Meeting Abstract
Choanocytes are the iconic feeding cells in sponges and are one of their most well studied cell types, yet surprisingly little is known about how they form. Our studies of glass sponges, which lack conventional choanocytes, prompted us to re-assess choanocyte chamber formation and function. In freshwater demosponges, a more readily studied model, choanocyte flagella beat to draw water through canals for food, respiration and evacuation of wastes. Highly proliferative cells maintain choanocyte chambers, yet choanocytes are seldom caught in the act of mitosis. We studied choanocyte formation in small freshwater sponges using time-lapse photography. In Spongilla lacustris a founding cell divides 4-5 times, producing 30-50 choanocytes. Chambers start by division of a founder cell, but thereafter, surprisingly, small mobile cells wandering through the mesohyl stop, change direction, and enter an existing choanocyte chamber then differentiating into choanocytes, becoming part of the choanocyte chamber as ‘immigrant choanocytes.’ We propose that feeding chambers form through similar processes across sponge groups, but that choanocyte chambers add new choanocytes through a variety of different processes. This discovery has implications regarding our understanding of the choanocyte lineage and the potential for cell differentiation in early metazoans.
