Nuclear division cycle in Neurospora crassa hyphae under different growth conditions

Abstract

Treatment with picolinic acid blocked Neurospora crassa nuclei in G1, and recovery from the treatment allowed a synchronous wave of deoxyribonucleic acid synthesis to occur. Nuclei, which appeared as compact globular bodies during the period of blockage, assumed a ring shape during the following S phase, which was also maintained in the G2 phase. The proportion of compact globular nuclei was much higher in hyphae growing at lower rates, whereas that of ring nuclei increased when the hyphae were growing at higher rates. Horseshoe nuclei (probably mitotic nuclei) and double ring nuclei were also observed in growing hyphae, but their frequencies were low and fairly independent of the rate of growth. The length of the S phase of the Neurospora nuclear division cycle was determined to be about 30 min. From the frequencies of the phase-specific nuclear shapes, the durations of the G1 phase and the combined S plus G2 phases were calculated. The results showed that variations in the growth rates of the mycelia were mainly coupled with variations in the G1 phase of the nuclear division cycle. For mycelia growing in minimal sucrose, the lengths of all of the phases of the nuclear division cycle were estimated.

Control of growth and of the nuclear division cycle in Neurospora crassa.

“…division cycle is an important aspect of the regulation of cell proliferation (30,77,83,109), although the relationships between the two processes are not yet completely understood. Whereas the growth metabolism of Neurospora has been extensively characterized as levels and rates of syntheses of protein, rRNA, tRNA, and polyadenylate-containing mRNA and protein degradation as discussed above, the information available in the literature on the nuclear division cycle in Neurospora is much less abundant (105,140). When young hyphae of N. crassa stained with Giemsa or Feulgen and crystal violet are observed by optical microscopy, different nuclear shapes are distinguishable: uniformly colored globular nuclei, ring-shaped nuclei double-ring nuclei, and horseshoe nuclei (105, 187, 188).…”

“…When young hyphae of N. crassa stained with Giemsa or Feulgen and crystal violet are observed by optical microscopy, different nuclear shapes are distinguishable: uniformly colored globular nuclei, ring-shaped nuclei double-ring nuclei, and horseshoe nuclei (105, 187, 188). Evidence obtained by arresting the progression of the cell cycle by treatment with picolinic acid has indicated that compact globular nuclei are most likely in the G1 phase and ring nuclei are most likely in the S and G2 phases, whereas double-ring and horseshoe nuclei are premitotic or mitotic shapes (105). The frequency of compact globular nuclei is much higher in hyphae growing at lower rates, whereas that of ring nuclei increases when the hyphae are growing at higher rates (105).…”

“…Evidence obtained by arresting the progression of the cell cycle by treatment with picolinic acid has indicated that compact globular nuclei are most likely in the G1 phase and ring nuclei are most likely in the S and G2 phases, whereas double-ring and horseshoe nuclei are premitotic or mitotic shapes (105). The frequency of compact globular nuclei is much higher in hyphae growing at lower rates, whereas that of ring nuclei increases when the hyphae are growing at higher rates (105). Taking into account the age distribution function of the nuclei (102,125), the durations of the G, and the S plus G2 phases at various duplication times have been calculated (Table 7) (105).…”

“…Critical protein content rquired for the onset of DNA replication, expresed as protein (tens of billions of amino acids) per gepnome equivalent. P. values were calculated from equation 9 with data obtained from Alberghina et al (7) andMartepni et aL (105) and assuming a constant length of TR (time required for DNA replication) equal to 30 min. lecular metabolism which characterizes different growth conditions in Neurospora as well as in other microorganisms, such as E. coli and S. cerevisiae.…”

Nuclear behavior in fungal hyphae

“…Phase-specific shapes are reported in N. crassa. G1 nuclei are compact and globular, S and G2 phase nuclei are ring-shaped [30].…”