Regulation of Cell Expansion

With the mounting evidence for subcellular hormone receptor sites and evidence for tissue and sometimes cellular specificity of certain plant hormone effects, it seems clear that the resolution of fundamental problems associated with plant growth and development will require an understanding of the processes of expansion, division, and differentiation at the cellular level. Nevertheless, it is often necessary and sometimes easier to study these processes as they occur in complex tissues. In this chapter the emphasis will be on the hormonal regulation of cell development, while recognizing that the processes involved are strongly influenced by both the physical constraints and metabolic activities of neighboring cells in complex tissues. 

The T-lymphocyte receptor (TCR) is involved in detection of foreign antigens, presented together with the major histocompatibility complex (MHC). Subsequendy, it regulates the clonal expansion of T cells. 

As compared to DCs, B cells are very poor APCs and play a major role as source for antibodies. Upon stimulation by antigens and in the presence of T cells at the border of the T-cell-B-cell area, adjacent to follicles, B cells become antibody-secreting cells and eventually form a germinal center (GC) response. GCs are specialized follicles for B-cell expansion, somatic hypermutation, and class switch recombination, processes that are regulated by T cells, follicular DCs, and other cells. In this process of B-cell maturation, Tregs seem to play a critical role, as in several immune diseases, which are characterized by aberrant antibody... 

It has become Increasingly obvious to us that regulation of water balance In Insects Is one of the keys to the success of these animals In their adaptation to such a wide variety of habitats. The complexities Involved In undertaking studies of such systems may require expansion of our Interdisciplinary approach so as to Include such diverse fields as biophysics, ecology, and cell biology. The subject Is a fascinating one, perhaps all the more so due to Its complexity, and promises to open up new areas In which Interdisciplinary research will play a role. 

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