Sporulation in the mold Neurospora crussa can proceed along three very different pathways, leading to the production of three types of spores. Two asexual sporulation pathways that lead to the formation of macroconidia and microconidia involve budding from hyphae by two different mechanisms. A much more complex sexual reproductive pathway involves the formation of a fruiting body called a perithecium, in which meiosis takes place and ascospores are formed in sac‐like cells called asci. Numerous mutations exist that affect (...) these developmental pathways, and genes have been isolated that are expressed preferentially during sporulation. The Neurospora sporulation pathways offer a simple system with which to study mechanisms and regulation of development that are usually obscured by complex cell‐cell interactions involved in animal and plant development. (shrink)

An early step in sporulation of the bacterium Bacillus subtilis, is the formation of two compartments in the developing sporangium: the mother cell and the forespore. These compartments differ in their programs of gene expression and developmental fate. The establishment of cell type within this simple developmental program, is accomplished by the compartmentalization of sigma subunits of RNA polymerase. The localization of these sigma factors results in compartment‐specific gene expression. Recent experiments have elucidated some of the early steps in (...) the establishment of 3V cell type. After septum formation, the activity of the sigma factor, σF, is confined to the forespore compartment. This, in turn, results in the localized expression of another developmental sigma factor, σG. The forespore localization of these two sigma factors, establishes the forespore line of gene expression. σF and σG also regulate mother cell events. σF activity in the forespore regulates the proteolytic processing of σE within the mother cell compartment. The localization σE activity leads to mother cell expression of another sigma factor, pro‐σK The proteolytic processing of pro‐σK to mature σK is controlled by the forespore sigma factor, σG Mature σK then directs the transcription of mother cell specific genes. Therefore, the initial localization of σF activity to the forespore compartment, orchestrates the establishment of cell type in both forespore and mother cell compartments. (shrink)

The phosphorelay of Bacillus subtilis, a kinase cascade that activates master regulator Spo0A ∼ P in response to starvation signals, is the core of a large network controlling the cell's decision to differentiate into sporulation and other phenotypes. This article reviews recent advances in understanding the origins and purposes of the complex dynamical behavior of the phosphorelay, which pulses with peaks of activity coordinated with the cell cycle. The transient imbalance in the expression of two critical genes caused by (...) their strategic placement at opposing ends of the chromosome proved to be the key for this pulsed behavior. Feedback control loops in the phosphorelay use these pulses to implement a timer mechanism, which creates several windows of opportunity for phenotypic transitions over multiple generations. This strategy allows the cell to coordinate multiple differentiation programs in a decision process that fosters phenotypic diversity and adapts to current conditions. (shrink)

Intercellular signaling plays an important role in spatially regulated developmental processes. Myxococcus xanthus C signal transmission during fruiting body formation requires motile, densely packed, well aligned cells. tThe fruiting body consists of two domains: an outer domain which has densely packed, well aligned, motile cells: and an inner domain of more loosely packed, non‐motile, sporulating cells. The two domains are characterized by different patterns of C‐dependent gene expression, which begins in the outer domain where C‐signaling is most efficient, and reaches (...) its maximum in the inner domain. These domains may be maintained by a dynamic mechanism which relies on passive transport of the sporulating cells from the outer domain, where sporulation is initiated, to the inner domain by the motile cells in the outer domain. (shrink)

The studies on the cAMP‐requiring mutants and their suppressors in the yeast, Saccharomyces cerevisiae, revealed that cAMP‐dependent protein phosphorylation is involved in the G1 phase of the cell cycle, in conjugation, and in the post‐meiotic stage of sporulation, and that inhibition of cAMP‐dependent protein phosphorylation is required to induce meiotic division.

Somatic complementation by fusion of two mutant cells and mixing of their cytoplasms occurs when the genetic defect of one fusion partner is cured by the functional gene product provided by the other. We have found that complementation of mutational defects in the network mediating stimulus‐induced commitment and sporulation of Physarum polycephalum may reflect time‐dependent changes in the signaling state of its molecular building blocks. Network perturbation by fusion of mutant plasmodial cells in different states of activation, and the (...) time‐resolved analysis of somatic complementation effects can be used to systematically probe network structure and dynamics. Time‐resolved somatic complementation quantitatively detects regulatory interactions between the functional modules of a network, independent of their biochemical composition or subcellular localization, and without being limited to direct physical interactions. BioEssays 25:950–960, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

Asymmetric cell division generates two cells that contain different regulatory proteins and express different fates. In an example of asymmetric cell division from B. subtilis, a site on the membrane of the dividing cell is chosen to establish the initial asymmetry. Recent results(1,2) show that a key regulatory protein, SpollE, is localized to one side of a sporulating B. subtilis cell, and subsequently functions in an asymmetric manner. SpollE is a phosphatase at the beginning of a regulatory cascade that leads (...) to activation of a cell fate‐determining transcription factor in only one daughter cell. (shrink)