Figure 5.

Complement component C3 and MAC/PF domain-containing proteins in Cnidaria. (a-e) In situ hybridization of C3-Am in Acropora. Expression first becomes apparent in scattered endodermal cells concentrated at the aboral end as the planula elongates from sphere to pear (a) and eventually to spindle (b). Endodermal expression continues post-settlement (c-e), becoming especially strong in the upper part of the polyp as it rises from the calcifying base (d). Post-settlement, the polyp consists of a series of hollow chambers interconnected beneath the mouth. The line of strong staining peripherally is the result of viewing the endoderm vertically, while elsewhere one is looking through the staining layer. (f) Domain map and presence (+)/absence (-) data for the various protein domains characteristic of complement C3 components in the Hydra, Nematostella and Acropora datasets. (g) In situ hybridization of the H. magnipapillata A2M-related gene. Hydra A2M-related transcripts are present in the endoderm along the whole body axis. Note that this Hydra gene lacks several of the C3-diagnostic domains that are present in the anthozoan C3s (see text). (h) Domain maps of major cnidarian MAC/PF proteins types. (i) Hydra Tx-60a in situ. The insert shows the sense control. (j) Hydra apextrin in situ. (k-o) Acropora apextrin in situ. Expression is first apparent in scattered ectodermal cells orally as the planula begins to elongate (k). At slightly later stages expression has spread toward the aboral end of the planula, still in scattered cells (l). As the elongation process continues, uniform strong expression is localized in all ectodermal cells in the oral two-thirds of the planula (m). The strong ectodermal expression is clearly apparent in this transilluminated transverse section cut from the central region of the planula (n). Following settlement, expression continues at the oral end of the planula, before frequently becoming limited to a narrow ring separating oral and aboral tissue (o).