Characterization of Polish Steinernema silvaticum isolates (Nematoda: Steinernematidae) using morphological and molecular data.

Four strains of entomopathogenic nematodes were isolated with a live trap method in southern Poland. The isolates were identified as Steinernema silvaticum based on morphological, morphometric and molecular data. Infective juveniles of Polish S. silvaticum isolates differ in body length from S. weiseri (951 vs 740 µm, respectively), and in the hyaline tail portion from S. kraussei (48 vs 38%, respectively). First-generation males of S. silvaticum are longer than those of S. kraussei, S. weiseri and S. ichnusae (1829 vs 1400, 1180 and 1341 µm, respectively). Males of S. silvaticum and a sister species S. kraussei can be distinguished by the distance from the anterior end to the nerve ring (142 vs 105 µm), spicule (66 vs 49 µm) and gubernaculum length (45 vs 33 µm), and the presence of a mucron. The analysis of internal transcribed spacer (ITS), D2-D3 and cox1 sequences of the tested nematodes revealed differences of 3-5%, 3% and 12-13%, respectively, from S. kraussei strains. The phylogeny of both nuclear and mitochondrial genes indicated close relationships of the Polish S. silvaticum isolates with S. kraussei, S. oregonense and S. cholashanense. The reproductive isolation of the studied isolates was confirmed by hybridization tests with other European feltiae-kraussei group representatives. This study has supplemented the original description of S. silvaticum with morphological and morphometric characterization of the first-generation males and females. This is also the first molecular study of this species based on a multi-gene approach.

Mechanisms involved in the development of the small intestine mucosal layer in postnatal piglets.

The use of complementary visualization and measurement techniques allowed accurate description and quantification of changes in the intestinal mucosal architecture and provided a comprehensive outlook on the dynamics of remodelling and maturation processes of the mucosal layer taking place in the small intestine of piglets from birth to weaning. The aim of the study was to examine the early postnatal development of the small intestine in pigs. Three techniques were used: scanning electron microscopy (measurements of villus density and shape, height of enterocytes and microvilli, cell exfoliation, and location of extrusion zones), optical microscopy (cross section, measurement of structures: villus length and width; crypt depth; mucosal thickness), and confocal microscopy (cell localization, apoptosis, exfoliation and migration). The postnatal development of the mucosal layer of the small intestine was reflected in changes in the density, length, width, and shape of villi, crypt depth, replacement of enterocyte population, and arrangement. The presence of deep transverse furrows on villus corpus and vacuolated fetal-type enterocytes in the mucosal layer of the small intestine, which are able to engulf large amounts of colostrum shortly after birth, appears to play an important role in the observed phenomenon of straightening of the villus height and increasing of the villus diameter shortly after birth. We hypothesized that the intestinal mucosal layer is compressed before birth and ready to unfold within a short time after birth.

Gradual disappearance of vacuolated enterocytes in the small intestine of neonatal piglets.

The unique feature of enterocytes in newborn mammals is the presence of an apical canalicular system (ACS) leading to production of large vacuoles, important for colostral macromolecule uptake. The vacuolated fetal-type enterocytes (VFE) enable transfer of colostral and milk proteins from the intestinal lumen across the epithelium without loosing their biological activity. First VFE are observed in the pig and lamb fetuses in the second trimester of pregnancy, located at the upper part of villi in the proximal region of the fetal small intestine and subsequently in the middle and distal regions. After birth the VFE are replaced with enterocytes lacking ACS. The present study aimed to investigate the depletion of VFE in the small intestine in the sow reared pig neonates during the first postnatal weeks using scanning electron microscopy (SEM). The SEM analysis demonstrated the gradual disappearance of vacuolated enterocytes in time. VFE remained in the jejunum for a few days after birth, whereas in the duodenum single VFE were present only at birth. In the proximal jejunum, the VFE were localized in the upper part of the villi, and disappeared until the day 3 of life. VFE were present in the mid and distal jejunum, and diminished gradually until day 14 of life. By the day 21 of life, the vacuolated cells were not observed neither in the jejunum nor ileum. In conclusion, morphology analysis of pig small intestinal mucosa suggests that replacement of fetal type vacuolated enterocytes is resumed within 21 days after birth.

Into the unknown--the death pathways in the neonatal gut epithelium.

Apoptosis is a fundamental process in the development of the fast growing intestinal mucosa. Apoptotic cells are present along the whole length of the villi and in the crypts. The mechanisms involved in the induction of apoptosis in the gut mucosa are still unknown. Cytokines are believed to play a role in auto- and paracrine models because the cells are dying in so-called "packets" containing neighboring cells. In the rapidly developing gut of neonates, the apoptosis rate is transiently reduced in the first days of life, enhancing the growth of mucosa. Afterwards, apoptosis plays a role in the exchange of the enterocyte population, facilitating maturation of the mucosa. The presence of autophagic cells has been confirmed for the first time in the developing gut. Deprivation of growth factors during feeding artificial milk formula led to an increased apoptosis rate. Supplementation with leptin reduced cell apoptosis and increased the mitosis-to-apoptosis ratio. Autophagy was also diminished. The key to healthy gut mucosa growth in early life, especially in fast-growing animals, is colostrum, which supplies nutritional and defensive components together with supplementary growth factors, cytokines and hormones essential for growth and maturation of gut mucosa.

Light and scanning electron microscopy evaluation of the postnatal small intestinal mucosa development in pigs.

Modifications in the structure of gastrointestinal mucosa is often used to evaluate gut function for instance during the development or in response to particular food components. Scanning electron microscopy (SEM) gives a chance to observe the surface of the gut epithelium in three dimensions. However, this technique is seldom used due to technical difficulties. The present study attempted to investigate the intestinal mucosa structure changes in the postnatal pig using light and scanning electron microscopy technique. Experiments were carried out on sow reared piglets from birth until 38 days of age. Piglets were sacrificed at birth and at the 3(rd), 7(th), 21(st) and 38(th) day of life. The entire gastrointestinal tract was immediately harvested and the whole thickness tissue samples were taken from the duodenum, jejunum and ileum for optical and scanning electron microscopy. SEM analyses corroborated with histometry made by optical microscopy. Moreover, a number of shape modifications of the villi and its surface have been observed. The development changes in small intestine mucosa during the first 3 weeks were manifested in shape, size and density of villi. In conclusion, the structure of small intestinal mucosa undergoes profound structural changes. SEM gives a new dimension in the investigation of gut mucosa.