Two clearly opposing views exist on the function of alpha-fetoprotein (AFP), a fetal plasma protein that binds estrogens with high affinity, in the sexual differentiation of the rodent brain. AFP has been proposed to either prevent the entry of estrogens or to actively transport estrogens into the developing female brain. The availability of Afp mutant mice (Afp(-/-)) now finally allows us to resolve this longstanding controversy concerning the role of AFP in brain sexual differentiation, and thus to determine whether prenatal estrogens contribute to the development of the female brain. Here we show that the brain and behavior of female Afp(-/-) mice were masculinized and defeminized. However, when estrogen production was blocked by embryonic treatment with the aromatase inhibitor 1,4,6-androstatriene-3,17-dione, the feminine phenotype of these mice was rescued. These results clearly demonstrate that prenatal estrogens masculinize and defeminize the brain and that AFP protects the female brain from these effects of estrogens.

We report the construction of the first complete genetic linkage map of the laboratory rat. By testing 1171 simple sequence length polymorphisms (SSLPs), we have identified 432 markers that show polymorphisms between the SHR and BN rat strains and mapped them in a single (SHR x BN) F2 intercross. The loci define 21 large linkage groups corresponding to the 21 rat chromosomes, together with a pair of nearby markers on chromosome 9 that are not linked to the rest of the map. Because 99.5% of the markers fall into one of the 21 large linkage groups, the maps appear to cover the vast majority of the rat genome. The availability of the map should facilitate whole genome scans for genes underlying qualitative and quantitative traits relevant to mammalian physiology and pathobiology.

The kidney has an important role in the regulation of acid-base homeostasis. Renal ammonium production and excretion are essential for net acid excretion under basal conditions and during metabolic acidosis. Ammonium is secreted into the urine by the collecting duct, a distal nephron segment where ammonium transport is believed to occur by non-ionic NH(3) diffusion coupled to H(+) secretion. Here we show that this process is largely dependent on the Rhesus factor Rhcg. Mice lacking Rhcg have abnormal urinary acidification due to impaired ammonium excretion on acid loading-a feature of distal renal tubular acidosis. In vitro microperfused collecting ducts of Rhcg(-/-) acid-loaded mice show reduced apical permeability to NH(3) and impaired transepithelial NH(3) transport. Furthermore, Rhcg is localized in epididymal epithelial cells and is required for normal fertility and epididymal fluid pH. We anticipate a critical role for Rhcg in ammonium handling and pH homeostasis both in the kidney and the male reproductive tract.

We report characterization of a novel isoform of lysyl hydroxylase (lysyl hydroxylase 3, LH3). The cDNA clones encode a polypeptide of 738 amino acids, including a signal peptide. The amino acid sequence has a high overall identity with LH1 and LH2, the isoforms characterized earlier. Conserved regions are present in the carboxyl-terminal portion of the isoforms and also in the central part of the molecules. Histidine and asparagine residues, which are conserved in the other isoforms and are known to be required for enzymatic activity, are also conserved in the novel isoform. The gene for LH3 (PLOD3) has been assigned to human chromosome 7q36 and rat chromosome 12. Gene expression of LH3 is highly regulated in adult human tissues. A strong hybridization signal, corresponding to an mRNA 2.75 kilobases in size, is obtained in heart, placenta and pancreas on multiple tissue RNA blots. Expression of the cDNA in vitro results in the synthesis of a protein that hydroxylates lysyl residues in collagenous sequences in a nontriple helical conformation.Collagen is a group of structural proteins that are found essentially in all tissues. To date, 19 different collagen types have been identified that participate in the assembly of various kinds of polymers in the extracellular matrix (1-4). Collagens form the structural building blocks of tissues, but it is also clear that they have important regulatory functions. Some collagens form scaffolds that keep cells in place within tissues, connect tissues within an organ, and facilitate attachment and migration of cells. Collagens can also form links between cells and matrices, and some regulate the assembly and properties of the scaffold-forming collagens (5). Recent reports indicate that collagen can directly serve as a ligand for receptor tyrosine kinases and, as a consequence of binding to the receptor, induces a cascade of phosphorylation in cells (6, 7).The biosynthesis of collagens includes several posttranslational modifications, one of which is hydroxylation of lysyl residues. Hydroxylysine occurs in the Y position of the repeating X-Y-Gly triplets within the helical region of the collagen molecule. Hydroxylysine also occurs in the sequence of nonhelical telopeptide regions of some collagen molecules, when glycine is replaced by either serine or alanine (1, 2,8). The amount of the hydroxylysyl residues varies considerably between different collagen types. Variation is also found within the same collagen type in different tissues and even within the same tissues in different physiological and pathological states (1, 2,8). In addition to collagens, hydroxylysine residues are found in some other proteins, these include C1q complement, acetylcholinesterase, mannose-binding proteins, bovine conglutinin, and anglerfish somatostatin 28. It should be noted, however, that all these proteins, with the exception of somatostatin 28, contain collagenous domains in their structure (1). Hydroxylysyl residues may be glycosylated to form galactosylhydroxylysyl or glucosylgalactosylhydrox...

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