Diagnostic contribution of individual components of adrenal function tests to diagnose canine hyperadrenocorticism.

There is limited information regarding the value of constitutive components of the ACTH stimulation test (ACTHST) and low-dose dexamethasone suppression test (LDDST) including serum baseline cortisol (BC), difference between post-ACTH stimulation cortisol (PC) and BC (ΔACTHC), cortisol concentration 4h after dexamethasone administration (4HC), difference between 4HC and BC (Δ4C), and the difference between cortisol concentration 8h after dexamethasone administration and 4HC (Δ8C). Therefore, the objective of this study was to determine if these components can predict hyperadrenocorticism, pituitary-dependent hyperadrenocorticism (PDH), or functional adrenocortical tumor (FAT) in dogs. Cortisol concentrations were normalized, as fold change (FC), to the PC reference interval upper limit. A total of 1267 dogs were included, with hyperadrenocorticism diagnosed in 537 (PDH, n=356; FAT, n=28; undetermined, n=153) and excluded in 730. The area under the receiver operating curves for BC, ΔACTHC, 4HC, Δ4C, and Δ8C to predict hyperadrenocorticism were 0.76 (95% confidence interval (CI), 0.73-0.79), 0.91 (95% CI, 0.89-0.93), 0.83 (95% CI, 0.80-0.87), 0.55 (95% CI, 0.50-0.60), and 0.67 (95% CI, 0.62-0.72), respectively. A diagnostic limit of ≥0.78 FC for ΔACTHC had excellent sensitivity (1.00; 95% CI, 0.74-1.00), but poor specificity (0.67; 95% CI, 0.64-0.71), to predict FAT in dogs with a positive ACTHST. A diagnostic limit of ≥-0.26 FC for Δ4C had excellent sensitivity (1.00; 95% CI, 0.79-1.00), but poor specificity (0.21; 95% CI, 0.18-0.26), to predict FAT in dogs with a positive LDDST. In hyperadrenocorticoid dogs that have positive ACTHST or LDDST results, ΔACTHC or Δ4C, respectively, could be used to exclude FAT.

The use of abbreviations in surgical note keeping.

Abbreviations are used to improve the speed of note keeping and to simplify patient notes. However studies have shown that they can reduce clarity, increase mistakes and cause confusion in management plans. Our review highlights the misuse of abbreviations in surgical note keeping.

Bull spermatozoa express receptors for platelet-activating factor

Platelet-activating factor (PAF; 1-O-Alkyl-2-acetyl-sn-glycero-3-phosphorylcholine) is a ubiquitous phospholipid that is implicated in the mediation of a wide variety of reproductive processes. To better understand the role of PAF in bovine reproduction, it was designed experiments to: (a) determine whether bull spermatozoa express receptors for PAF and (b) study the effect of exogenous PAF on in vitro sperm physiology (i.e., capacitation, acrosome reaction, motility, and fertilizing ability). Bull sperm express PAF receptor as determined by two approaches: RT-PCR and immunofluorescence. However, exposure of spermatozoa to different concentrations of exogenous PAF (10-11-10-6 M) did not affect capacitation, acrosome reaction or motility. Consistent with these findings, coculture of gametes in medium containing increasing concentrations of PAF (1 x 10-8-8 x 10-6 M) did not improve in vitro fertilization outcome as measured by percentage of inseminated oocytes reaching 2-cell stage 48 h after fertilization. In contrast, PAF at 8 x 10-6 M concentration significantly inhibited IVF. In conclusion, although bull sperm have PAF receptors, exposure of bull spermatozoa to exogenous PAF failed to enhance the sperm function parameters measured in this study. Additional studies are warranted to elucidate the biological role of PAF on bull spermatozoa.

El factor activador de plaquetas (PAF; del inglés Platelete Activating Factor; 1-O-Alkyl-2-acetyl-sn-glycero-3-phosphorylcholine) es un fosfolípido ampliamente distribuido que participa como mensajero mediador en diferentes procesos reproductivos. Para comprender mejor la participación del PAF en la fisiología espermática bovina se diseñaron experimentos para: (a) determinar si los espermatozoides de toro expresan receptores para PAF y (b) estudiar el efecto del PAF sobre el comportamiento de los espermatozoides bovinos in vitro (capacitación, reacción acrosomal y capacidad fertilizante). De acuerdo a los resultados obtenidos por RT-PCR e inmunofluorescencia, los espermatozoides de toro expresan receptores para PAF. Sin embargo, la exposición de los espermatozoides a concentraciones crecientes de PAF exógeno (10-11-10-6 M) no afectó la capacitación, reacción de acrosoma ni la motilidad. En concordancia con estos hallazgos, el cocultivo de gametas (ovocitos y espermatozoides) en medio al cual se le había adicionado PAF (1 x 10-8-8 x 10-6 M) no mejoró la tasa de fertilización medida como el porcentaje de ovocitos inseminados que alcanzaron el estadio de 2 células 48 hs después de la inseminación. Por el contrario, PAF a una concentración de 8 x 10-6 M inhibió significativamente la tasa de fertilización. En conclusión, a pesar de que los espermatozoides bovinos poseen receptores para PAF, el agregado de PAF al medio de cultivo no mejora las funciones espermáticas examinadas en el presente trabajo. Otros estudios serán necesarios para dilucidar la participación del PAF en la fisiología espermática del toro.

Disseminated melanoma in a dog with involvement of leptomeninges and bone marrow.

An 11-year-old, Black and Tan Coonhound dog was presented with a history of lameness of the right hind leg for 2 months, osteolysis in the right distal femur, a pulmonary mass, and a presumptive diagnosis of osteosarcoma. By cytologic examination, neoplastic melanocytes were noted from fine needle aspirates of the femoral and pulmonary masses. Postmortem examination revealed a disseminated melanoma involving the right femoral bone marrow, lung, multiple lymph nodes, and adrenal gland, with diffuse infiltration of the leptomeninges of the brain and spinal cord. This case report describes a unique presentation of canine melanoma, which in some ways resembles leptomeningeal melanomatosis, a rare human melanoma variant.

The TATA motif is a target for efficient transcriptional activation and nerve growth factor induction of the peripherin gene.

Three proximal elements, PER1, PER2, and PER3, have been implicated in the regulation of peripherin gene expression. PER1 contains the TATA motif and was identified as the principal mediator of neuronal specificity. Here, we demonstrate by transfection of constructs mutated in PER1 that the in vitro protein binding activity of PER1 is irrelevant to its function. However, mutations or substitutions in the TATA box decreased promoter activity by up to 80%. We have investigated this unusual preference for a particular TATA sequence in PC12 cells. In these cells, nerve growth factor induces neuronal differentiation, increasing peripherin gene expression 3-4-fold, while dexamethasone elicits chromaffin differentiation and a 3-fold decrease in peripherin mRNA. Experiments with stably transfected PC12 cells revealed that the specific TATA box of the peripherin gene was crucial for nerve growth factor response. However, it did not affect dexamethasone down-regulation. Therefore, nerve growth factor acts through an element essential for neuronal peripherin gene expression. The results predict that proteins interacting in the vicinity of the TATA box, by inference factors associated with the preinitiation complex, are important for peripherin gene regulation and provide new insights into the mechanisms underlying neuronal differentiation.

Transgenic mice bearing the polyomavirus large T antigen directed by 2.1 kb of the keratin 19 promoter develop bronchiolar papillary tumors with progression to lung adenocarcinomas.

Keratin 19 is an intermediate filament protein produced by cells of simple epithelia and basal cells of stratified epithelia of different organs. These cell types are associated with important human cancers. We have used the keratin 19 promoter to target the expression of the polyomavirus (Py) large T-antigen, an immortalizing oncogene known to bind to the tumor suppressor retinoblastoma gene product, to epithelial cells. Individuals of the transgenic mouse line K19PyLT-6 developed one or two nodules in one of their lungs. By histology, the nodules were papillary tumors that consisted of nonciliated epithelial cells of the terminal bronchioles. In addition, infiltrates emanating from the nodules were consistent with the development of pulmonary adenocarcinomas. In situ hybridization techniques demonstrated large T-antigen expression in the tumors. Primary cultures were established from a lung tumor dissected from a K19PyLT-6 transgenic mouse. These large T-antigen-expressing cell lines produced the keratin proteins reminiscent of the epithelial origin of the lung tumor. However, further molecular studies indicated that these cell lines did not express Clara cells or pneumocytes markers. s.c. injection of the cell lines into nontransgenic syngeneic mice produced tumors in 2 weeks that resembled malignant pulmonary adenocarcinomas. These animals, which display tumor progression in situ, and the cell lines derived thereof provide a useful system for the study of lung tumorigenesis.

Cloning and identification of genes differentially expressed in metastatic and non-metastatic rat rhabdomyosarcoma cell lines.

The objective of this study was to identify genes involved in invasion and metastasis using a rat rhabdomyosarcoma model (SMF-A and RMS-B cell lines). The SMF-A cell line was established from a metastatic nodule of an induced rhabdomyosarcoma in syngeneic F344 rats. Two cell lines with defined metastatic potentials, SMF-Ai and SMF-Da, were cloned from the SMF-A line. The cell line SMF-Ai is tumorigenic, highly invasive and highly metastatic. On the other hand, the revertant line SMF-Da is less tumorigenic, non-invasive and non-metastatic. We have isolated from a SMF-Ai cDNA library eight cDNA clones which are differentially expressed by the metastatic SMF-Ai and the non-metastatic SMF-Da cell line using Northern blot analysis. Five of these clones, smf-4, smf-6, smf-41, smf-42 and smf-44, are overexpressed in the SMF-Da cell line and have homology with beta-2-microglobulin, lactate dehydrogenase, ribosomal protein L38, ribosomal protein S4 and acidic ribosomal phosphoprotein P1, respectively. The three other clones, smf-7, smf-40 and smf-61, are overexpressed in SMF-Ai. Clones smf-40 and smf-61 show significant homology with the human TB3-1 gene and the human fus gene respectively. The clone smf-7 has no significant homology with known sequences. We also analyzed the expression of these clones in other rat rhabdomyosarcoma cell lines (RMS-B and their clones) and in tumors obtained by injection of these cell lines into rats or nude mice. Smf-61 and smf-7 were the only clones with a differential expression pattern associated with the invasive or metastatic potential of all cell lines examined. A preliminary study of the expression of smf-7 and smf-61 in other cancer cell lines also showed mRNA expression in two human rhabdomyosarcomas and a human epidermoid carcinoma suggesting the existence of genes homologous to smf-7 and smf-61 clones in human cancers. Our findings suggest an association between the expression of smf-7 and smf-61 and invasive or metastatic potential of rhabdomyosarcoma cells.

Correlation between cell differentiation stage, types of invasion, and hematogenous metastasis in experimental rhabdomyosarcomas.

Cancer malignancy is directly related to invasiveness and metastasis and inversely related to the degree of tumor differentiation. The relation between the stage of cell differentiation and the types of invasion leading to metastasis is not entirely clear. Intramuscularly transplanted rat rhabdomyosarcomas are good models to study cell differentiation, invasion, and metastasis. Rat rhabdomyosarcoma cell lines (SMF-Ai, SMF-Da, and RMS-B and its clones) with defined invasive and metastatic potentials have been established. The stage of myogenic differentiation was evaluated morphologically and by immunohistochemistry. Invasiveness was evaluated according to the infiltration of muscle fibers and basal lamina. The SMF-Ai line is highly invasive and metastatic. It is composed of premyoblasts that were involved in intercellular, translaminar, and transcellular invasion of muscle fibers. The SMF-Da line is noninvasive and nonmetastatic. It is composed of myoblasts. The RMS-B line and its clones were at different stages of differentiation and they differed in their invasiveness and metastatic potentials. In highly invasive and metastatic clones (RMS-Bg and RMS-Bc), premyoblasts were involved in translaminar invasion. Clones composed of myoblasts, rhabdomyoblasts, and myotubes only showing intercellular invasion did not present hematogenous metastasis. Our results demonstrate a correlation between premyoblastic stage of differentiation and translaminar invasion. The presence of translaminar invasion is directly related to hematogenous metastatic ability of rat rhabdomyosarcomas.

Arrangement of a cluster of three mouse type I keratin genes expressed sequentially during esophageal-type epithelial cell differentiation.

Keratins are intermediate filament proteins expressed in epithelial cells. They are divided into two groups, type I and type II, that must associate to form filaments. The genes encoding these proteins are clustered in two type-specific loci. In stratified epithelia, differentiation of the basal cells is accompanied by a switch in the expression of keratin genes. However, how this switch is controlled is not yet understood. We report here the cloning and mapping of a 55-kb region surrounding the keratin 19 (K19) gene in the mouse genome. This gene encodes a type I subunit expressed in simple and complex epithelia, notably in nonkeratinizing stratified epithelia of internal organs. In these tissues, it is expressed in basal cells and not in suprabasal cells, where the main type I subunit is keratin 13. Using probes corresponding to highly conserved sequences in intermediate filament proteins, we mapped two other genes downstream from the K19 gene. Restriction mapping and sequencing data indicate that they encode the mouse K15 and K13. The three genes are separated by about 5-6 kb, and they are in the same transcriptional orientation. Because the three genes are expressed together in stratified epithelia and because their order of expression during differentiation is the same as their order on the chromosome, we suggest that there is a relationship between their genomic organization and the control of their expression.

Rat myoblastic sarcoma cell lines. A model for the study of invasion, metastasis, and myogenic differentiation.

BACKGROUND: To understand the relation between differentiation and metastasis and to identify genes involved in invasive or metastatic potential of cancer cells it is necessary to develop experimental models allowing in vivo and in vitro studies. EXPERIMENTAL DESIGN: Cell lines with definite metastatic potentials have been established and cloned from a metastatic nodule of an induced rhabdomyosarcoma in syngeneic F344 rats. The parental cell line, SMF-A, is tumorigenic, highly invasive and metastatic. Another cell line, SMF-D, derived from the parental cell line, is also tumorigenic but not metastatic. Biopathologic differences between the metastatic and nonmetastatic SMF cell lines have been studied. RESULTS: The loss of metastatic potential of the SMF-D cell line was found to be stable and was accompanied by changes in in vitro invasiveness and in myogenic differentiation state. An immunohistochemical study of the expression of cytoskeletal proteins (vimentin, desmin, alpha-actins) indicates that desmin is undetectable in metastatic SMF-A cells, whereas it is strongly expressed in the nonmetastatic SMF-D cells. However, the two cell lines express vimentin but not sarcomeric alpha-actin. These observations suggest that SMF-A cells are of undifferentiated premyoblastic type and SMF-D cells, of myoblastic type. Our study suggests an association between the appearance of myogenic differentiation and the loss of metastatic potential in the SMF-D cell line. CONCLUSIONS: This rat myoblastic sarcoma model may prove useful for in vivo and in vitro studies of the metastatic potential of tumor cells. This model also lends itself to studies of the relation between invasive or metastatic potential and differentiation since the steps of myogenic differentiation are well known.

Cell-specific transcription of the peripherin gene in neuronal cell lines involves a cis-acting element surrounding the TATA box.

Peripherin is a neurone-specific intermediate filament protein expressed mostly in the peripheral nervous system. To localize sequences that are important for the regulation of peripherin gene transcription, we have functionally dissected its promoter. Transfection into different cell lines and deletion mapping of peripherin-lacZ hybrid constructs indicated that the first 98 bp preceding the transcription start site of the gene were sufficient to confer cell-type specific expression. DNase I footprinting experiments revealed three protected sequences in this region, that were named PER1, PER2 and PER3. The PER2 and PER3 elements, localized between -98 to -46, interact with proteins that seem widely distributed. Deletion of these elements severely decreased the level of reporter gene activity. The PER1 element, which overlaps the TATA box, interacts with a DNA-binding protein prevailing in peripherin expressing cell lines. However, the core promoter, which contains the PER1 element, was inefficient in driving gene expression. Experiments designed to test the contribution of each element showed that PER2 and PER3 were important in determining the level of expression, while PER1 was important for cell-type specificity. In fact the polyoma virus enhancer linked to the peripherin gene core promoter was found to limit reporter gene activity to peripherin expressing cell lines. Together, these experiments indicate that co-operative interactions between different regions of the promoter are necessary for efficient and cell-type specific transcription of the peripherin gene in a subset of neuronal cells.

Regulated expression of Krox-24 and other serum-responsive genes during differentiation of P19 embryonal carcinoma cells.

In order to identify genes that may play a role in the onset of the differentiation program elicited by retinoic acid, we analyzed, in P19 embryonal carcinoma cells, the expression of genes that are part of the early response of mouse fibroblasts to growth factor stimulation. In this paper, we show that a sequence-specific transcriptional activator, Krox-24, is rapidly induced, under conditions that promote differentiation of P19 cells. Expression of three other serum- and retinoic acid-stimulated genes (clones AC36, C1, and G39) was also studied. Induction of these genes occurs during the first 48 h of exposure of cells to retinoic acid, a period that precedes cell type determination. Our results suggest that different mechanisms regulate the expression of the Krox-24 gene in differentiating P19 cells. A labile repressor seems to be responsible for control of Krox-24 expression in P19 embryonal carcinoma cells. Inactivation of this repressor following retinoic acid treatment resulted in several peaks of activation of the Krox-24 gene, mediated by different mechanisms, some of which did not require de novo protein synthesis. In contrast, activation of AC36 required de novo protein synthesis, and that of C1 and G39 did not. The four genes are differentially expressed in several mouse tissues and during mouse embryonic development.

Coexpression of alpha-sarcomeric actin, alpha-smooth muscle actin and desmin during myogenesis in rat and mouse embryos I. Skeletal muscle.

Expression of vimentin, desmin, alpha-sarcomeric and alpha-smooth muscle actins in embryonic tissues of rat and mice was examined using an immunohistochemical approach. The results showed a similarity in the expression of desmin and alpha-actin isoforms (alpha-sr and alpha-sm) in skeletal muscle cells during murine feto-embryonic development. In the two species, coexpression of alpha-sr and alpha-sm actins has been observed in cardiomyoblasts, myotomal myoblasts and myotubes. The intensity of alpha-sm actin expression decreased during the terminal steps of myogenesis and disappeared completely in mature cardiomyocytes and myofibres. Desmin was expressed in all prefusion myoblasts (type 1 and 2 myoblasts), myotubes, and in myofibres. The appearance of desmin in myoblasts of somites preceded by a few hours the expression of the alpha-actins (alpha-sr and alpha-sm). Our study on vimentin expression, limited to rat embryos, revealed that somite premyoblasts expressed only vimentin, type 1 myoblasts expressed vimentin and desmin, and type 2 myoblasts (rhabdomyoblasts) expressed desmin and alpha-actins (alpha-sr and alpha-sm). Our study demonstrates the resemblance between feto-embryonic myogenesis and myogenic neoplastic differentiation: desmin appears before the alpha-actins in embryonic myoblasts, and can be considered as a marker of an initial step in myogenic differentiation. alpha-sm actin, considered as a striated muscle cell feto-embryonic actin, is expressed transiently in skeletal myoblasts and cardiomyoblasts during development and reappears during neoplastic transformation of skeletal muscle.

Differential regulation of keratin 8 and 18 messenger RNAs in differentiating F9 cells.

F9 embryonal carcinoma cells (F9EC) can be induced to differentiate in vitro into epithelial cells expressing keratin 8 (K8) and keratin 18 (K18). cDNAs corresponding to K8 and K18 mRNAs were cloned and used to study the change in the abundance of these mRNAs during differentiation of F9 cells into parietal endoderm-like cells by treatment with retinoic acid (RA) or with RA and dibutyryl cAMP (Bt2cAMP). Using an RNase protection assay, it was determined that K8 mRNA was induced slightly before K18 mRNA and that it accumulated to a greater extent than K18 mRNA. Furthermore, differentiation in presence of Bt2cAMP plus RA resulted in an earlier induction of the two mRNAs and a higher level of expression of K8 mRNA. These results indicate that K8 and K18 mRNAs are regulated differently in F9 cells.

Mouse keratin 19: complete amino acid sequence and gene expression during development.

The complete amino acid sequence of the mouse keratin 19 (K19) was determined from a partial sequence of cDNA isolated from a mouse (day 10.5) embryo library and an amplified genomic fragment. Analysis of the sequence reveals strong evolutionary conservation with other K19s. Examination of the expression of the gene encoding K19 (K19) during development using an RNase protection assay reveals it is expressed in extra-embryonic tissues by day 8.5 and in the embryo proper by at least day 9.5. Furthermore, the K19 gene is induced in differentiating F9 embryonal carcinoma cells. These results indicate that K19 is another keratin, in addition to the K8-K18 pair, which is synthesized early during mouse development. Finally, Southern analysis of the K19 gene reveals that it is found as a unique copy in the mouse genome, in contrast to what is found in humans, which have at least one processed pseudogene.

Transformation of NIH 3T3 cells by herpes simplex type 2 BglII n fragment and sub-fragments is independent from induction of mutation at the HPRT locus.

The effect of transfection of the herpes simplex virus type 2 transforming fragment BglII n and of its three Xhol subfragments on mutagenesis and morphological transformation was assayed in NIH 3T3 cells. While BglII n and the right hand portion of this fragment increased the number of transformed foci, no significant effects on the mutation frequency at the hprt locus were observed. Our results indicate that transformation by BglII n is independent from the induction of somatic mutations and suggest that other mechanisms must be considered to explain transformation by this sequence.

Lamins A and C appear during retinoic acid-induced differentiation of mouse embryonal carcinoma cells.

The lamin complement of nuclear matrix isolated from F9 embryonal carcinoma cells was studied during retinoic acid-induced differentiation in culture. Differentiation of the original cells into parietal endoderm-like cells was accompanied by the gradual appearance of lamins A and C while lamin B was present throughout all stages. Lamins were identified by their molecular masses, isoelectric points, recognition by a monoclonal antibody and a polyclonal antiserum, and by peptide mapping. The increase in the amounts of lamins A and C found in the matrix was due to de novo synthesis as no extranuclear pools of these lamins were detected in the undifferentiated cells. These results provide biochemical evidence that, as in amphibian embryogenesis, there are variations in nuclear lamina composition during mammalian development.

Expression of new proteins of the intermediate filament protein family in differentiating F9 embryonal carcinoma cell cytoskeleton.

Differentiation of F9 embryonal carcinoma cells by retinoic acid treatment results in extraembryonic endoderm-like cells. The effects of this process on the protein composition of the intermediate filaments were studied by two-dimensional gel electrophoresis and by immunoblotting. By this approach, two new proteins induced in differentiating cells, p57 and p54, were identified in cytoskeletal preparations enriched in intermediate filaments. The 57-kDa protein could be resolved into at least three components (pI 5.6-5.9), and the 54-kDa protein into at least two components (pI approximately 5.6). Both proteins reacted with a monoclonal antibody which recognizes an antigenic determinant common to all intermediate filaments. Based on these results, the two proteins were identified as members of the intermediate filament protein family. Partial digestion with V8 protease showed that p57 was different from vimentin, another intermediate filament protein present in these cells. p57 and p54 were also immunodetected by a polyclonal anti-keratin anti-serum, which suggests that these proteins share some homology with the keratins. These two proteins are different from the endodermal cytoskeletal protein A and B (endo A and endo B) keratins, which are known to be present in extraembryonic endoderm-like cells. They were also more abundant than endo A and endo B in differentiating F9 embryonal carcinoma cells, but almost undetectable in terminally differentiated extraembryonic endoderm-like cells, where endo A and endo B are readily detectable. This suggests that p57 and p54 have a different pattern of expression than endo A and endo B.

Identification of distinct messenger RNAs for nuclear lamin C and a putative precursor of nuclear lamin A.

The lamins are the major components of the nuclear matrix and are known as lamins A, B, and C with Mr 72,000, 68,000, and 62,000 when analysed by SDS PAGE. These three polypeptides are very similar, as determined by polypeptide mapping and immunological reactivity. Lamins A and C are so homologous that a precursor-product relationship has been proposed. Using an antiserum against nuclear matrix proteins that specifically immunoprecipitates the three lamins, we examined their synthesis in the rabbit reticulocytes lysate. Four bands of Mr 62,000, 68,000, 70,000, and 74,000 were specifically immunoprecipitated when polysomes or polyadenylated RNA were translated in vitro. By two-dimensional gel electrophoresis, the 68,000- and the 62,000-mol-wt proteins were identified as lamins B and C, respectively, and the 74,000-mol-wt polypeptide had properties of a precursor of lamin A. The mRNAs of lamin C and of the putative precursor of lamin A were completely separated by gel electrophoresis under denaturing conditions, and their respective sizes were determined. These results suggest that lamin A is not a precursor of lamin C.

The ovalbumin gene region: common features in the organisation of three genes expressed in chicken oviduct under hormonal control.

Two large DNA fragments overlapping the chicken ovalbumin gene have been isolated by molecular cloning. Analysis of these fragments provided a map of a 46,000-base pair region of the chicken genome. This region contains the complete ovalbumin gene (including its mRNA leader-coding sequence) and at least two other genes of unknown function. All three genes are orientated in the same direction and their expression in chicken oviduct is under hormonal control. The three genes share some sequence homologies, suggesting that duplications have occurred in the ovalbumin gene region in the course of evolution.