnotic drugs that vary in lipid solubility including alcohols, barbiturates, chloral hydrate, and urethane. Sleep-time values from each of these drugs were compared with ethanol-induced sleep times in the LS x SS RI strains. Significant genetic correlations were observed between ethanol-induced sleep time and those responses elicited by butanol, propanol, and chloral hydrate, but not by pentobarbital or secobarbital. When the partition coefficient (log P) values were compared with the genetic correlations, a significant relationship (r = -0.85) was observed. These data suggest that common genes mediate sedative-hypnotic reactions to ethanol and some drugs resembling it in log P value, and that anesthetic agents with low lipid solubility may be working through different mechanisms than drugs with greater lipid solubilities.

The use of recombinant inbred strains to study mechanisms of drug action.

Long-sleep (LS) and short-sleep (SS) mice which were selectively bred for sensitivity to the sedative-hypnotic effects of ethanol have been used extensively in the examination of sensitivity to ethanol as well as to other CNS depressants. Understanding the relationship between sensitivity to ethanol and other depressants using LS and SS mice has been limited to a two mouse line comparison because these mice do not exist as replicate lines. To circumvent this problem, DeFries et al. have bred LSXSS recombinant inbred strains (LSXSS RIs) from a cross of LS and SS mice. These mice are being characterized on their responses to a variety of CNS depressants and agents that interact with the GABAergic system. Preliminary results are presented here on the sensitivity of these LSXSS RIs to pentobarbital, phenobarbital, and flurazepam as measured by sleep times. Additionally, analyses of seizure susceptibility to the GABAergic antagonist, bicuculline, in 24 LSXSS RIs indicate that there is no significant relationship between this measure of GABAergic function and sensitivity to ethanol as measured by the sleep-time response. These results are presented in the context of questions that can be resolved using RIs in drug-abuse research.

Heterosis and resistance to DFP effects on spatial learning in C57BL X DBA hybrids.

The inbred mouse strains C57BL/6Ibg and DBA/2Ibg differ in their ability to exhibit spatial learning in the Morris water task. C57BL mice learn the task well and show impairment of spatial learning following disruption of cholinergic function. DBA mice show rudimentary spatial learning ability, and are not further impaired when cholinergic function is decreased. These mice may carry genes regulating a noncholinergic spatial learning system. To test this hypothesis, first generation (F1) hybrids between DBA and C57BL mice were tested for spatial learning in the Morris water task. The hybrids performed better than either parental strain, suggesting that both parents contributed genes for spatial learning ability. Chronic treatment with diisopropylfluorophosphate (DFP), which abolished spatial learning ability in C57BL mice, produced only minor impairments in the hybrids. The behavioral resistance to DFP occurred despite significant reductions in hippocampal and cortical muscarinic binding. The results suggest either that the hybrids inherited a noncholinergic neurochemical system influencing spatial learning from their DBA parents or that the DFP treatment did not disrupt cholinergic function to a sufficient degree to impair the superior learning abilities of the F1 hybrids.