We have previously demonstrated the association of the chicken lipocalin Ex-FABP with cartilage formation and inflammatory responses as a marker of these processes (Descalzi Cancedda et al., Biochim. Biophys. Acta 1482, 127-135, 2000). Here we report the isolation and characterisation of a new lipocalin gene laying upstream the Ex-FABP, thus representing the second member of a possible genomic cluster. This gene contains an open reading frame coding for a polypeptide of about 19 kDa. The amino-acid sequence revealed a conserved lipocalin secondary structure. Tissue distribution of the protein in developing embryos showed a preferential expression in the heart although mRNA transcripts could be detected also in muscle, lung and liver. The lowest expression was observed in the stomach, brain and skin. During endochondral formation of long bones, the protein is differentially distributed, as the transcripts, evidenced in the tibia by in situ hybridisation, are present in the hypertrophic cone of the cartilage and mostly absent in the area of the proliferating chondrocytes. Such developmental regulation was observed also in vitro in cultured chondrocytes where the transcripts were barely detectable in dedifferentiated cells but highly expressed in hypertrophic chondrocytes. The protein was also significantly induced by lipopolysaccharide stimulation of chondrocytes, indicating a possible involvement in acute phase response. Raising specific antibodies in a rabbit allowed validating, at the protein level, all the transcriptional data. Moreover, we gained evidence that the protein is actively secreted in the extracellular matrix surrounding the chondrocytes. Because of its peculiar expression in cartilage, this new protein was named chondrogenesis-associated lipocalin beta (thereafter referred to as CAL beta). The close similarity between Ex-FABP and CAL beta expression patterns supports the hypothesis of a genomic organisation in a cluster where both genes could be co-ordinately regulated.

中文翻译：

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CALbeta，与软骨形成和炎症有关的新型脂钙蛋白。

我们先前已经证明了鸡脂质运载蛋白Ex-FABP与软骨形成和炎症反应的关联作为这些过程的标志物（Descalzi Cancedda等人，Biochim.Biophys.Acta 1482，127-135，2000）。在这里，我们报告了一个新的脂蛋白基因的分离和表征，该基因位于Ex-FABP上游，因此代表了可能的基因组簇的第二个成员。该基因包含编码约19kDa的多肽的开放阅读框。氨基酸序列揭示了保守的脂环蛋白二级结构。尽管在肌肉，肺部和肝脏中也可以检测到mRNA转录本，但蛋白质在发育中的胚胎中的组织分布在心脏中优先表达。在胃，脑和皮肤中观察到最低的表达。在长骨的软骨内形成过程中，该蛋白质差异分布，因为通过原位杂交在胫骨中证实的转录本存在于软骨的肥大视锥细胞中，并且在增殖的软骨细胞区域中大多不存在。在体外培养的软骨细胞中也观察到了这种发育调节，其中在脱分化细胞中几乎不能检测到转录本，而在肥大性软骨细胞中则高度表达。脂多糖刺激软骨细胞也显着诱导了该蛋白，表明可能参与了急性期反应。在兔子体内培养特异性抗体可以在蛋白质水平上验证所有转录数据。此外，我们获得了证据，表明该蛋白质活跃地分泌在软骨细胞周围的细胞外基质中。由于其在软骨中的特殊表达，因此将该新蛋白命名为与软骨生成相关的脂质钙蛋白β（以下称为CALβ）。Ex-FABP和CAL beta表达模式之间的紧密相似性支持了一个基因组组织在一个簇中的假设，在簇中两个基因都可以被协调地调控。