Most degenerative diseases begin with a gradual loss of specific cell types before reaching a threshold for symptomatic onset. However, the endogenous regenerative capacities of different tissues are difficult to study, because of the limitations of models for early stages of cell loss. Therefore, we generated a transgenic mouse line (Mos-iCsp3) in which a lox-mismatched Cre/lox cassette can be activated to produce a drug-regulated dimerizable caspase-3. Tissue-restricted Cre expression yielded stochastic Casp3 expression, randomly ablating a subset of specific cell types in a defined domain. The limited and mosaic cell loss led to distinct responses in 3 different tissues targeted using respective Cre mice: reversible, impaired glucose tolerance with normoglycemia in pancreatic ? cells; wound healing and irreversible hair loss in the skin; and permanent moderate deafness due to the loss of auditory hair cells in the inner ear. These mice will be important for assessing the repair capacities of tissues and the potential effectiveness of new regenerative therapies.
For more than 140 years, pollen tube guidance in flowering plants has been thought to be mediated by chemoattractants derived from target ovules. However, there has been no convincing evidence of any particular molecule being the true attractant that actually controls the navigation of pollen tubes towards ovules. Emerging data indicate that two synergid cells on the side of the egg cell emit a diffusible, species-specific signal to attract the pollen tube at the last step of pollen tube guidance. Here we report that secreted, cysteine-rich polypeptides (CRPs) in a subgroup of defensin-like proteins are attractants derived from the synergid cells. We isolated synergid cells of Torenia fournieri, a unique plant with a protruding embryo sac, to identify transcripts encoding secreted proteins as candidate molecules for the chemoattractant(s). We found two CRPs, abundantly and predominantly expressed in the synergid cell, which are secreted to the surface of the egg apparatus. Moreover, they showed activity in vitro to attract competent pollen tubes of their own species and were named as LUREs. Injection of morpholino antisense oligomers against the LUREs impaired pollen tube attraction, supporting the finding that LUREs are the attractants derived from the synergid cells of T. fournieri.
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