Epithelial Splicing Regulatory Protein 1 (ESRP1) is a new regulator of stomach smooth muscle development and plasticity.

In vertebrates, stomach smooth muscle development is a complex process that involves the tight transcriptional or post-transcriptional regulation of different signalling pathways. Here, we identified the RNA-binding protein Epithelial Splicing Regulatory Protein 1 (ESRP1) as an early marker of developing and undifferentiated stomach mesenchyme. Using a gain-of-function approach, we found that in chicken embryos, sustained expression of ESRP1 impairs stomach smooth muscle cell (SMC) differentiation and FGFR2 splicing profile. ESRP1 overexpression in primary differentiated stomach SMCs induced their dedifferentiation, promoted specific-FGFR2b splicing and decreased FGFR2c-dependent activity. Moreover, co-expression of ESRP1 and RBPMS2, another RNA-binding protein that regulates SMC plasticity and Bone Morphogenetic Protein (BMP) pathway inhibition, synergistically promoted SMC dedifferentiation. Finally, we also demonstrated that ESRP1 interacts with RBPMS2 and that RBPMS2-mediated SMC dedifferentiation requires ESRP1. Altogether, these results show that ESRP1 is expressed also in undifferentiated stomach mesenchyme and demonstrate its role in SMC development and plasticity.

Analysis of the expression of p53 during the morphogenesis of the gastroesophageal mucosa of Gallus gallus domesticus (Linnaeus, 1758).

Ontogenesis comprises a series of events including cell proliferation and apoptosis and resulting in the normal development of the embryo. Protein p53 has been described as being involved in the development of several animal species. The aim of this study was to analyze the expression of protein p53 during the morphogenesis of the gastroesophageal mucosa of Gallus gallus domesticus and to correlate it with the histogenesis of structures present in this tissue. We used 24 embryos (at 12-20 days of incubation) and the thymus of two chickens. Immunohistochemical analysis was performed with the ABC indirect method. The expression of p53 in the gastroesophageal mucosa increased during the formation of the organ, mainly at the stages during which tissue remodeling and cell differentiation began. In the esophagus at stages 42 and 45, we observed immunoreactive (IR) cells in the surface epithelium and in early esophageal glands. In the proventriculus at stages 39-45, IR cells were present in the epithelial mucosa and rarely in the proventricular glands. In the gizzard after stage 42, we found IR cells mainly in the medial and basal epithelial layers of the mucosa and especially within the intercellular spaces that appeared at this phase and formed the tubular gland ducts. Thus, protein p53 occurs at key stages of development: in the esophagus during the remodeling of esophageal glands, in the proventriculus during the differentiation of the epithelium of the mucosa and in the gizzard during the formation of tubular glands.

The RNA-binding protein RBPMS2 regulates development of gastrointestinal smooth muscle.

BACKGROUND & AIMS: Gastrointestinal development requires regulated differentiation of visceral smooth muscle cells (SMCs) and their contractile activities; alterations in these processes might lead to gastrointestinal neuromuscular disorders. Gastrointestinal SMC development and remodeling involves post-transcriptional modification of messenger RNA. We investigated the function of the RNA-binding protein for multiple splicing 2 (RBPMS2) during normal development of visceral smooth muscle in chicken and expression of its transcript in human pathophysiological conditions. METHODS: We used avian replication-competent retroviral misexpression approaches to analyze the function of RBPMS2 in vivo and in primary cultures of chicken SMCs. We analyzed levels of RBPMS2 transcripts in colon samples from pediatric patients with Hirschsprung's disease and patients with chronic pseudo obstruction syndrome (CIPO) with megacystis. RESULTS: RBPMS2 was expressed strongly during the early stage of visceral SMC development and quickly down-regulated in differentiated and mature SMCs. Misexpression of RBPMS2 in differentiated visceral SMCs induced their dedifferentiation and reduced their contractility by up-regulating expression of Noggin, which reduced activity of bone morphogenetic protein. Visceral smooth muscles from pediatric patients with CIPO expressed high levels of RBPMS2 transcripts, compared with smooth muscle from patients without this disorder. CONCLUSIONS: Expression of RBPMS2 is present in visceral SMC precursors. Sustained expression of RBPMS2 inhibits the expression of markers of SMC differentiation by inhibiting bone morphogenetic protein activity, and stimulates SMC proliferation. RBPMS2 transcripts are up-regulated in patients with CIPO; alterations in RBPMS2 function might be involved in digestive motility disorders, particularly those characterized by the presence of muscular lesions (visceral myopathies).

Ontogeny of ghrelin mRNA expression and identification of ghrelin-immunopositive cells in the gastrointestinal tract of the Peking duck, Anas platyrhynchos.

Ghrelin is an acylated peptide and an endogenous ligand for the growth hormone secretagogue receptor (GHS-R), and stimulates growth hormone release and food intake in mammals. Peking duck is a very fast growing species of poultry. Although the sequence and structure of ghrelin have recently been determined, the expression of ghrelin in Peking duck has not been studied. Here, we investigated the tissue expression and distribution of ghrelin by RT-PCR and immunohistochemistry, respectively, in Peking duck at different stages of development. Ghrelin mRNA expression was mainly detected in the proventriculus and proventriculus-gizzard junction. It was first expressed, but weakly, on embryonic day 14 (E14); the expression increased by embryonic day 21 (E21), and was maintained at high levels between post-hatching-day 1 (P1) and post-hatching-day 60 (P60). Weak expression of ghrelin mRNA was also found in the gizzard and duodenum. In the gastrointestinal tract of growing Peking duck in P60, the largest number of ghrelin-ip cells was detected in the epithelium of the compound tubular glands in the proventriculus and the next largest number was in the proventriculus-gizzard junction. Very few ghrelin-ip cells were located in the epithelium of the simple tubular glands adjacent to the gizzard. No ghrelin-ip cells were observed elsewhere in the gastrointestinal tract. Ghrelin-ip cells were found in embryos as early as day E21; at the same time, the compound tubular glands in the proventriculus had formed. The numbers of ghrelin-ip cells on P1 were similar to those of E21 embryos. However, on P60, high numbers of strongly stained ghrelin-ip cells were found to be scattered in the epithelium of the compound tubular glands in the proventriculus. The density of ghrelin-ip cells (cells/mm(2)) in the proventriculus on P60 was significantly greater than those of P1 and E21 embryos. These results demonstrate that ghrelin is expressed in the Peking duck gastrointestinal tract, especially in the proventriculus, from mid-late-stage embryos to growing period and suggested an involvement of ghrelin in the development and biology of the gastrointestinal tract of the Peking duck.

Fine structure of smooth muscle cells grown in tissue culture.

The fine structure of smooth muscle cells of the embryo chicken gizzard cultured in monolayer was studied by phase-contrast optics and electron microscopy. The smooth muscle cells were irregular in shape, but tended to be elongate. The nucleus usually contained prominent nucleoli and was large in relation to the cell body. When fixed with glutaraldehyde, three different types of filaments were noted in the cytoplasm: thick (150-250 A in diameter) and thin (30-80 A in diameter) myofilaments, many of which were arranged in small bundles throughout the cytoplasm and which were usually associated with dark bodies; and filaments with a diameter of 80-110 A which were randomly orientated and are not regarded as myofilaments. Some of the aggregated ribosomes were helically arranged. Mitochondria, Golgi apparatus, and dilated rough endoplasmic reticulum were prominent. In contrast to in vivo muscle cells, micropinocytotic vesicles along the cell membrane were rare and dense areas were usually confined to cell membrane infoldings. These cells are compared to in vivo embryonic smooth muscle and adult muscle after treatment with estrogen. Monolayers of cultured smooth muscle will be of particular value in relating ultrastructural features to functional observations on the same cells.

Cytoplasmic filaments in developing and adult vertebrate smooth muscle.

An extensive study of adult and developing smooth muscle has revealed the widespread occurrence of a distinct filament with an average diameter of about 100 A (termed the 100 A filament). Unlike that of myofilaments, their appearance in longitudinal section is uniform, but in transverse section they have a round profile, occasionally exhibiting a less electron-opaque core. The 100 A filaments are almost invariably preserved under a variety of fixation procedures, whereas myofilaments, particularly the thicker filaments, are preserved inconsistently. The 100 A filaments appear to be randomly oriented throughout the cytoplasm, either singly or in small groups, although they are sometimes concentrated in the juxtanuclear region of the smooth muscle cells. The intimate association of 100 A filaments with dark bodies, in both developing and adult smooth muscle cells, may indicate that these filaments either play a role in dark body formation or, at least, constitute a part of the dark body. The 100 A filaments are conspicuous in developing smooth muscle cells and occasionally form networks or clusters; they appear to decrease in relative number as maturation proceeds, but considerable numbers are still present in adult tissue.

Light chains of chicken embryonic gizzard myosin.

1. Myosin from gizzards of 15-day-old chicken embryos was highly purified by ammonium sulfate fractionation in the presence of ATP and MgCl2, ultra-centrifugation and Sepharose 4B chromatography. 2. The myosin composed of heavy and three light chains as determined by sodium dodecyl sulfate (SDS) gel electrophoresis. The molecular weights of the light chains were 23,000 (L23), 20,000 (L20), and 17,000 (L17), respectively. The amount of L23 light chain decreased and disappeared, and the L17 light chain increased steadily in the course of development. The amount of L20 light chain did not change. 3. ATPase activity of the embryonic myosin was essentially the same as that of adult myosin. The change in the light chain pattern in the course of development did not correlate to the ATPase activity. 4. Antigenicity of the heavy chains in the embryonic myosin was the same as that of the adult heavy chains. However, antibodies to light chains were not detected in the antibodies to either the embryonic or adult myosins.

Isolation of the chick myosin alkali light chain gene expressed in embryonic gizzard muscle and transitional expression of the light chain gene family in vivo.

A chick embryonic myosin alkali light chain L23 gene that is expressed transiently at embryonic stages in chick skeletal, cardiac and smooth muscles and in brain continuously from embryo to adult stages, was isolated and characterized. Sequence analysis showed that the exonic sequence of this gene was identical with that of embryonic myosin light chain mRNA except for one base replacement. This gene is a single gene of 5200 bases, which is divided into seven exons by six introns, and the positions of inserts of all the introns are well-conserved as in the skeletal and cardiac muscle myosin alkali light chain genes. Therefore, this embryonic myosin light chain gene can be classified as a member of the myosin alkali light chain gene family, and these three genes may have originated from a common ancestral gene. Transcription of the embryonic light chain gene starts from the same initiation site 33 bases upstream from ATG in embryonic muscle tissues and brain. Comparison of the nucleotide sequence around the promotor region of the embryonic myosin light chain gene with the corresponding regions of the skeletal and cardiac myosin light chain genes showed that the 11-base consensus sequence (TCCTATTTATAG) is present about 100 bases upstream from the transcription initiation site in each gene.

A chicken embryo-specific myosin light chain (L23) appears to be identical with one of brain myosin light chains.

A novel embryo-specific myosin light chain of 23 kDa molecular weight (L23) was found previously in embryonic chicken skeletal, cardiac, and smooth muscles (Takano-Ohmuro et al. (1985) J. Cell Biol. 100, 2025-2030). When we examined myosin in embryonic and adult brain by two-dimensional electrophoresis, 23 kDa myosin light chain present in brain (Burridge & Bray (1975) J. Mol. Biol. 99, 1-14) comigrated with L23. Two monoclonal antibodies, EL-64 and MT-185d, were applied to clarify the identity of the brain 23 kDa myosin light chain and the chicken embryonic muscle L23. The two antibodies recognize different antigenic determinants in the L23 molecule; the former antibody is specific for L23, whereas the latter recognizes the sequence common to fast skeletal muscle myosin light chains 1 and 3, and also L23. The immunoblots combined with two-dimensional gel electrophoresis showed that both EL-64 and MT-185d can bind to the brain 23 kDa myosin light chain as well as the chicken embryonic muscle L23. These results indicate that chicken brain and chicken embryonic muscles contain a common myosin light chain of 23 kDa molecular weight.

Accumulation of tropomyosin in developing chicken gizzard smooth muscle.

Smooth muscle of chicken embryonic gizzards has been shown to contain 9 tropomyosin isoforms (E1, E2, E3, E4, E5, E6, E7, E8, and E9) in addition to alpha and beta isoforms (Hosoya et al. (1989) J. Biochem. 105, 712-717). At the early stages of development, the amount of these isoforms was larger than those of alpha and beta isoforms. However, they gradually decreased at later stages and finally disappeared completely after hatching. By using two-dimensional gel electrophoresis and an image analyzing system, we examined the process of tropomyosin accumulation in gizzard smooth muscle development. The accumulation patterns of tropomyosin isoforms and their relative molar ratios to actin in embryonic development were different from those in the stages after hatching. The relative molar ratio of tropomyosin to actin in the thin filament preparation of embryonic gizzards was lower than that of adult, and it gradually increased in the course of embryonic development.

Changes in myosin isozymes during development of chicken gizzard muscle.

The distribution of myosin isozymes in embryonic and adult chicken gizzard muscle were examined by electrophoresis in a non-denaturing gel system (pyrophosphate acrylamide gel electrophoresis), and both light and heavy chains of embryonic and adult myosin isozymes were compared. In pyrophosphate acrylamide gel electrophoresis, there were three isozyme components in embryonic gizzard myosin, but only one isozyme in adult gizzard myosin. The mobility of the fastest migrating embryonic isozyme was similar to that of the adult isozyme. The three embryonic isozymes differ from each other in the light chain distribution. Two of them contain an embryo-specific myosin light chain, which is characterized by its molecular weight and isoelectric point, whereas the other embryonic myosin isozyme contained the same light chains as the adult myosin. The pattern of peptide fragments of embryonic heavy chain produced by digestion with alpha-chymotrypsin in the presence of SDS was not distinguishable from that of adult myosin heavy chain. Thus there are myosin isozymes specific to embryonic gizzard muscle which exhibit embryo-specific light chain compositions, but are similar to adult gizzard myosin in their heavy chain structure.

Tropomyosin isoforms in developing chicken gizzard smooth muscle.

In the embryonic smooth muscle of chicken gizzards we found 4 high-Mr-type and 5 low-Mr-type tropomyosin isoforms in addition to alpha- and beta-isoforms reported already. The criteria by which they were identified as tropomyosin isoforms were as follows: 1) anomalous reduction of electrophoretic mobility in the presence of urea, 2) cross reactivity with antisera against tropomyosins, 3) inclusion in a tropomyosin preparation obtained by the usual method for tropomyosin purification, and 4) binding ability to skeletal muscle actin. At the early stages of development, the amounts of these isoforms were larger than those of alpha- and beta-isoforms, but they gradually decreased at later stages and finally disappeared completely after hatching. Our previous study of gizzard smooth muscle showed that the amount ratio of accumulated tropomyosin to gamma-actin was reasonably constant in the development after hatching, while, at the earlier embryonic stages (7-14 d of incubation), it was lower than expected. The isoforms found in this study were present in amounts large enough to bring the ratio at the earlier stages up to the constant amount ratio observed after hatching. Therefore, the coordinate accumulation of actin and tropomyosin was suggested to occur even at the embryonic stages.

Versatile roles for sonic hedgehog in gut development.

Sonic hedgehog (Shh) is a gene encoding a protein that can be secreted and act as a morphogen. The protein exerts versatile and important effects on the surrounding cells by binding a specific receptor, named patched. So far Shh has been shown to be involved in the morphogenesis and cytodifferentiation of many organ systems, such as notochord, floor plate, limb, pancreas, and pituitary gland, to mention only a few examples. Shh is also involved in the determination of left-right asymmetry, at least in the chicken embryo. Here we present evidence that Shh is one of the key genes whose activity is pivotal for the normal morphogenesis and differentiation of digestive organs. Epithelial Shh regulates the formation of stomach glands and stratification of the mesenchyme into connective tissue and smooth muscle. It exerts its effect often through the induction of bone morphogenetic protein (BMP) genes in the mesenchyme. Thus, Shh is a key player in the epithelial-mesenchymal interactions in the development of the gut.

Myosin light chain kinase expression during smooth muscle development.

The expression of smooth muscle myosin light chain kinase (MLCK) was investigated during chicken gizzard development. The molecular weight and the antigenic properties of MLCK did not change during development. The use of anion exchange high performance liquid chromatography (HPLC) enabled us to distinguish between MLCKs from post-hatched and adult chickens. A partial amino acid sequence determination of 4-day-old gizzard MLCK failed to disclose differences in the primary sequences of the two proteins. The results suggest that MLCK has the same primary sequence in all stages of gizzard development, although charge variants due to post-translational modifications may exist.

Development of smooth muscle: ultrastructural study of the chick embryo gizzard.

The growth and differentiation of smooth muscle in the chicken gizzard were studied by electron microscopy from the 10th day in ovo to 6 months after hatching; during this period the organ grows 1000-fold in weight. At the earliest stage studied, smooth muscle cells, interstitial cells, and fibroblasts are immature but can already be clearly distinguished. The structural components of muscle cells develop in a characteristic sequence. Mitochondria are more abundant in immature muscle cells (8% in 14 days embryos and 7% in 19 days embryos) than in the adult (5%). Caveolae are virtually absent in the 11 day embryo; they become more common at the end of embryonic life, but continue to increase in relative frequency after hatching. Gap junctions appear around the 16th day in ovo as minute aggregates of connexons, which then grow in size, probably by addition of new connexons. In the earliest stages studied, myofilaments occupy 25% of the cell profile and are assembled into bundles accompanied by dense bodies and surrounded by loosely arranged intermediate filaments. By contrast, membrane-bound dense bands are scarce until the latter part of embryonic life, an observation suggesting that myofilament formation and alignment is not a process initiated near the cell membrane or directed by the cell membrane, and that only late in development bundles of myofilaments become extensively anchored to dense bands over the entire cell surface: at that time myofilaments occupy more than 75% of the cell volume. The muscle cells increase about four-fold in volume over the period studied; the 1000-fold increase in muscle volume is mainly accounted for by an increase in muscle cell number. Mitoses are found in the gizzard musculature at all embryonic ages with a peak at 17-19 days; they occur in muscle cells with a high degree of differentiation. These cells divide at a stage when they are packed with myofilaments and form junctions with neighbouring cells: the mitotic process affects the middle portion of the cell, which takes up an ovoid shape and eventually divides, whereas the remaining portions of the cell do not differ in appearance from the surrounding muscle cells. At all stages of development the population of muscle cells has a uniform appearance (apart from the cells in mitosis), and the growth and differentiation seem to proceed at the same pace in all the cells. There are no undifferentiated cells left behind in the tissue for later development.

Cytochemical characterization of mucosubstances in the chick glandular stomach during embryonary and postnatal development.

The chick stomach is composed of two parts: glandular or proventriculus and muscular or gizzard which are morphological and functionally different. Since characterization of the mucosubstances in the adult stomach and its comparison with the embryonary stomach have not been made, we performed the study of the cytochemical characteristics of mucosubstances in the chick glandular stomach during the embryonic and post-natal periods, to obtain information on changes produced in these components during functional differentiation. In this work we established that during development, the epithelial cells of the superficial layer content predominantly glycoproteins and the glycosaminoglycans of the glands decrease when they begin to secrete other compounds, such as proteolytic enzymes necessary for digestion. This sequence of mucosubstances appearance is concordant with the increase of carbonic anhydrase, which reaches its highest specific activity from 15 to 20 days of incubation. In this period hydrochloric acid secretion increases and therefore, glycoprotein secretion becomes necessary to protect the mucous membranes.

Expression of smooth muscle caldesmon in developing chicken gizzard.

Caldesmon is an actin/calmodulin/tropomyosin protein located in the thin filaments of smooth muscle cells and microfilaments of nonmuscle cells. Two isoforms of caldesmon, h- and l-types, shown to exist in vertebrate smooth and nonmuscle cells respectively, are produced by alternative splicing of the caldesmon mRNA encoded by a single gene. To study the expression of smooth muscle specific h-caldesmon during the differentiation of mesenchymal cells into smooth muscle cells, soluble protein and total RNA from the gizzard primordium in the gut region of 5-day and gizzards of 7-, 9-, 13-, 17- and 21-day embryos and 2-days post-hatch chicks were extracted and analyzed for caldesmon expression at both protein and mRNA levels. Western blot analysis of proteins and immunofluorescence microscopy of tissue section were carried out using an antibody specific for h-caldesmon. Total RNA was analyzed by Northern blotting using a caldesmon cDNA probe, and h- and l-caldesmon cDNAs were identified due to the difference in their molecular sizes (4.8 and 4.1 kb respectively). The mRNA was also analyzed by reverse transcribed-polymerase chain reaction (RT-PCR) and Southern blot analysis. Our results show that the I-caldesmon mRNA was expressed at higher levels in the gizzard primordium during the early stages of development, and decreased gradually during growth. The h-caldesmon protein and mRNA, not expressed at day 5, is minimally expressed at day 7 and is fully turned on by day 9. Additionally, sequence analyses of the RT-PCR products of I-caldesmon showed that it lacked the spacer region, as predicted. RT-PCR analysis of total RNA gave two h-caldesmon fragments. These two fragments were identified as two different isoforms of h-caldesmon since they both contained the spacer region. They also showed homology in the region of exon 4 had differences in the region of exon 3b.

Identification of sugar residues in secretory glycoconjugates of the lining and glandular epithelium of the chick embryo gizzard using lectin histochemistry.

Using seven horseradish peroxidase-conjugated lectins we studied the distribution of glycoconjugate sugar residues in the lining and glandular epithelium of the gizzard in chick embryos from day 7 to 21 of incubation. At the outer layer of the lining epithelium all investigated sugar residues were present from day 7 onwards, except alpha-L-fucose, which was detected later. From day 9 some cells, which contained granules characterised by D-galactose-(beta 1--->3)-N-acetyl-D-galactosamine and N-acetyl-D-glucosamine, were observed in the inner part of the lining epithelium. Afterwards, although in different time periods, all investigated oligosaccharides were detected in intercellular spaces filled with mucous material. At first, the cells of the anlage of the tubular glands appeared to be characterised by D-glucosamine and alpha-D-mannose only. Afterwards, all the investigated sugar residues were detected. At hatching, the luminal glandular secretion showed all investigated sugar residues, except alpha-L-fucose, which was typical for the early formation of the tubular glands. Our data suggest that during the development of the gizzard three time periods of mucous release can be distinguished.

Gastric gross and microscopic lesions caused by the UNAM-97 variant strain of infectious bronchitis virus after the eighth passage in specific pathogen-free chicken embryos.

Herein we report a description of gross and microscopic lesions found in specific pathogen-free chicken embryos caused by UNAM-97 infectious bronchitis virus (IBV) variant strain after the eighth passage. Embryos were divided into three groups and were inoculated in the chorioallantoic sac with 0.2 mL of UNAM-97, Mass 41 IBV (positive control), or sterile PBS (negative control). Forty-eight hours later the allatoic fluid was taken and used to start a cycle of eight passages through 9-d-old embryos. Seven days after the last passage, embryos were harvested and macroscopic lesions in all organs were recorded. Proventriculus and gizzard samples were obtained from all embryos and routinely processed for microscopic and ultrastructural examinations. The UNAM-97 IBV variant strain caused two macroscopic lesions uncommon for Mexican strains: thin-walled proventriculus and gizzard, as well as urate accumulation within an extra-embryonic peritoneal sac, leaving the body through the umbilical duct and accompanied by the yolk sac. At microscopic level, two relevant findings were observed to be produced by this variant. In the proventriculus, there was a decrease in the gland papillary branching, while the gizzard showed a significant reduction in mucosa thickness and tubular-to-proliferative-cell ratio, as well as an absence of hyaline secretion in the lumen. Electrodense material scattered in proventricular and gizzard cells was observed, with a structure consistent with that of coronaviruses. These pathological chicken embryo findings have not been reported as being caused by other IBV strains in Mexico.

Developmental patterns of selected characteristics of the gastrointestinal tract of young turkeys.

Developing embryos and hatchling poults were sampled (n = 4) at Days 22, 24, 26, and 28 of incubation and at 1, 2, 4, 6, and 8 days after hatching, and selected characteristics of the gastrointestinal tract (GIT) were measured. Body weight increased linearly up to day of hatching and also from 2 to 8 days posthatching. Residual yolk weight decreased rapidly starting on Day 26 of incubation and was nearly depleted by 4 days posthatching. Changes in weight of segments of the GIT nearly paralleled the increase in body weight until day of hatching. Thereafter, weights of the proventriculus, small intestine, and pancreas increased more rapidly than body weight until 6 days after hatching. At this time, change in weight of small intestine and pancreas seemed to parallel that of body weight, whereas proventriculus weight continued to increase more rapidly. Gizzard weight, as a percentage of body weight, increased until Day 4 posthatching and then remained relatively constant through 8 days. Specific activities (SA) of pancreatic amylase, lipase, and trypsin were low until after hatching. Subsequently, amylase SA increased nearly threefold by Day 6. Lipase SA remained nearly constant between Days 1 and 8, and trypsin SA increased only slightly. Total activities of pancreatic enzymes, however, increased substantially after hatching, mainly because of increased pancreas weight. Jejunal maltase SA was high at hatching but decreased markedly by Day 4. This decrease in SA resulted in a notable reduction in total maltase activity of the jejunum despite an increase in jejunum weight.