Abstract
During larval development in instar IV brine shrimp, segment 1 grew by cell replication and cell differentiation. Cell cycle analysis revealed that the cell cycle was synchronized with the molt cycle. Mitosis occurred late in the instar and S phase began at hr 6 of the following instar. Three populations of cells comprised the dorsal integument. The medialโdorsal region did not grow. Cell enlargement occurred in the dorsalโlateral population while cell replication took place in the lateral population. The limb bud (ventral surface) grew in width by replication in the distal population, and in height by enlargement of the general epidermal cells in the proximal population. Expansion of each region of the integument was proportional to the cell growth in that region. Moreover, both growth processes were dependent on the level of nutrients and were enhanced by diets enriched in polyunsaturated fatty acids. A nutrientโdependent growth control point occurred in the G1 period. The commitment to replication and differentiation occurred by hr 2 of instar IV. The findings show that integumental growth is a result of regionspecific cell growth processes which are controlled by nutrients during the G1 period. ยฉ 1995 WileyโLiss, Inc.