Matrix metalloproteinase-2 (a.k.a. learn more Gelatinase A, or Mmp2 in zebrafish) is known to have roles in pathologies such as arthritis, in which its function is protective, as well as in cancer metastasis, in which it is activated as part of the migration and invasion of metastatic cells. It is also required during development and the regeneration of tissue architecture after wound healing, but its roles in tissue remodelling are not well understood. Gelatinase A is activated post-translationally by proteolytic cleavage, making information about its transcription and even patterns of protein accumulation difficult to relate to biologically relevant activity. Using a transgenic reporter of endogenous Mmp2 activation in zebrafish, we describe its accumulation and post-translational proteolytic activation during the embryonic development of the tail. Though Mmp2 is expressed relatively ubiquitously, it seems to be active only at specific locations and times. Mmp2 is activated robustly in the neural tube and in maturing myotome boundaries. It is also activated in the notochord during body axis straightening, in patches scattered throughout the epidermal epithelium, in the gut, and on cellular protrusions extending from mesenchymal cells in the fin folds. The activation of Mmp2 in the notochord, somite boundaries and fin folds associates with collagen remodelling in the notochord sheath, myotome boundary ECM and actinotrichia respectively. Mmp2 is likely an important effector of ECM remodelling during the morphogenesis of the notochord, a driving structure in vertebrate development. It also appears to function in remodelling the ECM associated with growing epithelia and the maturation of actinotrichia in the fin folds, mediated by mesenchymal cell podosomes.Obtaining endocrine data from alternative sample types such as baleen and other keratinized tissues has proven a valuable tool to investigate reproductive and stress physiology via steroid hormone quantification, and metabolic stress via thyroid hormone quantification in whales and other vertebrates. These alternative sample types provide an integrated measure of plasma levels over the period that the structure was growing, thus capturing months or even years of an individual’s endocrine history. Additionally, their robust and stable keratin matrix allows such samples to be stored for years to decades, enabling the analysis and comparison of endocrine patterns from past and modern populations. However, the extraction and analysis of hormones from baleen and other keratinized tissues remains novel and requires both biological and analytical validations to ensure the method fulfills the requirements for its intended use. We utilized baleen recovered at necropsy from southern right whales (Eubalaena australis) that died at Península Valdés, Argentina, using a commercially available progesterone enzyme immunoassay (EIA) to address two methodological questions 1) what is the minimum sample mass required to reliably quantify hormone content of baleen samples analyzed with commercially available EIAs, and 2) what is the optimal ratio of solvent volume to sample mass, i.e., the ratio that yields the maximum amount of hormone with high accuracy and low variability between replicates. We concluded that masses of at least 20 mg should be used whenever possible, and extraction is best performed using an 801 ratio of solvent to sample (volume of solvent to sample mass; μlmg). These results can help researchers to make informed methodological decisions when using a destructive extraction method with rare or unique specimens.Female sperm storage (FSS) has been demonstrated to occur in representatives from all major vertebrate groups and has been hypothesized to have several possible adaptive benefits that may maximize reproductive success of its practitioners. However, while the range of taxa that exhibit FSS and its possible evolutionary benefits have received significant attention in past years, the physiological mechanisms by which FSS occurs in vertebrates have only recently been explored. In this study, we examined the potential role of gonadal steroid hormones in regulating FSS in the bonnethead Sphyrna tiburo, a small hammerhead species in which females have been shown to be capable of storing male spermatozoa for up to 6 – 7 months following copulation. Like past studies on this species, we observed associations between plasma concentrations of the gonadal steroids 17β-estradiol, testosterone, and progesterone with FSS in female bonnetheads, suggesting roles for these hormones in regulating this process. Using immunohistochemistry, we also observed presence of androgen receptor, estrogen receptor alpha (ERα), and progesterone receptor in epithelial cells of sperm storage tubules in the bonnethead oviducal gland, as well as occurrence of ERα in stored spermatozoa, specifically during the sperm storage period. These results suggest that E2, T, and P4 may regulate certain aspects of FSS in bonnethead indirectly through actions on the female reproductive tract, whereas E2 may also have direct effects on sperm function. This is the first study on the regulation of FSS in sharks and has formed a basis for future work geared towards improving our understanding of this process in chondrichthyans.Since trastuzumab-resistance remains a major obstacle to the successful treatment of HER2-positive breast cancer, a detailed understanding of the mechanisms responsible is required to direct future pharmacotherapeutic strategies. Recently, several studies have indicated that the quiescent natures of cancer stem cells contribute to treatment resistance and tumor recurrence. Thus, in this study, we investigated the mechanism underlying trastuzumab resistance in a quiescent cell population using tumorsphere cultures and explored better therapeutic strategies to overcome trastuzumab resistance in HER2-positive breast cancer patients. We observed that most cells in SK-BR-3 tumorspheres were quiescent, showing the accumulation of cells at the G0/G1 phase as compared to cells in monolayer culture. Furthermore, SK-BR-3 tumorspheres exhibited enhanced EGFR/HER2 signaling, which was incompletely inhibited by trastuzumab, and subsequently led to trastuzumab-resistance. Interestingly, cytoplasmic estrogen receptor α (ERα) expression was markedly elevated in tumorspheres and was associated with enhanced EGFR/HER2 signaling.