Tildrakizumab (MK-3222), an anti-interleukin-23p19 monoclonal antibody, improves psoriasis in a phase IIb randomized placebo-controlled trial.

BACKGROUND: Tildrakizumab is a high-affinity, humanized, IgG1/κ, anti-interleukin (IL)-23p19 monoclonal antibody that does not bind human IL-12 or p40 is being developed for the treatment of chronic plaque psoriasis. OBJECTIVES: To evaluate the safety and efficacy of subcutaneous tildrakizumab in patients with moderate-to-severe chronic plaque psoriasis. METHODS: A three-part, randomized, double-blind, phase IIb trial was conducted in 355 adults with chronic plaque psoriasis. Participants were randomized to receive subcutaneous tildrakizumab (5, 25, 100, 200 mg) or placebo at weeks 0 and 4 (part I) and every 12 weeks thereafter until week 52 (part II). Study drug was discontinued at week 52 and participants were followed through week 72 (part III). Primary efficacy end point was Psoriasis Area and Severity Index (PASI) 75 response at week 16. Adverse events (AEs) and vital signs were monitored throughout the study. RESULTS: At week 16, PASI 75 responses were 33·3% (n = 14), 64·4% (n = 58), 66·3% (n = 59), 74·4% (n = 64) and 4·4% (n = 2) in the 5-, 25-, 100- and 200-mg tildrakizumab and placebo groups, respectively (P ≤ 0·001 for each tildrakizumab dose vs. placebo). PASI 75 response was generally maintained through week 52; only eight of 222 participants who achieved PASI 75 response at week 52 and continued to part III relapsed following discontinuation up to week 72. Possible drug-related serious AEs included bacterial arthritis and lymphoedema (part I), and melanoma, stroke, epiglottitis and knee infection (part II). CONCLUSIONS: Tildrakizumab had treatment effects that were superior to placebo, maintained for 52 weeks of treatment, and persisted for 20 weeks after cessation. Tildrakizumab was generally safe and well tolerated. These results suggest that IL-23p19 is a key target for suppressing psoriasis.

Daclizumab, a humanised monoclonal antibody to the interleukin 2 receptor (CD25), for the treatment of moderately to severely active ulcerative colitis: a randomised, double blind, placebo controlled, dose ranging trial.

BACKGROUND: An uncontrolled pilot study demonstrated that daclizumab, a humanised monoclonal antibody to the interleukin 2 receptor (CD25), might be effective for the treatment of active ulcerative colitis. METHODS: A randomised, double blind, placebo controlled trial was conducted to evaluate the efficacy of daclizumab induction therapy in patients with active ulcerative colitis. A total of 159 patients with moderate ulcerative colitis were randomised to receive induction therapy with daclizumab 1 mg/kg intravenously at weeks 0 and 4, or 2 mg/kg intravenously at weeks 0, 2, 4, and 6, or placebo. The primary end point was induction of remission at week 8. Remission was defined as a Mayo score of 0 on both endoscopy and rectal bleeding components and a score of 0 or 1 on stool frequency and physician's global assessment components. Response was defined as a decrease from baseline in the Mayo score of at least 3 points. RESULTS: Two per cent of patients receiving daclizumab 1 mg/kg (p = 0.11 v placebo) and 7% of patients receiving 2 mg/kg (p = 0.73) were in remission at week 8, compared with 10% of those who received placebo. Response occurred at week 8 in 25% of patients receiving daclizumab 1 mg/kg (p = 0.04) and in 33% of patients receiving 2 mg/kg (p = 0.30) versus 44% of those receiving placebo. Daclizumab was well tolerated. The most frequently reported adverse events in daclizumab treated patients compared with placebo treated patients were nasopharyngitis (14.6%) and pyrexia (10.7%). CONCLUSION: Patients with moderate ulcerative colitis who are treated with daclizumab are not more likely to be in remission or response at eight weeks than patients treated with placebo.

Weekly dosing of carboplatin increases risk of allergy in children.

BACKGROUND: Carboplatin (CBDCA) has been used increasingly to treat pediatric low-grade gliomas. Allergic reactions to CBDCA have been reported in 2% to 30% of children. The reason for this high incidence of allergy is unclear. METHODS: To determine the risk factors for CBDCA allergy, an historic cohort study was conducted for all children who received the drug during a 6-year period at the Lucile Salter Packard Children's Hospital at Stanford. The patients' medical records were reviewed for data on age, tumor type, CBDCA dose schedule, total number of doses, cumulative dosage, dose per treatment, other chemotherapy administered, and allergic reaction. RESULTS: Fifty-four children (mean age 7.2 years, 35 boys) were identified. Six children (11.1%) had an allergic reaction to CBDCA. All reactors had low-grade gliomas treated with weekly CBDCA and vincristine, with a dosage per treatment <500 mg/m2. Overall, six (75%) of eight children administered weekly CBDCA, 6 (46.2%) of 13 children with brain tumors, and 6 (40%) of 15 administered CBDCA dosage <500 mg/m2 manifested allergic reactions. Patients receiving more than five doses had significant risk for CBDCA allergy (relative risk [RR] = 11.8; 95% confidence interval [CI]: 1.5-94.1). Using logistic regression with multiple variables, weekly dose schedule was the most predictive covariate for allergic reaction (P < 0.000 1), and other factors were unrelated or redundant. CONCLUSIONS: Children with low-grade gliomas receiving CBDCA weekly are at significantly increased risk for CBDCA allergy. The repetitive, weekly dosing schedule of CBDCA appears to be a key risk factor for allergic reaction in brain tumor patients. The high frequency of allergy with weekly CBDCA warrants further consideration when planning future trials.

A multicenter, randomized, double-blind, placebo-controlled trial of high-dose intravenous immunoglobulin for oral corticosteroid-dependent asthma.

To determine the efficacy of high doses of intravenous gammaglobulin (IVIG) for the treatment of severe, steroid-dependent asthma in patients between 6 and 68 years of age, a randomized, double-blind, placebo-controlled multicenter clinical trial was conducted in private and university hospitals in the United States. Patients were randomized to one of three treatment arms: 2 g IVIG/kg/month (16 patients); 1 g IVIG/kg/month (9 patients); or 2 g iv albumin (placebo)/kg/month (15 patients). The treatment consisted of seven monthly infusions followed by a posttreatment observation period. The primary outcome measurement was mean daily prednisone-equivalent dose requirements, determined during the observation month preceding initiation of treatment and compared to the month preceding the seventh infusion. Secondary clinical endpoints measured were pulmonary function, frequency of emergency room visits or hospitalizations, and number of days absent from school or work. When adjusted for body weight, the mean dose requirements fell by 33, 39, and 33% in the placebo, IVIG (1 g/kg), and IVIG (2 g/kg) treatment arms, respectively. The differences between therapies were not statistically different (P = 0.9728). The mean percentage-of-predicted FEV1 fell in all three treatment groups during the treatment period but there was no significant difference between treatment groups (P = 0.8291). There was also no significant difference in the percentage of subjects requiring emergency room visits or hospitalizations or missing days of work/school, among the three treatment groups. The trial was terminated prematurely after interim analysis determined the adverse experience rate was different between the three groups. Three patients, all randomized to the 2-g/kg IVIG dose group, were hospitalized with symptoms consistent with aseptic meningitis. In summary, in this randomized, double-blind, placebo-controlled multicenter study, high doses of IVIG did not demonstrate a clinically or statistically significant advantage over placebo (albumin) infusions for the treatment of corticosteroid-dependent asthma. Subgroup analysis failed to identify markers predicting responsiveness. High-dose IVIG can also be associated with a significant incidence of serious adverse events.

Clinical differences among women with and without self-reported perimenstrual asthma.

BACKGROUND: Studies suggesting that 30% to 40% of asthmatic women report significant perimenstrual (late luteal phase) exacerbations of asthma are primarily retrospective, rely on subjective findings and do not demonstrate a consistent association between asthma and the menstrual cycle. OBJECTIVE: In this exploratory analysis, women with and without self-reported perimenstrual exacerbations of asthma (PMA) were examined prospectively to determine the association between asthma and the menstrual cycle and to characterize associated clinical factors. METHODS: Thirty-two adult asthmatic women with regular menstrual periods recorded daily asthma symptoms, medication use, and peak expiratory flow rate (PEFR) over six consecutive menstrual cycles, and underwent spirometry and methacholine bronchoprovocation during the luteal and follicular phases of 2 cycles. RESULTS: Nine of 32 subjects (28.2%) reported PMA. Daily means of rescue medication use and AM peak flow computed for each perimenstrual day demonstrated significant non-parallelism of group profiles; subjects with PMA had increasing inhaled short acting beta 2-agonist use and decreasing AM peak flow rates during the perimenstrual interval. Luteal-follicular phase differences in FEV1 or methacholine bronchoprovocation between the groups were not detected. Subjects with PMA were older (P=.007), had longer duration of asthma (P=.039), and increased baseline asthma severity (P=.076) compared with subjects without PMA. CONCLUSION: The findings of this study suggest that women with self-reported perimenstrual asthma demonstrate perimenstrual differences in rescue bronchodilator use and AM peak flow and appear to constitute a distinct subset of women with asthma who are older, have longer duration of asthma, and increased severity of asthma compared with women without self-reported perimenstrual asthma. These factors identify women who require close monitoring of their asthma during their menstrual cycles.

Role of epidermal-dermal tissue interactions in regulating tenascin expression during development of the chick scutate scale.

During normal chicken development tenascin begins to accumulate in the dermis of anterior metatarsal skin at the time of scutate scale ridge formation, and is localized in a distinct pattern along the outer scale surface. Anterior metatarsal skin from scaleless (sc/sc) embryos, which do not form scutate scales, begins to accumulate tenascin 4 days later than normal skin. This study shows that normal and scaleless anterior metatarsal dermis accumulate the same tenascin isoforms and undergo the same isoform changes in the post-hatch period, but there is less tenascin accumulated in scaleless dermis and there is no pattern to its distribution. In both normal and scaleless anterior metatarsal skin, tenascin mRNA is localized in the dermis and is distributed in the same way as the protein. Thus, scaleless skin is defective in the ability to accumulate appropriate amounts of tenascin and to maintain the tenascin in the patterned manner of normal. Recombinant skin cultures show that epidermal-dermal interactions are required for tenascin accumulation. The dermis specifies the way that tenascin is organized, but interaction with epidermis is required to maintain this organization. The epidermal role appears to be permissive because in heterotypic recombinants, neither scaleless anterior metatarsal epidermis nor normal footpad epidermis changes the way that tenascin appears in the normal anterior metatarsal dermis; and in reciprocal recombinants, normal anterior metatarsal epidermis does not change the way tenascin is accumulated in either scaleless anterior metatarsal dermis or normal footpad dermis.

Tumor necrosis factor release by murine macrophages stimulated by the cytotoxic ether lipid 1-O-hexadecyl-2-O-methyl-SN-glycero-3-phosphorylcholine (ET-18-O-OCH3).

The cytotoxic ether lipid 1-O-hexadecyl-2-O-methyl-SN-glycero-3-phosphorylcholine (ET-18-O-OCH3) is a structural analog of the mediator of inflammation platelet-activating factor (PAF). Recent studies demonstrated that ET-18-O-OCH3 activates human monocytes selectively at non-cytotoxic concentrations. The current studies determined the capacity of ET-18-O-OCH3 to stimulate release of TNF alpha by murine peritoneal macrophages. Macrophage receptors for ET-18-OCH3 and PAF were also assessed. ET-18-O-OCH3 and PAF stimulated TNF alpha release by resident BALB/c macrophages in the presence of LPS but not in the absence of this co-factor. In contrast, both ET-18-O_OCH3 and PAF stimulated TNF alpha release by thioglycollate-elicited macrophages in the absence of LPS although release was greater in the presence of this co-stimulus. Optimal stimulation of TNF alpha release occurred at 10(-14)-10(-11) M ET-18-O-OCH3 and PAF. Elicited macrophages and splenic macrophages from C57Bl/6 mice, unlike those from BALB/c mice, did not respond to 10(-15)-10(-8) M ET-18-O-OCH3 or PAF without or with LPS. Scatchard analysis of [3H]PAF binding to elicited BALB/c macrophages revealed the existence of high affinity receptors for PAF. In contrast, there was no evidence for receptors for ET-18-O-OCH3. ET-18-O-OCH3 did not compete with PAF for binding; macrophage activation by ET-18-O-OCH3 was not stereospecific; and, binding studies using [3H]ET-18-O-OCH3 did not reveal saturable binding characteristic of binding to specific receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of human HL-60 cell responses to chemotactic factors by antisense messenger RNA depletion of G proteins.

Chemotactic factors bound to receptors of the seven-transmembrane domain family signal leukocytes through associated guanine nucleotide-binding (G) proteins. Human leukocytes of the HL-60 line, which express G protein-coupled receptors for leukotriene B4 (LTB4) and N-formyl-methionyl-leucyl-phenylalanine (fMLP) after differentiation with vitamin D3 and transforming growth factor-beta, were transfected with expression plasmids containing antisense-oriented cDNAs encoding the alpha-chains of Go, Gi1, Gi2, and Gi3. Antisense mRNA for Go and Gi2 alpha-chains suppressed by over 80% the level of the respective G protein. Go-deficient HL-60 cells had depressed functional and intracellular calcium responses to LTB4 and fMLP, but no alterations in the responses of cyclic adenosine 3',5'-monophosphate (cAMP). In contrast, HL-60 cells deficient in Gi2 lost only responses of the intracellular concentration of cAMP. Antisense mRNA suppression of distinct G proteins thus may delineate some transductional requirements for cellular responses.

Induction of aggregation of Raji human B-lymphoblastic cells by vasoactive intestinal peptide.

Subsets of neurons in the thymic cortex, Peyer's patches and lymphoid tissues of the respiratory system deliver vasoactive intestinal peptide (VIP) at nanomolar concentrations. The possible effects of VIP on B-cell adhesiveness in these tissues were examined in studies of the homotypic aggregation (HA) of human B-lymphoblastoid cells of the Raji line, which express a mean of 27,950 VIP receptors/cell with a mean Kd of 0.8 nM. Mean HA, assessed microscopically, attained a maximum of 54% after 8 hr with 0.1 microgram/ml of phorbol 12-myristate 13-acetate (PMA) (P < 0.01) and 31% after 24 hr with 10(-8) M VIP (P < 0.05), as contrasted with 13% and 20% at the respective times in medium alone, and both stimuli also increased the mean size of aggregates. The presence of the phosphodiesterase inhibitor Ro 20-1724 permitted 10(-9) M VIP, which had no effect alone, to raise the mean cyclic AMP content of Raji cells by more than 10-fold and concurrently to elevate mean HA from 55% in medium alone at 48 hr to 70% and from 55% at 72 hr to 68% (P < 0.05 for both). Monoclonal antibodies to lymphocyte function-associated (LFA-1) adhesive protein and to intercellular adherence molecule-1 (ICAM-1) suppressed significantly the HA of Raji cells induced by VIP and PMA. The effects of VIP on compartmental immunity in the lungs and intestines thus may be mediated in part by increases in lymphocyte adhesiveness, which could contribute to the regional accumulation of specifically immunocompetent cells.

Activation of human neutrophil LFA-1 (CD11a) by leukotriene B4.

Homotypic aggregation (HA) of human neutrophils by the potent leukotactic factor, leukotriene B4 (LTB4), and phorbol myristate acetate (PMA) was evaluated by recording the net decrease in absorbency at 650 nm of suspensions of 10(7) neutrophils/ml in a microtiter plate reader, which was found to correlate with microscopic evidence of aggregation. LTB4-elicited HA was increased maximally by approximately one third above HA in buffer at 30 min, whereas PMA-induced HA reached a maximal level more than 2 1/2-fold higher than buffer control at 60 min. The involvement of LFA-1 in LTB4-induced HA of neutrophils was suggested initially by the inhibitory effect of monoclonal anti-CD18 and anti-CD11a antibodies. The binding to neutrophils of a monoclonal anti-LFA-1 antibody (NK1-L16) specific for an activation epitope of CD11a was increased a maximum of 28-fold and sixfold, respectively, after 1 and 5 min of preincubation with 10 nM LTB4 and fivefold after 5 min with PMA. Thus, both LTB4 and PMA induce an activating conformational change in the CD11a adherence receptor of human neutrophils.

Region-specific patterns of beta keratin expression during avian skin development.

The transient embryonic layers primarily composed of a periderm and subperiderm cover most regions of the chick embryo and are the first suprabasal cell layers covering the body ectoderm. This study presents evidence for regional variation in the expression of beta keratin in the embryonic layers. Here we show that the embryonic layers covering the anterior metatarsal region of the chicken hindlimb (scutate scale forming region) produce several members of the beta keratin family of polypeptides, designated beta (beta) 1-7. These specific polypeptides are later expressed in this region exclusively in the thick, cornified beta strata of mature scutate scales. In contrast to this sequence of events, the embryonic layers overlying the epidermis of the ventral foot pad (reticulate scale-forming region) and those covering the epidermis in apteric regions of the body produce beta keratin polypeptides beta 1-3 and beta 2,3, respectively, but no subsequent expression of these proteins occurs in the mature epidermises of these regions. Furthermore, we find that the embryonic layers of the skin overlying the anterior metatarsal region of birds homozygous for the mutation "scaleless" (sc/sc), which completely lack scutate scales, produce the same members of the beta keratin family, beta 1-7, as the embryonic layers and beta strata of normal scutate scales. Thus, the accumulation of specific beta keratin polypeptides in the developing anterior metatarsal region appears to occur in two distinct phases; first, an early region-specific expression in cells of the embryonic layers followed by a second phase of expression which occurs in conjunction with appendage morphogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Region-specific expression of scutate scale type beta keratins in the developing chick beak.

This study shows that different patterns of scutate scale type beta keratins are accumulated in the three adjacent structures of the embryonic chick beak: periderm, egg tooth, and cornified beak. The cornified beak accumulates all of the beta keratins of scutate scale except pp2,3. The periderm, which is the outermost, multilayered covering of the whole embryonic beak, accumulates only beta keratins 2,3, and p2,3 of the scutate scale pattern. The egg tooth, which is the rounded elevation on the dorsal surface of the upper beak, and the embryonic claw accumulate greatly reduced levels of 2,3 and p2,3 compared to scutate scale. Like cornified beak, the claw does not accumulate pp2,3, but both tissues express a potentially new beta keratin, beta keratin 8. Neither the histidine rich "fast" proteins (HRPs), which are expressed in embryonic scutate scales and feathers, nor the avian cytokeratin associated proteins (cap-1 and cap-2), which are expressed in scutate and reticulate scales, are expressed in any of the embryonic beak structures or in the claw. The implications of these findings with regard to regulation of terminal differentiation of avian skin are discussed.

The initial expression and patterned appearance of tenascin in scutate scales is absent from the dermis of the scaleless (sc/sc) chicken.

Morphogenesis of the anterior metatarsal skin (scutate scale region), from 9.5 to 12 days of development, results in the formation of orderly patterned scale ridges. It is after the initial formation of the Definitive Scale Ridge that the characteristic outer and inner epidermal surfaces differentiate. The hard, plate-like beta stratum, with its unique beta keratins, characterizes the epidermis of the outer surface, while the epidermis of the inner surface elaborates an alpha stratum. The anterior metatarsal region of the scaleless mutant does not undergo scale morphogenesis. Therefore, scale ridges do not form nor do the outer and inner epidermal surfaces with their characteristic beta and alpha strata. We have found that the extracellular matrix molecule, tenascin, first appears in the scutate scale dermis at 12 days of development when the scale ridge is established. Tenascin is found in the dermis only under the scale ridge and is not associated with the dermal-epidermal junction. Tenascin is not found in scaleless anterior metatarsal dermis at this time. As outgrowth of the Definitive Scale Ridge takes place, tenascin distribution correlates closely with the formation of the outer epidermal surface of each scale ridge. By 16 days of development tenascin is also found in close association with the dermal-epidermal junction. Tenascin does not appear in scaleless anterior metatarsal dermis until 16 days of development and then it is randomly and sparsely distributed at the dermal-epidermal junction. Tenascin's initial appearance and pattern of distribution in the scutate scale dermis and its abnormal expression in the scaleless dermis suggest that morphogenesis plays a significant role in regulation of its expression.

Expression of the cell adhesion molecules, L-CAM and N-CAM during avian scale development.

To examine the involvement of cell adhesion molecules in the inductive epithelial-mesenchymal interactions during avian scale development, a study of the spatiotemporal distribution of L-CAM and N-CAM was undertaken. During scutate scale development, L-CAM and N-CAM are expressed together in cells of the transient embryonic layers destined to be lost at hatching. The ongoing linkage of the cells of these layers by both CAMs sets them apart, early in development, as unique cell populations. L-CAM and N-CAM were also expressed simultaneously at the basal surface of the early germinative cells where signal transduction is presumed to occur. In spite of the differences in cell shape, adhesion, density and proliferative state between populations of epidermal placode and interplacode cells, the expression of L-CAM and N-CAM appeared to be uniform and nondiscriminating for these discrete cell lineages. The same pattern of L-CAM and N-CAM expression was observed during morphogenesis of reticulate scales that develop without placode formation. While L-CAM and N-CAM are present during the early stages of scale development and most likely function in cell adhesion, the data do not support a role for these adhesion molecules in the formation of the morphogenetically critical placode and interplacode cell populations. In both scale types, L-CAM became predominantly epithelial, and N-CAM became predominantly dermal as histogenesis occurred. Initially, N-CAM was concentrated near the basal lamina where it may be involved in the reciprocal epidermal-dermal interactions required for morphogenesis. However, as development of the scales progressed, N-CAM disappeared from the tissues. L-CAM expression continued in the epidermis and was intense on all suprabasal cells undergoing differentiation into either an alpha-stratum or beta-stratum. However, L-CAM was more prevalent on the basal cells of alpha-keratinizing regions than on the basal cells of beta-keratinizing regions.

Keratinization of the outer surface of the avian scutate scale: interrelationship of alpha and beta keratin filaments in a cornifying tissue.

The outer surface of adult Gallus domesticus scutate scale was studied as a model for epidermal cornification involving accumulation of both alpha and beta keratins. Electron-microscopic analysis demonstrated that the basal cells of the adult epidermis contained abundant lipid droplets and that filament bundles and desmosomes were distributed throughout the cell layers. Indirect immunofluorescence microscopy and double-labeling immunogold-electron microscopy confirmed that the stratum germinativum contained alpha keratin but not beta keratin. Beta keratins were first detected in the stratum intermedium and were always found intermingled with filament bundles of alpha keratin. As the differentiating cells moved into the outer regions of the stratum intermedium and the stratum corneum, the large mixed keratin filament bundles labeled increasingly more with beta keratin antiserum and relatively less so with alpha keratin antiserum. Sodium dodecyl sulfate-polyacrylamide gel analysis of vertical layers of the outer surface of the scutate scale confirmed that cells having reached the outermost layers of stratum corneum had preferentially lost alpha keratin. The mixed bundles of alpha and beta keratin filaments were closely associated with desmosomes in the lower stratum intermedium and with electron-dense aggregates in the cytoplasm of cells in the outer stratum intermedium. Using anti-desmosomal serum it was shown that these cytoplasmic plaques were desmosomes.

Identification, expression, and localization of beta keratin gene products during development of avian scutate scales.

Epidermal-dermal interactions influence morphogenesis and expression of the beta keratin gene family during development of scales in the embryonic chick. The underlying mechanisms by which these interactions control beta keratin expression are not understood. However, the present study of beta keratin gene expression during avian epidermal differentiation contributes new information with which to investigate the role of tissue interactions in this process. Using beta keratin-specific synthetic oligonucleotide probe, beta keratin mRNA was hybrid-selected from total poly A+ RNA of scutate scales. Seven beta keratin polypeptides were translated in vitro and could be identified by their positions in two-dimensional gels among the detergent-insoluble extracts of scutate scale epidermis. In vivo phosphorylation studies suggested that an additional three beta keratin polypeptides were present as phosphoproteins. The temporal appearance of beta keratin mRNA and the corresponding polypeptides was followed during scutate scale development. Polyclonal antiserum made against two of the beta keratin polypeptides was used for immunohistochemical and immunogold electron-microscopic analysis of beta keratin tissue distribution. Immunological reactivity was observed specifically along the outer scale surface in epidermal cells above the stratum germinativum. Immunogold beads were localized on 3-nm filament bundles. In situ hybridization with a beta keratin-specific RNA probe demonstrated that mRNA accumulated in the same regional manner as the polypeptides. This selective expression of beta keratin genes in specific regions of the developing scutate scale suggests that epidermal-dermal interactions provide not only for morphological events, but also for control of complex patterns of histogenesis and biochemical differentiation.

Expression of beta keratin genes during skin development in normal and sc/sc chick embryos.

The expression of RNA sequences specific for scale beta (beta)-keratins has been followed during skin development in normal and scaleless (sc/sc) embryos. Total RNA from skin at various stages (36-46) of development, as well as newly hatched chicks, was immobilized on nitrocellulose paper and hybridized with a [32P]cDNA probe to beta-keratins (pCSK-12). Sequences for beta-keratins showed patterns of expression which were specific for each genotype and scale type examined. During the development of normal scutate scales, which are characterized by the formation of a beta stratum, RNA with beta-keratin sequences first appeared at stage 40, and continued to accumulate through hatching. RNA with beta keratin sequences appeared in scaleless skin between stages 40 and 41, was greatly diminished by stage 44, and was no longer present at stage 46. In normal reticulate scales, which like scaleless skin, do not develop a beta stratum accumulation of RNA with beta-keratin sequences was limited to a brief embryonic period between stages 42 and 44. These patterns of RNA expression correlated well with the appearance of beta-keratin polypeptides, suggesting that beta-keratin synthesis may be controlled at the level of keratin mRNA transcription. Correlations between the patterns of beta-keratin expression and histological events suggest that the brief accumulation of beta-keratin mRNA in scaleless skin and normal reticulate scales is related to the formation of the subperiderm (a protective layer of cells, peculiar to embryonic skin) while the continuous accumulation of beta-keratin mRNA during scutate scale development reflects the formation of a beta stratum.