Leys Sally P, Eerkes-Medrano Dafne I
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G 2E9.
Biol Bull. 2006 Oct;211(2):157-71. doi: 10.2307/4134590.
Sponges are considered to be filter feeders like their nearest protistan relatives, the choanoflagellates. Specialized "sieve" cells (choanocytes) have an apical collar of tightly spaced, rodlike microvilli that surround a long flagellum. The beat of the flagellum is believed to draw water through this collar, but how particles caught on the collar are brought to the cell surface is unknown. We have studied the interactions that occur between choanocytes and introduced particles in the large feeding chambers of a syconoid calcareous sponge. Of all particles, only 0.1-microm latex microspheres adhered to the collar microvilli in large numbers, but these were even more numerous on the choanocyte surface. Few large particles (0.5- and 1.0-microm beads and bacteria) contacted the collar microvilli; most were phagocytosed by lamellipodia at the lateral or apical cell surface, and clumps of particles were engulfed by pseudopodial extensions several micrometers from the cell surface. Although extensions of the choanocyte apical surface up to 16 microm long were found, most were 4 microm long, twice the height of the collar microvilli. These observations offer a different view of particle uptake in sponges, and suggest that, at least in syconoid sponges, uptake of particles is less dependent on the strictly sieving function of the collar microvilli.
海绵动物被认为像它们亲缘关系最近的原生生物近亲领鞭毛虫一样是滤食性动物。特化的“筛”细胞（领细胞）有一个顶端环，由紧密排列的杆状微绒毛组成，围绕着一条长鞭毛。据信鞭毛的摆动会使水通过这个环，但捕获在环上的颗粒是如何被带到细胞表面的尚不清楚。我们研究了在一种樽海绵钙质海绵的大型进食腔中领细胞与引入的颗粒之间发生的相互作用。在所有颗粒中，只有0.1微米的乳胶微球大量附着在环微绒毛上，但在领细胞表面上这些微球数量更多。很少有大颗粒（0.5微米和1.0微米的珠子以及细菌）接触到环微绒毛；大多数被位于细胞侧面或顶端表面的片状伪足吞噬，并且颗粒团被距离细胞表面几微米处的伪足延伸部分吞噬。虽然发现领细胞顶端表面的延伸部分长达16微米，但大多数为4微米长，是环微绒毛高度的两倍。这些观察结果为海绵动物摄取颗粒提供了不同的观点，并表明，至少在樽海绵中，颗粒摄取较少依赖于环微绒毛严格的筛分功能。
