Micrognathia is a severe craniofacial deformity affecting appearance and survival. Previous studies revealed that multiple factors involved in the osteogenesis of mandibular bone have contributed to micrognathia, but concerned little on factors other than osteogenesis. In the current study, we found that ectopic activation of Fgf8 by Osr2-cre in the presumptive mesenchyme for masseter tendon in mice led to micrognathia, masseter regression, and the disrupted patterning and differentiation of masseter tendon. Since Myf5-cre;Rosa26R-Fgf8 mice exhibited the normal masseter and mandibular bone, the possibility that the micrognathia and masseter regression resulted directly from the over-expressed Fgf8 was excluded. Further investigation disclosed that a series of chondrogenic markers were ectopically activated in the developing Osr2-cre;Rosa26R-Fgf8 masseter tendon, while the mechanical sensing in the masseter and mandibular bone was obviously reduced. Thus, it suggested that the micrognathia in Osr2-cre;Rosa26R-Fgf8 mice resulted secondarily from the reduced mechanical force transmitted to mandibular bone. Consistently, when tenogenic or myogenic components were deleted from the developing mandibles, both the micrognathia and masseter degeneration took place with the decreased mechanical sensing in mandibular bone, which verified that the loss of mechanical force transmitted by masseter tendon could result in micrognathia. Furthermore, it appeared that the micrognathia resulting from the disrupted tenogenesis was attributed to the impaired osteogenic specification, instead of the differentiation in the periosteal progenitors. Our findings disclose a novel mechanism for mandibular morphogenesis, and shed light on the prevention and treatment for micrognathia.

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The application of a pulse radar in anechoic chamber imaging is a new way to obtain the electromagnetic characteristics of targets. However, the limited size of an anechoic chamber causes the coupling between the transmitted signal and echo so the target image cannot be accurately achieved. To solve this problem, an imaging method using a pulse radar in an anechoic chamber based on an amplitude modulation design is proposed in this paper. Firstly, amplitude modulation is performed to solve the coupling of the transmitted signal and echo. In order to cancel the false targets in the target image after the amplitude modulation, different amplitude modulation sequences are designed. Secondly, echo processing based on the designed amplitude modulation is discussed to obtain the target image. Simulations and experiments are conducted and the results show that the proposed amplitude design and echo processing method can accurately obtain the target image in an anechoic chamber.

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