Force generation on the epithelial surface
Without the ability to orient mechanical forces and adjust the mechanical properties a an attempts to achieve multicellularity is destined to remain a one dimensional chain, a  two dimensional sheet, or three dimensional sphere of cells, depending on the orientation of cell division. The production of forces from individual cells allows a tissue to sculpt itself through tissue bending and elongation events. These mechanical events in conjunction with controlled cell death are what allow organisms to take the variety of shapes we see in multicellular organism on earth. Changes in the mechanical properties of a tissue also directly effect the prognosis of certain diseases, such as cancer. With the adherent functions of cell-cell junctions and their connection to thick bundles of actin filaments it is no wonder these structures were first studied as possible regulators of force generation at the apical surface of epithelial tissues. To fully understand the amazing process of development and to understand, treat, and prevent disease such as cancer, we need a comprehensive understanding of how epithelial sheets regulate their mechanics.
Circumferential actomyosin
A key mechanical change in epithelial cells during development is the constriction of the apical surface of cells. This constriction shrinks the apical surface which causes the tissue to bend in on itself which is a key step for gastrulation to form primary tissue layers of the organism and neurulation to form the spinal cord. Using electron microscopy early studies in frog, newt, and chick, showed evidence that circumferential actin filaments directly associated with adherens junctions were likely driving apical constriction during neurulation \cite{Baker_1967,Burnside1971,Karfunkel1972}. Later immunostaining work in brush border cells induced to apically constrict highlighted that myosin associated strongly with cell edges before and after apical constriction \cite{Hirokawa1983}.  Using quick freeze deep etch electron microscopy Hirokawa and colleges most convincingly that in brushed border cells also apically constrict by squeezing in the adherens junctions first, leaving their apical surfaces bulging out \cite{Hirokawa1983}.  The contractile nature of the circumferential actomyosin network was demonstrated by islolating  the actomyosin apparatus from chicken epithelial cells. Upon addition of ATP to the purified actomyosin apparatuses the rings of actomyosin constricted \cite{Owaribe1982}.  Additional work on embryoing tissue wounds demonstrated the importance of supracellular junctional cables that from to close the wound via a purse string constriction method \cite{Martin1992} \cite{Nodder1997}. With all of this evidence it should not be surprising that the circumferential actomyosin was thought to be the only contributor epithellial mechanics for over 50 years.