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Bird embryos are exposed to maternal androgens deposited in the egg, but the role of these hormones in embryonic development and hatchling survival is unclear. To identify possible target organs, we used in situ hybridization to study the distribution of androgen receptor (AR) RNA in the developing zebra finch brain. The first brain expression domain of AR mRNA is in the hindbrain. From embryonic day 7 (E7) onward, when the hypoglossal motor nucleus (nXII) has just formed, there was AR mRNA expression in both its lingual (nXIII) and its tracheosyringeal (nXIIts) parts, and this was the major site of hindbrain expression at all embryonic stages and in both sexes. From E8 onward, we also found AR mRNA in the supraspinal motor nucleus (nSSp), which innervates neck muscles. Furthermore, the syrinx, the target of the nXIIts, contained AR mRNA by E10, localized principally in the perichondria. Muscle was first evident in the syringeal region at E9, but no AR was detected in syringeal muscles until after hatching. The expression pattern of AR in the zebra finch embryo suggests that maternal androgens act via AR in the brainstem and syrinx to influence hatching as well as acoustic and visual components of food-begging behavior. Maternal androgens seem unlikely to function in the development of sexual dimorphisms in the zebra finch nXIIts and syrinx, insofar as these are not evident until between 10 and 20 days posthatching. © 2002 Wiley-Liss, Inc.

The nonselective human corticotropin-releasing factor receptor 1 (hCRF-R1) and the ligand-selective Xenopus CRF-R1 (xCRF-R1) were compared. To understand the interactions of sauvagine and ovine CRF, both high-affinity ligands for hCRF-R1 but surprisingly weak ligands for xCRF-R1, chimeric receptors of hCRF-R1 and xCRF-R1 followed by double or multiple point mutations were constructed. Binding studies and cAMP assays demonstrated that the N-terminal domain exhibited the complete ligand selectivity of xCRF-R1. The important region was mapped between amino acids 70 and 89; replacement of amino acids Arg 76 , Asn 81 , Gly 83 , Leu 88 , and Ala 89 in hCRF-R1 with the corresponding amino acids of xCRF-R1 (Gln 76 , Gly 81 , Val 83 , His 88 , and Leu 89 ) resulted in a receptor that had ∼30-fold higher affinity for human/rat CRF than for sauvagine. Mutagenesis of these amino acids in xCRF-R1 to the human sequence completely abolished the ligand selectivity of xCRF-R1. Mutagenesis of amino acids 88 and 89 in hCRF-R1 or xCRF-R1 had only a minor (∼2.5-fold) effect on the ligand selectivity of the mutant receptor. Substitution of Arg 76 , Asn 81 , and Gly 83 in hCRF-R1 with the corresponding sequence of xCRF-R1 (Gln 76 , Gly 81 , and Val 83 ) resulted in a receptor with ∼11-fold higher affinity for human/rat CRF compared with ovine CRF or sauvagine. When only two of these three amino acids were mutated, no effect on the ligand selectivity was observed. On the basis of these data, it is suggested that amino acids 70–89 of CRF-R1 are important for the ligand binding site.