Mouse Eya genes are expressed during limb tendon development and encode a transcriptional activation function

Vertebrate limb tendons are derived from connective cells of the lateral plate mesoderm. Some of the developmental steps leading to the formation of vertebrate limb tendons have been previously identified; however, the molecular mechanisms responsible for tendinous patterning and maintenance during embryogenesis are largely unknown. The eyes absent (eya) gene of Drosophila encodes a novel nuclear protein of unknown molecular function. Here we show that Eya1 and Eya2, two mouse homologues of Drosophila eya, are expressed initially during limb development in connective tissue precursor cells. Later in limb development, Eya1 and Eya2 expression is associated with cell condensations that form different sets of limb tendons. Eya1 expression is largely restricted to flexor tendons, while Eya2 is expressed in the extensor tendons and ligaments of the phalangeal elements of the limb. These data suggest that Eya genes participate in the patterning of the distal tendons of the limb. To investigate the molecular functions of the Eya gene products, we have analyzed whether the highly divergent PST (proline-serine-threonine)-rich N-terminal regions of Eya1–3 function as transactivation domains. Our results demonstrate that Eya gene products can act as transcriptional activators, and they support a role for this molecular function in connective tissue patterning.

The notion of the Cambrian pananimalia genome.

The toil by photosynthesizing cyanobacteria and blue-green algae of nearly three billion years appeared to have finally resulted in the sufficient accumulation of molecular oxygen. So, the stage was set for the emergence, at the ocean bottom, of diverse animals that were consumers of molecular oxygen. It now appears that this Cambrian explosion, during which nearly all the extant animal phyla have emerged, was of an astonishingly short duration, lasting only 6-10 million years. Inasmuch as only a 1% DNA base sequence change is expected in 10 million years under the standard spontaneous mutation rate, I propose that all those diverse animals of the early Cambrian period, some 550 million years ago, were endowed with nearly identical genomes, with differential usage of the same set of genes accounting for the extreme diversities of body forms. Some of the more pertinent genes that are thought to be included in the Cambrian pananimalia genome are as follows. (i) A gene for lysyloxidase that, in the presence of molecular oxygen, crosslinked collagen triple helices to produce ligaments and tendons, thus contributing to the stout bodies of the Cambrian animals. (ii) Genes for hemoglobin; these internal transporters of molecular oxygen are today seen sporadically in members of diverse animal phyla. (iii) The Pax-6 gene for eye formation; the eyes of a ribbon worm to a human are organized by this gene. In animals without eyes, the same gene organizes other sensory systems and organs. (iv) A series of Hox genes for the anterior-posterior (cranio-caudal) body plans: these genes are also present in all phyla of the kingdom Animalia.