9407216 Smith Embryonic development in marsupial and placental mammals differs in a number of ways, one of the most important being that marsupials are born at an essentially embryonic stage. In previous studies, the PI has examined the morphological consequences of this pattern, with focus on what morphological adaptations allow marsupials to survive at such a premature level. In these previous studies a number of hypotheses about significant differences in the way marsupial and placental mammals develop were presented. In the current study some of these hypotheses will be tested. These are three specific aims. Specific aim 1 will test the hypothesis that the growth and differentiation of the brain controls or constrains the development of neurocranial skeletal tissues. To this end the interface and interaction between neural and skeletal tissues will be examined in detail in a variety of morphological ways. Specific aims 2 will examine the differentiation of cranial skeletal tissues at a molecular level. A number of extracellular matrix proteins as well as bone specific molecules are important in accumulation of these molecules will be examined using in situ hybridization and immunocytochemistry. This study will provide information on the mechanisms of bone formation. Specific aim 3 will test the hypothesis that patterns of development observed in previously studied systems are characteristic for other placental and marsupial mammals with broad-based comparative studies of development in a variety of mammals. This study will provide information on the variation in the ways that the skull can develop in mammals. This project is expected to provide basic data on the interaction of tissues during embryonic development and on the constraints that these interactions place on the evolutionary diversification of the skull in mammals. ***
