The diversity in colour patterns on butterfly wings provides great potential for understanding how developmental mechanisms may be modulated in the evolution of adaptive traits. In particular, we discuss concentric eyespot patterns, which have been shown by surgical experiments to be formed in response to signals from a central focus. Seasonal polyphenism shows how alternate phenotypes can develop through environmental sensitivity mediated by ecdysteroid hormones, whereas artificial selection and single gene mutants demonstrate genetic variation influencing the number, shape, size, position, (...) and colour composition of the eyespots. The expression patterns of the regulatory gene Distal-less reveal that these changes can arise at several different developmental stages, and the phenotypes indicate that some forms of changed pattern may occur much more readily than others. Further study of the genes, of the developmental mechanisms, and of the functions of the patterns will provide novel insights about the evolution of morphological diversity. BioEssays 21:391–401, 1999. © 1999 John Wiley & Sons, Inc. (shrink)

Fibroblast growth factors (FGFs) comprise a large family of developmental and physiological signaling molecules. All FGFs have a high affinity for the glycosaminoglycan heparin and for cell surface heparan sulfate proteoglycans. A large body of biochemical and cellular evidence points to a direct role for heparin/heparan sulfate in the formation of an active FGF/FGF receptor signaling complex. However, until recently there has been no direct demonstration that heparan is required for the biological activity of FGF in a developmental system in (...) vivo. A recent paper by Lin et al.(1) has broken through this barrier to demonstrate that heparan sulfate is essential for FGF function during Drosophila development. The establishment of a role for heparan sulfate in FGFR activation in vivo suggests that tissue-specific differences in the structure of heparan may modulate the activity of FGF. BioEssays 22:108–112, 2000. ©2000 John Wiley & Sons, Inc. (shrink)

Fibroblast growth factors (FGFs) comprise a large family of developmental and physiological signaling molecules. All FGFs have a high affinity for the glycosaminoglycan heparin and for cell surface heparan sulfate proteoglycans. A large body of biochemical and cellular evidence points to a direct role for heparin/heparan sulfate in the formation of an active FGF/FGF receptor signaling complex. However, until recently there has been no direct demonstration that heparan is required for the biological activity of FGF in a developmental system in (...) vivo. A recent paper by Lin et al.(1) has broken through this barrier to demonstrate that heparan sulfate is essential for FGF function during Drosophila development. The establishment of a role for heparan sulfate in FGFR activation in vivo suggests that tissue-specific differences in the structure of heparan may modulate the activity of FGF. BioEssays 22:108–112, 2000. ©2000 John Wiley & Sons, Inc. (shrink)

Immunofluorescent labelling demonstrates that human metaphase chromosomes contain hyperacetylated histone H4. With the exception of the inactive X chromosome in female cells, where the bulk of histone H4 is under‐acetylated, H4 hyperacetylation is non‐uniformly distributed along the chromosomes and clustered in cytologically resolvable chromatin domains that correspond, in general, with the R‐bands of conventional staining. The strongest immunolabelling is often found in T‐bands, the subset of intense R‐bands having the highest GC content. The majority of mapped genes also occurs in (...) R‐band regions, with the highest gene density in T‐bands. These observations are consistent with a model in which hyperacetylation of histone H4 marks the position of potentially active gene sequences on metaphase chromosomes. Since acetylation is maintained during mitosis, progeny cells receive an imprint of the histone H4 acetylation pattern that was present on the parental chromosomes before cell division. Histone acetylation could provide a mechanism for propagating cell memory, defined as the maintenance of committed states of gene expression through cell lineages. (shrink)