Influence of cell-to-cell variability on spatial pattern formation.

Many spatial patterns in biology arise through differentiation of selected cells within a tissue, which is regulated by a genetic network. This is specified by its structure, parameterisation and the noise on its components and reactions. The latter, in particular, is not well examined because it is rather difficult to trace. The authors use suitable local mathematical measures based on the Voronoi diagram of experimentally determined positions of epidermal plant hairs (trichomes) to examine the variability or noise in pattern formation. Although trichome initiation is a highly regulated process, the authors show that the experimentally observed trichome pattern is substantially disturbed by cell-to-cell variations. Using computer simulations, they find that the rates concerning the availability of the protein complex that triggers trichome formation plays a significant role in noise-induced variations of the pattern. The focus on the effects of cell noise yields further insights into pattern formation of trichomes. The authors expect that similar strategies can contribute to the understanding of other differentiation processes by elucidating the role of naturally occurring fluctuations in the concentration of cellular components or their properties.

Bacterial flora of the vagina during the menstrual cycle: findings in users of tampons, napkins, and sea sponges.

The recent association of menstruation, tampon use, and staphylococcal infection with toxic shock syndrome led us to study the association of menstruation and catamenial product use with changes in vaginal flora. Cultures of the cervical os were obtained in midcycle and during menstruation from 12 women who used napkins and 40 women who used tampons. Staphylococcus aureus was found during midcycle and menstruation in three women, during menstruation alone in six, and during midcycle alone in none, indicating a significant association of S. aureus with menstruation (p = 0.04). No difference was found in the rate of S. aureus colonization during menstruation in tampon users (18%) and napkin users (17%). In a similar study, cultures were taken for S. aureus and other aerobic bacteria from 58 tampon users and 25 users of sea sponges. Staphylococcal colonization was found to be increased during menstruation in both groups. Among the cultures done during menstruation, those from users of sea sponges were found to have significantly higher colonization rates with S. aureus, Escherichia coli and other Enterobacteriaceae. The association of sea sponges with a high rate of S. aureus colonization suggests that they are not an alternative to tampons for women seeking to decrease the risk of toxic shock syndrome.