Van De Vijver Research Articles

Expression signature of p53 status (p53 signature) for the prediction of TP53 mutation and prognosis in breast cancer

652 Background: The current risk evaluation criteria, such as the St. Gallen and NIH, are not sufficient for predicting which BC patients are at high risk for recurrence and mortality. The TP53 mutations are associated with worse RFS and OS, independent other risk factors in BC, but the p53 status is not simply determined and often determined incorrectly (Soussi et al. Nat Rev Cancer 2006). Our purpose was to identify the gene sets that determine expression signature of the p53 status and to correlate the gene expression profile (GEP) with clinical outcome. Methods: Comprehensive expression analysis (Agilent 41K human genome oligo microarray) and DNA sequencing of the TP53 gene in 38 Japanese BC (30 Stage I-II, 8 stage III-IV; 20 TP53 wt, 20 TP53 mt) were performed using RNA and DNA obtained from the microdissected frozen tumor samples. We determined a gene set consisted of 33 genes from differentially expressed genes depending on the p53 status in the 26 BC (training set) and validated the ability to predict p53 status in the remaining 12 BC (test set). Prognostic value of the gene set was analyzed in 29 BC (stage I or II), and were validated using publicly available dataset of the independent 295 BC (stage I or II), van de Vijver et al. NEJM 2002). Results: The GEP using the 33 genes, many of which related in cell cycle and cell division, predicted the p53 status (wt or mt p53 signature) accurately in the test set (accuracy: 83%, overall accuracy: 95%). The p53 signature has the ability to predict RFS of the 29 early BC (Log Rank, P=0.032). It divided the 295 early BC into 176 wt and 119 mt group, and also has the ability to predict both RFS and OS (Log Rank, both P<0.0001). This was also true when the cohort were stratified by ER status, LN status, St. Gallen criteria and NIH criteria, and retained the predicted value in ER+, LN+, LN-, St. Gallen (intermediate/high) and NIH (high) subgroups (Log Rank, P<0.0001). Conclusions: The p53 signature is a powerful and independent predictor of the outcome of disease in early breast cancer than standard systems based on clinical and histologic criteria. No significant financial relationships to disclose.

A clinical prognostic prediction of lymph node-negative breast cancer by gene expression profiles

To set up a method by use of gene expression data to predict the prognosis of breast cancer patients on the basis of genes as few as possible, but maintaining the accuracy of prediction, we reanalyze the data from van't Veer et al. (Nature 415:530-536, 2002) and van de Vijver et al. (N Engl J Med 347:1999-2009, 2002). A three-step method based on re-sampling strategy is employed to select the prognostic genes. And based on these genes, a predictive approach is established. Validation sets are used to testify the predictive power of the prognostic genes. We have discovered 13 genes as the most informative ones to predict the clinical outcomes of breast cancer patients with lymph node-negative. The validation results show the robust performances of these genes. And the results of further analysis illustrate the significant association of the prediction to the time of metastases and overall survival. Our predictive approach is useful in prognosis prediction for breast cancer patients with lymph node-negative. The gene markers provide valuable information for the progression of breast cancer and suggest potential target genes for treating the cancer.

Prognostic Gene Expression Signatures Can Be Measured in Tissues Collected in RNAlater Preservative

Gene expression signatures have the ability to serve in both prognostic and predictive capacities in patient management. The use of RNA as the starting material and the lability of this analyte, however, dictate that tissues must be snap-frozen or stored in a solution that can maintain the integrity of the RNA. We compared pairs of snap-frozen and RNAlater preservative-suspended tissue from 30 such paired lymph node-negative breast tumors and 21 such paired Dukes' B colon tumors. We assessed the correlation of gene expression profiles and prediction of recurrence based on two prognostic algorithms. Tissues stored in RNAlater preservative generated expression profiles with excellent correlation (average Pearson correlation coefficients of 0.97 and 0.94 for the breast and colon tumor pairs, respectively) compared to those produced by tissues that were snap-frozen. The correlation in the prediction of recurrence was 97% and 95% for the breast and colon tumor pairs, respectively, between these two types of tissue handling protocols. This novel finding demonstrates that prognostic signatures can be obtained from RNAlater preservative-suspended tissues, an important step in bringing gene expression signatures to the clinic.

The Syllable in Optimality Theory (review)

Reviewed by: The syllable in Optimality Theory Marc Pierce Caroline Féry and Ruben van de Vijver, eds. The syllable in Optimality Theory. Cambridge: Cambridge University Press. 2003. Pp. ix + 415. $100.00. (hardcover). This book contains 14 thematic chapters addressing various syllable-related issues from an Optimality Theory (OT) perspective, as well as an introductory overview. As the limitations of this forum preclude an exhaustive discussion of each analysis, I shall instead briefly outline the contents of the volume and then offer some general discussion. The first section consists of an introductory "Overview" by the editors. This chapter first sketches the role of the syllable in phonology and then examines its treatment within OT. The editors suggest that OT is particularly well-suited to capture the typology of the syllable (a claim accepted even by some opponents of OT, e.g., McMahon 2000). An overview of the contents of the book is then given. The second part, "Syllable Structure and Prosodic Structure", contains four papers. John J. McCarthy's "Sympathy, cumulativity, and the Duke-of-York gambit" examines Duke-of-York (DY) derivations (Pullum 1976), that is, derivations which "have the general form A → B → A, where underlying A passes through a B stage before returning to surface A again" (p. 24), within OT. McCarthy argues that there are two different types of such derivations, "vacuous" and "feeding"; in the first type, the B stage is motivated solely by "theory-internal assumptions of strict serialism" (p. 24), while in the second type, the B stage is "crucial for conditioning some further process" (p. 24). McCarthy reviews the evidence for a number of vacuous DY derivations, and concludes that such derivations are not problematic for OT, as they are "an expected consequence of the core premises of OT, constraint ranking and constraint violation under domination" (p. 32). As to feeding DY derivations, McCarthy contends that they do not exist, and that better analyses are available for any putative feeding DY derivations. In McCarthy's view, the problem of opacity in OT is best resolved by means of Sympathy Theory (McCarthy 1999), and the chapter concludes with an eloquent review of the applications of Sympathy Theory to opacity. The second paper in this section is "The Controversy over Geminates and Syllable Weight", by Stuart Davis, which takes up the problem of the representation of geminate consonants: are they consonants that are underlyingly moraic, or consonants underlyingly linked to two root nodes, or consonants linked to two skeletal slots? Based largely on the behaviour of geminates in Sinhala, Davis argues that geminates are underlyingly moraic, and suggests that alternative views of geminates fail to account for the Sinhalese material. Davis then discusses evidence from other languages, which has been raised in support of alternative views of geminates, and he concludes that this evidence does not in fact conclusively support alternative views. The next paper in this section is "The syllable as a unit of prosodic organization in Japanese", by Haruo Kubozono. While Japanese is normally considered a [End Page 75] mora language, rather than a syllable language, Kubozono argues persuasively that a number of phonological phenomena in Japanese, including mother-child language, emphatic mimetics, and the truncation of loanwords, can best be accounted for in terms of the syllable. Kubozono therefore concludes that "the syllable is no less indispensable than the mora is in Japanese" (p. 118). The final paper in this section is "Prosodic weight", by Draga Zec, which takes up the problem of describing syllable weight. Zec argues that "syllable weight in terms of mora count is the sole weight mechanism associated with the syllable as a prosodic constituent" (p. 123), but that higher level prosodic constituents like the foot and the prosodic word can "impose their own minimal sonority thresholds" (p. 124). Data from English, Mordvin, Old Church Slavonic, and Asheninca are adduced in support of Zec's claims. The third part, "Nonmoraic syllables and syllable edges", begins with Paul Kiparsky's "Syllables and moras in Arabic"; a more extensive treatment of this data can be found in Kiparsky (forthcoming). This chapter focuses on syllable-based phenomena in three groups of Arabic dialects (VC-dialects, C-dialects, and CV...

Advances in the Treatment of Breast Cancer

The biennial Madrid Breast Cancer Conference has become one of the leading summer meetings dedicated to reviewing and discussing the most relevant advances in breast cancer research. Seminal, practice-changing results have been presented and reviewed in different sessions and symposia, embracing various aspects from molecular genetics to advances in imaging, staging and treatment in the different settings of the disease. Oncologists need improved tools to select treatments for individual patients. Most cancer treatments benefit only a minority of the patients to whom they are administered. Prognostic and predictive factors play important roles in the treatment of breast cancer, but very few such factors are used in clinical practice and prognostic relevance remains unclear. The ability to predict which patients are most likely to benefit from a given treatment would not only save patients from unnecessary toxicity and inconvenience, but might also facilitate their receiving drugs that are more likely to help. The current standard tools used to test new therapies in early breast cancer are Phase III randomized adjuvant trials. Such trials are large, expensive and take years to achieve their outcome. Neoadjuvant or primary systemic therapy (PST) trials might offer the eventual possibility of a more rapid and less resource-demanding alternative, at least for some therapies, if short-term surrogate clinical, pathologic or biologic end points could be identified that might predict for long-term outcome in adjuvant trials. Genome-wide monitoring of gene expression using DNA microarrays makes it possible to study thousands of genes in a tumor sample with a single experiment. By looking for an association between the gene expression pattern and tumor behavior, it should be possible to identify new prognostic and predictive factors. Dr M Van de Vijver (Rotterdam, The Netherlands) and his team have previously identified a 70gene expression profile (GEP) associated with an increased risk for developing distant metastases within 5 years. More recently, they identified consistent features in the transcriptional response of normal fibroblasts to serum and used this wound-response signature to reveal links between wound healing and cancer progression in the same tumors. By combining the 70-GEP (good-prognosis and poor-prognosis tumors) and the wound signature (activated and quiescent tumors), subgroups of patients with markedly different prognoses can be identified [1]. One serious limitation of microarray expression profiling, however, is that it is an RNA assay that requires fresh or well-preserved frozen tissue for extraction of viable RNA. Consequently, some investigators use microarrays to screen the genes for those factors associated with outcome and then develop classifiers for clinical applications that are based on subsequent studies using reverse transcriptionpolymerase chain reaction (RT-PCR) of the selected genes. This was the approach used and reviewed in detail by Dr S Paik (PA, USA) in developing the Oncotype Dx® risk score for patients with lymph node-negative, estrogen

ERRATUM

In the 15 September issue of the Journal in the article by Wensing et al. (Wensing AMJ, van de Vijver DA, Angarano G, et al. Prevalence of Drug-resistant HIV-1 variants in untreated individuals in Europe: implications for clinical management. J Infect Dis 2005; 192:958–66), there are the following 2 errors: The legend, or caption, currently below figure 1 should be below figure 2, and the legend currently below figure 2 should be below figure 1; the publisher regrets this error. Also, the second P value in figure 1 should be .048, as it is in the text (not .48); the author regrets this error

MORPHOLOGICAL STUDIES OF DISTRIONELLA INCOGNITA (REICHARDT) WILLIAMS (BACILLARIOPHYCEAE) FROM NORTH AMERICA WITH COMMENTS ON THE TAXONOMY OF DISTRIONELLA WILLIAMS

Detailed morphological observations at the light microscopy (LM) and scanning electron microscopy (SEM) levels were made on North American populations of Distrionella incognita (Reichardt) Williams (=Fragilaria incognita Reichardt). Results are used to show the distinctiveness of this taxon from closely related species and to justify its separation from Fragilaria Lyngbye as suggested by Williams (1990a). The protologue of Distrionella Williams is herein emended to include features newly discovered under SEM. Likewise, two recently described species and a form, Fragilaria germainii Reichardt and Lange-Bertalot, Fragilaria husvikensis Van de Vijver, Denys et Beyens, and Fragilaria germainii fo. acostata Lange-Bertalot are here transferred to Distrionella based on LM and SEM data presented by their original authors. Relationships among these taxa and other morphologically related species are discussed in this work. Ecological attributes are provided for habitats that support Distrionella incognita in North America.

Gene Expression Analysis of Immune-Mediated Arrest of Tumorigenesis in a Transgenic Mouse Model of HER-2/neu-Positive Basal-Like Mammary Carcinoma

We previously showed that a vaccine combining interleukin 12 and allogeneic p185(neu)-positive mammary carcinoma cells completely prevented multifocal mammary carcinogenesis in HER-2/neu transgenic mice. To identify the molecular events responsible for effective tumor prevention and to define the tumor gene expression signature, we used microarrays to analyze the expression profile of mammary tissue of untreated transgenic mice and of vaccine-treated, tumor-free mice at different time points. Mammary tissue from vaccinated mice displayed a gene expression profile different from that of untreated, tumor-bearing mice but similar to that of normal/hyperplastic mammary gland. Comparison of treated and untreated mice at 15 weeks of age revealed up-regulation of genes encoding antibodies, chemokines, gamma-interferon-induced genes and inflammatory molecules, and down-regulation of early genes induced by tumor development. The gene expression signature of HER-2/neu-transformed tumor cells showed modulation of genes promoting proliferation, angiogenesis, migration, invasion, and metastasis and inhibiting apoptosis and immune response. Meta-analysis of microarray data on human breast cancer showed that the signature of tumors arising in murine HER-2/neu transgenic model correctly classified human HER-2/neu-expressing tumors and normal breast tissue. Moreover murine and human HER-2/neu-positive tumors share the signature of basal-like breast cancers. This gene expression analysis reveals the immune events associated with prevention of tumor development and shows that HER-2/neu transgenic mice represent a good model of a poor-prognosis group of human breast tumors.

Function-dependent Conformational Changes of the ABCG2 Multidrug Transporter Modify Its Interaction with a Monoclonal Antibody on the Cell Surface

The human ABCG2 protein is an important primary active transporter for hydrophobic compounds in several cell types, and its overexpression causes multidrug resistance in tumors. A monoclonal antibody (5D3) recognizes this protein on the cell surface. In ABCG2-expressing cells 5D3 antibody showed a saturable labeling and inhibited ABCG2 transport and ATPase function. However, at low antibody concentrations 5D3 binding to intact cells depended on the actual conformation of the ABCG2 protein. ATP depletion or the addition of the ABCG2 inhibitor Ko143 significantly increased, whereas the vanadate-induced arrest of ABCG2 strongly decreased 5D3 binding. The binding of the 5D3 antibody to a non-functional ABCG2 catalytic center mutant (K86M) in intact cells was not affected by the addition of vanadate but still increased with the addition of Ko143. In isolated membrane fragments the ligand modulation of 5D3 binding to ABCG2 could be analyzed in detail. In this case 5D3 binding was maximum in the presence of ATP, ADP, or Ko143, whereas the non-hydrolysable ATP analog, adenosine 5'-(beta,gamma-imido)triphosphate (AMP-PNP), and nucleotide trapping by vanadate decreased antibody binding. In membranes expressing the ABCG2-K86M mutant, ATP, ADP, and AMP-PNP decreased, whereas Ko143 increased 5D3 binding. Based on these data we suggest that the 5D3 antibody can be used as a sensitive tool to reveal intramolecular changes, reflecting ATP binding, the formation of a catalytic intermediate, or substrate inhibition within the transport cycle of the ABCG2 protein.

Ranging of older male elephants introduced to an existing small population without older males: Pilanesberg National Park

The African elephant Loxodonta africana is one of the key components of African savanna. Not only do they play a crucial role in the ecosystem (Dublin et al. 1990; Van de Vijver et al. 1999), but they also provide one of the integral parts of sustainable conservation through ecotourism (e.g. Brown 1993) and consumptive utilisation (Taylor 1993). The ever-expanding transformation of savanna land-use through human settlement is resulting in the isolation of elephants into small populations. Furthermore, in South Africa, the reclamation of ranch land as game areas has resulted in the reintroduction of elephant to a large number of small, isolated, fenced reserves.

Genome-scale profiling of gene expression in hepatocellular carcinoma: Classification, survival prediction, and identification of therapeutic targets

The heterogeneous nature of human hepatocellular carcinoma (HCC) has hampered both treatment and prognostic predictions. Gene expression profiles of human HCC were analyzed to define the molecular characteristics of the tumors and to test the prognostic value of the expression profiles. By applying global gene expression analyses, including unsupervised and supervised methods, 2 distinctive subclasses of HCC that were highly homogeneous for both the underlying biology and the clinical outcome were discovered. Tumors from the low survival subclass had strong cell proliferation and antiapoptosis gene expression signatures. In addition, the low survival subclass displayed higher expression of genes involved in ubiquitination and sumoylation, suggesting an etiologic involvement of these processes in accelerating the progression of HCC. Genes most strongly associated with survival were identified by using the Cox proportional hazards survival analysis. This approach identified a limited number of genes that accurately predicted the length of survival and provided new molecular insights into the pathogenesis of HCC. Future studies will evaluate potential diagnostic markers and therapeutic targets identified during the global gene expression studies. Furthermore, cross-species similarity of gene expression patterns will also allow prioritization of a long list of genes obtained from human gene expression profiling studies and focus on genes whose expression is altered during tumorigenesis in both species.

PINNULARIA SOFIA VAN DE VIJVER & LE COHU SPEC. NOV., A NEW SPINE-BEARING, CHAIN-FORMING PINNULARIA SPECIES FROM THE SUB-ANTARCTIC REGION

The spine-bearing diatom Pinnularia sofia Van de Vijver & Le Cohu spec. nov. is described from the sub-Antarctic Heard Island. The morphology of this species was examined using the scanning electron microscopy (SEM). The most striking feature of the new taxon is the presence of three groups of wart-like or spathulate spines that connect adjacent valves to form short chains comprising 2 to 6 individuals. The taxonomical position of the new taxon is discussed, comparing it with similar freshwater Pinnularia taxa present on the same island, such as P. subantarctica (Manguin) Van de Vijver & Le Cohu and its variety elongata (Manguin) Van de Vijver & Le Cohu, as well as the elusive P. circumducta Manguin. A short review is made of all spine-bearing and/or colonial Pinnularia taxa described so far. Notes on its ecology are included.

Who takes responsibility for care failures?

The unacceptable behaviour of Sir Philip Watts, former chairman of Shell, and his Dutch colleague, Mr Van de Vijver, has been aired copiously in the press in recent weeks. The corporate image of Shell belied internal strife and misrepresentation of ‘proved’ oil and gas reserves over many years. Essentially they lied and they have rightly forfeited their jobs and their reputations. However, at the end of the day loss of investor confidence was the main consequence and no lives have been lost. Shell will now be dissected and voyeurs of all descriptions will offer armchair advice regarding the firm’s structure and culture. Compare this to avoidable loss of life or compromised levels of health and social care, which attract little comment and where the organizations responsible are rarely held accountable in the same way.

Amplification of a 280-Kilobase Core Region at the ERBB2 Locus Leads to Activation of Two Hypothetical Proteins in Breast Cancer

Amplification of the ERBB2 oncogene at 17q12 is clinically the most relevant genetic aberration in breast cancer and several studies have linked ERBB2 activation to poor clinical outcome. The development of targeted antibody-based therapy for ERBB2-overexpressing tumors and the possible role of ERBB2 as a predictor of chemotherapy treatment response have further emphasized the essential role of ERBB2 in breast cancer. Here, we performed a detailed characterization of the molecular events occurring at the ERBB2 amplicon in primary breast tumors. Analysis of the amplicon structure in 330 breast tumors by fluorescence in situ hybridization to a tissue microarray revealed a 280-kb common region of amplification that contains 10 transcribed sequences, including eight known genes. The expression levels of these 10 transcripts were determined in 36 frozen samples of grade-matched ERBB2-amplified and -nonamplified (as determined by fluorescence in situ hybridization) primary breast tumors by using quantitativereal-time reverse transcriptase-polymerase chain reaction. A highly significant association between amplification and expression levels was observed for six of these genes, including ERBB2 and two uncharacterized hypothetical proteins, MGC9753 and MGC14832. These results support the recent findings on the influence of copy number on gene expression levels and highlight novel genes that might contribute to the clinical behavior of ERBB2-amplified breast tumors.

Immigrant–majority group differences in cognitive performance: Jensen effects, cultural effects, or both?

When a positive correlation occurs between g-loadedness of a cognitive test and variable X, the result is termed a “Jensen effect.” Virtually all Dutch studies comparing immigrants with Dutch show that the differences in mean scores on intelligence tests are dependent on the g loading of the tests and are therefore clear Jensen effects. However, Helms-Lorenz, van de Vijver, and Poortinga [Intelligence 31 (2003) 9] challenge the overwhelming finding of Jensen effects and suggest that group differences on measures of phenotypic intelligence are more strongly caused by cultural differences than by g. We attempted to replicate Helms-Lorenz et al.'s finding of absence of Jensen effects on two large samples that took both culture-loaded and culture-reduced tests. We found proof of Jensen effects, a very large language bias effect in one specific intelligence test, and quite small cultural bias effects in the remaining intelligence tests. It appears that Helms-Lorenz et al.'s findings are an outlier among all empirical studies, which may be caused by the use of an unrepresentative set of tests.

Enhancing evolvability with mutation buffering mediated through multiple weak interactions

The evolutionary adaptability of a system is dependent on three organizational properties, self-organizing dynamics that are hierarchically organized, component redundancy, and multiple weak interactions [Towards high evolvability dynamics, in: G. van de Vijver, S. Salthe, M. Delpos (Eds.), Evolutionary Systems, Kluwer Academic Publishers, Dordrecht, 1998, pp. 147–169]. This study reports on the use of the dual dynamics network model as an aid in understanding the role multiple weak interactions play in enhancing evolutionary adaptability. Dual dynamics networks are self-organizing systems that consist of simple components that change local state due to the coupled influences from connected components exerting strong discrete decision-making influences and from groups of components exerting multiple weak influences [J. Theor. Biol. 193 (1998) 287]. The dual dynamics model has been enhanced to support investigations of properties relevant to a system’s capacity for evolvability, such as structure–function relationships, neutrality, adaptive tolerance, and evolutionary search performance. Three network types are investigated, each utilizing a different method of coupling strong and weak influences. The results demonstrate that the manner of coupling multiple weak interactions into the systems dynamics significantly affects the structure–function maps and the consequent evolvability characteristics. Specifically it is found that a form of coupling, denoted as linear modulation, enhances evolutionary adaptability. Linear modulation coupling requires that the weak interactions be integrated with strong interactions in a manner that implies a linear ordered relation between the possible state values of the components of the systems. When coupling functions that do not imply such an ordering of local state values are used, evolutionary adaptability is decreased.

Focus on breast cancer.

We would like to acknowledge Fredi Rojo for his assistance in the preparation of the figures.

Adapting Instruments for Use in Multiple Languages and Cultures: A Review of the ITC Guidelines for Test Adaptations

Summary: To facilitate the development of valid multicultural/multilingual tests, the International Test Commission (ITC) prepared the ITC Guidelines on Test Adaptations. This paper reviews the current version (cf. Van de Vijver & Hambleton, 1996 ), which consists of 22 guidelines on recommended practices pertaining to context, development, administration, documentation, and test-score interpretation, by identifying key principles in test adaptations and comparing them to a content analysis of the ITC Guidelines. The content analysis revealed a number of inconsistencies and ambiguities in a few guidelines, and proposals for reformulating them are given. A checklist to supplement the more narrative guidelines would also be helpful. Nevertheless, the review clearly demonstrates that the ITC Guidelines on Test Adaptations address key principles in test adaptations and constitute a significant standard or “code of conduct” in this field.

Canada Stream: A Glacial Meltwater Stream in Taylor Valley, South Victoria Land, Antarctica

The McMurdo Dry Valleys of South Victoria Land, Antarctica, form the largest of the desert oases found along the coast of Antarctica. Although this region is an extreme cold desert, glacial meltwater streams, which flow for 6-10 wk during the austral summer, are a prominent feature of the landscape. Canada Stream is in Taylor Valley and is one of 3 major streams draining Canada Glacier. The surrounding landscape is characterized by an absence of plant life, an underlying permafrost at a depth of 0.5 m, and prominent "patterned ground" features, which are large (3-5 m across) polygonal patterns formed through freeze/thaw cycles. In contrast to the barren landscape, many of the streams contain perennial algal mats and mosses, illustrating that the presence of liquid water allows for a photosynthetically based ecosystem even under the harshest conditions. Canada Stream is one of 10 streams that flow into Lake

N-terminal 10- and 12-kDa POMC fragments stimulate differentiation of lactotrophs.

Medium conditioned by a highly enriched population of gonadotrophs, cultured as reaggregates in the presence of 0.01 nM GnRH, was concentrated, separated on a reversed-phase HPLC column, and tested for activity on lactotroph development in pituitary reaggregate cell cultures of 14-day-old rats. The number of cells expressing prolactin (PRL) mRNA was estimated by image analysis after in situ hybridization of paraffin-embedded sections. The number of these cells entering the mitotic cycle was estimated by autoradiography of [3H]thymidine ([3H]T) incorporation. One HPLC column fraction expanded the section area occupied by PRL mRNA cells without displaying an effect on [3H]T labeling of these cells, indicating that this fraction induces differentiation in the lactotroph lineage. The latter fraction was further purified on a second reversed-phase HPLC column, a gel filtration column, and a final reversed-phase HPLC column. From the last column, four substances were isolated that all selectively induced differentiation of lactotrophs. Each of them had an N-terminal amino acid sequence identical to the N-terminal domain of rat proopiomelanocortin (POMC). As determined by mass spectrometric analysis, the M(r)s were 10,091, 10,289, 12,238, and 12,247 Da, respectively. The C-terminal extension of these compounds is possibly up to Gln74 for the former two compounds and up to Gly95 for the latter two. Authentic purified human POMC(1-76) mimicked the effects of the purified 10- and 12-kDa rat POMC fragments. The present data suggest that certain isoforms of rat POMC(1-74) and human POMC(1-76) can stimulate lactotroph growth through a differentiation-inducing action on progenitor cells.