Similarly, Hoxc10 is expressed in exponentially growing mouse C2C12 myoblasts; however, Hoxc10 protein was undetectable both in quiescent myoblasts after serum starvation and in differentiated myotubes. H0XC10 is degraded early in mitosis by the cell-cycle regulatory enzyme, anaphase-promoting complex, further indicating a role in cell-cycle progression and proliferation.
Together, these results indicate that H0XC10 is expressed not only during differentiation, as expected for a homeoprotein, but also in response to proliferative stimuli. H0XC10 may have a similar role in the early development of endometrium and endometrial proliferation. This hypothesis is supported by the high levels of H0XC10 expression that we detected in the proliferative phase as compared with the secretory phase in the endometrium. Similarly, H0XC11, H0XD10, and H0XD11 may be involved in proliferation rather than differentiation.
H0XC10, H0XC11, H0XD10, and H0XD11 expression is noted in the proliferative phase of the menstrual cycle, when estrogen is the predominant steroid hormone affecting the uterus.