No abstract

We have demonstrated the selective secretion of high mol wt PRL series (big big PRL) in women with hyperprolactinemia and normal ovarian function. This observation suggests that big big PRL is immunologically similar, but biologically less active, than monomeric or little PRL. In this study we determined the molecular size heterogeneity of immunoreactive PRL in the serum from two ovulatory hyperprolactinemic women (subjects A and B) who had large amounts of serum big big PRL during a menstrual cycle and/or gestation. Serum samples obtained throughout the menstrual cycle (days 6, 10, 14, 17, 23, and 28, taking as day 1 the first day of bleeding) and pregnancy (weeks 7, 9, 11, 15, 20, 25, 30, 34, and 38) were fractionated by gel filtration chromatography. PRL was identified in column eluates by specific RIA. Two additional pregnant women, one with a bromocriptine-treated PRL-secreting adenoma (subject C), and a normal woman (subject D) were studied. Big big PRL was the predominant species throughout the different phases of the menstrual cycle in subject B, comprising 70-80% of the total immunoreactive PRL. Most of the remainder was big PRL, and little PRL was present in only small amounts (6-12%) during the luteal phase. During their pregnancies, the serum PRL in subjects A and B initially was mostly big big PRL, but later in gestation the PRL composition shifted from the high mol wt variants to little PRL. The infant's cord (subject A) and peripheral (subject B) serum at birth contained appreciable quantities of big big and big PRL, respectively. These results indicate that structural changes in PRL occur during pregnancy and the menstrual cycle which are probably influenced by the hormonal environment. In addition, the occurrence of larger mol wt PRL species in the serum of the infant of a hyperprolactinemic mother suggests that the presence of high proportions of big big PRL in the serum is genetically determined.

Skeletal muscle morphogenesis depends upon interactions between developing muscle fibers and the extracellular matrix (ECM) that anchors fibers to the myotendinous junction (MTJ). The pathways that organize the ECM and regulate its engagement by cell-matrix adhesion complexes (CMACs) are therefore essential for muscle integrity. Here, we demonstrate the impact of transmembrane protein 2 (tmem2) on cell-matrix interactions during muscle morphogenesis in zebrafish. Maternal-zygotic tmem2 mutants (MZtmem2) exhibit muscle fiber detachment, in association with impaired laminin organization and ineffective fibronectin degradation at the MTJ. Similarly, disorganized laminin and fibronectin surround MZtmem2 cardiomyocytes, which could account for their hindered movement during cardiac morphogenesis. In addition to ECM defects, MZtmem2 mutants display hypoglycosylation of α-dystroglycan within the CMAC, which could contribute to the observed fiber detachment. Expression of the Tmem2 ectodomain can rescue aspects of the MZtmem2 phenotype, consistent with a possible extracellular function of Tmem2. Together, our results suggest that Tmem2 regulates cell-matrix interactions by affecting both ECM organization and CMAC activity. These findings evoke possible connections between the functions of Tmem2 and the etiologies of congenital muscular dystrophies, particularly dystroglycanopathies.

Skeletal muscle morphogenesis depends upon interactions between developing muscle fibers and the extracellular matrix (ECM) that anchors fibers to the myotendinous junction (MTJ). The pathways that organize the ECM and regulate its engagement by cell-matrix adhesion complexes (CMACs) are therefore essential for muscle integrity. Here, we demonstrate the impact of transmembrane protein 2 (tmem2) on cell-matrix interactions during muscle morphogenesis in zebrafish. Maternal-zygotic tmem2 mutants (MZtmem2) exhibit muscle fiber detachment, in association with impaired laminin organization and ineffective fibronectin degradation at the MTJ. Similarly, disorganized laminin and fibronectin surround MZtmem2 cardiomyocytes, which could account for their hindered movement during cardiac morphogenesis. In addition to ECM defects, MZtmem2 mutants display hypoglycosylation of α-dystroglycan within the CMAC, which could contribute to the observed fiber detachment. Expression of the Tmem2 ectodomain can rescue aspects of the MZtmem2 phenotype, consistent with a possible extracellular function of Tmem2. Together, our results suggest that Tmem2 regulates cell-matrix interactions by affecting both ECM organization and CMAC activity. These findings evoke possible connections between the functions of Tmem2 and the etiologies of congenital muscular dystrophies, particularly dystroglycanopathies.

Background Atrioventricular valve development relies upon the precisely defined dimensions of the atrioventricular canal (AVC). Current models suggest that Wnt signaling plays an important role atop a pathway that promotes AVC development. The factors that confine AVC differentiation to the appropriate location, however, are less well understood. Results Transmembrane protein 2 (Tmem2) is a key player in restricting AVC differentiation: in zebrafish, tmem2 mutants display an expansion of AVC characteristics, but the molecular mechanism of Tmem2 function in this context remains unclear. Through structure‐function analysis, we demonstrate that the extracellular portion of Tmem2 is crucial for its role in restricting AVC boundaries. Importantly, the Tmem2 ectodomain contains regions implicated in the depolymerization of hyaluronic acid (HA). We find that tmem2 mutant hearts exhibit excess HA deposition alongside broadened distribution of Wnt signaling. Moreover, addition of ectopic hyaluronidase can restore the restriction of AVC differentiation in tmem2 mutants. Finally, we show that alteration of a residue important for HA depolymerization impairs the efficacy of Tmem2 function during AVC development. Conclusions Taken together, our data support a model in which HA degradation, regulated by Tmem2, limits the distribution of Wnt signaling and thereby confines the differentiation of the AVC.