| Popis: |
In this study, we have monitored the spatial distribution of S-phase cells during successive stages of normal feather morphogenesis using the specific marker BrdU. We also disturbed the development program by administration of hydrocortisone on the chorioallantoic membrane of 6.5-day chick embryos and examined the resulting pattern of BrdU incorporation. Our results show that a specific spatio-temporal pattern of cell proliferation occurs during successive stages of feather development and that this pattern accounts for the growth of feather buds according to the cephalocaudal orientation. Our experimental analysis showed that the stage-dependent alteration of feather morphogenesis (as shown by Züst, Ann. Embryol. Morphogen. 4, 1971 and confirmed by Démarchez et al., Dev. Biol. 106, 1984), is based on a stage-dependent alteration of the proliferation pattern in the epidermis. Forty-eight hours after treatment, non-induced epidermis ceases DNA synthesis and is unable to form placodes. Induced epidermis at the placodal and dermal condensation stages fails to produce the cohorts of S-phase cells responsible for the caudal outgrowth and the slanting shape of the buds. These young buds display anarchic proliferation in the whole epidermis possibly resulting in the appearance of "curly" feathers. Together, these results show the importance of the spatial pattern of ectodermal and mesodermal cell proliferation during the normal feather morphogenesis. Moreover, they corroborate the particular role of epidermis both in the establishment of feather rudiments and in the cephalocaudal orientation of the feathers. |
