Fluorescence microscopic examination coupled with digital videoimage analysis of 4',6-diamidino-2-phenylindole-stained sporulating cells of Bacillus megaterium or Bacillus subtilis revealed a striking condensation of the forespore nucleoid. While both mother cell and forespore compartments had equal amounts of DNA, the forespore nucleoid became >2-fold more condensed than the mother cell nucleoid. The condensation of the forespore nucleoid began after only the first hour of sporulation, 2 to 3 h before expression of most forespore-specific genes including those for small, acid-soluble spore proteins, and was abolished in spoO mutants but not in spoIl or spoIll mutants. It is possible that this striking condensation of forespore DNA plays some role in modulating gene expression during sporulation.Sporulation in Bacillus species is characterized by the appearance of a number of new gene products at defined times during this differentiation process. This temporal pattern of gene expression is regulated in large part by ordered changes in the specificity of the cell's RNA polymerase through alterations in the pattern of associated sigma factors (10,12). In addition to temporal control of gene expression, sporulation is characterized by spatial control of gene expression. A key event early in sporulation is the appearance of an asymmetric septum dividing the cell into large and small compartments, with the small cell destined to become the forespore which will be engulfed by the larger mother cell. As would be expected, given the morphological difference between mother cell and forespore compartments, there are different patterns of gene expression in the two compartments (20,23). The differential gene expression in these compartments is also due, at least in part, to differences in RNA polymerase sigma factors, with one foresporespecific sigma factor (@rG) and one mother cell-specific sigma factor (0rK) identified to date (12,23,25). While this difference in sigma factors may explain much of the differential gene expression in the two compartments after the third hour (t3) of sporulation, it is not clear how this compartmentspecific difference in sigma factors is established, i.e., how compartment-specific gene expression is initiated. One formal possibility is that there is some difference in the structure of the genomes in the forespore and mother cell. Surprisingly, this possibility has not been considered in recent years, despite early evidence, primarily from light microscopy, that the forespore nucleoid becomes significantly condensed during sporulation (15,16,28,29). While forespore nucleoid condensation was clearly an early event in sporulation, this early work unfortunately did not precisely place the change within the time framework of the overall differentiation process, in particular with respect to synthesis of various sporulation-specific gene products. Consequently, we undertook an analysis of gross nucleoid structure during sporulation by using fluorescence microscopy of 4',6-diamidino-2-phenylindole...

No abstract

The plasma membrane of the mature guinea pig sperm is segregated into at least four domains of different composition. Previous studies have shown that some proteins localized within these domains are free to diffuse laterally, suggesting that barriers to protein diffusion are responsible for maintaining the nonuniform distribution of at least some surface proteins in mature sperm. The different membrane domains appear sequentially during sperm morphogenesis in the testis and during later passage through the epididymis. To determine when diffusion barriers become functional during sperm development, we examined the diffusion of two proteins that are expressed on the cell surface of developing spermatids and become segregated to different plasma membrane domains during the course of spermiogenesis. Both proteins exhibited rapid lateral diffusion throughout spermiogenesis, even after they become localized to specific regions of the surface membrane. These results suggest that barriers to membrane diffusion form concomitantly with membrane domains during spermiogenesis.

No abstract

No abstract