Biomedical subjects

Alejandro Correa

Publications and source records attributed to Alejandro Correa.

5 recordsLinked to original sources

PubMed2004

Transcriptional response to glucose starvation and functional analysis of a glucose transporter of Neurospora crassa.

The response to glucose availability in Neurospora crassa was characterized by measuring transcript levels of 1335 genes represented on a cDNA microarray. We found that 19% of the 1335 genes were regulated at least twofold in response to glucose deprivation. Several sugar transporter homologs were found to be regulated by glucose. Functional analysis of one of these, hgt-1, indicates that it encodes a high-affinity glucose transporter. Comparing N. crassa profiling data with the published diauxic shift data from Saccharomyces cerevisiae revealed that the two fungi share similar, but not identical, transcriptional response patterns. Regulation of transcript levels measured by microarray analysis is consistent with previous measurements of central metabolism enzyme activities for N. crassa. Transcripts of genes for ethanol fermentation and the tricarboxylic acid cycle are abundant in glucose-rich medium, consistent with N. crassa carrying out a high rate of both fermentation and respiration simultaneously.

Adaptation, Physiological↗

PubMed2003

Multiple oscillators regulate circadian gene expression in Neurospora.

High-density microarrays were used to profile circadian gene expression in Neurospora crassa cultures grown in constant darkness. We identified 145 clock-controlled genes (ccgs). The ccgs peaked in mRNA accumulation at all phases of the day, with the majority peaking in the late night to early morning. The predicted or known functions of the ccgs demonstrate that the clock contributes to a wide range of cellular processes, including cell signaling, development, metabolism, and stress responses. Although the period of rhythm of most of the ccgs was found to depend on the well characterized frequency (FRQ)-based oscillator, three ccgs appeared to have a rhythm that was significantly short in the long period (29-h) frq7 mutant strain. These ccgs accumulate mRNA rhythmically with a circadian period in a frq-null strain, confirming the existence of a second oscillator in N. crassa.

Circadian Rhythm↗

PubMed2002

The Neurospora crassa pheromone precursor genes are regulated by the mating type locus and the circadian clock.

Pheromones play important roles in female and male behaviour in the filamentous ascomycete fungi. To begin to explore the role of pheromones in mating, we have identified the genes encoding the sex pheromones of the heterothallic species Neurospora crassa. One gene, expressed exclusively in mat A strains, encodes a polypeptide containing multiple repeats of a putative pheromone sequence bordered by Kex2 processing sites. Strains of the opposite mating type, mat a, express a pheromone precursor gene whose polypeptide contains a C-terminal CAAX motif predicted to produce a mature pheromone with a C-terminal carboxy-methyl isoprenylated cysteine. The predicted sequences of the pheromones are remarkably similar to those encoded by other filamentous ascomycetes. The expression of the pheromone precursor genes is mating type specific and is under the control of the mating type locus. Furthermore, the genes are highly expressed in conidia and under conditions that favour sexual development. Both pheromone precursor genes are also regulated by the endogenous circadian clock in a time-of-day-specific fashion, supporting a role for the clock in mating.

Amino Acid Sequence↗

PubMed2002

Neurospora clock-controlled gene 9 (ccg-9) encodes trehalose synthase: circadian regulation of stress responses and development.

The circadian clock of Neurospora crassa regulates the rhythmic expression of a number of genes encoding diverse functions which, as an ensemble, are adaptive to life in a rhythmic environment of alternating levels of light and dark, warmth and coolness, and dryness and humidity. Previous differential screens have identified a number of such genes based solely on their cycling expression, including clock-controlled gene 9 (ccg-9). Sequence analysis now shows the predicted CCG-9 polypeptide to be homologous to a novel form of trehalose synthase; as such it would catalyze the synthesis of the disaccharide trehalose, which plays an important role in protecting many cells from environmental stresses. Consistent with this, heat, glucose starvation, and osmotic stress induce ccg-9 transcript accumulation. Surprisingly, however, a parallel role in development is suggested by the finding that inactivation of ccg-9 results in altered conidiophore morphology and abolishes the normal circadian rhythm of asexual macroconidial development. Examination of a clock component, FRQ, in the ccg-9-null strain revealed normal cycling, phosphorylation, and light induction, indicating that loss of the conidiation rhythm is not due to changes in either the circadian oscillator or light input into the clock but pointing instead to a defect in circadian output. These data imply an interplay between a role of trehalose in stress protection and an apparent requirement for trehalose in clock regulation of conidiation under constant environmental conditions. This requirement can be bypassed by a daily light signal which drives a light-entrained rhythm in conidiation in the ccg-9-null strain; this bypass suggests that the trehalose requirement is related to clock control of development and not to the developmental process itself. Circadian control of trehalose synthase suggests a link between clock control of stress responses and that of development.

Circadian Rhythm↗

PubMed2002

Distinct signaling pathways from the circadian clock participate in regulation of rhythmic conidiospore development in Neurospora crassa.

Several different environmental signals can induce asexual spore development (conidiation) and expression of developmentally regulated genes in Neurospora crassa. However, under constant conditions, where no environmental cues for conidiation are present, the endogenous circadian clock in N. crassa promotes daily rhythms in expression of known developmental genes and of conidiation. We anticipated that the same pathway of gene regulation would be followed during clock-controlled conidiation and environmental induction of conidiation and that the circadian clock would need only to control the initial developmental switch. Previous experiments showed that high-level developmental induction of the clock-controlled genes eas (ccg-2) and ccg-1 requires the developmental regulatory proteins FL and ACON-2, respectively, and normal developmental induction of fl mRNA expression requires ACON-2. We demonstrate that the circadian clock regulates rhythmic fl gene expression and that fl rhythmicity requires ACON-2. However, we find that clock regulation of eas (ccg-2) is normal in an fl mutant strain and ccg-1 expression is rhythmic in an acon-2 mutant strain. Together, these data point to the endogenous clock and the environment following separate pathways to regulate conidiation-specific gene expression.

Aerobiosis↗