Temporal control of development is an important aspect of pattern formation that awaits complete molecular analysis. We identified lin-57 as a member of the C. elegans heterochronic gene pathway, which ensures that postembryonic developmental events are appropriately timed. Loss of lin-57 function causes the hypodermis to terminally differentiate and acquire adult character prematurely. lin-57 ...

Mitochondrial DNA from the extinct dusky seaside sparrow (Ammodramus maritimus nigrescens) was compared in terms of nucleotide sequence divergence to mitochondrial DNAs from extant populations of seaside sparrows. Analyses of restriction sites revealed a close phylogenetic affinity of A. m. nigrescens to other sparrow populations along the Atlantic coast of the United States but considerable ge...

Tissue from the lower intestine of two species of sparrow, the house sparrow Passer domesticus and savannah sparrow Passerculus sandwichensis was sectioned in an unbiased manner and examined quantitatively using stereology. The tissue was processed for light microscopy, and scanning and transmission electron microscopy to examine the extent to which microvilli enhanced the epithelial surface ar...

Gambel's white-crowned sparrow, Zonotrichia leucophrys gambelii, is a long-distance migrant that, in contrast to other subspecies of white-crowned sparrow, does not form vocal dialects. I studied the process of vocal development in the field and laboratory to determine how it differed from the process in three other subspecies previously studied. Four common song types existed in a random spati...

Neural progenitors alter their output over time to generate different types of neurons and glia in specific chronological sequences, but this process remains poorly understood in vertebrates. Here we show that Casz1, the vertebrate ortholog of the Drosophila temporal identity factor castor, controls the production of mid-/late-born neurons in the murine retina. Casz1 is expressed from mid/late ...