Question

1/ a/ Describe the characteristics of true multicellularity in animals. Your answer should include: collagen (what is it, what does it do, etc.), gap junctions vs tight junctions, cell differentiation, totipotency and more.

b/ To what extent are the characteristics of multicellularity given in part a shown by Volvox, sponges and cnidarians?

Answer 1

a) Multicellular organisms differ from each other with respect to the types of embryonic development and differentiation. For instance, by definition every multicellular organism possesses multiple cells that remain associated following cell division. But while plant and animal species generate at least a dozen different types of cells, with groups of cells organized into tissues and organs.

Extracellular matrix (ECM) is an essential component of the cells and it was pivotal during the transition of unicellular organisms to multicellular animals (metazoans). The ECM comprises a basement membrane (BM) that underlies epithelia cells, and an interstitial matrix (IM) that is positioned between cells in the intercellular spaces and undergoes continuous controlled remodeling . Yet, a major gap in cell biology is to understand how cells generate and interact with the ECM.

Collagen protein superfamily is a major component of ECMs. In vertibrates it comprises of a total 28 types (I–XXVIII) that are derived from a total of 46 α-chains across the superfamily.

b) Simpler multicellular organisms, such as sponges, volvox and cnidarians possess less number of cell types and do not produce tissues or organs. Furthermore, animal embryos undergo gastrulation, a process by which groups of cells migrate or change position with respect to each other, but plant embryos do not. It turns out there are many different ways to be multicellular.