Supplementary File 7.fasta from Novel protein from larval sponge cells, Ilborin, is related to energy turnover, calcium binding and is conserved among marine invertebrates

Sponges (phylum Porifera) are early-branching animals, whose outwardly simple body plan is underlain by a complex genetic repertoire. The transition from a mobile larva to an attached filter-feeding organism occurs by metamorphosis, a process accompanied by a radical change of the body plan and cell transdifferentiation. The continuity between larval cells and adult tissues is still obscure. In a previous study, we have produced polyclonal antibodies against the major protein of the flagellated cells covering the larva of the sponge Halisarca dujardinii, used them to trace the fate of these cells and shown that the larval flagellated cells transdifferentiate into the choanocytes. In the present work, we identified the sequence of this novel protein, which we named Ilborin. A search in the open databases showed that multiple orthologues of the newly identified protein were present in sponges, cnidarians, flatworms, ctenophores and echinoderms, but none of them has been described yet. Ilborin has two conservative domains: triosephosphate isomerase-barrel, which has enzymatic activity against macroergic compounds, and canonical EF-hand, which binds calcium. mRNA of Ilborin is expressed in the larval flagellated cells. We suggest that the new protein is involved in the calcium-mediated regulation of energy metabolism, whose activation precedes metamorphosis.

多孔动物门（Porifera）海绵是早期分化的动物类群，其外观简洁的身体构型背后，蕴藏着一套复杂的遗传储备。该类群从可移动的幼体到固着滤食性成体的转变，通过变态发育完成——这一过程伴随身体构型的剧烈重塑与细胞转分化。目前，幼体细胞与成体组织之间的细胞连续性仍不明确。在既往研究中，我们针对海绵Halisarca dujardinii幼体表面鞭毛细胞的主要蛋白制备了多克隆抗体，利用该抗体追踪此类细胞的命运，并证实幼体鞭毛细胞可转分化为领细胞（choanocytes）。本研究中，我们鉴定出该新型蛋白的编码序列，并将其命名为Ilborin。对公开数据库的检索结果显示，海绵、刺胞动物、扁形动物、栉水母动物与棘皮动物中均存在该新鉴定蛋白的多个直系同源基因，但此前均未被报道。Ilborin包含两个保守结构域：其一为具有针对高能化合物酶促活性的磷酸丙糖异构酶桶状结构域（triosephosphate isomerase-barrel），其二为可结合钙离子的经典EF-hand结构域（EF-hand）。Ilborin的mRNA在幼体鞭毛细胞中表达。我们推测，该新型蛋白参与钙离子介导的能量代谢调控，这一调控通路的激活发生于变态发育之前。